Strong Winter Storm Impacting portions of Plains and Midwest Early Week

A strong winter storm is pushing across the Great Plains tonight. North of the low will experience widespread blizzard conditions and heavy snow. South of the low milder conditions with rain.

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Infrared image, but with surface frontal analysis added, valid at 6 pm CST.

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Parts of far southern Nebraska, into Iowa have a tight gradient between little to no snow vs. heavy snow with high winds. An example…my location in Lincoln, NE where the National Weather Service is calling for 3-4 inches for the day Monday and just added the county under a blizzard warning after 24 hrs ago thinking the area would only receive up to 1 inch with gusty winds and much better travel conditions.

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A difference less than 24 hrs makes. Lincoln now expects up to half a foot of snow (see below) and places expecting 7-8 inches are now expecting 12-18 inches!

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The whole system has been trending southeastward in the models and in reality and so the official forecast has been trended slightly higher and significantly so in places of central and northeastern Nebraska which may get up to a foot with isolated amounts up to 18 inches! The bigger story are winds which may gusts 35-50+ mph across much of the north-central Plains during the night and during the day Monday. This will induce the blizzard conditions, with very low visibilities.

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Conditions will improve across Nebraska and South Dakota by tomorrow evening as the storm shifts northeastward, continuing to impact northern Iowa and southern Minnesota, as well as Wisconsin and upper Michigan with locally heavy snow and gusty winds.

If you’re in an area under blizzard or winter storm warnings, stay off the roads during the worst of the conditions unless absolutely necessary as the roads will be treacherous and visibility poor, particularly outside major cities, where snow can blow around easily. If you have to travel, drive slowly and with care.

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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.

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Powerful nor’easter offshore Long Island Thursday afternoon.
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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).

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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.

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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.

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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.

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“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

Multiple Arctic Air Surges Expected Into Next Week

After periods of very abnormally warm weather, surges of very cold air from the Arctic will be barreling out of Canada starting Thursday into next week.

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European model model depiction of morning temperatures over the US and southern Canada at 6 am CST Tuesday 12/26. May be colder with winds.
These cold surges are a result of a highly amplified jet stream which has been shifting around North America for the past few weeks with a strong ridge over the Western US and trough over the US. However, the ridge is retreating over the Eastern Pacific and intensifying into Alaska, heating up the Arctic and putting southern Canada and the US in the ice box.

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US Global Forecast System model forecast for 6 pm CST Thursday 12/21 showing highly amplified wave pattern of atmosphere at 500 millibar pressure surface (approximately 18,000 ft altitude).

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“HOT” Arctic. Temperatures in Barrow, AK running over 30 degrees F above normal on Thursday (normal high is -3 F). Normal low is -15 F. That abnormal warmth will become less intense, but persist into next week.
The Storm Prediction Center does have a marginal risk of severe weather ahead of this week’s major frontal system over Southeast TX Friday. The risk appears to be for a isolated severe thunderstorm wind gusts over 60 mph and low risks of tornadoes.

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Here in the land of the corn? We should peak in the upper-30s tomorrow morning and then have falling temperatures and increasing winds during the afternoon with freezing drizzle with increasing breezy conditions out of the northwest. Not much snow accumulation expected here, although it could get slick from some of the freezing precipitation. Anyone else in the middle of the country, be careful as the cold air moves in if you’re on the roads!


Quick update on the Thomas Fire in California:

As of this post, the fire burned 272,000 acres…the 2nd largest in California state history (within less than 1500 acres of the state record). It has killed two people, including a firefighter. It is 60% contained. It began December 4th.

No significant rainfall is expected is expected in Southern California through the end of the month based on computer models. The Eastern Pacific ridge of high pressure seems to have a dominant grip on the region unfortunately. A combination of a La Nina pattern and climate change-induced extremely low Arctic sea ice and warm Arctic causing an incredibly amplified jet stream which tends to produce “stuck” and “stale” patterns.

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European model forecast accumulated precipitation through 12/30 showing the possibility of little to no measurable rain or snowfall in much of the Southwest US. Been little to be had in that region in December.
We can only wait and see if the lack of rain and snow forecast in the models in fact verifies for the Southwest US.

Happy first day of (astronomical) winter!

–Meteorologist Nick Humphrey