Mesoscale Precipitation Discussion 0662
NWS Weather Prediction Center College Park MD
515 PM EDT Sat Jul 12 2025

Areas affected...Northern VA...Central MD...Washington D.C.

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

Valid 122115Z - 130115Z

SUMMARY...Slow-moving thunderstorms with very heavy rainfall rates
of up to 2.5 inches/hour will result in concerns for urban flash
flooding across portions of the Washington D.C. metropolitan area.

DISCUSSION...Radar imagery and late-day GOES-E satellite imagery
shows strong thunderstorms developing and expanding in coverage
across areas of northern VA, central MD and notably the western
suburbs of Washington D.C.

MLCAPE values of 1500 to 2500+ J/kg are in place across the region
and this coupled with PWs of 1.75 to 2 inches will yield rainfall
rates of locally 1.5 to 2.5 inches/hour with the stronger
convective cores.

Small-scale mesoscale boundaries near the Potomac River and with
outflow associated with the existing thunderstorm activity is
promoting new convective development in a moist and unstable
airmass. This airmass is characterized by MLCAPE values of 2000 to
3000 J/kg with PWs of 1.75+ inches.

Given the thermodynamically favorable environment along with a
likelihood for additional small-scale mesoscale boundary
collisions over the next few hours, additional shower and
thunderstorm activity is expected to linger through the early to
mid-evening hours. Thereafter, conditions should improve with the
exhausting of daytime heating and related instability.

Some localized storm totals of 3+ inches will be possible with
this shower and thunderstorm activity given slow cell-motions.
These rains will pose an urban flash flood threat to especially
the western suburbs of the Washington D.C. metropolitan area
including portions of northern VA and central MD.

Orrison

ATTN...WFO...AKQ...LWX...

ATTN...RFC...RHA...NWC...

LAT...LON   39267732 39127685 38607695 38127732 37997764
            38177808 38627805 39067773