Mesoscale Precipitation Discussion 0535
NWS Weather Prediction Center College Park MD
1034 PM EDT Tue Jul 24 2018

Areas affected...Portions of MD & PA

Concerning...Heavy rainfall...Flash flooding possible

Valid 250234Z - 250634Z

Summary...Showers and thunderstorms are increasing in coverage
between Chesapeake Bay and central PA.  Hourly rain totals to 1.5"
with local amounts to 3" are possible over saturated ground.

Discussion...A 0200 UTC surface analysis reveals a vague
stationary front extending from west-central VA across northern MD
and eastern PA.  Near and north of the boundary showers and
thunderstorms are showing some increase in coverage and intensity.
 An upper level circulation near the WV/VA/KY border junction and
weak shortwaves crossing the NC/VA border and moving up the
Chesapeake are aiding ventilation aloft.  Precipitable water
values of 1.8-2.2" exist across the area per GPS data and 00z
soundings.  Effective bulk shear of 20-30 kts within a region of
unidirectional flow with height is occasionally organizing short
bands.  ML CAPE 500-1000 J/kg exists in this region, which has
been slowly decreasing over time.

While the mesoscale guidance has been placed too far to the west
thus far with the convective activity, radar imagery shows some
slight westward drift over the past couple hours.  Much of this
area has saturated soils from previous days of rainfall, so it
would not take much to cause issues.  Hourly rain totals to 1.5"
have been seen on radar estimates with some of this activity.  The
mesoscale guidance has a signal for 3" amounts over the next
several hours, which might be achievable for as long as MU CAPE
values can remain >= 500 J/kg within this saturated air mass.

Roth

ATTN...WFO...BGM...CTP...LWX...PHI...

ATTN...RFC...MARFC...NERFC...

LAT...LON   42437546 41307530 41017541 40107573 39677611
            38827664 39587760 42067774