MESOSCALE PRECIPITATION DISCUSSION 0747
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
827 AM EDT THU OCT 20 2016
 
AREAS AFFECTED...WESTERN WA...NORTHWEST OR 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 201225Z - 202100Z
 
SUMMARY...HEAVY RAINS WILL CONTINUE THROUGH THE MORNING...WITH
IMPROVING CONDITIONS TOWARD MID-AFTERNOON.

DISCUSSION...HEAVY RAINS CONTINUE THIS MORNING ACROSS THE COASTAL
RANGES OF WESTERN WA AND STRETCHING INTO THE HIGHER TERRAIN OF THE
CASCADES AS A WELL-DEFINED FETCH OF PACIFIC MOISTURE CONTINUES TO
STREAM NORTHEAST ALONG A WELL-DEFINED FRONTAL ZONE AND THEN INLAND
ACROSS THE PACIFIC NORTHWEST. GOES-SOUNDER PWATS OFFSHORE THE WEST
COAST SHOW A RIVER OF 1.2 TO 1.4 INCH PWATS ALONG AND JUST AHEAD
OF THE FRONT...AND THESE VALUES ARE CONFIRMED BY GPS MONITORS
ACROSS WESTERN OR AND WESTERN WA. THESE PWATS ARE RUNNING ABOUT 3
STANDARD DEVIATIONS ABOVE NORMAL AND ARE CONTRIBUTING TO MORE
EFFICIENT RAINFALL PROCESSES THAT ARE ENHANCING RAINFALL RATES.
OBSERVED 1-HOUR RATES OVER THE LAST SEVERAL HOURS CONTINUE TO
APPROACH 0.50"/HR ACROSS THE SOUTH FACING SLOPES OF THE OLYMPICS
AND ALSO INTO THE WEST FACING SLOPES OF THE CASCADES. SOME AREAS
HAVE RECEIVED CLOSE TO 2 INCHES OF RAIN IN JUST THE LAST 6 HOURS.

THE NORTHEAST ADVANCE OF A SHORTWAVE TROUGH AND AN ACCOMPANYING
130-150 KT UPPER JET MAX WILL SEND THE COLD FRONT GRADUALLY
SOUTHEAST AND INLAND ACROSS THE PACIFIC NORTHWEST TODAY...WHICH
WILL ALLOW THE CURRENT BAND OF HEAVY RAIN IMPACTING THE REGION TO
ADVANCE DOWN INTO NORTHWEST OR. THE HIRES GUIDANCE FROM 00Z
SUGGESTS A GRADUAL THINNING OUT OF THE DEEPER MOISTURE ACROSS THE
REGION THIS AFTERNOON...AND SO THE RAINFALL RATES SHOULD BEGIN TO
TAPER DOWN BY LATER TODAY. THE STRONGER JET DYNAMICS WILL ALSO
BEGIN TO BYPASS THE REGION WHICH WILL HELP TO DIMINISH THE OVERALL
COVERAGE AND ORGANIZATION OF THE HEAVIER RAINS.

ADDITIONAL RAINFALL AMOUNTS THROUGH MID-AFTERNOON OF UP TO 2 TO 4
INCHES CAN BE EXPECTED...WITH SOME ISOLATED HEAVIER AMOUNTS NOT
OUT OF THE QUESTION. GIVEN THE RAINFALL THE REGION HAS SEEN OVER
THE LAST WEEK...SOME RUNOFF PROBLEMS WILL BE POSSIBLE WHICH
INCLUDES CONCERNS OF MUDSLIDES AND DEBRIS FLOWS AROUND BURN SCAR
AREAS.

ORRISON

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

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

LAT...LON   49132179 49072082 48472022 47552052 46562110 
            46062113 45222190 45102252 45352266 45652270 
            45582315 45112350 45382402 45832416 46422424 
            46972417 48052459 48412425 48202299 48822241