Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Mon Aug 25 2025 17:25:34

AWUS01 KWNH 251725
FFGMPD
AZZ000-CAZ000-252330-

Mesoscale Precipitation Discussion 0999
NWS Weather Prediction Center College Park MD
124 PM EDT Mon Aug 25 2025

Areas affected...Southern Arizona...

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

Valid 251730Z - 252330Z

SUMMARY...Monsoon convection with rates up to 2"/hr.  Localized
1.5-2.5" pose possible widely-scattered localized flash flooding.

DISCUSSION...A compact but atypically strong retrograding
shortwave can be seen well in composite RADAR mosaic near Blythe
starting to turn more northerly across the Lower Colorado Valley.
The associated debris clouds will hamper insolation to build
instability, however, the upwind areas over the Sonoran Desert has
received solid insolation with anomalous moisture remaining across
southern AZ.  Surface Tds in the low to mid-60s combined with core
of CIRA LPW up to 700mb, extends through much of southern AZ as
well, with only mid-level drying at 700-500mb layer directly south
of the boarder; providing enhanced buoyancy with CAPEs already
building over 2000 J/kg, on their way to 2500-3000 J/kg with
limited capping.   Total PWats of 1.75" are above normal, about
1.5-2 standard anomalies and being loaded mainly near cloud base
(and below) should allow for solid efficiency.

GOES Visible imagery shows, low level convergence along the upwind
edge of outer band of the MCV is producing thunderstorms, that had
been weaker, but with influx of increasingly unstable air from the
desert, are starting to deepen and broaden.  Low level flow is
still responding to the exiting MCV and broader upglide into the
strong divergence aloft from the expanding right entrance to the
50+kt 3H jet streak across S NV/SE CA, as such, back-building
(upwind propagation) may maintain for a few more hours allowing
for effective slow cell motions increasing totals up to 2".

Through the late morning/early afternoon, as the MCV exits, winds
are expected to further strengthen with westerly upslope
components across southeast AZ terrain across Cochise, SE Pima and
S Graham counties.  Vigor of low level upslope is likely to
significantly increase toward/after 21z, with 15-20kts of westerly
flow at 850mb.  Peak heating/updraft strength and flux into the
terrain, rates should increase to 1.5"/hr with some 2"/hr rates
peaking toward 22-00z.  Probabilities/Hi-Res CAM suite suggest
best overall cells are likely to be along and just north of the
US/Mexico border with a spot or two of 1.5-2.5" totals.  With a
bulk of the rain occurring in sub-hourly bursts and hard ground
conditions, increased run-off suggest widely-scattered incidents
of flash flooding are possible into the early evening.

Gallina

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!8HObKstHlnYfdGf5gVZMB6GcnHye6stn_-6pmLbaY-nN5YWhtre8o-uGlFf4ohSB6T2g=
-royNrvDuHby_XxCYQO3TgU$  for graphic product...

ATTN...WFO...PSR...TWC...

ATTN...RFC...STR...NWC...

LAT...LON   33981380 33801324 33001185 33221030 32611001=20
            31641000 31251023 31231108 31591220 31871308=20
            32511428 32941465 33401478 33821434=20

=3D =3D =3D
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