High Amplitude Jet Stream Pattern To Lead to Extremely Abnormal Temps for Central/Eastern US; “Blow Torch” Heat to Arctic.

The US will be a land of extremes as a high amplitude jet stream…the story of this winter continues to impact the US as very abnormally cold temperatures impact the Central US and (later) the Great Lakes region, with very abnormal heat spreading northward into the Eastern third of the country mid-week. Sunday, much of the Great Plains were experiencing temperatures 20-25 degrees F above normal (~10-12 degrees C). As the week progresses, the jet stream amplitude over North America will intensify and bring highs of 30 degrees F (15+ C) or greater above normal mid-week to the Ohio and Tennessee Valleys into the mid-Atlantic and New England states. This means mid-Spring highs on the East Coast and a resumption of well below freezing temps over the Central and Northern Plains.

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In addition to the abnormal temperatures, another major story will be potentially heavy rainfall across a wide swath of the Midwest and Deep South ahead of the accompanying cold front which will push eastward mid-week. Abundant moisture from the Gulf of Mexico will aid in the generation of rainfall, some of which will help short term drought conditions, but could also produce flash flooding.

Moderate risk of flash flooding over portion of Texas, Oklahoma, much of Arkansas and southern Missouri Tuesday.
Tuesday evening forecast surface map showing widespread moderate to heavy rainfall likely from Texas to Michigan.

The Arctic Ocean has been experiencing an extraordinarily warm winter with consistent high heat to the region (relative to regional norms). As a result, sea ice has been suffering severely as the combination of high amplitude high pressure ridging and ocean cyclones push heat, wave action and wind into the sea ice sheet, along with very abnormal sea surface temperature right up against the sea ice (9-18 degrees F/5-10 degrees C above normal). Sea ice extent is currently running at the lowest on record in the history of human civilization, rapid melting already in progress in the northern Bering Sea, and 2017 annual sea ice volume was the lowest on record. The current max extent this season occurred on February 6th. The current earliest maximum peak extent is February 25th in 2015. The current record year for record minimum peak extent is 2017…2018 is currently beating that record and has the 2nd lowest year-to-date volume as well.


The sea ice is showing some signs of refreezing after its early February peak. However, more extreme heat is to come as more storms from both the Bering Sea and the North Atlantic advance heat and moisture into the Arctic Ocean this week. One storm will move over far Eastern Siberia and into the Chukchi Sea on Tuesday. Wednesday, another, stronger storm will approach Greenland, moving over the Canadian Archipelago Thursday, slowly shifting toward the Beaufort Sea Friday.


Note the last two sea level pressure images for 2/23 and 2/24. Not only the strength of the cyclone (in blue) but the tightly packed lines of equal pressure (isobars) between the low pressure system and the strong high pressure system over the Barents Sea, north of Scandinavia. These tightly packed isobars represent a very strong pressure gradient which will result in very strong southerly wind gusts (near hurricane-force) and intense wave action striking the sea ice sheet of the Arctic Ocean mid to late week. This in combination with the very warm, moist air moving into the region will make for a “blow torch” of heat from the Atlantic, eroding the cold conditions of the Arctic, stunting the freeze season further. This will likely lead to further ceasing or recession of sea ice as well.

GFS forecast high temperature for Thursday, showing above freezing temperatures penetrating into the deep Arctic. This may continue into Friday. Today through Tuesday will feature near or above freezing temperatures moving out of the Bering Sea into the southern Chukchi Sea as well.

I’ve been tracking the Arctic all season and there has been a shocking level of persistent warmth in the region with 2-3 degrees C above normal temps (for the region) being quite common many more extreme day higher than that. The Arctic Ocean basin may experience, as a region, anomalous temperatures of an incredible 6-8 degrees C above normal Tuesday-Saturday. This is relative to the 1981-2010 average. However, as climate change is abruptly warming the Arctic region, leading to rapid sea ice loss compared to the past, relative to the late 19th and mid 18th centuries (in the early era of human generated climate change), the anomalies are likely 0.7 or 1  degree C higher than that, respectively.

GFS Anomalous temperature forecasts for the Arctic region valid 00 UTC Feb 23rd. Extreme heat by regional standards over the Arctic for much of the week.

The implications for the collapse of sea ice are quite serious. The sea ice sheet regulates the jet stream by making the Arctic region permanently cold across a wide area. As long it it remains permanent with only modest seasonal melt, it can behave much like a continental ice sheet would behave on the atmosphere (like in Antarctica). The jet stream exists because the Arctic atmosphere is cold throughout the vertical column. The strong temperature gradient with the mid-latitudes is what makes it exist. But with abrupt warming of the Arctic caused by the collapsing ice sheet (which feeds back on accelerating such a collapse), this weakens the jet stream and has been causing it to become wavier with increasingly more extreme and frequent high amplitude patterns (which feedback and melt the Arctic more). Such research has been conducted by scientists such as Dr. Jennifer Francis of Rutgers University and others, showing the jet stream slowing and becoming higher in amplitude since the 1960s. Such abrupt warming also leads events such as “sudden stratospheric warming” and “splitting” of the polar vortex, supporting Arctic blasts to the south and abundant heat transport to the Arctic.

