MESOSCALE PRECIPITATION DISCUSSION 0018
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1003 PM EST THU JAN 21 2016
 
AREAS AFFECTED...SOUTHWESTERN-MOST OR/NORTHERN CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 220303Z - 221503Z
 
SUMMARY...A NEGATIVELY TILTED UPPER TROUGH APPROACHING NORTHERN CA
COULD LEAD TO HOURLY RAIN RATES IN EXCESS OF 0.50" BETWEEN 07-15Z.

DISCUSSION...A FRONTAL ZONE AND ITS PARENT NEGATIVELY-TILTED UPPER
TROUGH ARE APPROACHING NORTHERN CA AT THIS TIME, WITH AN
ASSOCIATED ATMOSPHERIC RIVER EMANATING FROM THE VICINITY OF HI (A
PINEAPPLE CONNECTION).  PRECIPITABLE WATER VALUES ARE CURRENTLY
0.8-1", WITH VALUES ABOVE 1.25" OFFSHORE PER SATELLITE-DERIVED
VALUES AND RECENT RAP GUIDANCE.  LOW-LEVEL INFLOW OF CLOSE TO 60
KTS HAS BEEN NOTED ON THE ARCATA CA VAD WIND PROFILE.  HOURLY RAIN
RATES ARE CURRENTLY NEAR 0.10" NEAR AND EAST OF THE SHASTA
NATIONAL FOREST PER MESONET OBSERVATIONS.  AMSU DERIVED HOURLY
RAIN RATES OF 0.5-0.75" LURK SOUTHWEST OF CAPE MENDOCINO, PER AN
SAB/NESDIS SATELLITE BRIEFING.

THE CAM GUIDANCE SUGGESTS THAT THE UPPER TROUGH SHOULD DRIVE THE
ATMOSPHERIC RIVER/FRONTAL ZONE TO THE COAST AROUND 07Z, WHICH
SHOULD LEAD TO AN INCREASE IN HOURLY RAIN RATES TO NEAR OR ABOVE
0.50".  THE CAM GUIDANCE SHOWS LOCAL AMOUNTS IN THE 2-3" RANGE
THROUGH 15Z AS THIS BOUNDARY WORKS SLOWLY INLAND.  EVEN IN THE
WAKE OF THE FRONT, SOUTHERLY LOW-LEVEL INFLOW INTO THE
SOUTH-FACING MOUNTAINS IS SLOW TO FADE DURING THE MORNING HOURS,
WITH 35-40 KT INFLOW INTO THE TOPOGRAPHY EXPECTED BY 15Z.

ROTH

ATTN...WFO...EKA...MFR...MTR...REV...STO...

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

LAT...LON   43022389 42312347 42202205 41642131 41282108 
            40412092 39382101 40072174 40932221 40762275 
            39802273 38262255 38562345 39202393 39852408 
            40392460 41582438 42682447