Mesoscale Precipitation Discussion 0466
NWS Weather Prediction Center College Park MD
1205 AM EDT Tue Jun 17 2025

Areas affected...northern WV into far western MD

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

Valid 170400Z - 170900Z

Summary...Some persistence of 1.0-1.5" localized hourly rainfall
amounts may allow for isolated instances of flash flooding.

Discussion...Relatively weak low-level convergence and moisture
transport in the vicinity of a quasi-stationary surface front and
inverted trough of low pressure is maintaining a cluster of heavy
showers and thunderstorms with efficient rainfall (1.0-1.5" hourly
localized amounts, per MRMS) over northern portions of WV. The
mesoscale environment in the vicinity of this cluster of
convection is characterized by a maxima of surface based
instability (SB CAPE of 500-1500 J/kg) with little to no
convective inhibition, precipitable water values of 1.7-1.9 inches
(near record levels, per PIT sounding climatology), and effective
bulk shear of 25-30 kts. Low-level moisture transport is only
expected to increase over the next few hours, as the pressure
gradient tightens with a deepening low over the northern Great
Lakes and an upper-level trough over the Mid-South both making
their way eastward. Isentropic lift is expected to become more
pronounced as a result (concentrated on the 300-305K surface,
generally between the 900-800 mb isobaric surface), and this
appears to be favorably offset by idealized divergence aloft in
the vicinity of the right-entrance region of a 70 kt jet streak at
250 mb (centered over north-central PA and arcing ESE-SE).

While 00z hi-res CAM signals are rather limited (with the 00z HREF
suite largely absent of QPF, with the exception of the 00z ARW),
the hourly HRRR runs have started to initialize and pick up on the
convection (02z more significantly so, depicting some 1-3"
totals). While the HRRR seems to want to kill off the convection
rather quickly, the 00z ARW indicates the potential for the
persistence of ~1"/hr localized rates (with slow progression and
backbuilding allowing for localized 2-3" QPF). Given the rather
favorable aforementioned environment for heavy rainfall (with a
particular focus on the highly efficient warm rain processes, as
wet bulb zero heights are around 12k feet) with very sensitive
terrain and wet antecedent conditions (1-3 hr FFGs of 1" or less).
Isolated instances of flash flooding are possible.

Churchill

ATTN...WFO...LWX...PBZ...RLX...

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

LAT...LON   39697956 39517895 38957909 39017986 39238091
            39498097 39668073