Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri Jun 09 2023 03:51:05

AWUS01 KWNH 090351
FFGMPD
MTZ000-090900-

Mesoscale Precipitation Discussion 0448
NWS Weather Prediction Center College Park MD
1150 PM EDT Thu Jun 08 2023

Areas affected...Much of Montana

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

Valid 090345Z - 090900Z

Summary...Localized rainfall rates of 1-2"/hr to continue,
additional scattered instances of flash flooding likely (with a
significant instance or two of flash flooding possible).

Discussion...A broken line of thunderstorms is moving slowly
northwest across much of Montana late this evening, with the
heaviest cores producing rainfall rates of 1-2"/hr (per MRMS
estimates). The mesoscale environment remains supportive of
additional scattered instances of flash flooding over the next
several hours, with highly anomalous moisture indicated by PWATs
of 1.1-1.4 inches (remarkably above the annual max moving average
that occurs in late July, per GGW sounding climatology), ample
remaining instability with MU CAPE of 500-2000 J/kg, and modest
effective bulk shear of 20 kts (though favorable diffluence aloft,
despite the lack of shear). Storms look to continue to propagate
slowly northwestward (with the deep layer mean wind ~10 kts),
moving towards the higher pool of instability (as well as an axis
of deep layer moisture flux convergence, per latest RAP analysis).

Given the anomalously moist tropospheric column and relatively
slow storm motions, scattered instances of flash flooding are
likely to continue in association with rainfall rates of 1-2"/hr.
Some training of these rates are also likely, with some localities
having the potential to receive an additional 2-3"+ of rain
through 09z (per 00z HREF neighborhood exceedance probabilities of
20-40% and 10-20% for 2" and 3" thresholds, respectively). Given
that much of the region has seen 300-600% of normal rainfall over
the past week, a significant instance or two of flash flooding
cannot be ruled out (especially considering that 6-hr FFGs locally
are as low as 1").

Churchill

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!4J0VAmz2yLG7LDw2OxjZZojDvnVKLYF2Ti05WCUUKC8CsX2GR1Bz-MUb3HJPUZ699hwV=
LTJOwomX_IITGRnuosHc9j4$  for graphic product...

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

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

LAT...LON   48921041 48170739 47040558 45470569 45060729=20
            45830837 46390930 47071090 47461260 48651302=20
=20=20=20=20=20=20=20=20=20=20=20=20

=3D =3D =3D
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