Mesoscale Precipitation Discussion 0915
NWS Weather Prediction Center College Park MD
745 PM EDT Wed Aug 21 2024
Areas affected...in and near Arizona
Concerning...Heavy rainfall...Flash flooding possible
Valid 212345Z - 220545Z
Summary...Showers and thunderstorms with heavy rain continue to
move across and in the vicinity of Arizona. Hourly rain totals to
2.5" with local amounts of 4" remain possible over the next
several hours.
Discussion...An MCV is evident in veggie band imagery east of
Wickenburg AZ. Surrounding the periphery of the circulation are
showers and thunderstorms with heavy rainfall, with radar
estimates up to 2.5" in an hour as of late. This has been caused
by cell mergers and short bouts of cell training. Precipitable
water values are anomalously high, 1-1.5" at elevation and
1.5-1.75" across the desert floor. Effective bulk shear remains
near 25 kts per SPC mesoanalyses. CIN is setting in, and MU CAPE
across the region is 1000-2000 J/kg.
The expectation is for a slow decrease in the magnitude and
breadth of the heavy rainfall in and near AZ. Whether or not
convection with heavy rainfall moves over portions of Las Vegas
itself is a question mark as it lies very near the moisture
gradient, but some new activity has developed near the CA/ NV/AZ
border. With the MCV continuing to drift north-northwest, the
mesoscale guidance suggests that the feature should be sufficient
to overcome CIN to some degree and be able to tap the MU CAPE
available. Hourly rain totals to 2.5" with local amounts to 4"
remain possible where cells train, merge, or mesocyclones form,
with issues expected to be closer to the MCV center with time.
This degree of rainfall would be problematic in arroyos/dry
washes, burn scars, slot canyons, and urban areas.
Roth
ATTN...WFO...FGZ...GJT...PSR...SLC...TWC...VEF...
ATTN...RFC...CBRFC...CNRFC...NWC...
LAT...LON 37711205 37430943 35510906 32250907 31190929
31341181 32341377 34051590 35491553 36771435
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