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March 4, 2011 / Dave Gorham

A Mix of Winter and Spring across U.S: Snow, Flooding, Severe Storms

[The following is a slightly edited version of the ImpactWeather Storm Development Outlooksm which is generated daily during severe weather outbreaks that affect a substantial part of the country.  The SDO is emailed to ImpactWeather clients.  – Dave]

Heavy Rain and Severe Weather Risk on Track for the Southeast U.S.

Heavy, Wet Snow Risk on Track for the Interior Northeast

Another Major Winter Storm and Severe Weather Threat Next Week

Discussion: A strong disturbance will move across the Great Plains bringing an increasing chance of showers and thunderstorms this afternoon and evening from northeast Texas northeastward through central Illinois and Indiana. Be advised that a few of these storms may be strong to severe late Friday, especially over eastern Oklahoma, southern Missouri, Arkansas, and northern Louisiana. Showers and thunderstorms will shift quickly east and south, bringing an increasing risk of heavy rainfall and flooding to a large part of the Ohio Valley, Tennessee Valley, and Deep South on Saturday, before continuing eastward towards the Atlantic Seaboard on Sunday. Although a few severe storms with hail, strong winds, and isolated tornadoes are possible again on Saturday over the Deep South, the primary threat will be from locally heavy rainfall.

General rainfall amounts are forecast to average from 1-3 inches, however isolated totals as high as 5 inches are possible. The best chance of heavy rainfall will be in the area extending from eastern Mississippi, Alabama and north Georgia northward across the Ohio Valley through Saturday, with additional heavy rainfall likely along the Eastern Seaboard, especially into coastal New England Sunday into the first part of Monday. Please be advised that rising rivers and localized flooding will remain a threat for much of the Ohio and Tennessee River Valleys through the weekend as this storm moves through. Saturated terrain from previous rainfall will allow flooding to occur more rapidly.

Image: ImpactWeather StormWatch

North of the severe thunderstorm and heavy rainfall threat areas, widespread heavy, wet snow and mixed freezing rain will be possible from eastern Iowa eastward across lower Michigan into southeast Canada. Snow accumulations of three to six inches are expected over much of this region with isolated higher amounts. By far the heaviest snow is expected to fall across southeastern Canada where 8-12 inches of snow could easily fall with isolated higher amounts up to 18 inches or more. On Monday, a secondary area of low pressure is expected to quickly strengthen off the New England coast bringing a chance of very heavy snow over most of New England, just north and west of the Boston area. Snow accumulations across most of this regin should average 6-12 inches with locally higher amounts up to 18-24 inches. Most of the snow across interior New England will end Monday evening.

Image: ImpactWeather StormWatch

Long-range Blizzard Threat: As the eastern system departs the area later in the day on Monday, our attention will shift to the west over the Rocky Mountains and Great Plains as yet another major winter storm system takes shape. Strong low pressure is forecast to quickly organize over the central Rockies late in the day on Monday and shift quickly east and northeast across the Central Plains, Midwest, and Great Lakes through Wednesday, bringing a good chance of heavy snow from Idaho and Utah eastward across the Northern Plains and Upper Midwest.

Falling snow is forecast to increase in coverage and intensity over the Rockies through the day on Monday, before shifting eastward across northern Nebraska and South Dakota Monday evening through Tuesday morning. Falling snow will then shift east across northern Iowa, Minnesota and most of Wisconsin on Tuesday afternoon and evening before shifting eastward into Michigan and most of the interior Northeast next Wednesday and Thursday. Be advised that several ingredients are coming together across this region of the country which may result in a heavy accumulation of snow. In addition to the snow, strong northerly winds will likely accompany this storm system resulting in the possibility of widespread blowing and drifting snow with near-blizzard to blizzard conditions, especially across the Northern Plains and Midwest. Temperatures may be as much as 20-25 degrees below normal.

Image: ImpactWeather StormWatch

Image: ImpactWeather StormWatch

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