After severe weather outbreak, storms exit East Coast on Thursday

WEATHER NEWS: After severe weather outbreak, storms exit East Coast on Thursday

What was advertised to be a potentially significant tornado outbreak on Wednesday failed to spin up the “strong, long-track” twisters anticipated, with mainly shorter-lived twisters forming within a line. Even so, damaging wind gusts were widespread, and at least one fatality was reported.

Blizzard delivering record April snowfall in northern Plains this week

It wraps up the main event in what has been the latest multiday severe weather episode to torment the south so far this month, coming on the heels of the most active March for tornadoes on record.

The cold front that instigated all the severe weather is exiting the East Coast Thursday, but not before bringing scattered thunderstorms, a few of which may be strong to severe. Fortunately, its departure marks the commencement of a more tranquil pattern set to build in over the Lower 48, with cooler temperatures replacing recent springlike warmth in the East.

On Monday, severe thunderstorms dropped softball-sized hail and a few tornadoes near and west of Little Rock. Tuesday’s storms were most heavily concentrated in Texas and Iowa; an EF3 tornado that made an unusual 90 degree left-hand turn narrowly missed crossing Interstate 35 near the town of Salado, Tex., about 40 miles north of Austin, with another major tornado observed near Gilmore City, Iowa.

Tornadoes touch down in Iowa and Texas on Tuesday

A cold front swept through much of the south Wednesday, producing widespread damaging winds that left at least one person dead in Arkansas when a tree fell onto their mobile home. A number of tornadoes also developed, and storm surveys are underway.

On the storm’s cold side, blizzardlike conditions hit in Bismarck and Montana starting Tuesday, dropping unusually high amounts of snow for this time of the year, and into southern Canada on Wednesday. Action is expected to wind down on Thursday.

A level 1 out of 5 “marginal risk” of severe weather is up for much of the Eastern Seaboard on Thursday, covering cities such as Albany, Baltimore, D.C., Richmond, Raleigh, Charlotte and Panama City, Fla. An acutely greater threat — a level 2 out of 5 slight risk — is present between Springfield, Mass., and Philadelphia, including New York City, Hartford and Newark.

Thunderstorms will begin to develop during the late morning or early afternoon. While there is a sharp 20-degree temperature contrast between the air ahead of the front and that behind it, along with a considerably drier air mass building in, there are several key ingredients lacking in severe storms — wind shear is on the weak side, with the main storm center also well northwest of the cold front, and relatively meager instability out ahead of the line. Only isolated severe weather is expected.

Some storms might stir up gusty winds to 60 mph. Otherwise, most other cells will be accompanied by heavy rain and brief winds gusting between 30 and 40 mph, along with some lightning.

D.C. and Baltimore should see the scattered thunderstorm threat begin around 2 to 4 p.m., although a few showers or a rumble could continue behind the front into evening. In this area, most showers or storms should be quick hitting and not cause much problem.

Storms reach the Philadelphia to New York City corridor in the later afternoon. That region is closer to stronger winds aloft and may see more feisty storms than to the south.

Next widespread severe weather odds

Following Thursday’s front, there are signs that severe weather chances may flatline for the next week or so in the contiguous United States. That’s for several reasons.

For starters, cooler air is expected to descend from Canada and waft over the eastern United States. Ordinarily, a severe weather pattern is composed of cold air over the western United States at high altitudes and comparatively milder, humid surface air banked up in the East. That allows lobes of western chill to pinch off and drift east, where they kick up pockets of unstable air into showers and thunderstorms. The opposite is the case presently, cutting back the risk of storms.

Moreover, the upper-air pattern over the United States will become one dominated by zonal, or west to east, flow. That means the jet stream will be oriented roughly west to east, devoid of the energetic dips and kinks that whip through it. Those “troughs” are integral for allowing upper-air disturbances to hitch a ride east.

The jet stream is ordinarily the divider between warm air to the south and frigid air farther north. Cold air flows south within the jet stream’s dips as warm air surges northward in the ridgelike crests. That allows for punctuated clashes of the air masses. Without any waves in the jet stream, there’s much less west to east temperature contrast — instead, it becomes a pallid, gradual south to north gradation.

On Friday, there’s a level 1 out of 5 marginal risk for severe weather over the Ozarks, which will ooze south into East Texas, Louisiana and Mississippi, as well. A very remote chance of damaging winds or an isolated tornado can’t be ruled out.

There may be some severe weather over the central Plains toward the middle of next week, but there are no clear signs of a notable tornado risk — though it’s still too far out in the future for many details. The next significant wave of storms that looks poised to pose widespread severe weather could swing through the southern United States by the weekend of April 23.

Before then, a long-range model used by the Storm Prediction Center simulates a dearth of active weather in the next seven to 10 days. This model output is updated each day.

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