AWUS01 KWNH 021237

FFGMPD

AZZ000-UTZ000-NVZ000-CAZ000-021800-



Mesoscale Precipitation Discussion 0571

NWS Weather Prediction Center College Park MD

836 AM EDT Wed Jul 02 2025



Areas affected...High Deserts of California and Nevada



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



Valid 021235Z - 021800Z



Summary...Showers and thunderstorms blossoming across the High

Deserts of the Southwest will continue through the morning.

Despite fast motion, rainfall rates of 0.5"/hr could result in

instances of flash flooding.



Discussion...The regional radar mosaic this morning shows rapidly

expanding showers and embedded thunderstorms blossoming across

southeast CA and southern NV. These storms are developing despite

modest instability (SPC RAP analysis 500 J/kg of MUCAPE) but with

a steady increasing trend noted. This instability is overlapping

with PWs that are as high as 0.8 to 1.2 inches, or above the 90th

percentile for the date. Offsetting the modest thermodynamics,

forcing for ascent is increasing downstream of a strengthening

upper trough digging across CA leaving height falls and spokes of

vorticity/PVA across the Southwest, collocated with a low-level

convergence axis on the periphery of an 850mb moisture surge out

of Arizona. This ascent is helping to cause the rapid increase in

convective coverage this morning.



Rainfall rates have been estimated via KESX to be as high as

0.5"/hr at times, which despite rapid storm motions on 850-300mb

mean winds of 20-25 kts from the south, has produced 3-hr rainfall

according to MRMS of up to 0.75 inches. As the ascent continues to

maximize through the morning downstream of the upper trough, the

low-level flow surges higher moisture northeast, and instability

climbs through the morning, activity should expand and intensify.

Although the CAMs are struggling with the coverage and intensity

of ongoing convection, the environment suggests that storms should

continue for several more hours, and the HRRR-forced UA WRF

indicates rain rates will continue at as much as 0.5"/hr through

this aftn with a slow northward advance of heavy rainfall. At the

same time, convection will likely build repeatedly into the

greater thermodynamics over the High Deserts of CA, with lines of

storms training south to north producing locally as much as 1.5"

of rain.



These impressive rain rates will move across soils that are

saturated above the 90th percentile with respect to 0-40cm depths

according to NASA SPoRT. While impacts due to this rainfall are

likely to be isolated and focused across any sensitive terrain

features or urban areas, where any longer-duration training can

occur through the next several hours, instances of flash flooding

are possible.





Weiss



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



ATTN...WFO...HNX...LKN...PSR...SGX...SLC...VEF...



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



LAT...LON   38391576 38031475 37381394 36081394 34941409 

            34231431 33861470 33831530 33981583 34391647 

            34911710 35691768 36621780 37941705