Severe Weather Threats for Central Plains Monday-Wednesday

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.

 

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European Model forecast depiction of trough of low pressure in the upper-atmosphere over the Western US (forecast for 7 am CDT Tuesday May 1st). This system will contribute to severe weather for the Great Plains Monday-Wednesday.

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.

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Schematic of a classic supercell thunderstorm.

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-

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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-

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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-

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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.

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European Model forecast depiction of Precipitable Water at 7 pm CDT Wednesday (how much atmospheric moisture is available for precipitation in an instantaneous moment). This does not say how much will fall, but just how moisture laden the atmospheric column is. The plume of abnormally high PW will mean the potential for storms with locally heavy rainfall.
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European Model forecast depiction of dew point temperature at 1 am CDT Thursday May 3rd. Dew point is a measure of atmospheric moisture. The air behind the warm front and ahead of the dry line is warm and moist (with dew points above 60 F at this time), while the air ahead of the warm front is cool, with less moisture. The air behind the dry line is extremely dry and warm (dew point temperatures in the teens and 20s F).
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European Model forecast simulated upper-atmospheric water vapor imagery for 7 pm CDT Wednesday. The computer model simulates what the weather satellite water vapor channel may see Wednesday night as far as cloud structures. Water vapor imagery is a special type of infrared imagery where water vapor concentration in the upper atmosphere can be detected based on its “brightness temperature” (upper atmosphere is moist, it appears bright, upper atmosphere is dry, it appears dark, meaning water vapor is warm, located at lower level of the atmosphere). Here, the water vapor imagery is enhanced with colors to better interpret the temperature of the condensed water (clouds). We can see intense thunderstorm formation over Kansas at this time (likely supercells) with some further development into Oklahoma as well. This is NOT LIKELY how it will look exactly Wednesday evening, only a general idea of the storm structures based on the larger-scale flow pattern and expected ingredients for storm formation.

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

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Stay safe out there today! Severe storms likely and in progress.

Nebraska is in the ice box still…but big storms, including tornadoes and significant straight line wind damage possible in parts of Indiana and Kentucky today.

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Warm, moist air, and lots of vertical wind shear. Good set up for some nasty severe weather.

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Prominent severe weather threat is between the polar and subtropical jets (northerly and southerly branches, respectively). In between, lots of mass is being removed allowing for storms to explode from below, intensify rapidly and maintain themselves in the highly sheared environment (winds rapidly increasingly with height).

There is a lot of speed shear, but not as much change in direction with height, which favors lines of storms. So the threat for damaging winds is quite significant, hence the “moderate risk” (4 out of 5 on the overall scale by the Storm Prediction Center) for a 45% chance of damaging wind reports within 25 miles of a point within the given region, and a 10% or higher chance of winds over 74 mph (hurricane-force). However, a significant tornado risk also exists for storms which do isolated themselves earlier this afternoon. So remain vigilant if you are in these areas and tell anyone you know to remain ready to take cover this afternoon and evening!

My part of Nebraska?

Unseasonably cold. Just straight up…cold. Starting off spring as if it were February with temperatures 25-30 degrees F below normal for highs and 15-20 degrees below normal for lows. Will have some recovery later this week, but near normal conditions (+-5 degrees F) don’t appear consistently likely until early next week. Thursday may give us a one day break with mid-50s (normal is around 60 F). So far our warmest day this year was March 3rd (73 F). The Great Plains have been part of the very wild weather pattern impacting much of the mid to upper mid-latitudes this year thanks to a highly oscillating jet stream with periods of very cold and very warm conditions relative to local norms. Much of Europe has gone through the same with very cold Arctic air mass spells, while the parts of the East Coast had record heat in February, followed by multiple cold and heavy snow periods from damaging nor’easters. All while the Arctic roasted in heat waves in this winter (relative to their norms) has significant heat and moisture moved northward, hitting sea ice hard. Here in my locality, we’ve had the roller-coaster ride of going from a a high of 4 to a high of 56 in ten days (January), a high of 22 to a high of 65 in seven days (February; and actually the high was 58 two days before that high of 22…ha!) to our mid-May days in early March (low-70s). Now after the last 5 days of March in the more seasonable 50s to low-60s, we’re spending the first three days of April barely above freezing. Winter was wild and Spring is starting off confusing weather even by spring standards. At least it’s not record breaking cold, it is unusually cold regardless though. Looking forward to the actual warmth of spring again.

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.

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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)
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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).

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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.

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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).
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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. 