If the ice sheet collapses completely (no more in summer, low to little meaningful extent in the polar night), you get even more abrupt warming of the sea surface from below and above through collapse of the ocean thermocline (persistently cold water “cap” atop somewhat warmer water) and air temperature inversion (warmer air atop cold surface air) as well as from the much reduced albedo (white, reflective surface). The warming atmospheric column with height further reduces the temperature gradient with the mid-latitudes, weakening the jet further and causing more extreme “wave action”, greater blocking patterns as you get these big waves and little eastward progression of systems and the polar jet actually retreats farther north. This can dramatically shift precipitation patterns northward could cause much hotter, drier conditions in the mid-latitudes. It’s been a major concern for a long time in in climate change science, but a process thought to be of concern in the “high emissions” scenarios of the mid to late 21st century as increasing aridity across the mid-latitudes would destroy forests and not allow crops to be grown where they are currently grown because of increasing extreme heat (or storms). So this would have impacts not only in the Arctic, but also in the mid-latitudes. Unfortunately, a recent phrase has been increasing use the past few years. “Faster than expected”. Some prominent researchers openly admit an ice-free Arctic may be possible before 2020. See also HERE.

I’ll have more on the situation in the Arctic this week as well as the heavy rainfall in the US. Also, keep an eye on Tropical Storm Gita approaching New Zealand to start the week!

–Meteorologist Nick Humphrey


Effect of Sun-Mon Arctic Ocean Storm on Sea Ice

You may remember I posted last Friday about the major North Atlantic storm which was expected to move into the Arctic Ocean Sunday and Monday producing hurricane-force winds, 30 ft+ waves and temperatures over 40 degrees F above normal (near or even above freezing in places). Well that storm advanced through the Arctic and now noticeable effects can be seen (via satellite analysis) on sea ice concentration (amount of ice vs. open water in a given area) and on sea ice sheet growth and resulting extent.

North Atlantic Surface Analysis valid at 06 UTC February 5th (midnight CST) showing the 958 millibar low pressure system off shore northeast Greenland entering the Arctic Ocean from the North Atlantic basin. (US National Weather Service)
Global Forecast System model analysis valid 12 UTC February 5th (6 am CST). This shows the very strong sustained winds and (by Arctic standards north of 80N) extremely warm temperatures during the height of the storm. This was thanks to very strong warm air advection from the Atlantic Ocean. The system had a sub-tropical connection with heat and moisture originating from the subtropical western Atlantic. Average temperatures in many places should be -30 to -15 F (-34 to -26 C). (earth.nullschool.net)

Included are two images of the sea ice concentration…one I saved from the February 3rd, another just posted for February 6th. Lighter blues are for 90-95% concentration, with yellows and reds being for 75-90%.

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Extent growth basically stopped between February 3-6 (near 13,300,000 sq km for four days).

2018 year-to-date extent (currently at record lows) vs 2016 extent (previous daily record lows for this time of year) and the 1980s average. Sea ice extent and volume collapse is underway in the Arctic Ocean because of Anthropogenic Climate Change caused by abrupt warming in the Arctic (notable since the 1980s, accelerating since the 2000s). 

More very above normal temperatures will hit the Arctic this weekend as a powerful blocking high pressure system over the Pacific (sound familiar…) raises temps once again across Alaska and allows storm tracks to head for the Bering Strait and Chukchi Sea once again. Meanwhile, the Atlantic side will continue to remain “open” with another storm also moving into the region this weekend. No storm appears to be nearly as powerful as the Sunday-Monday event, but the litany of systems bringing at least some wind, wave action and temps not far below the freezing point of salt water is no good for the Arctic.

Temperature anomaly (degrees above or below average) forecast by the GFS model for the Arctic region valid 18 UTC February 10th (noon CST). Normal is based on 1981-2010 baseline. To approximate the major effect of anthropogenic climate change since the end of the 18th century add +0.9 degrees C (K).
GFS maximum temperature forecast valid 18 UTC February 10th (noon CST). Very warm air temperatures on both the Atlantic and Pacific entrances to the Arctic Ocean.

Arctic sea ice is extremely important for everything from Arctic regional ecology, marine biology to effects on overall warming of the Arctic Ocean and surrounding land areas (and permafrost). There is also evidence that the rapid warming of the Arctic because of anthropogenic climate change is altering the polar jet stream circulation which may be leading to an increased frequency and magnitude of extreme weather events. 

Sea ice thickness and thickness anomalies in January 2018. (Zach Labe)

–Meteorologist Nick Humphrey



Discussion of Final Analysis of 2017 Hurricane Harvey

The 2017 North Atlantic Hurricane season was a devastating one in terms of loss of life as well as property damage for the United States and the Caribbean. The National Hurricane Center released its post-season report on Harvey which caused great destruction to parts of Southeast Texas and Southwest Louisiana. What follows is a brief summary and discussion of Harvey based on info from that report as well as other sources related to Harvey’s impacts. The full report is linked at the end of this post in the references.

Meteorological Discussion

What became Harvey was originally a tropical disturbance which came off the West Coast of Africa on August 12th. It is common during August and September for land-based thunderstorm complexes known as mesoscale convective systems to move westward off the African coast near or south of the Cape Verde (also known as the Cabo Verde) Islands and later develop into long-lived tropical cyclones. Harvey was a classic “cape-verde” type storm as it would later develop into a tropical depression with a well-defined center on August 16th.

