Severe storms could break more than the heat in eastern US

Powerful and damaging thunderstorms that have been focused mostly on the Midwest in recent days will turn their attention to the eastern United States through midweek.

As a cold front gains momentum, severe thunderstorms, many packing high wind gusts, will erupt and roll from the eastern Great Lakes, Ohio Valley and middle Mississippi Valley to the Appalachians and Atlantic Seaboard into Wednesday night and beyond in some cases, AccuWeather meteorologists warn.

The storms can trigger regional power outages and lead to major travel delays as they approach and pass through the major metro areas. Tree and property damage will be likely in some communities. Some of the most intense storms that reach high into the atmosphere can also produce hail.

In recent days, severe storms have packed quite a wallop in the Midwest and part of the interior Northeast. During Monday night alone, hundreds of incidents of high winds and wind damage occurred from Iowa to Illinois and Indiana as a large complex of severe thunderstorms covered hundreds of miles and triggered multiple tornadoes in the Chicago area.

AccuWeather meteorologists believe the complex met the National Weather Service definition of a derecho where there were consistent incidents of high wind gusts (58 mph or greater) over a distance of at least 400 miles. Close to 300,000 utility customers were without power from Iowa to Illinois and Indiana in the wake of the storms for a time on Tuesday, according to poweroutage.us.

On Tuesday afternoon, a tornado may have been the cause of significant damage in the upstate city of Rome, New York. Multiple vehicles were tossed around, utility poles were blown over and some structures were damaged.

Even though conditions that produced the powerful thunderstorm complex are changing, it does not mean that storms cannot be severe at the local and regional levels.

"The front is pushing into a zone of very hot and very humid air so it would not take much to produce heavy and gusty thunderstorms at the very least in a number of locations," AccuWeather Chief On-Air Meteorologist Bernie Rayno said.

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Brief urban flooding can occur in any metro area where downpours persist. Toronto received several hours of heavy rain and caused some city streets to look like rivers with multiple vehicles becoming swamped on Tuesday morning.

Another heavy rain spot was in east-central Missouri and west-central Illinois on Tuesday. From 1-3 inches of rain fell on the area surrounding St. Louis. Locally higher amounts occurred and pushed small streams out of their banks. A dam near Nashville, Illinois, located to the southeast of St. Louis, was at risk of failure.d

In the 24-hour period ending at noon, local time on Wednesday, from 4-8 inches of rain fell on portions of Arkansas and resulted in flash flooding. In Flippen, Arkansas, which is located in the Ozark Mountains, much of that rain fell in six hours or less on Wednesday morning.

As the cold front continues to press on at midweek, so will the likelihood of severe thunderstorms.

The midweek severe weather threat is forecast to extend from Maine southward to the Carolinas and northern Georgia, then westward to eastern portions of northeast Texas. Where severe thunderstorms are anticipated in parts of the area, a moderate risk of severe weather will be centered along Interstate 95 from southern Maine to eastern Virginia, as well as areas farther to the west in Virginia. A moderate risk means that numerous severe thunderstorms are likely to occur.

Similar to Tuesday, the main threats to lives and property will stem from powerful wind gusts and frequent lightning strikes. However, torrential downpours can also hinder travel. The AccuWeather Local StormMax™ wind gust for Wednesday's storms is 75 mph.

The risk of flash flooding is of equal concern as up to a couple of inches of rain could pour down in an hour's time in the I-95 corridor.

On Thursday, the overall intensity of severe weather may be somewhat reduced to a more sporadic nature. However, there will be at least some risk of locally damaging thunderstorms packing high winds and torrential downpours centered not only on the Carolinas but also much of Georgia and central and southern Virginia.

Locally heavy and gusty thunderstorms may extend westward to parts of the lower Mississippi Valley as well Thursday.

As the storms settle over the Southeast states from Thursday into the weekend, where the cold front is forecast to stall, the incidents of flash flooding are likely to increase as beneficial rain in drought areas becomes more problematic.

"A general 1-3 inches of rain is likely to fall from late this week to early next week," AccuWeather Meteorologist Elizabeth Danco said, "But where those downpours persist, amounts may reach or exceed 6 inches during the period."

Some of the more intense downpours can bring rainfall rates of 1-2 inches per hour for a time, which is more than enough to lead to urban flooding problems.

Even in a pattern where downpours become the major problem for outdoor plans, some storms can pulse enough during the afternoon and early evening hours to trigger locally damaging wind gusts in the Southeastern states.

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