8:45 AM (Sat.) | ***Strong storms/soaking rain in the Mid-Atlantic later this afternoon into tonight with strong cold front...higher risk of severe weather in DC and Philly...lower in NYC***
Paul Dorian
Overview
Soaking rain is on the way for the Mid-Atlantic region and there is a threat for strong-to-severe thunderstorm activity as well from later today into tonight. The greatest risk of severe weather will be in the DC-to-Philly corridor with lesser chances across New York City. The main severe weather hazard with this advancing strong cold front will be damaging wind gusts, but hail and even isolated tornadoes are on the table. The front pushes off the east coast by early Sunday paving the way for a cooler and breezy finish to the weekend and a secondary cold front will pass through on Sunday night paving the way for even cooler conditions on Monday.
Details
The early morning began with some low clouds and patchy fog in the DC-to-Philly corridor, but as a warm front lifts northward, some sunshine will break out and the breeze will pick up noticeably from a southerly direction. At the surface, a strong cold front is situated over the eastern Ohio Valley this morning and it will slowly edge its way to the east during the next several hours. Meanwhile, the associated upper-level support will evolve into a “negatively-tilted” trough orientation by later in the day allowing for very strong upward motion to develop across the eastern Mid-Atlantic region from DC-to-Philly and including surrounding areas such as the Delmarva Peninsula and New Jersey. (Delmarva, New Jersey).
Showers and thunderstorms have already formed over eastern Ohio and West Virginia this morning and they will work their way eastward during the next several hours. As the upward motion increases in the atmosphere and daytime heating intensifies, the atmosphere will become more and more unstable and some the thunderstorms will likely intensify into strong-to-severe levels. Given the strong low-level jet that is expected to form near the frontal boundary zone, strong and potentially damaging wind gusts will likely become a threat with a line of thunderstorms likely to form later in the day. In addition, some signs point to a “backing” of surface flow later in the day and this may allow for a “spin” in the atmosphere to develop as a line of thunderstorms approaches. This could result in a few isolated tornadoes as the storms move through with perhaps the greatest risks in SE PA and the Delmarva Peninsula. The threat for the active weather will begin in the early-to-mid afternoon hours in the DC metro region and the mid-to-late afternoon near Philly. While there can be strong storms in and around the NYC metro region, the risk for severe weather is lower than in places farther to its south and west such as DC and Philly as cooler (marine) air will keep the atmosphere more stable in the northern Mid-Atlantic. The threat of storms will extend to near midnight across coastal sections of New Jersey and the Delmarva Peninsula.
In terms of rainfall, this frontal passage will actually bring some much needed amounts of generally 0.50-1.50 inches although locally higher amounts are possible in any strong thunderstorm. Temperatures today will climb into the 70’s ahead of the cold front and will be confined to the 60’s on Sunday for afternoon highs and then it’ll turn even cooler on Monday following the passage of a secondary cold front on Sunday night.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com