Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Wed Jun 18 2025 20:35:22

AWUS01 KWNH 182035
FFGMPD
NYZ000-PAZ000-OHZ000-190200-

Mesoscale Precipitation Discussion 0479
NWS Weather Prediction Center College Park MD
434 PM EDT Wed Jun 18 2025

Areas affected...Western NY...Northwest PA...Extreme Northeast OH

Concerning...Heavy rainfall...Flash flooding likely

Valid 182035Z - 190200Z

SUMMARY...Flash flooding likely to continue as shortwave
approaches helping to expand convective coverage which will remain
slow moving and very efficient with 1.5-2"/hr rates and localized
totals to 3"+.

DISCUSSION...While the symmetric, mature main upper-low near
southern Lake Michigan dominates the GOES-E WV suite, there
remains a more subtle but similarly impactful compact wave
crossing central Lake Erie currently.  This wave is providing
solid DPVA and enhanced west-southwesterly 20-25kts of inflow
while corralling highly anomalous sub-tropical moisture across the
Lower Great Lakes.  A well defined surface front exists north of
the Lakes in the Ontario Peninsula and just north of the St.
Lawrence river Valley, but the cold lakes have provided strong
differential heating boundaries to help develop strong
thunderstorms earlier this afternoon.  Given this upstream wave,
cells have been very slow moving to the northeast with overall
best motions driven by propagation/redevelopment along outflow
boundaries which have become numerous across the area of concern
(please see graphic for some deliniation).

Given the deep moisture over AoA 2" in Total PWat and deep warm
cloud layers near 12-14Kft; efficient rainfall production has
resulted in 2"/hr rates and numerous incidents of flash flooding.
This trend is likely to maintain itself through the next 3-4 hours
as outflows intersect seeking out remaining pockets of 2000 J/kg
unstable air pockets.  Inflow from the southwest and some weak
isallobaric response has limited cell motions and with broader
slabs of ascent with merging boundaries/broader updrafts similar
1.5-2"/hr rates are likely to expand and perhaps intersect/overlap
with initial burst resulting in some localized totals to 3"+
further inducing other localized incidents of flash flooding
(especially in urban centers).

As the evening progresses, stronger convergence along the
shortwave trough axis now nearing the PA/OH state line, will act
as final bout merging and sweeping up the remaining active
convection.  Simple mergers may further enhance sub-hourly rates.
As such, scattered to numerous incidents of focused/localized
flash flooding are considered likely through exhaustion of
instability and/or shortwave moves through from west to east.=20

Gallina

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!6EH5Ic01KSZo8ndipk2DzepOHfl6LQgQ7QlgDXImhodUE5V0FdxSiNqp-Q9TU8Ir8Pzj=
ujENHkb-Ylopuv45dV0U1bY$  for graphic product...

ATTN...WFO...BGM...BUF...CLE...CTP...PBZ...

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

LAT...LON   43617639 43217584 42617587 41987662 41567726=20
            41167831 40957936 40858030 41088068 41858061=20
            42447964 42897909 43387893 43407700=20

=3D =3D =3D
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