Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sat May 27 2023 18:58:33

AWUS01 KWNH 271858
FFGMPD
MTZ000-WYZ000-IDZ000-ORZ000-WAZ000-280100-

Mesoscale Precipitation Discussion 0356
NWS Weather Prediction Center College Park MD
257 PM EDT Sat May 27 2023

Areas affected...Northern Rockies

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

Valid 271900Z - 280100Z

SUMMARY...Meandering thunderstorms across the Northern Rockies and
interior Northwest may lead to flash flooding this afternoon.

DISCUSSION...A broad upper low positioned over the northwestern
U.S. and strong surface based heating is responsible for a
blossoming field of convection throughout the region. PWs from
eastern WA, northern ID, and northern MT are at or above the 90th
climatological percentile with the region at-large ranging between
0.7-0.9". RAP mesoanalysis shows the atmosphere has grown
considerably unstable with 0-3km lapse rates continuing to
steepen. One of the most noteworthy aspects to the excessive
rainfall potential is the RH values within the column. 17Z RAP
soundings from northern ID to western MT showed low-mid level RH
values >90%, to go along with low LCLs and warm cloud layers
several thousand feet deep in some cases. SBCAPE has been steadily
rising to 250-500 J/kg, with values closer to 1000 J/kg in central
MT.

Despite the lack of effective bulk shear, widespread storms
developing this afternoon will be slow moving. RAP mesoanalysis
shows 850-300mb winds that are <5 knots in some cases. While there
is a lack of shear to maintain healthy updrafts, the storms will
contain downpours thanks to the environment being so favorable for
efficient warm rain processes. Soils are also sensitive in
northern and central ID, as well as western MT where AHPS 7-day
rainfall amounts are as high as 300-400% of normal in some cases.
The 12Z HREF does suggest rainfall rates could top 0.75"/hr, with
a slight chance that the most intense storms could approach 1"/hr.
Given the slow storm motions, excessive rainfall rates,
anomalously saturated environment, and susceptible soils, there is
the potential for flash flooding this afternoon from the Columbia
River Basin to the central High Plains of Montana and the Tetons
of western WY. Unusually saturated soils, reside in or near burn
scars, poor drainage areas, and areas along steep slopes are most
prone to possible flash flooding.

Mullinax

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!817zjxGNnq02vr3Ea_rCwoj7wN7UqfVKQAHI2IVYihu9UHIGetaxj-g5tUaTWE8zH7DD=
FFT5ae6FGXDZa6eVWtpakXE$  for graphic product...

ATTN...WFO...BOI...BYZ...GGW...MSO...OTX...PDT...PIH...RIW...
TFX...

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

LAT...LON   49101625 49061458 49091311 49071120 49000947=20
            48790827 47340825 45810900 44330901 43230926=20
            42490969 42141111 42741214 43411144 44321142=20
            44351228 43671388 43941609 44551742 45191824=20
            46601786 48841778=20

=3D =3D =3D
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