Mesoscale Precipitation Discussion 0342
NWS Weather Prediction Center College Park MD
1232 AM EDT Mon Jun 02 2025

Areas affected...central to eastern AZ

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

Valid 020430Z - 020900Z

Summary...Showers and thunderstorms are expected to expand in
coverage and intensity across central to eastern AZ over the next
4-5 hours. Rainfall of 0.5 to 1.0 inches in an hour or less with
repeating and training could result in a few instances of flash
flooding.

Discussion...GOES West imagery at 04Z showed a closed mid to
upper-level low over the Baja California/Sonora border, about to
move into southwestern AZ with a secondary subtle vorticity max
moving north out of Pima County into south-central AZ. A RAP
estimated 70-80 kt upper level jet streak was located over the
northern Gulf of California, just southeast of the low's center,
with divergent and diffluent flow downstream of the upper jet
streak across a good portion of AZ. MRMS composite reflectivity
and infrared satellite loops over the past 3 hours have shown
waves of more intense rain/thunderstorms moving into southeastern
AZ from Mexico (compared to earlier in the day) along with a
number of embedded transient mesoscale circulations contained
within. Recent gauge reports over eastern Santa Cruz County have
shown between 0.5 and 0.7 inches of rain in an hour. SPC
mesoanalysis data from 04Z showed MLCAPE of 500-1000 J/kg south of
the AZ/MX border, but quickly dropping off to less than 500 J/kg
into south-central and southeastern AZ.

Over the next few hours, rounds of heavy rain will likely continue
to move into southeastern and eastern AZ following the favorable
upper level forcing ahead of the closed low along with instability
and anomalous precipitable water values (1.45 inches at the TUS
00Z sounding...well above the SPC sounding page's climatological
max). Southerly to south-southwesterly flow at 700 mb (20-30 kt)
along with deeper layer steering flow of the same orientation will
support repeating and training cores of heavy rain at times,
allowing for 0.5 to 1.0 inches in an hour or perhaps as short as
30 minutes.

Over central to south-central AZ, as the closed low center edges
closer, RAP forecasts show MLCAPE increasing into the 250-750 J/kg
range given an increase in low level moisture and cooling
mid-level temperatures. This may allow for the development of a
few thunderstorms by 08-09Z given DPVA, capable of hourly rainfall
near 1 inch.

Across both central to eastern AZ, a few areas of flash flooding
may develop given overlap with areas of sensitive terrain, remnant
burn scars, and/or urban centers.

Otto

ATTN...WFO...EPZ...FGZ...PSR...TWC...

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

LAT...LON   35251122 34770987 33760912 32020894 31040934
            31091098 31431181 32121264 33981269 35091234