Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sun Jun 04 2023 18:32:07

AWUS01 KWNH 041832
FFGMPD
MTZ000-WYZ000-IDZ000-050030-

Mesoscale Precipitation Discussion 0424
NWS Weather Prediction Center College Park MD
231 PM EDT Sun Jun 04 2023

Areas affected...Central MT...Northern WY...Southeast ID

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

Valid 041830Z - 050030Z

SUMMARY...Blossoming field of thunderstorms in portions of the
northern Rockies may cause flash flooding, especially in rugged
terrain and areas with overly saturated soils.

DISCUSSION...A meandering upper low over northern UT and a ribbon
of 500mb vorticity tracking northwest out of Colorado is set to
provide modest PVA over the region as the atmosphere continues to
destabilize, courtesy of daytime surface based heating. The
region's moisture content remains exceptionally high for early
June, as NAEFS for 18Z today and 00Z this evening both show PWATs
in the 90-99th climatological percentile. These PWATs are
generally around 0.5-.0.75", but some areas in northern WY and
central MT could eclipse 1.0" PWATs this afternoon according ot
the latest RAP. The latest RAP also shows MLCAPE rising to
500-1,000 J/kg in the valleys and high plains of northern WY and
central MT, while the mountainous terrain from southeast ID, the
Tetons, Absaroka, and Big Horns range between 100-250 J/kg.

Mean layer 850-300mb winds are 20-25 knots and out of the
southeast. Storms forming off the mountainous terrain will track
into the more unstable and moist air-mass in south-central MT.
Area averaged soundings from developing thunderstorms on the 17Z
HRRR showed profiles that featured low-mid level RH values as high
as 90% and skinny CAPE profiles aloft. Corfidi upshear vectors
were also lower than 10 knots in some sampled cells. The 12Z HREF
showed 6-hr QPF > 10-yr ARI probabilities were in the 20-40%
range, which provided some probabilistic evidence of the
potentially anomalous rainfall rates this afternoon. One of the
most notable factors supporting a flash flood threat this
afternoon are the overly saturated soils in parts of the region.
South central MT, in particular, has received >600% of normal
rainfall in the last 7-days.

Locations that have been subject to heavy rainfall over the past
1-2 weeks are most prone to possible flash flooding this
afternoon. Other areas, such as along complex and rugged terrain,
in poor drainage areas, and more urban developed communities could
also contend with flash flooding this afternoon.

Mullinax

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!-N5mMxiNpMBjKSZCr_UHyW-NSzsM7pcw7eMKGj7hoyRYnJN7b3AscI1oiwP67pBKpD74=
q92-uzhzsaBVNNSHFCltxEM$  for graphic product...

ATTN...WFO...BYZ...PIH...RIW...TFX...

ATTN...RFC...CBRFC...MBRFC...NWRFC...NWC...

LAT...LON   47711019 47450930 46760870 46300796 45850728=20
            45200687 44030657 43230658 42500761 42570917=20
            43231030 42601129 42771223 44041161 44801150=20
            45501150 46631179 47441108=20

=3D =3D =3D
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