The depression intensified into a storm and given its name 12 hrs after initial development. It peaked over the open Atlantic at 40 knots (~45 mph), moving over the islands of Barbados and St. Vincent on August 18th. However, increasing vertical wind shear (increasing winds with height tilting and blowing the thunderstorms away from the low pressure center) over the central Caribbean Sea lead to Harvey’s dissipation to a remnant low later that day.

Harvey moving over Barbados and St. Vincent on August 18, 2017.

The remnant circulation moved over the Yucatan Peninsula on Aug 22nd and redeveloped into a tropical depression over Bay of Campeche on August 23rd, 150 n mi west of Progreso, Yucatan, Mexico.

The initially poor organization of the reformed Harvey transitioned to a period of rapid intensification late on the 23rd as deep convection began to concentrate near the center. This was aided by an environment of light shear, very warm sea surface temperatures and high mid-level moisture. Intensification would continue until landfall on the 26th. Harvey reached Category 3 midday on the 25th and intensified into a Category 4 as it made its landfalls on the Texas coast early August 26th (the evening of the 25th local time). The initial landfall was on San Jose Island, TX as a Category 4 with maximum sustained winds of 130 mph (115 knots) with a second landfall on mainland Texas in northeast Copano Bay as a Category 3 with maximum sustained winds of 120 mph (105 knots). Wind damage was extreme and devastating in Aransas, Nueces, Refugio and the eastern part of San Patricio Counties. 15,000 homes were destroyed and 25,000 homes damaged. The City of Rockport was hit the hardest as the Category 3+ wind field moved into that area causing both extensive wind and surge impacts. The highest surge observed in Harvey was generally in the range of 9-11 ft.

Hurricane Harvey approaching landfall on the Texas Coast the evening of August 25, 2017 (local time).
Hurricane Harvey making landfall in Texas as seen by radar. Note the “lumpy”, wavy undulations within the eye (such as near Rockport and north of Port Aransas in this image). These are mesovortices where winds may have been locally stronger within the inner eye wall of the hurricane.

Harvey meandered in light steering currents, “stuck” between a mid-tropospheric high pressure system over the Four Corners states and another mid-troposphere high over the Gulf of Mexico. Torrential rains fell over Houston Metro and the Golden Triangle near a stationary front which formed on the north and east side of Harvey.


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The rainfall of Harvey was truly incredible. A storm total of 60.58 inches was confirmed Nederland, TX; 60.54 inches in Groves, TX. Much of the heaviest precipitation fell in the first 72 hrs of the event. Previous continental US record for a tropical cyclone is 48 inches in Medina, TX (1978). The extreme nature of Harvey was displayed in that 18 values over that continental record of 48 inches reported across southeastern TX, with 36-48 inches recorded across the Houston metro area. However, Multi-Sensor Precipitation Estimates (MPE), which includes radar-derived rainfall intensity estimates suggests 65-70 inches where few observations were available or observations failed early in the event. Maximum rainfall measured in Louisiana was 23.71 inches in Vinton, LA, with MPE suggesting a more representative 40 inches as Southeast Southwest LA obs were sparse.

By Jordan Tessler for Capitol Weather Gang.



The large-scale or synoptic set up for the Harvey exceptional rainfall event is not particularly unique. Heavy rain bands formed along a modest frontal boundary situated initially near Houston, then the Golden Triangle region in Southeast TX (Beaumont, Port Arthur, Orange, TX area). Enhanced convergence and convective lift with warm cloud droplet precipitation processes allowed for enhanced rainfall rates in abundant thunderstorms. The combination of extremely high rainfall rates of up to 5-7 inches per hour and the stationary nature of the near coastal frontal boundary and Harvey itself contributed to the extreme total accumulation and massive flooding.

Training rain bands moving over the Houston Metro area the morning of August 27, 2017.
Very heavy rainfall in the Golden Triangle region of east TX the early morning of August 30, 2017.

NOAA analysis determined that areas of Southeast TX experience a flood with an annual probability of <0.1% (equivalent to a >1000 year flood event). I believe this is one of the most important parts of the National Hurricane Center report, so I’ll quote it:

While established records of this nature are not kept, given the exceptional exceedance probabilities, it is unlikely the United States has ever seen such a sizable area of excessive tropical cyclone rainfall totals as it did from Harvey.

Mesoscale Precipitation Discussion by the National Weather Service – Weather Prediction Center on August 27, 2017. Historic, devastating flooding underway in the Houston Metro Area at the time.

In addition to storm surge, wind and flooding rains, Harvey produced 57 tornadoes (many in the Houston Metro area) and killed 68 people directly with an additional 35 indirect deaths. All direct deaths were in Texas and it was the deadliest tropical cyclone for Texas since 1919. All but three direct deaths were caused by freshwater flooding.

According to NOAA, preliminary damage analysis suggests estimated damages of $125 billion, making Harvey the second-costliest hurricane on record in the North Atlantic basin, only behind Hurricane Katrina, when adjusted for inflation.

