Severe storms, isolate tornado risk in Mid-Atlantic on Friday

WEATHER NEWS: Severe storms, isolate tornado risk in Mid-Atlantic on Friday

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A springtime severe weather risk has materialized over the Eastern Seaboard, with the chance of scattered severe thunderstorms with damaging straight-line winds and isolated tornadoes. A tornado watch was issued early Friday from areas between the Mason-Dixon Line and the North Carolina Piedmont, and a broader risk of severe weather exists farther north toward the New York City Tri-State area.

Storms may come in multiple rounds — an initial appetizer round marking the rejuvenated leftovers of Thursday’s storms, and a secondary batch of storminess along a cold front during the afternoon and evening. The latter is predicated on a few hints of sun breaking out after the first line of storms, which would heat the ground and allow the atmosphere to recover.

Update: Tornado watch in effect until 2 p.m. for D.C. area

It’s possible that additional tornado watches will be issued farther north or also reissued to accommodate the afternoon severe weather threat.

A level 2 out of 5 slight risk for severe weather has been drawn by the National Weather Service Storm Prediction Center to include much of the Interstate 95 corridor along the East Coast. Cities like Charleston, Raleigh, Richmond, Washington D.C., Baltimore, Philadelphia and Newark are all encompassed in the severe weather risk.

There were preliminary reports of a possible tornado touchdown in Goode, a community near Lynchburg in Bedford County, central Virginia shortly after sunrise. Twenty homes were reportedly damaged and two mobile homes were destroyed.

A low pressure system over southern Michigan is stirring up a sprawling counterclockwise whirlpool-like swirl in the atmosphere. It’s entrained a tongue of warm, humid air northward over the East Coast while simultaneously dragging cold air southeast in its wake. That’s left a cold front draped near the Appalachians.

A secondary low forming along this front near the Blue Ridge may enhance low-level easterly winds, bolstering spin. Simultaneously, a pocket of cold air, low pressure and spin aloft nestled within a dip in the jet stream is passing overhead. In addition to juicing up the atmosphere and cooking up thunderstorms, the change of wind speed and/or direction with height, known as wind shear, will foster rotation within storms.

Storms will be low-topped — in other words, they won’t be overly tall, so large hail isn’t a concern. In fact, some cells may not even produce much thunder or lightning.

Morning storms have taken the form of a broke line. It’s possible that embedded kinks of rotation develop within the line, but tornado risk has diminished some.

Behind that first line, however, clearing skies could amplify the risk of a few rotating afternoon supercells with low-end tornado potential.

The first round is ongoing now and should approach the Chesapeake Bay by 2 p.m.

It’s probable that the next round will develop ahead of and along the cold front between 6 and 11 p.m. That second band will be stronger if more sunshine is present behind the first storms.

The second round would be more isolated in nature and have a greater chance of producing an isolated tornado or for cells to acquire supercell characteristics. Those storms will be more common south of the Mason-Dixon Line.

Storm mode is a source of uncertainty. Lone, discrete supercells are easier to rotate than, say, a line or bowing segment of thunderstorms. (Think about spinning a top on a table — it would be easier if it was a small circle than, say, a large elongated line or rectangle.) If supercells form with the second round of storms, tornado risk would be greater.

Where severe storms could interrupt Memorial Day weekend

Likewise, atmospheric recovery is a wild card. Does clearing ensue behind that initial batch to help the atmosphere recover? Or does low-level moisture make for cloud cover that keeps the landscape socked in and cooler? It’s wholly unknown.

That said, if you live in the Mid-Atlantic and see sunshine after lunch, that’s a bad sign.

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