MESOSCALE PRECIPITATION DISCUSSION 0770
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
403 PM EST FRI NOV 18 2016
 
AREAS AFFECTED...NORTHWEST CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 182102Z - 190902Z
 
SUMMARY...THE WARM CONVEYOR BELT CIRCULATION OF A DEEP LAYERED
CYCLONE IS EXPECTED TO LEAD TO RAIN RATES INTO THE 0.5-0.8" AN
HOUR RANGE MAINLY AFTER 04Z.

DISCUSSION...A DEEP LAYERED CYCLONE CURRENTLY NEAR 44N 137.5W IS
MOVING SLOWLY TOWARDS THE WEST COAST.  ITS COLD FRONT HAS MADE IT
PAST THE 119TH PARALLEL AND IS APPROACHING NORTHWEST CA, WITH
LIGHT RAIN BEGINNING TO SHOW UP AT THE EDGE OF AREA RADAR IMAGERY.
 A RECENT SATELLITE BRIEFING BY SAB/NESDIS INDICATES A MARKED
STRENGTHENING IN UPPER LEVEL DIVERGENCE WEST OF THE OR/CA COAST AT
THIS TIME.  PRECIPITABLE WATER VALUES ARE CURRENTLY 0.2-0.4" ALONG
THE CA COAST AHEAD OF THE SYSTEM PER GPS INFORMATION, BUT IN THE
1-1.25" RANGE WITHIN THE SYSTEM'S WARM CONVEYOR BELT/NEAR ITS COLD
FRONT PER SSMIS/AMSU PRECIPITABLE WATER FIELDS.  THE LOW-LEVEL
INFLOW IS OUT OF THE SOUTH-SOUTHEAST AT ~40 KTS PER NEARBY VAD
WIND PROFILES.

THE RAP GUIDANCE BRINGS THE FRONTAL ZONE ASHORE AFTER 04Z, AROUND
THE TIME A WEAK BAROCLINIC LEAF SEEN IN WATER VAPOR IMAGERY NEAR
33.5N 134W AT THE PRESENT TIME WOULD BE APPROACHING CA.  THE 06Z
AND 12Z GFS-BASED INTEGRATED WATER VAPOR TRANSPORT INDICATES THAT
THE WARM CONVEYOR BELT CIRCULATION SATISFIES THE ATMOSPHERIC RIVER
DEFINITION UNTIL AROUND THE TIME OF THE FRONT'S CROSSING OF THE CA
COAST WHEN TRANSPORT SLOWLY WEAKENS AFTER THE PASSAGE OF THE
BAROCLINIC LEAF.  LOW-LEVEL INFLOW VEERS TO A MORE SOUTH TO
SOUTHWESTERLY DIRECTION THEREAFTER, APPROACHING 60 KTS AT 700 HPA.
 RAP AND SREF MEAN FORECASTS INDICATE THAT MUCAPES SHOULD RISE
INTO THE 200-400 J/KG RANGE DUE TO COOLING ALOFT CAUSED BY THE
DEEP LAYERED CYCLONE.  THIS SHOULD ALLOW HOURLY RAIN RATES TO RISE
INTO THE 0.5-0.8" RANGE NEAR AND AFTER FRONTAL PASSAGE, WHICH
SHOULD BE IN THE FORM OF RAIN FOR THE COASTAL RANGES AND
ELEVATIONS BELOW ~4000 FEET WITHIN THE SHASTA SISKIYOU RANGE (THE
SNOW LEVEL COORDINATED WITH THE EKA AND MFR FORECAST OFFICES). 
THE CAM/MESOSCALE GUIDANCE INDICATES LOCAL AMOUNTS OF ~2", MAINLY
IN THE 05-09Z PERIOD.  

ROTH

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

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

LAT...LON   41992366 41142346 40882301 40642255 38702297 
            38322323 38362325 38722361 38942383 39752397 
            40282444 40882434 41632434 41952429