MESOSCALE PRECIPITATION DISCUSSION 0060
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
124 PM EST WED MAR 09 2016
 
AREAS AFFECTED...WESTERN WA...NORTHWEST OR 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 091823Z - 100623Z
 
SUMMARY...APPROACHING WAVE AND ATMOSPHERIC RIVER TO BRING MODERATE
TO AT TIMES HEAVY RAINFALL TO THE AREA...

DISCUSSION...AN IMPRESSIVE ATMOSPHERIC RIVER OFF THE WEST COAST
WILL MOVE ASHORE LATER TODAY INTO TONIGHT...BRINGING WITH IT A
HEAVY RAINFALL THREAT. SYNOPTIC SUPPORT WILL BE PROVIDED BY AN
APPROACHING SHORTWAVE...AND WITHIN THE LEFT EXIT REGION OF A
STRONG UPPER JET. THIS LARGE SCALE ASCENT WILL FAVOR A DEEPENING
AREA OF SURFACE LOW PRESSURE MOVING NORTHEAST INTO SOUTHERN
CANADA. VERY IMPRESSIVE WIND FIELDS ASSOCIATED WITH THIS
SYSTEM...WITH DEEP SOUTHWESTERLY FLOW NEAR OR ABOVE THE
CLIMATOLOGICAL MAX VALUES FOR THIS TIME OF YEAR ALL THE WAY FROM
500 MB TO 850 MB. 

THUS NO SURPRISE THAT THE STRENGTH OF THE ATMOSPHERIC RIVER
MEASURED PER INTEGRATED WATER VAPOR TRANSPORT IS ALSO NEAR RECORD
STRENGTH. COMBINE THIS MOISTURE TRANSPORT AND UPSLOPE FLOW WITH
THE SYNOPTIC FORCING AND EXPECT A PERIOD OF MODERATE TO LOCALLY
HEAVY RAINFALL ACROSS THE TERRAIN OF WESTERN WA. THE MAIN LIMITING
FACTOR FOR TOTAL AMOUNTS WILL LIKELY BE THE DURATION...WITH ABOUT
A 12 HOUR WINDOW WHERE THE BEST MOISTURE/FORCING OVERLAP. ALSO THE
MAGNITUDE OF MOISTURE AS MEASURED BY PRECIPITABLE WATER WILL BE IN
A RAPIDLY DECREASING STATE THROUGH OVERNIGHT.

WIDESPREAD HOURLY RAINFALL RATES BETWEEN 0.25"-0.5" ARE EXPECTED
TO OVERSPREAD WESTERN WA AFTER 21z...WITH PEAK INTENSITY BETWEEN
21Z AND 06Z...WITH ISOLATED HOURLY RATES AS HIGH AS 0.75" IN AN
HOUR ACROSS THE FAVORED UPSLOPE TERRAIN NEAR THE OLYMPICS. HIGH
RES MODEL CONSENSUS IS FOR 1.5"-3" OF PRECIPITATION BETWEEN 18Z
AND 06Z ACROSS THE COASTAL AND CASCADE RANGES OF WA AND INTO
NORTHWEST OR. ISOLATED 12 HOUR AMOUNTS AROUND 5" SEEM POSSIBLE IN
THE FAVORED UPSLOPE TERRAIN NEAR THE OLYMPICS. 


CHENARD

ATTN...WFO...OTX...PDT...PQR...SEW...

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

LAT...LON   49452183 49022075 48042042 47202061 46532071 
            46052088 45772139 45582187 45602247 45542278 
            45212322 44912349 44732390 44852421 45352446 
            46802477 49122450