–Meteorologist Nick Humphrey
–Meteorologist Nick Humphrey
After a start to a 2018 tornado season which has featured numerous tornadoes across the Deep South and even scattered tornadoes out West, but not a single tornado in Nebraska, Kansas or Oklahoma, it appears near certain the tornado drought for the Great Plains will come to an end early next week. Something which as been missing thus far…pattern favorable to severe for widespread severe thunderstorms across the Central and Southern Plains…will ramp up beginning Monday across the High Plains, shift eastward Tuesday with a peak higher-end risk for more widespread severe storms Wednesday. The jet stream, the river of air separating the cold Arctic from the warmer mid-latitudes will send a major trough of low pressure over the Western US, temporarily cooling that region down, warming up the Plains, bringing in greater moisture from the Gulf of Mexico and setting up the ingredients for multiple days of severe storms.
A brief review since it’s been forever since the Plains have had severe weather and there might finally be something in my neck of the woods. Severe weather is defined by the phenomena. In the US, the criteria, which weather warnings revolve around are 1) large hail of 1 inch or larger, 2) damaging wind gusts of 50 knots/58 mph or higher or 3) a tornado. Severe convection (thunderstorms) needs three major ingredients to maximize their potential. 1) Instability, 2) Moisture, 3) Wind Shear. Instability is positive buoyancy (tendency to rise). This is aided not only by heat, but also by moisture as moist air is less dense than dry air at the same temperature. Wind shear is the change in speed and direction of the wind with height. Winds which turn and increase in speed rapidly with height can promote storm rotation, allow them to form isolated cellular structures called supercells. These can be long-lived, self-maintained and produce the most intense severe weather.
Of the three days I’m most concerned about for severe weather this week, Wednesday appears to be the most serious for the Central/Southern Plains for significant severe weather. But let’s take a quick look at all three days.
Monday, April 30th-
The National Weather Service Storm Prediction Center has a Slight Risk of severe weather (2/5 on the scale) for much of the high plains from Texas through Kansas and then, extending farther eastward into Central/NE Nebraska into SE South Dakota. This covers a 15% chance of severe thunderstorms within 25 miles of a point. A more “Marginal Risk” exists surrounding it. This would be for the afternoon and evening hours as a weak disturbance moves out of the Rockies, increasing wind shear and temperature-based instability (upper-atmosphere cooling relative to warming near the surface…warm air rises into colder air) modestly for isolated severe weather. Large hail and damaging winds are the primary hazards, but moisture will be limited, keeping the event from being widespread.
Tuesday, May 1st-
Beyond Day 3, there are now categorical outlooks, only probabilities. A 15% chance of severe thunderstorms within 25 miles of a point exists over Eastern Nebraska, Western Iowa, much of northern and Central Kansas into Western Oklahoma. This will likely be a bit more vigorous event from Monday, with the Tuesday disturbance being stronger with better shear profiles, more low level moisture available, and the combination of abnormally warm temperatures and higher moisture will mean higher atmospheric instability for tall, intense thunderstorms with strong updrafts. The storms will likely begin as supercells across Nebraska and Kansas before merging in the evening into an organized structure known as a “mesoscale convective system”. Basically a larger scale complex which can bring locally heavy rain and extensive damaging wind gusts. The initial storms will form along a cold front and threaten damaging winds, large hail and an isolated tornado.
Wednesday, May 2nd-
Wednesday is currently the most serious day for severe weather, but some uncertainty still exists. A 30% chance of severe thunderstorms within 25 miles of a point exists from extreme SE Nebraska, across much of Kansas, into western and central Oklahoma. A greater 15% area extends beyond that, including my area of Lincoln, NE. Wednesday, the main upper-level trough of low pressure over the West (seen in the above map) begins to shift eastward and a surface mid-latitude cyclone sets up over the central and southern Plains. A dryline (boundary separating warm, moist air from the Gulf of Mexico to the east from dry desert air from the Southwest US) will be located north-south somewhere over central KS/OK with a warm front either over Southeast Nebraska or Northeast KS (this is in question). The ingredients overall suggest robust thunderstorms forming along the dryline and near the area of low pressure (at the the intersection of the dryline and warm front) either in the afternoon or early evening Wednesday which vigorous supercells capable of producing large hail, some significant, damaging winds and multiple tornadoes. A possibility exists for a few of the tornadoes to be strong (EF2+; see more about the Enhanced Fujita Scale) and because of the persistent upper-level dynamics and buoyancy, storms could last after dark, posing nocturnal hazards. Later, storms will eventually merge producing greater high wind and heavy rain threats. Isolated flash flooding could be an issue Wednesday night from any heavy rain events.
