MESOSCALE PRECIPITATION DISCUSSION 0803
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1003 AM EST FRI DEC 23 2016
 
AREAS AFFECTED...COASTAL/TRANSVERSE RANGES OF SOUTHERN CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 231502Z - 240302Z
 
SUMMARY...AN AMPLIFYING UPPER TROUGH AND IMPINGING COLD FRONT ARE
EXPECTED TO BRING HOURLY RAIN RATES TO 0.50"+, MAINLY AFTER 22Z,
WHICH COULD CAUSE ISSUES IN AND NEAR BURN SCARS.

DISCUSSION...SATELLITE IMAGERY SHOWS AN UPPER TROUGH DEEPENING
NEAR THE 133RD MERIDIAN, WITH UNSTABLE STRATOCUMULI NEAR ITS AXIS
NORTH OF 37 LATITUDE.  THE LIGHTNING DETECTION NETWORK HAS SHOWN
SOME STRIKES LATELY ~300 MILES WEST OF SAN FRANCISCO. 
PRECIPITABLE WATER VALUES NEAR THE CA COAST RANGE FROM 0.5-1" PER
GPS DATA.  LOW-LEVEL INFLOW IS ROUGHLY OUT OF THE SOUTHWEST AT
25-40 KTS PER 700 HPA AND 850 HPA VAD WIND PROFILE INFORMATION. 
SPC MESOANALYSES INDICATE MLCAPES AND MUCAPES OF 100+ J/KG
OFFSHORE THE NORTHERN AND CENTRAL CA COAST.

WITH TIME, THE DEEP LAYERED FLOW SHOULD BECOME MORE
ALIGNED/UNIDIRECTIONAL OUT OF THE SOUTHWEST TO WEST-SOUTHWEST,
NEARLY NORMAL TO THE TERRAIN.  AS THE UPPER TROUGH AMPLIFIES,
LOW-LEVEL INFLOW IS EXPECTED TO RISE TO 50+ KTS AT 700 HPA BETWEEN
01-03Z PER RAP MASS FIELDS -- THIS MAGNITUDE IS NORMALLY SEEN WHEN
HOURLY RAIN RATES EXCEED 0.5" NEAR THE WEST COAST.  PRECIPITABLE
WATER VALUES ARE ALSO FORECAST TO EXCEED 1".  THE 09Z SREF MEAN
INDICATES CAPE VALUES RISE TO 200-300 J/KG LATER THIS AFTERNOON
INTO THIS EVENING, WHICH COULD AUGMENT RAIN EFFICIENCY AND ALLOW
FOR EMBEDDED THUNDERSTORMS.  THE TIME OF HEAVIEST RAINFALL IS
EXPECTED BEYOND 22Z AFTER THE FRONT PASSES GROVER CITY/LOMPOC. 
HOURLY RAIN RATES OF 0.5"+ WERE EXPLICITLY FORECAST BY THE 00Z ARW
AND RECENT HRRR RUNS WITHIN THE TOPOGRAPHY AS WELL AS CHANNEL
ISLANDS NATIONAL PARK OFFSHORE.  SUCH RATES WOULD CAUSE ISSUES IN
AND NEAR BURN SCARS. LOCAL MAXIMA SHOULD PEAK NEAR 2" WITH THIS
PROGRESSIVE SYSTEM.  HIGHER ELEVATIONS OF THE TRANSVERSE RANGES
COULD SEE A CHANGEOVER TO SNOW AT THE END OF THE DISCUSSION PERIOD
AS TEMPERATURES ALOFT COOL AFTER FRONTAL PASSAGE.  

ROTH

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

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

LAT...LON   35762139 35672041 35551999 35141945 35031903 
            34801866 33971883 33801998 33992052 34802080 
            35312107