Mesoscale Precipitation Discussion 1059
NWS Weather Prediction Center College Park MD
810 PM EDT Wed Sep 25 2024
Areas affected...Southern Virginia into West Virginia
Concerning...Heavy rainfall...Flash flooding possible
Valid 260009Z - 260600Z
SUMMARY...Localized flash flooding into the overnight as moisture
ahead of Helene streams over a stationary front and into the
eastern slopes of the Appalachians.
DISCUSSION...The northern end of the moisture plume in advance of
Helene is lifting across NC and will cross a persistent front over southern/southwestern VA rest of the evening. Scattered
thunderstorms have broken out along this frontal zone and to the
west there remains terrain enhanced rainfall along the eastern
slopes of the Appalachians. There were two main areas of heavy
rain in this region over the past day, farther east over the NC/VA
border last night, and earlier today west of the stationary front.
The main focus for heavy rain into the overnight is generally
progged to be between these two areas, but this is where the Blue
Ridge is, so a bit of a broader swath as been drawn for possible
flash flooding.
Instability is sufficient with MLCAPE of 1000 to 2000 J/kg and
moisture influx has been noted with low level southerly flow will
increase from 15 to 30 kt through midnight which will reinforce PW
around 1.7". Deep layer mean flow is around 30kt which should keep
activity east of the Blue Ridge progressive, but localized
rainfall over 1"/hr may cause some flooding issues. Terrain
enhanced rates of 1"/hr will also cause concern...flash flooding
is considered possible into the overnight.
Further activity in the southern Mid-Atlantic is likely into
Thursday, so please be on the look out for updated heavy rainfall
info.