MESOSCALE PRECIPITATION DISCUSSION 0617
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
437 PM EDT WED AUG 02 2017

AREAS AFFECTED...SRN CA/SRN AND WRN AZ INTO SRN NV

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

VALID 022034Z - 030145Z

SUMMARY...SLOW MOVING STORMS CAPABLE OF RAINFALL RATES OF 1-2
IN/HR ARE EXPECTED TO BECOME MORE WIDESPREAD THIS AFTERNOON FROM
SRN/WRN AZ INTO SRN CA AND AS FAR NORTH AS FAR SRN NV. THESE
STORMS WILL POSE A FLASH FLOOD THREAT THROUGH AT LEAST 01Z.

DISCUSSION...EXPERIMENTAL GOES 16 VISIBLE IMAGERY AS OF 20Z SHOWED
A MESOSCALE CIRCULATION OVER MARICOPA COUNTY AZ...TRACKING TOWARD
THE WEST. CLEARING TRENDS HAVE BEEN NOTED IN SKY COVER OVER THE
PAST COUPLE OF HOURS FROM MUCH OF SRN CA INTO SWRN AZ AND
CONVECTIVE ACTIVITY WAS SUBSEQUENTLY INCREASING ALONG THE
PENINSULA RANGES OF SRN CA...FAR SWRN AZ AND S-CNTRL AZ. WATER
VAPOR IMAGERY INDICATED A STRONGLY DEFINED MID-UPPER LEVEL
VORTICITY MAX OVER NRN BAJA CALIFORNIA WITH HIGHLY DIFFLUENT FLOW
PRESENT FROM SRN CA INTO WRN AZ.

PRECIPITABLE WATER VALUES PER RECENT GPS SITES WERE IN THE 2 TO
2.25 INCH RANGE EXTENDING FROM THE COAST OF SRN CA TO S-CNTRL
AZ...CONFIRMED WITH AN 18Z RAOB FROM YUMA SHOWING 2.2 INCHES. THE
18Z YUMA SOUNDING ALSO SHOWED LITTLE TO NO CIN REMAINING AND 0-6
KM MEAN FLOW OF 4 KT FROM THE SOUTHEAST INDICATIVE OF WEAKLY
ORGANIZED BUT SLOW MOVING STORMS. SIMILAR TO YESTERDAY...700 MB
FLOW REMAINS SLIGHTLY ENHANCED...10-20 KT...FROM CNTRL AZ INTO
SWRN CA TO THE SOUTH OF MID-LEVEL RIDGING SITUATED OVER CNTRL NV.

GIVEN THE OBSERVED CLEARING TRENDS ALLOWING FOR INCREASED HEATING
AND SUBSEQUENT CAPE GENERATION...CONVECTIVE ACTIVITY IS EXPECTED
TO INCREASE AHEAD OF THE AFOREMENTIONED CIRCULATION IN S-CNTRL AZ
WITH SLOW STORM MOTIONS AND LIKELY SHORT LIVED BUT INTENSE
RAINFALL RATES OF 1-2 IN/HR TOWARD THE CO RIVER VALLEY. CONVECTION
IN SRN CA IS ALSO EXPECTED TO BECOME ANCHORED ALONG THE TERRAIN
WITH SLOW MOVEMENT AND TRAINING LEADING TO A FLASH FLOOD THREAT
ABOVE THE LOW LEVEL INVERSION NOTED ON THE 12Z NKX SOUNDING.
LASTLY...AS CONVECTION LIKELY INCREASES OVER THE HIGHER TERRAIN OF
NWRN AZ THIS AFTERNOON...IT SHOULD MOVE SWWD INTO THE BUILDING
INSTABILITY NEAR THE TRI-STATE REGION OF NV/CA/AZ POSING A FLASH
FLOOD THREAT INTO THE EARLY EVENING.

OTTO

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

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

LAT...LON   35871421 35701361 34601249 33391165 32591146
            31911149 31471209 31761337 32321513 32321586
            32321665 32621690 33171719 33491739 33751760
            34021780 34151809 34361822 34781807 34771689
            34701633 34871583 35441525 35711484