Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri Jun 23 2023 23:42:32

AWUS01 KWNH 232342
FFGMPD
SDZ000-NDZ000-MTZ000-WYZ000-240540-

Mesoscale Precipitation Discussion 0573
NWS Weather Prediction Center College Park MD
741 PM EDT Fri Jun 23 2023

Areas affected...central/southern Montana, northeastern Wyoming,
and portions of western South Dakota

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

Valid 232340Z - 240540Z

Summary...Flash flood potential continues across the discussion
area, with the greatest risk persisting across southern and
central Montana through 06Z.

Discussion...A broad band of convection has materialized across
the discussion area extending from central Montana (near HLN)
east-southeastward through BLX to northeastern Wyoming near GCC.=20
Convection along the western and central portions of this axis was
moving very slowly westward due to modest wind fields aloft.=20
Low-level easterlies were maintaining surface-based buoyancy near
the storms (500-1000 J/kg MLCAPE), while slow storm motions and 1
inch PW values were resulting in multiple areas of 1-2 inch/hr
rain rates that were exceeding local FFG thresholds (in the 1
inch/hr range).  Flash flooding will remain likely (and
potentially widespread) over the next 4-6 hours as this axis of
precipitation only slowly lifts northward.

Farther east into southeastern Montana, eastern Wyoming, and
western South Dakota, that same convective band was
forward-propagating to the east at around 20 knots.  The faster
storm motions were limiting rainfall totals so far, although spots
of 1-2 inch rain rates were noted especially with individual cells
from northeast of Casper to northwest of Rapid City.  The slightly
faster movement of storms in these areas suggests that flash flood
potential is a bit more isolated compared to points north and
west, and should be moreso tied to individual convective evolution
and any potential backbuilding.  Storms should gradually exit
Wyoming while spreading into more of western South Dakota through
the early overnight hours.

Cook

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!6qxL-6C-cqX7G-ZRGTMCv_XlvkEEjf69SUsz89Bw473yMkaIDMLLDOoN7uYSV5nuH9Z8=
yc_dUmSu_cQA00b4Q_iiZ8I$  for graphic product...

ATTN...WFO...ABR...BIS...BYZ...CYS...GGW...RIW...TFX...UNR...

ATTN...RFC...MBRFC...NWC...

LAT...LON   47900564 46900366 45640149 44150086 43120148=20
            43070372 43120566 44780636 45230745 45190874=20
            45271016 46961115 47591068 47890938=20

=3D =3D =3D
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