Connection to Anthropogenic (human-caused) Climate Change

During and immediately following the events of Hurricane Harvey, there was intense controversy over even discussing climate change as it related to the extreme events related to Hurricane Harvey. Even mentioning climate change in reference to an individual extreme weather event. A lot of opinions were thrown about, but the science of climate change has evolved dramatically in the past 10 years and climate researchers have a much better understanding of many of the connections between climate variables and the statistics of weather which make up the recent past and current climate. From this, attribution studies can be conducted to determine a likelihood of connection to the changing climate regime. A attribution study was done by World Weather Attribution (#2 below) and the probabilistic statistical analysis determined that the record rainfall from Harvey was approximately a) 3 times more likely and b) 15% more intense in terms of rainfall rate because of climate change. One location witnessed a return period for extreme rainfall of 9000 years with a high degree of statistical confidence. The impacts were consistent with what would be expected with 1 degree C+ of global warming since the late 19th century (the world has thought to have begun warming because of humanity since the mid 18th century). I did an extensive post previously during this most recent hurricane season on the climate change connection with includes references to numerous recent peer reviewed papers HERE.



#1 – Harvey Report (National Hurricane Center, 2018)

#2 – Oldenborogh et al. 2017

See my previous posts in this blog on Hurricane Harvey from last August HERE.

–Meteorologist Nick Humphrey

Abrupt Climate Change Tipping Elements

While anthropogenic climate change is generally discussed in the context of gradual change (perhaps, “gradual” by standards of human lifetimes…still extremely fast by geological timescales…), there are tipping elements in the climate system which have the potential to cause very abrupt and extremely rapid shifts in climate states on regional and (more importantly) global scales. Tipping points are still somewhat controversial in the science of climate change, but there is precedence for it in the paleoclimate record; from the ice age cycles to some of the most infamous extinction-level events in Earth’s history where species simply had no chance to adapt.

I’ve discussed the concept of abrupt climate change previously and suggested that we are currently in a period of abrupt climate change. “Abrupt” defined as events occurring within less than a normal human lifetime which normally do not do so. Many scientists have studied the potential in the present or past of abrupt climate change (or quasi-“runaway” global warming which is abrupt) including Dr. James White, Dr. Jennifer Francis, Dr. Peter Wadhams, Dr. David Wasdell, and many others. Much research has looked at abrupt climate change as a function between a forcing mechanism on a system and a “breaking system” (a negative feedback) which stops the system from reaching a tipping point. However, if the forcing overcomes the breaking and forces it over the tipping point, there is the abrupt (temporally rapid and structurally changed) shift to a new climate state vastly different from the previous state (see excellent discussion on the topic by Dr. David Wasdell…a climate scientist who’s done peer review work for the Intergovernmental Panel on Climate Change of the UN).

Tipping Elements. (Postdam Institute for Climate Impact Research).

Our current more abrupt climate change…which one may argue began in the 1980s with a more rapid rise in global air and sea surface temperatures, decrease in sea ice extent/volume, ocean acidification, land glacier retreat, among other climate change signals (noted by both the IPCC as well as the US in recent climate reports)…appears to have been caused by our rapidly increasing emissions of greenhouse gasses, including carbon dioxide in the atmosphere since the 1960s. CO2 concentration was around 315 parts per million molecules of air in 1960 (compared to 285 ppm at the end of the 19th century). We’re already near 410 ppm in 2017…twice an increase in concentration in nearly the same amount of time. Methane, a short-term (150+ times more powerful as carbon dioxide within a few years), but extremely powerful greenhouse gas has also rapidly increased because of both human and natural sources.


However, as anthropogenic climate change continues to evolve, assuming no *significant* human intervention (specifically removal of carbon dioxide and cooling of the Arctic), may lead to further tipping points being reached within the climate system which may accelerate change further. Changes which can happen over the course of just years. These more specific “sub-system” tipping points are of particular interest to some of the previous researchers mentioned. So let’s discuss a couple of interest…

Tipping Point #1: Arctic Sea Ice Sheet Collapse

Personal opinion here…I firmly believe of all the abrupt climate change tipping points, this one is likely the most imminent. Arctic sea ice has been rapidly decreasing in extent and thickness (and therefore, volume) since the 1980s. Numerical climate models in the past have attempted to predict the collapse of sea ice (what some refer too as the effective “ice free” Arctic in the warm season…roughly 10% of the Arctic Ocean Basin without ice or less). Previous predictions have called for dates such as the 2080s and more recently, the 2040s. Now there are scientists such as Dr. Paul Beckwith and Dr. Peter Wadhams and others openly giving a likelihood that the first “ice free” or “blue ocean” event will occur by or before 2020! 2017 witnessed the record low annual Arctic sea ice volume, caused by very thin tenuous ice. Where widespread, thick ice used to exist in the Arctic, tenuous thin ice only remains, ready to be destroyed by random storms and influxes of heat from the Atlantic and Pacific…a process which is already happening.


What is important about this tipping point? If most of the ice disappears from the Arctic Ocean, albedo (reflectivity) in the northern hemisphere will be significantly reduced, replacing white ice with very dark ocean, warming the Arctic Ocean column and warming and moistening the atmosphere (also clouding it, retaining heat in the polar night, making new sea ice difficult to form). Of course, this more rapid heating of the Arctic will more rapidly raise the overall average temperature of Earth as well. Note…there has not been an “ice-free” Arctic over in over 3 million years! It will also have have implications on the jet stream which depends on temperature gradients between the mid-latitudes and the Arctic for it’s strength and progression of waves around the globe – it would become much weaker, shift farther north and exhibit much greater amplitude waves with stagnant, extreme weather (see HERE and HERE).