For me personally, the the greatest threat for severe weather Wednesday seems to be to my south, but given the lead time, I’m watching to see how the position of the warm front ends up. If it migrates northward in the forecast and my areas is more solidly in the “warm sector”, then we will be just under as much of a hazard as the current 30% area is now. However, I note from forecast experience that warm fronts in severe storm events are notoriously challenging to forecast for as even the day of the event as they can have difficulty moving as far northward as expected because of the cold air they must erode out ahead of them. Much can also depend on the storms the previous day and how they effect the overall regional environment (temperature profiles, areas of instability, position of fronts, etc). But Monday-Wednesday all have potential to be hazardous days with Wednesday being a more potentially significant tornado day after months of silence.
So stay tuned early next week. The weather will definitely be news yet again this Spring! Stay safe and be ready this week in these regions!
–Meteorologist Nick Humphrey
Today/tomorrow’s mid-latitude cyclone on the Great Plains and Midwest will be a powerful one and one which will provide something for everyone. Blizzards, wind, severe storms, flash flooding, fire…pick your poison, Nature will provide.
In places like Minneapolis and much of Nebraska, this storm threatens to be a historic late-season April heavy snow or blizzard event. In the southern Midwest and South, it threatens heavy rain, flooding and a tornado outbreak. On the southern Plains, strong winds and arid conditions, could further yesterday’s extreme fire behavior. Stay safe out there folks!
A reminder, I will be interviewed on the internet-based program Environmental Coffeehouse at 9 pm EDT/6 pm PDT tonight! A livestream will be available on their public FB page (so you should be able to see it regardless of whether you have a FB page or not). I will discuss abrupt climate change and increasing extreme weather events and how current events (ocean heatwaves, changing jet stream, etc) connect to our rapidly changing climate.
If you’re wondering why all this is happening…VERY amplified…or in other words…very wavy jet stream pattern bringing extremely cold air (by April standards) down from from Canada to meet with up with extreme warm air (again by April standards) up from the south. Temps in 20s and 30s to the north with a high of 101 in Western Oklahoma yesterday to the south. Right now Lincoln, NE (where I am) is hitting 80 degrees for the first time this year. Tomorrow, Lincoln will peak in the mid-30s with falling temperatures!
The front end of this trough caused the development of the surface cyclone over Nebraska, intensifying deep moisture movement from the Gulf of Mexico (which, by the way, as a moisture source region, is running well above normal to start the year) and as and providing the deep vertical wind shear (rapidly increasing wind speeds with height) need to generate sustained severe thunderstorms. A recipe for a multi-threat mid-latitude frontal system. And it will not stop anytime soon. Saturday night, the threat will spread eastward, where a significant ice storm event may be possible for portions of upstate New York. In fact, Saturday afternoon, there may be much of Pennsylvania in the 70s while much of Upstate New York may be in the 20s! Incredible temperature contrasts for such a relatively higher latitude location.
—Meteorologist Nick Humphrey
Quite the day out in weather world, although you wouldn’t know it from looking outside here in the land of the corn. Beautiful day, although still waiting for the leaves to make an appearance. Soon enough, but the sun shines bright overhead. Calming and peaceful for a walk later.
After a winter which was tumultuous with big temperature swings (sometimes 50 degrees F within days), it’s nice to have a little stability for some days. Looking near or mildly above normal temperatures the next several days with periods of rain showers. Our winter in this region was less than 0.5 C below normal relative to 1981-2010, but running 0.5-1 C above normal relative to 1881-1910 when factoring the effect of climate change. And temperatures from anthropogenic climate change began rising globally after the mid-1700s, so late-19th century values are still conservative on the changes which have occurred here. People around here were complaining about how cold it was this winter. It could’ve been a lot worse as we had a few 60 and 70 degree temperatures in February mixed with the 10s and 20s for highs in January and February! Just wild.
