Active Weather Week Across the Nation’s Heartland

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An active weather pattern is shaping up across the central and eastern U.S. this week as a strong low pressure system and its associated fronts move eastward. Showers and thunderstorms will continue to develop across this region as we head into the afternoon hours. Widespread severe storms will be possible across the Central and Southern Plains and into the Missouri River Valley. There will be an elevated risk of severe storms across eastern Nebraska, Iowa, northern/western Missouri, eastern Kansas, and into eastern/central Oklahoma. The main threats will be frequent lightning, large hail, damaging winds in excess of 60 mph and isolated tornadoes.

 An elevated risk (indicated in orange) of severe storms will exist across this region. Image: ImpactWeather StormWatch

The warm front associated with this strong low pressure system across the Plains will move northeastward today across the lower Great Lakes and Ohio Valley. Isolated severe storms will be possible this afternoon into the early evening across this region. The main threats from any severe storms that develop will be occasional to frequent lightning, strong winds in excess of 50 mph, small to moderate hail and isolated tornadoes.

 Severe thunderstorm threat for Monday, June 20th. Image: ImpactWeather StormWatch

Tomorrow, the strong low pressure system will move northeastward from the Plains into the Upper Midwest. A cold front will extend from the area of low pressure southward and interact with daytime heating and instability to produce a risk of strong to severe thunderstorms. An elevated risk of severe storms will be possible across northern Arkansas, Missouri, eastern Iowa, much of Illinois, southern Wisconsin, Indiana, southwestern Michigan and far western Ohio. Severe thunderstorms will be capable of producing frequent lightning, large hail, damaging winds in excess of 60 mph and isolated tornadoes with the best chance of activity during the afternoon and evening hours. A slight risk for strong to severe storms will also extend as far east as the Appalachians and Mid-Atlantic in association with a warm frontal boundary with storms also possible as far south as central Texas and Louisiana.

 Severe thunderstorm threat for Tuesday, June 21st. A moderate risk of severe storms is indicated in orange, while a slight risk is indicated in yellow. Image: ImpactWeather StormWatch

 Here’s a magnified version of the same map, showing the moderate risk (orange) of severe storms on Tuesday. Image: ImpactWeather StormWatch

On Wednesday, the low pressure will slow down and drift across the Upper Midwest and Great Lakes while gradually weakening. Showers and thunderstorms will remain possible across a large portion of the eastern U.S. with a few strong to severe storms possible along the associated cold front stretching from the Upper Midwest southward through the Ohio Valley, Tennessee Valley, Mid-Mississippi Valley and into Louisiana and east Texas. Strong to locally severe storms will also extend from the low pressure system eastward across the Great Lakes and into the Mid-Atlantic and Northeast. Primary threats from any thunderstorms that develop on Wednesday will be occasional to frequent lightning, hail, strong wind gusts and isolated tornadoes.

 Image: ImpactWeather StormWatch

In addition to the threat for strong to severe thunderstorms, this slow-moving low pressure system coupled with abundant moisture will allow for locally heavy rainfall through the first half of the week from the Northern Plains eastward through the Upper Midwest and into the Great Lakes. General rainfall amounts will range from 1 to 3 inches by Wednesday evening; however, isolated heavier totals in excess of 4 to 5 inches will be possible. This will likely lead to a continued threat of lowland and river flooding, as well as a threat for localized flash flooding at times.

 Here is a map indicating forecasted 3-day rainfall amounts from Monday through Wednesday. Image: ImpactWeatherStormWatch

Elsewhere, we’re already three weeks into the 2011 hurricane season so what’s going on in the Atlantic?  We seem to be off to a fairly slow start as you can see in this TropicsWatch Daily Briefing, a sample of our brief daily video outlook.

As for the drought-stricken south-central U.S., the upper Texas coast, at least, is expecting precipitation this week. More on that tomorrow.

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