Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Thu Jul 06 2023 22:07:20

AWUS01 KWNH 062207
FFGMPD
NEZ000-SDZ000-MTZ000-WYZ000-070405-

Mesoscale Precipitation Discussion 0646
NWS Weather Prediction Center College Park MD
606 PM EDT Thu Jul 06 2023

Areas affected...southern Montana through eastern Wyoming, western
South Dakota, and northwestern Nebraska

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

Valid 062205Z - 070405Z

Summary...Isolated to scattered convection should produce areas of
heavy rainfall and localized flash flooding through the early
evening hours.

Discussion...Low-level upslope/southeasterlies and abundant
sunshine has fostered deep convective development especially along
and just downstream of ridgelines and terrain from south-central
Montana into north-central Wyoming.  The storms are embedded
within modest westerly flow aloft (around 20-25 knots), allowing
for slow eastward storm motions at around 15 knots or so.  The
slow storm motions and brief heavy rainfall near the convection
was boosting rain rates into the 1 inch/hr range, while FFG
thresholds ranged from as low as 0.75 inch/hr across portions of
south-central Montana to around 1-1.5 inch/hr across eastern
Montana.  A few spots were experiencing rain rates exceeding FFG
thresholds, suggesting that a localized/isolated flash flood
threat exists currently with this activity.

This flash flood risk should remain isolated in the near term.=20
Over time, models/CAMs suggest that convection will gradually
increase in coverage, although this will likely occur in tandem
with somewhat faster storm motions as cells grow upscale and begin
to forward-propagate to the east.  This process should keep the
flash flood risk isolated and tied to areas of training and/or
cell mergers that can materialize and prolong local rain rates
through the evening.  Latest indications are that storms should
exit southern Montana through the early evening (00-01Z), while
reaching the WY/SD/NE border areas in that same timeframe.  Cells
will gradually migrate eastward into western SD/NE through the end
of the MPD period (04Z).

Cook

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!6qbhM1EU5rLT3zhVaqkCaHsF8CQ8NW--RlH736o8sM-QwBrq3IJCfknWBUHyOJdnbU87=
rBxWPwbuELOXkG7B7jaCay4$  for graphic product...

ATTN...WFO...BYZ...CYS...GGW...LBF...RIW...TFX...UNR...

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

LAT...LON   46930971 46900699 45980422 44680262 43820215=20
            42870228 42040289 41760434 42240584 42850665=20
            43970718 44720805 45320937 46010992=20

=3D =3D =3D
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