Actually reminds me of a story in the coffee shop of a mother and adult daughter discussing this past winter. The daughter saying how “normal” it was to have these huge swings in temperature and crazy weather (snow then short-sleeve weather). Mother saying “Well I remember when I was young, it would be more consistently cold with a lot more snow, not like now”. What’s normal has changed with time in a lot of world, but you wouldn’t know it unless the different generations notice and chit chat about it.
Our chances of snow appear to be over. Never say never, as the East Coast seems to be getting blasted by these cold storms, but when you start seeing these consistent mild conditions finally, it’s usually a sign of the seasonal transition…finally.
I do have some concern over this Spring’s tornado season I must say. La Nina periods in the El Nino Southern Oscillation tend to be known for quite intense tornado outbreaks. Trying to get a science paper reading in about it this week if I can. The Gulf of Mexico waters are running above normal for moisture, the South has been quite warm overall with record warm days and months this winter. And jet stream dynamics continue to be favorable for bringing periodic shear profiles for significant severe weather. The atmosphere put on quite a show this weekend in the Deep South where it is climatologically favorable for tornado activity. Reminds me to prep an emergency kit. We do have a weather radio, but with things like tornadoes and urban flooding, you never know when you will need a little more to get through a few days of darkness and no refrigeration.
While, it’s quiet here, the West and East Coasts are being battered by major winter storms to start Spring. Very strong upper-level trough over the eastern third of the country and another over the Eastern Pacific means the 4th nor’easter of the month in the East and huge atmospheric river event in Southern California. Heavy snow or flooding/mudslides?
Good mid-week to all and stay safe in these stormy areas!
–Meteorologist Nick Humphrey
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.
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.
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.
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.
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
I thought it would interesting to look at the past 5 months (September-January) as there have been some notable trends at the seasonal level which have led to major impacts within the US. Some of this is driven by the cool phase of the El Nino Southern Oscillation (La Nina) in the tropical Pacific, while in the longer-term, they are being driven by increasingly more powerful influence of anthropogenic climate change on global temperatures and natural variability.
The most notable climate anomalies the past several months since the beginning of Meteorological Autumn (Sept 1st) have been very abnormal heat…particularly in the Western US and increasing dryness across much of the nation.
The rapid increase in drought conditions since late Autumn was initially caused by the jet stream favoring the northern tier states and southern Canada, with strong upper-atmospheric high pressure over the West contributing to the abnormal warmth. However, by January, the pattern changed with the jet stream becoming much more higher in amplitude over the US. The strong ridging remained over the Eastern Pacific and Western US, but strong dips in the jet stream have thus far brought abundant cold air masses into the center and eastern third of the country. These continental Arctic air masses have also been quite dry, making it difficult for many places to recover from drought conditions. In many cases, the situation has worsened.
One thing to notice as far the heat is concerned for January 2018. Although there was a wide swath of the US with below normal temperatures, the 9 states out West had their Top 10 warmest January on record vs. no states with a Top 10 coldest. So even with a high amplitude jet stream opening up Arctic air to much of the US, high heat (by winter norms) still dominated the US average with the 35th warmest January on record, in the top 30% out of 124 years. In addition, Alaska witnessed very abnormal warmth. Barrow had its warmest November on record (more than 16 F above normal) while the whole state had its warmest January on record. Also in January, Ketchikan, AK measured its (and Alaska’s) highest daily January temperature on record of 67 degrees F in the Panhandle. While La Nina and other “teleconnections” (multi-month and sub-seasonal atmospheric circulation patterns) are creating conditions favorable for these abnormal conditions, anthropogenic climate change is clearly having an impact on the intensity of warm regions over cold regions and the tendency for more frequent drought conditions (and longer wildfire seasons), especially in the Western US.
It appears February will be a repeat of January, although it may end up warmer overall if long-term models work out. And with this, meteorological winter may end on very abnormally warm and exceptionally dry note.
–Meteorologist Nick Humphrey
2/11/18: Edited to add February 8th Drought Monitor.
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.
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%.
Extent growth basically stopped between February 3-6 (near 13,300,000 sq km for four days).
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.
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.
–Meteorologist Nick Humphrey