MESOSCALE PRECIPITATION DISCUSSION 0055
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EST FRI FEB 17 2017

AREAS AFFECTED...SRN CA

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

VALID 171858Z - 180058Z

SUMMARY...THE HEAVIEST RAINFALL RATES OF THE DAY ARE EXPECTED TO
OCCUR IN THE NEXT 6-8 HOURS ACROSS THE TRANSVERSE RANGES OF SRN
CA. STEADY HOURLY RATES OF .5 TO 1.0 IN/HR...LOCALLY
HIGHER...SHOULD LEAD TO 6 HOUR RAINFALL TOTALS OF 3-5 INCHES.
FLASH FLOODING WILL BE A CONCERN...ESPECIALLY ACROSS BURN SCAR
LOCATIONS.

DISCUSSION...GOES W RAPID SCAN IMAGERY SHOWED THE COLDEST CLOUD
TOPS ADVANCING INTO SANTA BARBARA AND VENTURA COUNTIES WITH
SEVERAL OBSERVATIONS ALONG THE SANTA YNEZ MOUNTAINS REPORTING
HOURLY RAIN RATES OF ABOVE 0.75 IN/HR AND A FEW ABOVE 1 IN/HR.
THIS AREA IS LOCATED WITHIN A REGION OF STRONG UPPER LEVEL
DIFFLUENCE AHEAD OF A CLOSED LOW WHICH CONTINUES TO DEEPEN PER
WATER VAPOR IMAGERY. VISIBLE AND INFRARED CHANNELS SHOWED TWO
SEPARATE AXES OF COLDER CLOUD TOPS...EACH TIED TO UPPER LEVEL 
DIVERGENCE RELATED TO A POSSIBLE FORK IN THE EXIT REGION OF A
POWERFUL MID-LEVEL JET ROUNDING THE BASE OF THE TROUGH AXIS.

ALTHOUGH THE CORE OF HIGHER PRECIPITABLE WATER VALUES SEEN IN THE
BLENDED TPW PRODUCT ARE INFLATED...SHOWING IN EXCESS OF 2.5 INCHES
TO THE WEST OF POINT CONCEPTION AS OF 12Z...IT DOES AGREE WITH
SHORT TERM RAP FORECASTS OF THE MOVEMENT OF THE AXIS OF STRONGEST
MOISTURE FLUX...STEADILY SHIFTING EAST TOWARD ORANGE...WRN
RIVERSIDE AND NWRN SAN DIEGO COUNTIES BY 01Z ALONG WITH GRADUAL
WEAKENING.

DESPITE GRADUALLY WEAKENING MOISTURE...PWAT VALUES OF 1.2 TO 1.3
INCHES COMBINED WITH 850 MB WINDS OF 50-60 KTS ORTHOGONAL TO THE
TERRAIN AND WEAK ELEVATED INSTABILITY UP TO 250 J/KG WILL CONTINUE
TO SUPPORT HEAVY RAINFALL RATES IN EXCESS OF 1 IN/HR AT TIMES. THE
MOVEMENT OF THE MOISTURE FLUX AXIS SUPPORTS ANYWHERE FROM 3-5 HRS
OF THESE RAINFALL RATES AT ANY GIVEN LOCATION ALONG THE TRANSVERSE
RANGES...WITH 6 HR TOTALS OF 3-5 INCHES POSSIBLE BY 01Z.

OTTO

ATTN...WFO...HNX...LOX...SGX...

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

LAT...LON   35281820 34821820 34641780 34591741 34451697
            34201704 33971684 33661705 32951734 33421800
            33611850 34011934 34362030 34882027 35011985
            34961921 35031872 35221836