286
AWUS01 KWNH 221852
FFGMPD
NMZ000-AZZ000-UTZ000-230050-

Mesoscale Precipitation Discussion 0490
NWS Weather Prediction Center College Park MD
250 PM EDT Sat Jun 22 2024

Areas affected...Southwest U.S.

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

Valid 221850Z - 230050Z

SUMMARY...An increase in the coverage of showers and thunderstorms
this afternoon capable of producing high rainfall rates will once
again pose concerns for areas of flash flooding. Any localized
slot canyons, burn scars, and the normally dry washes will be the
most susceptible to see runoff and flash flooding concerns.

DISCUSSION...The midday GOES visible satellite imagery shows a
substantial cloud deck extending from central and southern AZ
northeastward across northern and central NM in connection with a
deep plume of lingering tropical moisture formerly connected to
Tropical Storm Alberto which previously came across Mexico.
However, there is a fair amount of boundary layer heating taking
place, and especially over areas of southeast AZ into west-central
NM where there are some areas of showers and thunderstorms
developing.

SBCAPE values are on the order of 500 to 1000+ J/kg locally, but
these magnitudes are expected to increase over the next few hours
as additional solar insolation takes place. Meanwhile, the PWs are
anomalously very high for this time of the year and as high as 3
to 5+ standard deviations above normal and above the 95th
percentile from southern AZ through central NM.

An additional uptick in the coverage of showers and thunderstorms
can be expected through the afternoon hours that will be capable
of producing very heavy rainfall rates that may approach or
locally exceed 2 inches/hour from areas of southern AZ through
central NM where the CIRA-ALPW data confirms the aforementioned
tropical moisture plume extending well into the 500/300 mb layer.
Areas adjacent to this across northern AZ and southern UT should
have less efficiency where there is drier air near the top of the
column, and thus convection here that does initiate near the
terrain will tend to have relatively lower rainfall rates.

The 12Z HREF guidance overall suggests the Mogollon Rim area and
portions of southeast AZ should have the heaviest rainfall
potential given a combination of deeper moisture, instability and
orographics. Some rainfall totals of 2 to 3 inches, with isolated
heavier amounts will be possible.

Isolated to scattered instances of flash flooding will once again
be possible given the thermodynamic environment and orographic
focus of much of the convection this afternoon. The localized slot
canyons, areas near burn scars, and the normally dry washes will
be particularly sensitive to the high rainfall rate potential and
thus at greatest risk for flash flooding.

Orrison

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

ATTN...WFO...ABQ...EPZ...FGZ...PSR...SLC...TWC...VEF...

ATTN...RFC...ABRFC...CBRFC...WGRFC...NWC...

LAT...LON   38541133 36711084 36320918 36750695 36950571
            36790460 36210402 35240394 34290452 32980518
            32510620 32520779 32200860 31420937 31291082
            31361155 31731256 32381296 33961259 35221312
            36551325 38511241