Monday, May 14, 2012

Updating Tonight's Rains

As we work into the evening hours, there are lots of showers around to our west and there are a number of thunderstorms to our south.  Rain and thunder are organizing in two or three distinct areas -- first, over Pennsylvania with the steadier batches of rain that have traveled through most of Central Pennsylvania during the course of the day.  Second, with a line of thunderstorms in the Carolinas.  Third, a more disorganized (for now) area of rain and thunder across the Appalachians with the upper level low.  Computer modeling continues to focus on parts of this second area of rainfall for the brunt of activity this evening and tonight as the Carolina thunderstorm activity persists to our south this evening but then organizes farther north and northeast as the night progresses.

What that means for us is that we'll have off and on rains west of the city this evening, becoming steadier and heavier later tonight if the models are right.  All three main models (GFS, EURO, NAM) continue to suggest this moisture plume to our south organizes and lifts northeast through the evening, reaching our area after Midnight.  The question then shifts to where the heavier rain ends up falling -- whether it's west of I-95 in general like the GFS suggests, or if it's along I-95 as the Euro suggests predominately...or if a "duel train" sets up with the spine of the Appalachians getting the majority of the heaviest rainfall but a secondary plume of heavier rains falls across the Delaware Valley.  The difference is whether Philly picks up about an inch (GFS) of rain tonight and early tomorrow or if it's closer to two inches (Euro and NAM).

The splitting of hairs and parsing of details aside, it does appear that a round of heavy rain could lift through portions of the region after Midnight and continue into the morning rush hour.  Depending on how quick this rain lifts through, we could get into a lull for a while (perhaps even some sun west of the city?) that could help get the atmosphere primed for more thunderstorm activity tomorrow evening, especially south and west of Philadelphia.