994
AWUS01 KWNH 201944
FFGMPD
AZZ000-NVZ000-CAZ000-210130-

Mesoscale Precipitation Discussion 1036
NWS Weather Prediction Center College Park MD
343 PM EDT Fri Sep 20 2024

Areas affected...Southern CA...Far Southern NV....Far Northwest
AZ...

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

Valid 201945Z - 210130Z

SUMMARY...Slow moving, back-building cells with rates of 1"/hr may
pose localized 1-1.5" totals and possible flash flooding
conditions.

DISCUSSION...GOES-W and Regional RADAR mosaic have started to
depict increasing convective activity in both coverage and
vertical depth with peak heating of the day.  The highly
anomalous, over 3.5 standard anomaly units from climatology, core
of the closed low is bottoming out across SW California with
vorticity center at the southern base; this is allowing for an
elongation/stretching of the mid-level deformation zone to extend
across SW to NE San Bernadino county with increased deep layer
convergence.  Given steepening lapse rates with cold air advection
aloft, surface heating into the 80s is starting to support surface
based CAPE values from 500-1000 J/kg to develop over the Southern
California Deserts toward the Colorado River Valley near S Nevada.
 While deep layer moisture is a bit limited with only Tds in the
upper 40s, low 50s and total PWat values in the .75 to 1" range.
The convergence within the band and orographic ascent confluent
across the San Bernadino/Little Bernadino/San Jacinto Ranges
supports stronger vertical development and sufficient moisture
flux to support .5-1"/hr rates.

Limited cell motions given proximity to the closed low/deformation
zone will allow for very slow/stationary motion with upstream
redevelopment/backbuilding along the deformation band across NE
CA.  Propagation may also allow cells along the mountain ridges
into the Cochella Valley with time.  This may allow for spotty
.75-1" totals with an isolated 1.5" total remains possible.  Given
naturally low FFG values less than these hourly rates and
potential; an isolated flash flooding incident or two is
considered possible across the area through the late
afternoon/evening hours.

Gallina

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...PSR...SGX...VEF...

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

LAT...LON   36051537 35651447 35091429 34421518 33621507
            33231522 33321587 32881615 32921657 33461673
            33991720 34191765 35011753 35581699 36001605