Mesoscale Precipitation Discussion 0378
NWS Weather Prediction Center College Park MD
750 AM EDT Fri Jun 06 2025

Areas affected...Central Appalachians...Northern
Mid-Atlantic...Southern NY State

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

Valid 061150Z - 061750Z

SUMMARY...Scattered showers and thunderstorms will generally tend
to expand in coverage by midday across the central Appalachians,
the northern Mid-Atlantic, and southern NY state. At least
isolated areas of flash flooding will be possible given heavy
rainfall rates and locally wet antecedent conditions.

DISCUSSION...The early morning GOES-E WV suite shows a fairly
well-defined shortwave impulse advancing east through the upper OH
Valley which will be crossing gradually into the central
Appalachians and northern Mid-Atlantic by midday. This energy
coupled with a quasi-stationary front and multiple waves of low
pressure riding northeast along it is already producing some
locally heavy showers and thunderstorms across far eastern OH, the
northern WV Panhandle and far western PA.

While instability is quite modest with only about 500 to 750 J/kg
of MUCAPE in place where the axis of convection is occurring, the
diurnal heating cycle by later this morning through midday will
facilitate stronger boundary layer instability. This coupled with
local orographics and differential heating boundaries, along with
a weak upper-level jet streak (associated with the aforementioned
shortwave trough) should support a gradual expansion of convective
activity that will encompass the central Appalachians and stretch
northeastward across the northern Mid-Atlantic and southern NY
state.

The PW anomalies early this morning are running about 1.5 standard
deviations above normal with CIRA-ALPW data showing rather strong
concentrations of moisture in the 850/500 mb layer ahead of the
shortwave impulse. This coupled with the increasing instability
over the next several hours should favor increasingly efficient
rainfall rates that by later this morning may reach 1.5+
inches/hour.

Cell-motions are forecast to be relatively slow, and with some of
the activity capable of briefly training over the same area, some
3-hourly rainfall totals of as much as 2 to 3 inches will be
possible. Given the locally wet antecedent conditions that are in
place, these heavier rainfall rates/totals may cause at least some
isolated ares of flash flooding and this will include some urban
flooding impacts as well.

Orrison

ATTN...WFO...ALY...BGM...BUF...CLE...CTP...ILN...LWX...PBZ...
PHI...RLX...RNK...

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

LAT...LON   43127592 42817468 42037441 41467499 40477713
            39197893 37678073 37748220 38738324 39908286
            40858186 41888015 42747773