We’ve been tracking a stationary front all week long, and it will continue to dominate this week’s weather across a large portion of the nation. Beginning this Wednesday, a developing low pressure over the Central Plains will begin to erode the front, and by this weekend the front will have dissipated thanks to a sweeping cold front on the backside of this low pressure. Before then, however, problems will continue to arise, especially this Wednesday with severe thunderstorms and flooding rains near the front.
An area of heavy rain and thunderstorms located over the Central Plains will ultimately dissipate midday as the atmospheric dynamics become non-conducive to support this storm complex. Before then, however, localized flooding will be possible especially in eastern Nebraska, where this June has already been wetter than normal. Then in the afternoon and overnight hours, the low pressure will really begin to take over. Several hours of heavy rain is likely near the region where Iowa, South Dakota, and Minnesota meet, which is where the center of low pressure is located. This is also the general region where we are most concerned for flash flooding. The Weather Prediction Center has this area at a moderate risk for flash flooding, which is just below the high risk on their excessive rainfall scale.
Now to the south and east, isolated severe storms will be possible ahead of the cold front, which will slowly move east. This afternoon and evening, the line of scattered, strong to severe thunderstorms will span from the Quad Cities region to as far south as the Red River Valley. Damaging winds and small hail will be possible in small towns, and a tornado or two cannot be ruled out, especially in eastern Iowa near the triple point, which is where the fronts meet the low pressure.
Severe thunderstorms will also be possible near the stationary front spanning from the Ohio River Valley through the southern Mid-Atlantic region. Scattered, heavy thunderstorms will develop during the afternoon and evening hours across the region, generally tracking to the south and east. There may even be a line of storms that moves near the Mason-Dixon Line in the evening, affecting cities like Philadelphia, Baltimore, and Washington, DC with rain and thunder. The best risk for any severe storms will be from eastern West Virginia through the Tidewater of Virginia. All of these areas will also be at risk for localized flash flooding.
A wave of low pressure riding this stationary front will also be responsible for bringing a round of light to moderate rain with embedded thunder to parts of the northern Mid-Atlantic region and southern New England Wednesday night. Cities such as New York City and Providence can expect rain overnight, clearing out by 8am the latest. Rain should remain south of the Massachusetts Turnpike, so Boston can expect a dry night.
On Thursday, the stationary front will begin to be on the move as the low pressure slowly makes its track to the east along with its upper-level low overhead. Some flash flooding will remain a concern across the Midwest as well as in the Mississippi River Valley and southern Mid-Atlantic. Rounds of rain and thunderstorms will be commonplace near the center of low pressure over Iowa. To the east, a shield of rain and thunderstorms will lift to the north and east ahead of a warm front, spanning from near the low pressure through Ohio and Tennessee River Valleys. Meanwhile to the west ahead of the cold front, isolated severe thunderstorms will be possible from the ArkLaTex up through the Mid-Mississippi River Valley.
Much of the Mid-Atlantic and Northeast will be able to salvage a beautiful, dry Thursday as high pressure suppresses the moisture to the south and west. A few spotty storms may roll in during the evening hours into the central Appalachian Mountains.
It’s not until Friday when showers and storms will track back into parts of the northeastern US. Back to the west, the low pressure will begin to occlude over the Midwest, meaning that dry air will wrap in and toward the center of the low. This indicates a weakening of the synoptic-scale storm. Along the warm front, rounds of showers and embedded thunder will span from the Great Lakes through the Mid-Atlantic while hit or miss thunderstorms affect areas in the warm sector south of the front. There will also be the risk for a few severe storms across the Ohio and Tennessee River Valleys ahead of the still-present cold front.
The flood risk will continue to dwindle but very localized flooding still cannot be ruled out in the central Appalachian Mountains as a more widespread shield of rain affects the region. Showers and thunderstorms will then begin to creep into New England on Saturday, which may pose a risk for some severe weather. We’ll detail this more as Saturday approaches and the forecast certainty increases.
Through Friday night, a widespread one to two inches of rainfall is forecast. Some parts of the Midwest may receive over three inches due heavy, training thunderstorms.