Major storm enters the Plains, dropping heavy snow and spawning severe weather

Infrared satellite image from last night shows intense supercells along the leading edge of Arctic air over Colorado and Nebraska.

What has been billed as the first major severe weather maker of the spring is also already delivering, and preparing to produce, potentially record breaking late-season snowfall from the eastern Rockies into the northern Plains, along the north side of its storm track.

Winter storm warnings now stretch from Utah to Minnesota, and blizzard warnings are up for locations near Denver, where schools and many businesses are closed today.

An additional 3-6 inches of snow (on top of similar amounts already fallen) is possible around Denver. Temperatures there are still in the teens today, compared to highs near and above 70 yesterday. Locations further to the north and northeast are expected to take the brunt of the heaviest snow as the storm develops further.

Where the strongest winds mix in, near zero visibility “white out” conditions are possible, thanks to sustained winds as high as 20-40 mph along with higher gusts. Temperatures, even during the day in what’s almost mid-April, should mainly hover in the teens and 20s throughout the region impacted by snow. Not too springlike.

Warning map across the country midday on April 9 shows a broad region under the gun for wintry weather. Of note, the winter weather advisories in Oklahoma where severe weather may first occur today. (NOAA)

The storm is atypical enough that, yesterday, veteran meteorologist Paul Douglas wrote in his WeatherNation blog, “I’ve seen a lot of things in 40 years of meteorology, but I can’t remember the last time I saw 20-30″ snowfall amounts during the second week of April. Portions of the High Plains may be temporarily shut down…”

Indications are that the heaviest of the snowfall is likely to generally target the South Dakota and Nebraska border region eastward, where a large swath of one to two feet of the white stuff is possible. Significant totals in excess of half a foot could be realized from parts of the Rockies through Nebraska, South Dakota, southern North Dakota, Iowa, Minnesota, and Wisconsin.

Probabilities of snowfall in excess of 4″ and 8″ for today across the Rockies and northern Plains. (NOAA Weather Prediction Center)

Christopher Burt, over at Weather Underground, had a timely post on the subject of April snowstorms a few days ago.

He noted, “The fact is that the greatest snowfalls ever experienced on earth have occurred during the month of April. For portions of the High Plains, Rocky Mountains, and Sierra Nevada April often produces the heaviest accumulating snowstorms.”

Burt pointed out that several states which are targeted by this snowstorm have seen all-time snowfall records set during the month of April before. Some spots in Wyoming, North Dakota and Montana recorded major storms as late as the end of April, or even May!

This weather mess is all being driven by a large upper-level low pressure system moving out of the west that spawned a consolidating surface low pressure over the Plains. As of midday, the low was located over Kansas and it was moving east northeast. The storm is expected to move toward the Great Lakes the next few days.

To the south of the low, a seasonably warm and moist air mass is set to clash with cold and dry air rushing in behind the storm. Many of the ingredients for severe storms are present as is often the case in April, the typical start of the peak severe thunderstorm season across the country.

tornado_blizzard_warnings_april8
Tornado warnings just northeast of counties under blizzard warnings late evening on April 8. (NOAA)

Already impressive front-running dynamics related the storm helped produce large supercells late yesterday, like this photogenic one in Colorado. Several of these isolated rotating storms brought reports of tornadoes in northeast Colorado, northwest Kansas and into Nebraska late in the evening. This happened while Arctic air was spilling into the region. In some cases, snow was falling just miles away.

The Storm Prediction Center has placed a large swath from Iowa and Illinois back into Texas under a severe weather risk today, with a specific highlight of central Oklahoma and north Texas for the potential of hail 2″ in diameter or greater.

What were fairly sporadic reports of severe weather over the western Plains the past two days (Sunday | Monday) should become a more widespread severe weather event today into tonight as the cold front rushes out into the increasingly warm and unstable air mass.

This morning, SPC wrote in part that:

LATEST MODEL GUIDANCE REMAINS IN GOOD AGREEMENT IN SUGGESTING THAT INCREASING HEIGHT FALLS AND LOW-LEVEL UPLIFT/CONVERGENCE ALONG THE COLD FRONT WILL FOSTER THE DEVELOPMENT OF SURFACE-BASED TSTMS BY MID TO LATE AFTERNOON FROM CNTRL/ERN KS INTO SWRN OK.

Convective outlook details for today and information for Wednesday and Thursday from the Storm Prediction Center this morning. (NOAA)
Convective outlook for today and for Wednesday and Thursday, from the Storm Prediction Center as of today’s midday update. (NOAA)

There is some uncertainty as to how the storms play out after development, but the cold front is expected to fairly quickly overcome the dry line across the Plains this afternoon. It is often that dry line wind shift out ahead of the front that becomes a conduit for the most significant tornado activity.

While it does not appear to be a setup for a classic large-scale tornado outbreak, multiple modes and rounds of severe weather — eventually favoring the long squall line with possible isolated embedded tornadic activity — will ensure that many locales need to keep an eye to the sky for the potential of damaging storms well into the night.

Those at highest risk, for mainly damaging wind and large hail, include a corridor from Kansas City to Oklahoma City to Dallas, as well as surrounds.

 Temperature change in the last 24 hours ending noon EDT April 9. (The Weather Channel)
Temperature change in the last 24 hours ending 1 p.m. EDT April 9. (The Weather Channel)

As the storm slowly churns to the northeast: the Midwest, Ohio Valley, and the Gulf Coast will be under the severe weather threat tomorrow. That potential shifts further east to mainly the Ohio Valley and Southeast on Thursday. Again, the main severe weather worry is expected to be damaging wind and/or large hail, but some tornadoes are also possible.

In the D.C. area, the odds for rain, maybe heavy, and probably with some rumbles of thunder in the region increases by late Thursday night into Friday. For now, any concern about truly severe weather late in the week is fairly minimal for our part of the Mid-Atlantic, though it’s something we’ll keep an eye on.

Ian Livingston is a forecaster/photographer and information lead for the Capital Weather Gang. By day, Ian is a defense and national security researcher at a D.C. think tank.
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Dan Stillman · April 9, 2013