Mesoscale Precipitation Discussion 0124
NWS Weather Prediction Center College Park MD
508 AM EDT Mon Apr 01 2024

Areas affected...portions of Maryland, Delaware, far southern
Pennsylvania, and the District of Columbia

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

Valid 010907Z - 011307Z

Summary...Bands of west-to-east moving convection are producing
spots of 0.5-0.75 inch/hr rain rates across far northern Virginia,
with slightly lower rates near Washington, D.C.  These rates could
cause a few areas of flash flooding (especially in urban areas)
through morning rush hour and midday.

Discussion...A fairly focused band of convection has continued
through the night along a warm frontal zone extending from
southern Ohio through northern Virginia this morning.  Along this
frontal zone, mostly elevated convection has materialized, with
support for updrafts coming primarily from convergence on the nose
of strong 850mb flow amid marginal/weak instability.  The
orientation of this convergence/instability axis was generally
parallel to westerly flow aloft, however, allowing for training. 
Observations and MRMS suggest focused axes of 0.4-0.75 inch/hr
rain rates have materialized from near Winchester, VA to near
Gaithersburg, MD over the past 1-2 hours.

Over time, eastward movement of this band of convection will allow
for migration into areas of the DC/Baltimore urban corridor, where
FFGs are considerably low (in the 0.5-0.75 inch/hr range).  This
should cause at least isolated flash flood potential to emerge
across low-lying and sensitive areas over the next 2-3 hours. 
FFGs are also likely to be exceeded in spots.  The northward
movement of the warm front and aforementioned convergence zone may
be mitigating factors for a larger, more widespread flash flood
threat, with heavier precipitation expected to shift toward the
MD/PA border region through mid-morning.

Cook

ATTN...WFO...AKQ...CTP...LWX...PHI...

ATTN...RFC...MARFC...NWC...

LAT...LON   39887731 39617556 38817506 38627512 38697636
            39167791 39497877 39757823