This tipping point could set off other issues such as prolonged heat waves and droughts, leading to other tipping events such as forest diebacks (and then wildfires) and methane releases in the high tundra and methane clathrates from subsea permafrost in Arctic continental ice shelves (more on clathrates). This would release more carbon into the atmosphere. Abrupt changes in precipitation distribution (dryness or heavy precipitation) and extreme heat would pose threats to agricultural production which is very sensitive to individual weather events, let alone the climate stability which we’ve been accustomed too for the past 10,000 years since the end of the last glacial period.

Tipping Point #2: Equatorial Super Rotation

Another rather daunting tipping point is actually a common feature of several planets in our own solar system. It is called equatorial super-rotation. None of the previous scientists have dealt with this topic, but it is of interest to me as a meteorologist and is actually not a current feature of Earth’s atmosphere. It is a phenomena in which the atmosphere around the tropics and subtropics actually spins faster than the planet’s rotational velocity. This super rotational velocities occur on the terrestrial planet Venus and the Jovian planets (such as Jupiter and Saturn).

How would this occur on Earth from anthropogenic climate change and what would be the impacts on climate? Well, typically, the Earth’s tropical circulatory pattern involves structures known as Hadley Cells which features rising motion near the Equator and sinking motion in the subtropical regions. Air at the surface then flows equatorial-ward towards a convergence zone (the Intertropical Convergence Zone or Monsoon Trough) with the Coriolis force turning the air flow toward the right/left in the northern/southern Hemisphere, generating the easterly trade winds. The Hadley Cell expands and migrates north and south depending on the seasons between the two hemispheres.


With climate change however, increasingly extreme surface heating in the tropics is theorized to possibly lead to a situation where a single Hadley Cell develops, becoming extremely powerful and expansive. This would lead to the center of it straddling the equator with a strong upper-level equatorial westerly jet (the super-rotational flow).  Significant areas experiencing hyper-aridity would exist over much of the mid-latitudes as far less moisture is transported from the tropics and high precipitation regions would be found much further poleward than found in the current climate regime. This tipping point in modeling isn’t expected until late century, but again, given the rate at which observed changes in the climate system are evolving relative to the limitations of modeling, it is not truly known when such a tipping point could actually be initiated.

Human Societal Tipping Points…

Of course, with anthropomorphic climate change, one of the biggest issues is humanity’s ability to deal with increasingly rapid and extreme changes and harms. Humans depend need food, water, and shelter to thrive and when repeated meteorological (hurricanes, tornadoes, floods, etc) and climatological (long-term agricultural and hydrological droughts) disasters strike, society can take very serious hits. Much of the world depends on agriculture from the US and China, for example. Freshwater resources around the world are under increasing stress from overuse by increasingly growing populations. More and more people are crowding into cities which will be under the influence of urban heat islands which may deal with hotter temperatures as the climate warms.

Projected decadal Palmer Drought Index based on local norms during course of 21st century. Timeline based on “high-emissions” scenario of IPCC, which does not account for certain tipping elements, only human emissions. Climate Change expected to cause hyper-aridity (for US, equivalent to 1930s Dust Bowl conditions) throughout US/Europe, South Africa and Amazon without significant human intervention, well beyond current measures. Note wetter conditions in high latitudes.

The ability of humanity to deal with the changes ahead will be by far the most significant challenge in the coming years ahead.

–Meteorologist Nick Humphrey

The Science Behind “Atmospheric Bomb” Cyclones

The first full week of January featured a powerful winter storm – known as a nor’easter – intensify off the east coast of the United States causing snowfall from the North Florida to Maine into Atlantic Canada, along with widespread power outages from strong winds as well as storm surge flooding and battering waves.

Powerful nor’easter offshore Long Island Thursday afternoon.
Vehicles navigate Monument Square on Sunday in North Adams, Massachusetts, which was under a snow emergency. Gillian Jones / AP

The storm underwent rapid intensification known in meteorological slang as “bombogenesis”. An “atmospheric bomb” occurs when a developing cyclone’s low pressure center intensifies explosively…defined as at least 1 millibar or 1 hectopascal drop per hour on average during a 24 hr period. This system had a pressure drop of 54 millibars in 24 hrs (1004 to 950 millibars). This bombogenesis phase can occur in both frontal cyclones seen in the mid-latitudes such as with this week’s storm or with tropical cyclones. A famous example would be Hurricane Patricia in the Eastern Pacific in 2015 which experienced a minimum central pressure drop of 95 millibars during a 24 hr period (967 to 872 millibars).


Bombogenesis in mid-latitude cyclones occurs when there are favorable jet stream dynamics which allow for strong vertical motion, to force air up and away from a developing surface low. These include very strong upper-level winds and diverging flow. This allows for a high rate of decrease in surface pressure, intensifies the pressure gradients, reinforces the “conveyor belts” of warm, moist air flowing into the cyclone for clouds, releases latent heat and producing precipitation, which further strengthens the storm.


For frontal cyclones, the most intense atmospheric “bombs” occur when you have a merging or “phasing” of the northern and southern jet streams (basically the polar jet with much colder air to its north and the subtropical jet with far richer moisture sources to its south). This “phasing” of jet streams occurred with the most recent nor’easter.

Upper-atmospheric air flow maps from Wed-Thurs morning showing the phasing of the polar and sub-tropical branches of the jet stream, which intensified the massive East Coast nor’easter.


