Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Wed Aug 21 2024 18:19:03

AWUS01 KWNH 211818
FFGMPD
NMZ000-AZZ000-UTZ000-NVZ000-220016-

Mesoscale Precipitation Discussion 0912
NWS Weather Prediction Center College Park MD
218 PM EDT Wed Aug 21 2024

Areas affected...in and near portions of Arizona

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

Valid 211816Z - 220016Z

Summary...Showers and thunderstorms are expected to expand in
coverage through the afternoon hours.  Hourly rain totals to 2.5"
are possible, which would be problematic in areas with burn scars,
slot canyons, arroyos/dry washes, and urban areas.

Discussion...The combination of an upper level trough moving
across portions of the West, an upper low moving southwest of AZ,
and an MCV across southern AZ have combined to produce an area of
rain with embedded showers and thunderstorms over south-central
AZ, which appear well captured by the 12z HREF guidance.  A
moisture plume around these systems extends across AZ into
southeast UT.  Precipitable water values are 1-1.5" in the
mountains and 1.5-1.75" in the desert per GPS data.  Temperatures
at 700 hPa are around 3C cooler than this time yesterday providing
less of a mid-level capping inversion and promoting an earlier
convective start time and greater potential cell coverage.=20
Effective bulk shear of ~30 kts helped to organize the convective
band in southern AZ.  CIN remains but is eroding at the present
time.  ML CAPE of 500-1500 J/kg lies across the region.

Daytime heating is expected to add 1000-1500 J/kg of ML CAPE with
time in more sunny areas, and 500+ J/kg in cloudier areas.  Given
the changes in the environment since this time yesterday, a
greater flash flood risk appears to exist.  Hourly rain totals to
2.5" are possible where any random mesocyclones form, cells of
various organization merge, or cells train within the deep layer
south to south-southwesterly wind flow.  This would be problematic
in burn scars, slot canyons, urban areas, and dry washes/arroyos.=20
Flash flooding is expected to be between isolated to widely
scattered.

Roth

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!_CxrkOEb6nCVLU99UdFrCsRO_lFZblnT_rYCIoAs6blDl-h-e5xY1nyWUuhQXM9K9q6j=
KOGaL_uTVVIvr_NbTgGljLo$  for graphic product...

ATTN...WFO...EPZ...FGZ...GJT...PSR...SLC...TWC...VEF...

ATTN...RFC...CBRFC...NWC...

LAT...LON   37860927 34450914 31250902 31051108 31941262=20
            33891385 36071425 37611272=20

=3D =3D =3D
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