Mesoscale Precipitation Discussion 0123
NWS Weather Prediction Center College Park MD
1256 AM EDT Mon Apr 01 2024

Areas affected...portions of Arizona

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

Valid 010454Z - 011054Z

Summary...A few slow-moving thunderstorms continue to develop
across southwestern Arizona, with local rain rates approaching 1
inch/hr on an isolated/spotty basis.  This pattern could continue
for a few more hours this evening/overnight, prompting isolated
flash flooding.

Discussion...Very cold temperatures aloft (-24 to -28C at 500 hPa
per SPC Mesoanalysis) continues to support isolated to scattered
convective development across the discussion area.  The
temperature profiles were supporting areas of 250-750 J/kg of
surface-based CAPE amid 0.7 inch PW values and weak steering flow
aloft (especially in western Arizona), supporting slow storm
motions.  One cell nearly stalled recently approximately 70 miles
east of BLH/Blythe, CA, which has promoted local rain rates
approaching 1 inch/hr.  Satellite imagery indicates strong ascent
entering the discussion area from the west in tandem with a couple
of mid-level shortwave troughs across the northwestern Baja
Peninsula and Lower Colorado River Valley.  This pattern aloft is
supporting ongoing convection, and should continue to do so for at
least another 3-4 hours despite slow boundary layer cooling during
that time.

As mid/upper disturbances continue to travel eastward, it is not
out of the question that the Phoenix Metro and surrounding areas
could experience locally heavier rain rates tonight.  Local FFGs
are only in the 0.75 - 1.50 inch/hr range and the lower end of
that range could be exceeded especially where local cell
mergers/cold pool generation support prolonged rainfall from
stalled or erratically moving cells.  Sensitive and/or urbanized
areas are most likely to experience impacts, although the isolated
nature of the convection through the night suggests that the flash
flood risk should remain isolated through 10-11Z.

Cook

ATTN...WFO...FGZ...PSR...TWC...VEF...

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

LAT...LON   35291346 35221237 34211153 32921142 32231171
            31921252 32301383 33041494 34371501 35181440