“Bomb” cyclones are nothing new. Unfortunately for us who have to live and deal with their impacts, human-induced climate change has forced our world to retain a significant amount of heat energy. These major changes on climate in just the past 20-30 years have caused statistical changes in observed weather. And one of those changes is in rapid intensification of cyclones. With tropical cyclones, there is evidence that a warming ocean and lower atmosphere (with greater moisture/latent heat release) is playing a role in increasing the frequency of rapidly intensifying tropical cyclones (here’s a paper by Kishtawal et al. on the topic). With mid-latitude cyclones, there is ongoing debate on the issue. However, there ongoing research suggests that in addition to thermodynamic roles, the increasing “waviness” of the polar jet stream theorized to occur in a warming world may have impacts on mid-latitude weather and long-term climate patterns. High amplitude jet streams produce greater mixing of air masses at lower levels of the atmosphere between the polar regions and sub-tropics (a process known as temperature advection). The increase in jet stream amplitude acts as a feedback to further amplify Arctic warming rapidly relative to the mid-latitudes as much warmer air advects into the far north (jet slows slightly with less temperature gradient, but becomes much more amplified, enhancing warming further). While the effect of the mid-latitudes circulation patterns on the Arctic seems more well-established because of the rapid changes in the far north, climate scientists are in much higher disagreement on the effects of feedbacks back on the mid-latitudes. Dr. Jennifer Francis (Rutgers University; see short webinar on possible connection between Arctic warming and mid-latitude extreme weather), among other scientists continue to do research actively on jet stream dynamics in the mid-latitudes with regards to climate change. But such a combination of warming energy sources and amplified jet stream patterns could further the development “bomb” cyclones in the future as the world continues to warm, at least while there remains strong temperature gradients between air masses to fuel mid-latitude storms (mid-latitude cyclones may be weaker and/or found much farther north in a much warmer planet). And there has already been a statistically detectable shift northward in winter storm tracks in the Northern Hemisphere and an increase in the severity (intensity of cyclones and precipitation rates) and frequency of “atmospheric river” events in the Eastern Pacific toward North America since the 1950s (see Key Finding #4-5/Chapter 9 of US Climate Report).

What “bomb” means as far as hazardous impacts will depend on the specific storm, but when it comes to ocean storms, like what was witnessed this week, obviously, damaging winds, heavy surf, storm surge flooding and heavy precipitation which can cause dangerous disruptions are what are all possible. In this case, much of it was all snow and ice. In the warm season, it can be flooding rainfall. But human-induced forcing (retaining of heat in Earth’s system) is now known to play a role in the attribution of the intensification of these large-scale weather systems within the changing climate regime.

–Meteorologist Nick Humphrey

Major Pattern Change for North America and Arctic Next Week.

A major weather pattern shift will be occur next week for North America into the Arctic as the jet stream…which already has been largely higher in amplitude and experiencing some blocking with little eastward progression of long-waves in the upper-atmosphere, will becoming extremely amplified (north-south) next week bringing very warm air up into Alaska, Yukon and the Arctic Ocean and a modified Arctic air mass from Nunavut and the Northwest Territories of Canada into the central US. Let’s take a look at things.

The current pattern dominating North America has been strong ridge of high pressure over the Western US or Eastern Pacific with a prominent trough over the eastern US with some fluctuation in the wave pattern east or west, but not much significant change, except in the center of the country which has seen more significant swings between these two states. The east, including even the Southeast saw significant snow. The west has seen abnormal warmth with record fires in California. Currently the ridge of upper-atmosphere ridge is forecast by US and European models to build to an extremely high amplitude the end of next week north over portions of Alaska and Yukon and into the margins of the Arctic Ocean. This as a very intense trough is forced south over the US.

European model forecast for the wave pattern of the mid-level atmosphere valid 6 pm CST 12/23.
This extreme amplification will drive an Arctic surface air high pressure system out of the Northwest Territories with very cold air this week, with this air mass advancing into the US beginning Thursday into this weekend. Meanwhile stormier conditions will moving from the Bering Sea into the Chukchi Sea driving up temperatures in the far north. And California with all the fires? Remains abnormally warm and dry.

Temperatures the afternoon of Christmas Eve (European Model forecast).

Greatest signal for low to no precipitation the next 10 days is south-central to southern CA into much of AZ and NV.
The Arctic:

As I spoke about in a previous post, the Arctic is having its second warmest year on record and lowest annual sea ice volume on record as climate change continues to abnormally warm the Arctic. The highly amplified wave pattern is much a product of the current weak La Nina pattern. However, the intensity of the amplification and resulting amplified warming of the Arctic is also a function of the long-term global warming regime dominating the polar region and causing record warmth and reductions in sea ice. I noticed this amplified wave pattern will have interesting impacts on the Arctic weather pattern and possibly the tenuous sea ice beginning next week.

Right now, a prominent surface high pressure region…associated with the Beaufort Gyre…is over the Arctic Ocean north of Alaska and eastern Siberia. By the middle of next week, this gyre will weaken as strong low pressure systems approach the Arctic from both the Bering Sea and the far North Atlantic.

Prominent high pressure of the Beaufort Gyre over the sea ice of the Arctic Ocean.

