Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Tue Aug 05 2025 06:57:52

AWUS01 KWNH 050656
FFGMPD
MTZ000-051200-

Mesoscale Precipitation Discussion 0870
NWS Weather Prediction Center College Park MD
256 AM EDT Tue Aug 05 2025

Areas affected...southeastern Montana and vicinity

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

Valid 050655Z - 051200Z

Summary...Backbuilding convection will pose a threat of isolated
flash flooding across southeastern Montana and vicinity over the
next 3-5 hours (through 12Z/6a MDT).

Discussion...Recent radar/satellite imagery depicts a localized
axis of backbuilding convection mainly across rural areas of
southeastern Montana between Billings and Sheridan.  The storms
backbuilding due to quick recharge of appreciable instability
aloft from very steep upstream mid-level lapse rates and
southwesterly flow aloft.  Weak mid-level waves moving through
this flow were also providing a focus for ascent across the
region, leading to backbuilding and repeating convection.  Areas
of 1 inch/hr rain rates were being estimated beneath the storms
per MRMS, which isn't surprising given 1-1.3 inch PW values=20
within a moist axis near the storms (just downstream of a surface
trough/dryline).  The current pattern suggests that a few hours of
heavy rainfall could result in spots of 3-4 inch rainfall totals
across the region through 12Z/6a MDT this morning.

CAMs suggest that eventually, upscale growth into a forward
propagating complex will limit the extent of repeating rainfall,
though this process may take a few hours to unfold.  Furthermore,
local FFG (around 1-1.5 inch/hr) was already being exceeded in
spots and more areas could experience FFG exceedance given the
aforementioned mesoscale-to-synoptic pattern.  Localized areas of
flash flooding are possible - especially from areas near I-90 in
southern Montana and eastward along/near US 212 across the
southeastern part of the state.

Cook

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!762EaUzioaiNYFSgyhFHbT3HDm6rehidDaGlzYEcw2zPBBNAW8CXrS3ec43vn1zQ-soM=
omnskIbTW3m5qUSsQJQuOao$  for graphic product...

ATTN...WFO...BYZ...GGW...

ATTN...RFC...KRF...NWC...

LAT...LON   46670491 46200416 45290404 45030484 45010719=20
            45200802 45560803 46210768 46650666=20

=3D =3D =3D
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