Scattered severe thunderstorms featuring strong, damaging winds are possible across parts of the Northeast and interior Mid-Atlantic on Friday, including Philadelphia, Baltimore, Cleveland and New York. Heavy downpours and isolated severe storms will materialize during the early afternoon hours ahead of a sharp cold front moving through the Ohio Valley.
There’s even a low risk of an isolated tornado.
The Storm Prediction Center has issued a marginal risk (level 1 out of 5) for severe weather over much of the Northeast on Friday.
Off-and-on rain and showers were already ongoing over portions of New York State and Pennsylvania on Friday morning. The extent to which these showers clear and sunshine builds will determine the magnitude and areal coverage of storms during the afternoon.
Regardless, “it will be a windy day even outside thunderstorms” for many in the interior Northeast, wrote the National Weather Service in Binghamton, N.Y. Widespread 40 mph wind gusts were occurring, pumping in unseasonably warm, humid air from the south ahead of the cold front.
Storms are forecast to develop over western Pennsylvania and Upstate New York by about noon, racing to the northeast and arriving along New York’s border with Vermont and Massachusetts by about 4 p.m. A storm or two might make it all the way to the coast by sunset.
It’s unclear how far south storms will build along the cold front, but any storms that do form could impact the New York-New Jersey-Connecticut area, Philadelphia, or even Baltimore during the evening commute. The greatest risk will be present farther north and west.
A limiting factor for severe storms Friday will be the amount of cloud cover present. That cuts back on daytime heating, reducing the amount of instability, which is the energy available for lifting air and brewing storms. As a result, storms Friday will likely be shallow and low-topped, perhaps struggling to produce much, if any, lightning.
With high winds in the low to mid levels of the atmosphere, any storms that form will have the potential to transfer some momentum down to the ground in the form of damaging wind gusts.
“It will not take very strong convective cores to mix down very strong [60+ mph] winds aloft,” wrote the National Weather Service in Mount Holly, N.J.
There’s also sufficient low-level wind shear — a change in wind speed and/or direction with height at the lowest levels of the atmosphere — for forming rotating thunderstorms. That could present an outside chance of a tornado occurring. The risk for that is low.
While tornadoes would be a very unlikely occurrence, even a single one could also have a high impact. It’s often difficult to communicate low probability-high impact events.
As always in severe weather situations, it is important to have a way to get notified if dangerous weather is approaching. One way to do this is to enable wireless emergency alerts (WEA) on your phone.