European Model depiction of low pressure system advancing into the Arctic Ocean from the Bering Sea on Christmas Eve. This may be the strongest in a series of lows (2-3) beginning late week. Stormy conditions will also impact areas near Svalbard (islands just east of northeast Greenland) late-week and weekend.
The Gyre is vulnerable because of the areas of open water and tenuous sea ice which remains over the Chukchi Sea…record low extent for this time of year. The ice being cold creates the surface high pressure system and clockwise circulation. But last year, this gyre collapsed because of slow sea ice growth allowing for storms with warm, moist air to move into the Arctic and further slowed sea ice growth. It appears this may be forecast to happen again during the tail end of this month.

European Model forecast surface temperatures showing well above normal temps shifting northward late week into Christmas Eve over the Arctic Ocean north Svalbard and the Chukchi Sea. While exact values will change, general pattern appears likely.
Depending on the strength of the low pressure systems, not only will the tenuous sea ice in the Arctic…widespread areas 1.5 meters or less in thickness (less than a meter in the Chukchi Sea)…deal with more warm air temperatures limiting sea ice growth, but also wave action which may destroy the ice, particularly from the Pacific side as cyclones are expected to move across the Arctic from the Pacific. We’ll see how much impact those storms have and how intense they are. If the upper-level wave pattern is as amplified as forecast by models 5-8 days out (no reason to think otherwise as he reach the point of good reliability for the upper-atmosphere), it’s a good set up for strong low pressure systems to develop in both the North Pacific and North Atlantic. And with the highly amplified blocking high over the Eastern Pacific, storms will be forced to track into Alaska and into the Chukchi and Beaufort Seas and deep Arctic Ocean.

–Meteorologist Nick Humphrey

Arctic Sea Ice Extent Rapidly Decreasing Because of Climate Change; Weather & Climate Implications

Today, NOAA presented the State of the Arctic report at the American Geophysical Union annual conference in New Orleans. The news from the report was devastating for potential weather and climate impacts. Lots of important info to talk about from this! Let’s summarize:

  1. Annual Arctic sea ice extent is the lowest in 1600 years. This is based on proxy data (tree rings, lake sediments, ice cores from the Greenland Ice Sheet). There has been an abrupt decrease in extent during the 20th century (continuing to present). 24991395_10215050817330895_108575701643656859_n
  2. Arctic sea ice extent reached a record minimum in the warm season in 2012. However, 2015-17 witnessed consecutive record low maximum extents in the cold season. 2016 also had the lowest extent on record in November or December. 2017 is also witnessing top two or three low daily extents in November into December, with record low sea ice in the northern Bering Sea and the Chukchi Sea (north of the Bering Strait between Alaska and Russia). Also very notable, sea ice VOLUME (which includes thickness of ice) has continued to suffer with 2015-17 in the top 4 for the lowest volume on record going back to 1979 (and based on decreasing of sea ice extent and thickness, likely much much longer than that). Multi-year ice…ice more than a year old…is now nearly extinct in the Arctic Ocean.

    Arctic Sea Ice Volume since 1979. Note consistent and accelerating collapse of sea ice volume. Arctic ice volume may fall below the 2012 record at some point in the month of September in the next several years.
  3. The Arctic had its warmest year on record in 2016 and its second warmest year on record in 2017 in reliable records. The climate of the Arctic is warming to the point that permafrost is increasingly melting releasing methane and carbon dioxide, methane emissions from what are called methane hydrates (methane gas locked in water ice) are increasing from the very shallow continental shelves surrounding the Arctic Ocean and mid-latitude weather patterns are becoming altered because of reduced sea ice (more on this shortly). The Arctic tundra is also greening at an increasing rate because of rapid warming.
  4. NOAA specifically states that “the Arctic shows no signs of returning to a reliably frozen region of recent decades” because of continued climate change related warming.

Discussion – Leaving the Ice Age Era:

One thing that we must remember about the sea ice of the Arctic Ocean (and the Southern Ocean around Antarctica) is that sea ice is a product of Ice Age eras. Our planet has had a tendency historically to flip between two global climate equilibrium states with dramatically different regional weather and seasonal patterns. The Ice Ages and the Hot House “Jurrasic Park” climates have been the two long-term dominating climate regimes in Earth’s history. One characterized by huge ice sheets and low sea levels, the other characterized by no ice sheets, no sea ice and high sea levels. Human civilization has flourished in the latest interglacial period in the Ice Age era because the climate has remained largely stable for roughly 10,000 years (-1 to +0.5 degrees C relative to mid-20th century climate) and mild enough to for extensive agriculture and settlements.

Estimated temperature of Planet Earth from 550 million years ago to the end of the 20th century.

But now, because of Anthropogenic Global Warming (AGW) from climate change, we are leaving that stability in the geologic blink of an eye.

Projected rise in global temperature of 4 degrees C/8 degrees F (relative to mid-20th century) during the 21st century relative to the past 10,000 years.

