Mesoscale Precipitation Discussion 0917
NWS Weather Prediction Center College Park MD
353 AM EDT Thu Aug 22 2024
Areas affected...northwestern AZ into southeastern NV and
southwestern UT
Concerning...Heavy rainfall...Flash flooding possible
Valid 220752Z - 221330Z
Summary...Thunderstorms are expected to continue to expand across
northwestern AZ and southwestern UT through 13Z. Some expansion
into southeastern NV may also occur along with rainfall rates of
1-2 in/hr. At least a localized flash flood threat will result.
Discussion...0730Z infrared satellite and lightning imagery showed
that while convection was decreasing over north-central AZ, new
development was occurring over western and northwestern AZ. New
cells observed on radar imagery were relatively small with an
average movement toward the northeast but occasional backbuilding
and training has been observed. According to the 07Z SPC
mesoanalysis, 500 to 1500 J/kg MLCAPE was observed over western
and northwestern AZ into adjoining NV and UT, with a notable
recent increase centered near the tri-state region of NV/UT/AZ
(+400 to 600 J/kg over past 3 hours). Farther south, a long-lived
MCV was observed on infrared satellite over far southern Yavapai
County which was likely associated with enhanced southeasterly
winds into northwestern AZ. Low level convergence co-located with
an anomalous moisture feed (PWATs ~1 to 1.5 inches) emanating from
the northern Gulf of California was helping to support the recent
nocturnal development of storms.
Recent University of Arizona WRF and select CAM guidance from 00Z
seems to support the conceptual model for thunderstorms continuing
for several more hours within the lingering instability plume to
the northwest of the MCV. SW to NE training will be possible with
these storms which will support hourly rainfall of 1-2 inches and
possible flash flooding. As the MCV continues a motion toward the
north to north-northeast, moisture and increasing instability are
expected to build northward into southwestern UT. Nocturnal
thunderstorm development is expected to expand into portions of
southwestern UT through the remainder of the morning while
continuing over portions of northwestern AZ and possibly building
into southeastern NV. While coverage may remain somewhat low, at
least a localized flash flood threat will persist across these
regions through about 13Z.
Otto
ATTN...WFO...FGZ...PSR...SLC...VEF...
ATTN...RFC...CBRFC...CNRFC...NWC...
LAT...LON 38441348 38321258 37801195 36631162 34991203
34181291 34391384 35101470 35901526 36921520
38171465
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