Heavy rain, strong winds and storms to sweep South, East Coast

A classic spring storm system is rolling across the eastern United States, bringing an assortment of inclement weather. Severe thunderstorms are possible Friday and Saturday over much of the South and Southeast, with possible tornadoes, strong winds and flooding.

The same storm system will combine with another disturbance over the Great Lakes, swinging rain, strong winds and coastal flooding up the East Coast over the weekend.

On Friday, a Level 2 out of 5 risk of severe weather spans much of the Interstate 20 corridor from Texas to Alabama, and covers Lufkin, Tex.; Baton Rouge; Jackson, Miss; and Montgomery and Mobile, Ala. That’s where a few tornadoes are possible Friday afternoon.

Much of that same zone from northeastern Louisiana through Georgia and even the high terrain of the Carolinas is at risk of flooding rains. The National Weather Service has drawn a Level 3 out of 4 “moderate” risk for flash flooding and excessive rainfall, particularly near and south of Interstate 20 from Birmingham to Atlanta and south to Montgomery.

An elongated zone of low pressure stretches from the Texas-Louisiana border to near Chicago. Ahead of it, southerly winds are drawing north a warm, moist air mass that contains instability, or fuel for thunderstorms. That will set the stage for strong to severe thunderstorms in advance of a cold front, which is being dragged east by the low-pressure zone.

The jet stream, meanwhile, will be slicing overhead, inducing a change of wind speed and/or direction with height. Near the ground, winds from the south and southeast will prevail, while winds blow from the southwest higher up. That means that any storm clouds that grow tall enough could rotate. That could lead to the formation of a couple of tornadoes.

It’s unclear, however, how far north the leading edge of the warm air, demarcated by a warm front, will get. That will determine the overall expansiveness of severe storms. It’s possible that storms riding near the warm front, which looks to span from Jackson to Montgomery, could take advantage of a bit of extra low-level twist.

Thunderstorms were ongoing across Mississippi and north-central Louisiana around lunchtime, and will spread east and potentially intensify through the afternoon. “A tornado threat exists this afternoon into tonight from parts of Louisiana to southern/eastern Alabama,” the Weather Service wrote. “Large hail or strong-severe gusts are possible over the same areas.”

The threat of severe thunderstorms and a few tornadoes will arrive in the Southeast on Saturday. Atlanta is in a Level 2 out of 5 risk zone, which reaches from the Florida Panhandle to southern North Carolina. Jacksonville, Fla.; Charleston, S.C.; Savannah, Ga.; and Wilmington, N.C., are also included.

Heavy rains, flooding in the South

Training downpours, or those that move repeatedly over the same areas, will be a problem in the South. That’s especially true in southern Alabama.

Flood watches stretch from northern Louisiana to western South Carolina.

An initial slug of rainfall stretching from northern Louisiana to northern Alabama, predicted to drop 1 to 3 inches, will shift into Georgia on Friday night. In its wake, a second batch of downpours is expected to develop. That could deliver additional rainfall of 1 or 2 inches, leading to totals up to 5 to 6 inches.

Some weather models even simulate totals of up to 7 inches along the Alabama-Georgia border, which is a legitimate concern. While the ground has been relatively dry lately and can handle heavy rains, that would prove too much and would cause flooding.

Eastern U.S. rains and coastal flooding

The system will be a waterlogged one for many on the East Coast, but remember that it’s initially flanked by another system taking a path from the Great Lakes to northern New England (before the two systems merge Sunday over New England). That means there could be two separate rainfall maximums, with lower amounts in between.

One maximum is probable in the Carolinas. Two or 3 inches is possible in South Carolina, with 1 or 2 inches in North Carolina. The other maximum is expected from Pennsylvania through Maine, with 1 to 1.5 inches generally predicted.

There will be lesser rainfall in the eastern Mid-Atlantic — from around Washington, D.C., and Richmond eastward to the Delmarva Peninsula. A half-inch to an inch is likely in Washington, Baltimore and Philadelphia.

Much of the rain is expected to fall Saturday and Saturday night in the Southeast and Mid-Atlantic before reaching New England Saturday night into Sunday.

Coastal flooding will be a concern, too. Air feeding into the large low pressure zone will induce southeasterly winds — meaning onshore flow that pushes water against the coast. Coastal flood watches and advisories are being issued for many coastal communities in the Mid-Atlantic, where water levels 1 to 3 feet above typical will cause some concerns for shoreline inundation Saturday afternoon and night, especially around high tide. Portions of coastal New England could also experience minor to moderate coastal flooding, mainly on Sunday.

Meanwhile, gusty winds to 40 to 55 mph at the shoreline can’t be ruled out from the Delmarva to Cape Cod.

As cold air filters in on the storm system’s northwestern flank, plowable amounts of snow are forecast in the Adirondacks of New York as well as the high elevations of interior New England on Saturday night through Sunday.

Jason Samenow contributed to this report.

Source: www.washingtonpost.com

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