377
AWUS01 KWNH 180001
FFGMPD
AZZ000-UTZ000-180329-

Mesoscale Precipitation Discussion 0893
NWS Weather Prediction Center College Park MD
800 PM EDT Sat Aug 17 2024

Areas affected...South-Central Utah, northern Arizona

Concerning...Heavy rainfall...Flash flooding likely

Valid 172359Z - 180329Z

Summary...Considerable impact flash flooding will continue across
south-central Utah and northern Arizona past 0z as additional
cells with .75-1"/hr rainfall rates persist for a few more hours.

Discussion...Throughout the afternoon, training showers and
thunderstorms with 0.75-1"/hr rainfall rates have produced
numerous instances of considerable impact flash flooding across
south-central Utah and northern Arizona. In a region of generally
high radar quality in southern Utah and northern Arizona, rainfall
estimates of 1-1.25" are noted over the last six hours where the
most intense cells have trained.

Upstream of the current storms, trends in the Day Cloud Phase RGB
and experimental LighningCast suggest additional development is
underway in a cumulus field over north-central Arizona. In spite
of some overturning by the convection, steep mid-level lapse rates
and plentiful moisture transport into the region continue to
support 1000-2000 J/kg of MUCAPE and 1.1-1.2" PWATs (above the
90th percentile for FGZ and GJZ) near the storms per RAP and
objective analysis estimates. Effective shear remains impressive
as well, with 40-50 kts noted.

Aided by strong upper diffluence and a weak shortwave near the
Four Corners, periods of training convection should continue for a
few more hours across the region before eventually diminishing
with loss of daytime heating. Through 3Z, HREF neighborhood
probabilities maintain a 20-35% chance of rainfall rates exceeding
.5"/hr. In light of ongoing impacts, this will continue the flash
flooding threat (some of which could be significant) for another
few hours.

Asherman

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

ATTN...WFO...FGZ...GJT...SLC...VEF...

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

LAT...LON   40381221 39821035 37180989 35461092 35151246
            35901369 37211399 39321350