Graphic for MPD #0792

MESOSCALE PRECIPITATION DISCUSSION 0792
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
348 PM EDT SAT SEP 09 2017

AREAS AFFECTED...SOUTHERN CA...CENTRAL/WESTERN AZ...FAR SOUTHERN
NV

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 091945Z - 100030Z

SUMMARY...SMALL CLUSTERS OF SLOW-MOVING AND HEAVY SHOWERS AND
THUNDERSTORMS CONTINUE TO DEVELOP. ADDITIONAL FLASH FLOODING
CONCERNS WILL EXIST THROUGH THE AFTERNOON HOURS.

DISCUSSION...COLD-TOPPED CONVECTION CONTINUES OVER AREAS OF
WESTERN AZ AND SOUTHERN CA IN ASSOCIATION WITH A SHORTWAVE TROUGH
LIFTING NORTH-NORTHEAST OUT OF THE SOUTHWEST AND INTO THE GREAT
BASIN. THE CONVECTION HAS BEEN TENDING TO EXPAND A BIT MORE IN
COVERAGE OVER THE LAST COUPLE OF HOURS AS STRONGER DIURNAL HEATING
HAS RESULTED IN A MODERATELY UNSTABLE AIRMASS CHARACTERIZED BY
MLCAPE VALUES OF 1500 TO 2000+ J/KG. THE MOISTURE PROFILE STILL
REMAINS RATHER DEEP WITH GPS-DERIVED PWATS OF 1.6 TO 1.8 INCHES
NOTED OVER AREAS OF SOUTHERN CA AND FAR WESTERN AZ.

THE DEGREE OF COLDER CLOUD TOPS AND INCREASING
INSTABILITY...COUPLED WITH THE HIGH PWAT ENVIRONMENT WILL BE
CONDUCIVE ENHANCED RAINFALL RATES THAT WILL APPROACH 2 INCHES/HR.
ALREADY THERE HAVE BEEN 3-HOUR TOTALS OF 2 TO 3 INCHES OVER PARTS
OF IMPERIAL COUNTY IN SOUTHERN CA FROM EARLIER CONVECTION.

THE HIRES MODELS COLLECTIVELY APPEAR TO BE A TAD UNDERDONE THROUGH
THE SHORT-TERM WITH THE DEGREE OF CONVECTIVE COVERAGE AND AMOUNTS.
GIVEN THAT THERE HAVE BEEN A FEW CELL-MERGERS...THERE IS AT LEAST
A MODEST DEGREE OF CONVECTIVE ORGANIZATION THAT SHOULD CONTINUE TO
FEED OFF THE INCREASING SURFACE-BASED INSTABILITY OVER THE NEXT
FEW HOURS. EXPECT CONVECTION TO GRADUALLY LIFT FARTHER NORTH WITH
IMPACTS POTENTIALLY REACHING UP INTO FAR SOUTHERN NV THROUGH THE
MID-LATE AFTERNOON HOURS. EXPECT RAINFALL TOTALS OF AS MUCH AS 2
TO 4 INCHES THROUGH 00Z. CONVECTION THOUGH SHOULD WEAKEN TOWARD
EVENING...BUT IN THE SHORT-TERM...FLASH FLOODING WILL BE LIKELY.

ORRISON

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

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

LAT...LON   36931446 36791226 35761171 34611177 33231215
            32171295 32151417 32531519 32551616 32801653
            33501680 34721646 35841581


Last Updated: 356 PM EDT SAT SEP 09 2017