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

–Meteorologist Nick Humphrey

 

 

Meteorological Analysis of January 22, 2017 Great Plains/Midwest Blizzard As It Happened

Here is a meteorological analysis I did on Monday of the blizzard which raked much of the Central Plains and upper Midwest from Nebraska and Kansas to Minnesota and Wisconsin with heavy snow and high winds. It was recorded around 11:30 am CST Monday. Those who follow me on my Facebook page (also see my feed on the sidebar) were able to see it right after it was uploaded, but I’m posting it here for those interested in hearing me discuss the event as it happened. Peak snow totals up to a foot and a half resulted in parts of Nebraska, Iowa and Minnesota. Lincoln and surrounding parts of the town only saw 2-3 inches but the totals increased dramatically not far west and north. We got off easy compared to the one foot and greater totals in northeast Nebraska. Winds gusts throughout the region peaked 45-60 mph. You can hear the noise of the high wind through my door in the video.

By the way, my son Bruce makes a guest appearance as he tries to turn off my computer while recording. Haha.

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.

Thomas Fire in Southern CA becomes 5th largest in state history; 230,000 acres and growing

The Thomas Fire of Ventura and Santa Barbara Counties in Southern California has now become (as of Sunday Night) the 5th largest fire in California State history. And based on trends and fire weather expected, it may go for the state record (273,246 acres).  After winds decreased somewhat Friday afternoon-Saturday, they picked up again on Sunday, causing extreme fire growth to an incredible 50,000 acres and reducing the containment from 15% to 10%.

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Growth of Thomas Fire since last Tuesday’s ignition.
Since the fire developed last early-morning Tuesday, it has exhibited extreme fire behavior in intense Santa Ana winds with gusts of 45-80 mph, fanning flames and, more importantly, embers far downwind of the actual fire. Currently, 790 structures have been destroyed with the evacuation of over 88,000 people. A 70 year old woman died after being overtaken by the fire following suffering severe injuries in a car crash. In San Diego County, another woman was badly burned over 50% of her body in the Lilac Fire while helping horses escape from a thoroughbred training facility.  And speaking of horses…46 horses were confirmed killed at San Luis Rey Downs where the trainer was badly injured. The death toll will likely rise among the horses as 450 horses were there when the fire rapidly struck. Many burned to death refusing to leave their stables or running back into them, while others died from shock even after initially safely away from the fire’s path. Meanwhile, another 29 horses suffered a similar fate at a ranch in Los Angeles County’s Creek Fire.

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Dry or low precipitation conditions expected in mid-range computer models (this forecast depiction by the Global Forecast System; GFS) for much the Southwest US and Great Plains through December 20th.

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Forecast upper-atmospheric wave pattern valid noon CST Monday by the GFS. Powerful ridge of high pressure over the West will continue dry, very abnormally mild conditions while colder weather remains over the eastern US.
Unfortunately, high fire danger will continue through Monday with gusts over 45 mph allowing the Thomas Fire and any other fires which develop to easily spread and do so rapidly. Conditions should relax Monday night before possible re-intensification on Tuesday. As mentioned, the Thomas Fire may reach record territory tomorrow based on trends. And as of now, NO significant measurable rainfall is expected in California (or much of the Southwest US and Great Plains) the next 10 days. A blocking upper-atmospheric high pressure pattern over the Eastern Pacific will certainly allow for intensification of drought conditions and continued dryness and moderate to high fire danger for days to come. I should also note, fire danger will also be elevated on parts of the High Plains. Much of Eastern Colorado into Western Kansas are under red flag warnings for Monday because of expected elevated breezy conditions and low humidity with dry fuels.

—Meteorologist Nick Humphrey

First Game of World Series Tonight…Weather Headline: HOT

The World Series begins tonight in Los Angeles between the LA Dodgers and the Houston Astros. And it begins with record heat in Southern California. Today, in fact, downtown LA is setting a record high for the day and it is the warmest temperature on record for so late in the year. This was after a record high of 102 was set for downtown LA yesterday. So far it has reached 103 downtown and the official high may be higher before the day is done.

First pitch for the World Series is at 5 pm PDT this evening. While temperatures will decrease somewhat by that time, game time temperatures will be in record territory for a World Series Game (95-100 degrees F). The hottest World Series first pitch on record was from a game (cannot remember which) in 2001 in Phoenix when the NY Yankees played on the road against the Arizona Diamondbacks in a starting game temperature of 94 degrees.

In addition to heat, fire danger remains VERY high across Southern California as Santa Ana winds intensified today and will continue into tomorrow. RED FLAG WARNINGS are in effect for parts of SoCal. Gusts of 50-60 mph have caused problems for firefighters as they dealt with brush fires in Granada Hills this morning and Rancho Cucamonga this afternoon (LA Times). 

(Map of Rancho CucamongaMap of Granada Hills)

Game 2 of the World Series (First Pitch at 5 pm PDT Wed) should be slightly “cooler”, but still quite hot…expecting temperatures to start the game in the mid-90s (92-97 degrees F). If you’re going to these games or doing any outdoor activity at all in Southern California…lots of water and be careful with anything that sparks or burns!

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US Global Forecast System forecast temperatures at 5 pm PDT Tuesday.

Enjoy the game! Go American League and go Astros!

–Meteorologist Nick Humphrey