Freak April Snowstorm – Significant Severe Storm Outbreak Apr 8, 2013
NWS Riverton Wyoming: Heavier band of snow tracking north across Fremont County this afternoon. Here's what the WYDOT webcam showed in Riverton at 1:42 p.m. More snow on the way tonight

 

I’m sitting here, in a Monday funk, mourning the apparent death of spring, at least over the Plains and Upper Midwest. The calendar insists that it’s April 8, but as far as the atmosphere is concerned it’s March 1, give or take. An unusually intense storm (for the second week of April) will impact the central USA with heavy wet snow, heavy rain capable of urban and river flooding, and deeper into the warm, humid air, a significant severe storm outbreak, with a potential for a few large, violent tornadoes: central Plains today and Tuesday, pushing into the Mississippi Valley and Mid South by Wednesday and Thursday.

Highlights:* Near-blizzard conditions are possible in the Denver area Tuesday; where as much as 5-9″ of snow will fall.* Models print out some 20-30″ amounts across South Dakota, with plowable snows pushing across Minnesota into Wisconsin Wednesday and Thursday.* Chicago may pick up 3″ of rain by Thursday, complicating stream and river flood forecasts – I expect some level of urban flooding as well.* A few large, violent, long-track tornadoes are possible tomorrow from Austin and Dallas to Kansas City. By Wednesday the threat shifts to Shreveport, Little Rock, Memphis, St. Louis and Louisville.Details:3-5 Week’s Worth of Rain by Thursday. The NAM model prints out very heavy rainfall amounts for the Upper Midwest and Great Lakes, as much as 2-3″ or more of liquid water. Most of that water will fall as heavy wet snow over the Plains and portions of the Upper Midwest.

Spring On Indefinite Hold. The latest numbers are impressive.  People from Denver to Pierre to the Twin Cities and central Wisconsin may be impacted; the heaviest (20-30″) snowfall amounts from the Nebraska Panhandle into South Dakota and southwestern Minnesota. This will be a heavy, wet snow, capable of downing trees – I expect power outages over the High Plains by Tuesday evening.

 

Confirmation. The models are coming into alignment, showing the heaviest snowfall amounts from Nebraska into South Dakota and southwestern Minnesota, where some 12″+ amounts seem imminent. This could still be a plowable snowfall for the Twin Cities by Wednesday and Thursday, with some 5-10″ amounts extending toward Wausau, Appleton and the Green Bay, Wisconsin markets.

High-Resolution Models. All the models put the heaviest amounts in the same counties – it’s really a question of degree (and quantity). A period of ice (sleet and freezing rain) may cut down on final snowfall amounts from St. Cloud and the Twin Cities to Rochester, Minnesota – but precipitation will fall as mainly snow for Pierre, Sioux Falls and even the Denver area.

 

Mile High Mess. Snow arrives tonight in Denver, peaking tomorrow, when an increase in wind speed may trigger near-blizzard conditions. I’m comfortable (wrong word) predicting 5-9″ for the Denver area by the time snow tapers Wednesday.

 

Blizzard Potential Index. One of the many value-added models we run here at Alerts Broadcaster is the BPI, the Blizzard Potential Index, factoring in snowfall rates, wind speeds and predicted visibilities. The worst of the storm along Colorado’s Front Range is forecast to come Tuesday afternoon.

 

 

Living Up To Its Reputation. A year ago flowers were in bloom, lawns were greening up, boats in the water. Not this year. Enough cold air will feed into the storm for Tuesday rain to mix with ice Wednesday, changing to mostly snow late Wednesday into Thursday. A plowable, 4-8″ accumulation of slush is possible in the Twin Cities (heaviest amounts northern and western suburbs). Minor power outages are possible at MSP, due to the high water content in the snow.

 

Remarkable Extremes. I don’t think I’ve ever seen this. Alerts Broadcaster models predict highs topping 100F over southern Texas, while holding in the 20s over Colorado and New Mexico over the next 72 hours. The resulting temperature gradient will help to spin up an unusually intense storm over the Plains states.

On Track For A Significant Severe Storm Outbreak. Although not as expected to be as violent as outbreaks in 2011, the stage is set for supercell thunderstorms capable of large, long-lasting tornadoes capable of significant destruction. The risk is greatest tomorrow from Dallas to Oklahoma City and Wichita – the threat shifts into the Mississippi Valley by Wednesday.Friday Storm Potential. A few severe thunderstorms are likely in the Atlanta area late Thursday, possibly pushing into D.C., the Delaware Valley and New York City by Friday afternoon. Although the potential for tornadoes will be small, some storms may produce large hail and damaging straight-line winds. Friday’s PM commute may be a real mess across the Northeast.

Summary: 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, starting tomorrow, spilling over into Thursday. Disruptions to travel and the power grid may be considerable, especially from Denver into Nebraska and South Dakota. Ice changing to snow will create poor to treacherous travel conditions over Minnesota and Wisconsin. The worst conditions in Minneapolis and Milwaukee will probably come Thursday. The slow forward motion of the storm will prolong rainfall across the Midwest, accelerating run-off and stream/river flooding, especially southern Wisconsin into the Chicago and Indianapolis area by midweek.

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