MESO: Nws Weather Prediction Center College Park Md

AWUS01 KWNH 262227
FFGMPD
UTZ000-AZZ000-270401-

MESOSCALE PRECIPITATION DISCUSSION 0225
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
626 PM EDT MON AUG 26 2013

AREAS AFFECTED...CENTRAL AZ...SOUTHERN UT

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 262226Z - 270401Z

SUMMARY...WIDELY SCATTERED THUNDERSTORMS ARE SLOWLY GROWING IN
COVERAGE ACROSS PORTIONS OF AZ, WHICH SHOULD MIGRATE INTO SOUTHERN
UT WITH TIME. REGIONAL FLASH FLOODING IS POSSIBLE IN AREAS WHERE
CELLS TRAIN.

DISCUSSION...WIDELY SCATTERED THUNDERSTORMS ARE SLOWLY INCREASING
IN COVERAGE AND STRENGTH, PER RECENT RADAR IMAGERY. AZ AND
SOUTHERN UT HAVE SEEN CAPE VALUES BUILD TO AROUND 2000 J/KG DUE TO
SOLAR INSOLATION TO THE EAST OF A BAND OF CLOUDS EXTENDING FROM
THE CYCLONE ONCE KNOWN AS IVO -- LOCATED WEST OF BAJA CALIFORNIA.
DIVERGENCE ALOFT IS BEING SPONSORED BY A COMBINATION OF AN UPPER
LEVEL TROUGH ACROSS THE PACIFIC NORTHWEST AND A RETROGRADING UPPER
LEVEL DISTURBANCE MOVING THROUGH NORTHERN MEXICO. PRECIPITABLE
WATER VALUES ARE IN THE 1.25-2.25 INCH RANGE ACROSS THIS REGION,
WHICH IS BETWEEN THE 90TH AND 95TH PERCENTILES FOR LATE AUGUST AND
SHOULD ALLOW FOR ABOVE AVERAGE PRECIPITATION EFFICIENCY FOR THE
REGION. THE STRONGER CELLS ARE EXPECTED TO HAVE RAINFALL RATES OF
1-2" PER HOUR.

INFLOW AT 700 HPA IS AROUND 20 KNOTS FROM THE SOUTHEAST, THOUGH
LOW-LEVEL WIND SHEAR VALUES DO NOT APPEAR TO BE SUFFICIENT TO
ORGANIZE CONVECTION A GREAT DEAL. THE LATEST GUIDANCE FROM SAB
INDICATES CONVECTIVE COVERAGE SHOULD INCREASE THROUGH THE
REMAINDER OF THE AFTERNOON. CELL TRAINING IS POSSIBLE, WHICH
COULD LEAD TO LOCAL RAINFALL AMOUNTS OF 2-4 INCHES. ACTIVITY
SHOULD FADE FROM EAST TO WEST DUE TO STRENGTHENING RIDGING ACROSS
THE CENTRAL UNITED STATES WHICH ERODES PRECIPITABLE WATER VALUES
ACROSS EASTERN AZ WITH TIME. REGIONAL FLASH FLOODING IS
CONSIDERED POSSIBLE UNTIL 04Z, WHEN THE LATEST HRRR/RAP GUIDANCE
INDICATES PRECIPITATION ACTIVITY SHOULD BE ON THE DOWNTURN DUE TO
EXHAUSTING CAPE.

ROTH

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...GJT...TWC...FGZ...SLC...PSR...VEF...

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

LAT...LON 31271103 31351138 31701245 32001326 33581363 35871385
37031307 37591214 37901097 37431030 36121092 33921108
32161058 31381059 31361091 31271103

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