Probably the most important regulars of climate during Interglacials are the “refrigerators” of the north and south…the Arctic Ocean sea ice and Antarctic Ice Sheet (also Greenland Ice Sheet). However, as temperatures warm because of human carbon dioxide emissions trapping heat in the global climate system, that heat warms the atmosphere and ocean, attacking the sea ice by providing excess latent heat of melting. For the Arctic, this reduces the sea ice extent and volume decade after decade. Eventually, it will get to a point, where sea ice will become so thin and tenuous, it will undergo collapse to what has been called a “blue ocean” event with 1,000,000 sq km or less ice at a minimum in September (2012 extent minimum record was 3.41 million sq km). The 2016 and 2017 extent minimums were in the top 10 with 4.14 and 4.64 million sq km, 2nd and 8th respectively. 8 of the top 10 warm season minimum extents (in km) have occurred since 2010 in the now 39 year record. The Arctic Ocean and lower atmosphere are warming and becoming more like the high latitude North Atlantic. Eventually sea ice is expected to disappear completely in the warm season in the Arctic. Some climate scientists have suggested over the past several years that the “blue ocean” event resulting from a collapse of sea ice extent could occur between 2015-2020 or so as multi-year ice has nearly gone extinct, leaving thin ice vulnerable to quick melting and battering waves from cyclones. Computer models have been terrible at dealing with the end of sea ice in the Arctic, suggesting it would stick around into the second half of this century.

Discussion – Weather and Climate Implications:

So why does loss of sea ice matter? Sea ice regulates the climate of the world in multiple ways. It acts as large white surface which reflects most of the shortwave solar radiation from the sun (high albedo). As a result, it keeps the Arctic and Northern Hemisphere (and world) cooler than otherwise. It’s wide physical presence means heat entering the Arctic Ocean goes into melting the ice in the warm season (latent heat of melting; heat goes into phase change of water from solid to liquid) instead of heating the ocean and atmosphere dramatically (sensible heat to change temperature). Losing sea ice ends its presence as a climate regulator, allowing for more abrupt warming of the atmosphere-ocean system and increasing moisture content in the atmosphere (water vapor is an additional greenhouse gas; and increased clouds may reflect some radiation, but also can limit cooling in darkness). In addition, the Arctic Ocean will warm as it is a dark surface (low albedo). Increasing ocean warming in the marginal seas of the Arctic Ocean is already leading to increased methane emissions from the shallow continental shelves (as subsea permafrost thaw the clathrates) and more rapid warming will lead to an increase in emissions of methane and carbon dioxide from land permafrost (see discussion by Arctic climate scientist Dr. Peter Wadhams of Cambridge University on YouTube). Methane is over 100 times more powerful greenhouse gas than carbon dioxide on a timescale of several years (it dissipates far faster in the atmosphere, but sudden releases can increase warming quickly). And all of these feedbacks will much more quickly destroy the sea ice extent through further warming for a longer period in the warm season until ice disappears completely.

Increased warming of the Arctic also has impacts on mid-latitude weather. There has been research suggesting that the jet stream can be strongly influenced by Arctic warming and sea ice extent (see discussion by Dr. Jennifer Francis on YouTube). This can include a weakening of the upper-level jet stream which depends on the temperature difference between the upper-level mid-latitudes and polar atmosphere (known in meteorology as “baroclinic instability”). This weakening can lead to the jet stream developing high-amplitude waves more frequently, allowing for powerful upper-level ridges of high pressure to develop and cause blocking of the progressive westerly flow. This blocking can cause more frequent stagnant weather for locations, developing droughts in some areas through prolonged dryness, long periods of heavy precipitation in other regions as well as places of very abnormally warm temps (greater extreme summer heat) vs. colder temperatures (but the warmth always significantly outpaces the cold). Increased warming of the atmosphere in general also increases rainfall rates. In addition, paradoxically, while parts of the mid-latitudes may go through below normal temps and cold weather, the powerful ridging can produce extremely abnormally warm temperatures over the Arctic regions, intensifying the warming of the far north.

An identical pattern to this has largely set up over the Northern Hemisphere November into December.

Powerful high-amplitude ridges over the Eastern Pacific and North Atlantic. Pattern relatively stagnant at this time.
Reanalysis of the average temperature of Earth and specified regions over the last 30 days (1981-2010 baseline…add 0.7 C to compare to late 19th century). Note extensive, persistent anomalous warmth of the Arctic.

These effects may overall lead to more abrupt warming of the world as a whole as well as (more importantly) changes in rainfall and snowfall patterns, relevant for crops and food security from increasing summer extremes (heat stress and heavy rainfall) and water resources (snow pack, groundwater, etc). Also relevant for forest health (destruction by increasing wildfires as well as bug infestations killing hundreds of millions of trees in the Western US). And a running theme in stories on climate change recently? “Faster than expected” or “Faster than previously thought”. The importance of Arctic sea ice cannot be overstated and, unfortunately, this major tipping point…which I would consider a “keystone” tipping point because of what effects it can have down the line on other parts of the climate system…seems to be on the brink. It has been 2.6 million years since significant sea ice did not regularly exist in the warm season in the Arctic Ocean.

The statistics of weather has already changed significantly because of global warming with far more extreme heat events, drought periods and heavy precipitation events than in the mid-20th century (see presentation by Dr. Aaron Thierry on shift to more extreme weather conditions; starts 12:30 min, recommend watching through 20:30 min; also see discussion of climate change on increasing extreme events by Dr. Stefan Rahmstorf). Going past tipping points far earlier than expected by climate models will increase the likelihood for far more extreme weather events as weather patterns and circulations change (in some cases difficult to predict ways). Clearly, the world still needs adequate mitigation and adaptation measures to deal with these rapid and possibly abrupt changes.

For more info into how climate change influenced global extreme weather events in 2016, see the latest report (issued today) by the American Meteorological Society with attribution studies on last year’s significant events.

–Meteorologist Nick Humphrey

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