MESOSCALE PRECIPITATION DISCUSSION 0647
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
418 PM EST MON NOV 16 2015
 
AREAS AFFECTED...WESTERN WA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 162100Z - 170600Z
 
SUMMARY...A ROBUST ATMOSPHERIC RIVER CONTINUES TO AIM FOR WESTERN
WA. HEAVIER RAINS WILL ARRIVE TOWARD EVENING AND CONTINUE
OVERNIGHT.

DISCUSSION...WV AND IR SATELLITE IMAGERY THIS AFTERNOON SHOWS A
POWERFUL WEST/EAST ORIENTED H25 JET OF LOCALLY OVER 170 KTS STILL
FOCUSED JUST SOUTH OF AN AMPLIFYING SHORTWAVE AND ASSOCIATED LOW
CENTER NOW MOVING INTO CENTRAL BRITISH COLUMBIA. THIS ENERGY IS
DRIVING VERY STRONG WARM ADVECTION TOWARD THE WA COASTAL RANGES
INCLUDING THE OLYMPIC PENINSULA.

FACILITATING THE LARGER SCALE FORCING IS THE NOSE OF A 50 TO 60 KT
WESTERLY LOW LEVEL WHICH WILL BE ARRIVING ACROSS THE OLYMPIC
PENINSULA BY 00Z...AND COINCIDING WITH THIS WILL BE THE ARRIVAL OF
A WELL DEFINED WARM FRONT WHICH IS STILL OFFSHORE CURRENTLY. PWATS
ARE EXPECTED TO PEAK IN THE RANGE OF 1.0 TO 1.2 INCHES BETWEEN 00Z
AND 06Z OVER WESTERN WA...AND THIS MOISTURE EXTENDS WELL UPSTREAM
ALONG A FRONTAL ZONE SOUTH OF THE GULF OF AK. THE INCREASING PWATS
THIS EVENING AND ARRIVAL OF STRONGER LARGE SCALE FORCING SHOULD
GENERATE HEAVIER RAINFALL RATES WHICH WILL FALL OVER ALREADY
SATURATED TERRAIN OF WESTERN WA.

A 1900Z AMSU PASS INDICATES OFFSHORE RAINFALL RATES OF 0.25 TO
0.35 INCHES/HR JUST AHEAD OF THE WARM FRONT...AND THE 12Z ARW AND
12Z NMMB SUGGEST THESE RAINFALL RATES ARRIVING BY 00Z AND
CONTINUING OVERNIGHT. THE PRESENCE OF STRONG ONSHORE FLOW AND
OROGRAPHIC FORCING THOUGH WILL LIKELY ENHANCE RATES A BIT
FURTHER...AND IT IS EXPECTED THAT SOME RATES OVER THE HIGHER
TERRAIN OF THE COASTAL RANGES WILL EXCEED 0.50 INCHES/HR AT TIMES.

WILL CONTINUE TO MONITOR...BUT EXPECT THE HEAVIEST RAINFALL
AMOUNTS TO BE ON THE ORDER OF 2 TO 4 INCHES THROUGH ABOUT 06Z WITH
ISOLATED AMOUNTS POSSIBLY EXCEEDING 5 INCHES OVER THE COASTAL
RANGES AND ESPECIALLY THE OLYMPICS. LESSER AMOUNTS OF UP TO A
COUPLE OF INCHES ARE EXPECTED FARTHER INLAND TO JUST WEST OF THE
CASCADES. HOWEVER...ADDITIONAL HEAVY RAINS ARE EXPECTED AFTER THIS
TIME FRAME.

ORRISON

ATTN...WFO...PQR...SEW...

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

LAT...LON   49302327 48752195 47792184 45932238 46012381 
            46782454 48792466 49262400