Isolated severe thunderstorms are possible across the Gulf Coast and the Mid-Atlantic, as well in to parts of central Pennsylvania. The cold front continues to move eastward across the Appalachian Mountains. Heavy showers and a few strong gusts are possible in the Mid-Atlantic and central Appalachia. Meanwhile in the southern U.S., ongoing heavy thunderstorm activity will influence the potential for an isolated severe gust or two, with a low chance of medium sized to large hail.
Discussion… For the Gulf Coast, morning sounding observations showed a modestly unstable environment with instability near 1,000 to 1,500j/kg. While surface to mid-level wind fields appear relatively weak i.e. 20-30 knots average, an upper-level jet streak is moving over the region and will potentially aid upper air forcing, allotting isolated medium to large hail perhaps to 1.0 inch in diameter. A large, multi-cellular cluster of thunderstorms over the coastline of the Gulf of Mexico continues to move east-northeast along an axis of robust theta-E advection (theta-E is potential temperature in air parcels). Kinematic and thermodynamic analyzations off the current mesoscale analysis indicate water loading and high precipitable water values near 0.75″ – 1.00″ of liquid; flash flooding could be possible across the southern Gulf states. Doppler radar scans indicate very heavy precipitation in the stronger cores and I will mention the possibility of an isolated wet-microburst across eastern Louisiana, southern Mississippi and Alabama as storms move inland.
Mid-Atlantic and central Pennsylvania / Appalachia… The warm front continues to drift northeastward through the region where surface temperatures have warmed into the middle-upper 60s and into the lower 70s. Despite ambient cloud cover hindering any robust surface heating, moisture content and water loading could yield an isolated strong gust or two as storms migrate into the region later this afternoon. The 1200z observed soundings from Washington D.C. and Wallops Island, Virginia, indicate meager CAPE (instability) values near 500-750j/kg. While instability is fairly weak, the low-level jet is near 40+/- knots and winds become more unidirectional in the mid-levels, increasing to 50-60 knots. The unidirectional wind shear will enhance the potential for an isolated damaging wind event if storms can become strong enough with the ongoing clearing in central Appalachia based off the visible satellite. Also, a small to medium sized hail event, up to penny size, cannot be ruled out. Heavy rain could be possible in any organized cluster of thunderstorms, so minor flash flooding of urban creeks and streams is possible across the region.
While the severe weather risk if much lower today, the main hazards will be possible flash flooding and isolated wind events. Remember: If a roadway is flooded, turn around and don’t drown! An update will be issued if/as needed later this evening if flood potential enhances across the eastern portion of the nation. This forecast is valid through tonight.
…Forecast initialized 2:28pm EDT / 1828z, 3/26/15…
– Student Meteorologist Harrison Sincavage, Penn State University.