MESOSCALE PRECIPITATION DISCUSSION 0671
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
240 AM EST WED DEC 09 2015
 
AREAS AFFECTED...SWRN WASHINGTON / WRN OREGON 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 090739Z - 091330Z
 
SUMMARY...THE CORE OF THE 0.50+ IN/HR RAINFALL RATES WILL SHIFT
SOUTH DOWN THE OREGON COAST TO THE OREGON/CALIFORNIA BORDER BY
ABOUT 12Z. THE TOTAL DURATION OF THESE HIGHER RAINFALL RATES OVER
ANY GIVEN SPOT IS EXPECTED TO BE SHORTER...RELATIVE TO THE DAY ON
TUESDAY...BUT FLOODING IMPACTS WILL CONTINUE TO IMPACT ALREADY
SATURATED SOILS.

DISCUSSION...WATER VAPOR IMAGERY AT 07Z SHOWED A STEADILY
PROGRESSING SHORTWAVE TROUGH APPROACHING THE WASHINGTON/OREGON
COASTS...WITH AN OCCLUDED/COLD FRONT ANALYZED JUST AHEAD AT THE
SURFACE. PRECIPITABLE WATER VALUES OF 1.1 TO 1.2 INCHES WERE
FOUND...PER GPS DATA...AT THE NOSE OF AN ATMOSPHERIC RIVER LOCATED
JUST AHEAD OF THE COLD FRONT...WHICH WAS AIMED INTO THE N-CNTRL
OREGON COAST AT 07Z. AN AMSU PASS AT ROUGHLY 0530Z SHOWED MAXIMUM
RAIN RATES WITHIN THE CORE OF THE ATMOSPHERIC RIVER TO BE 0.27
IN/HR...WHICH WHEN ACCOUNTING FOR OROGRAPHICS...COULD BE UP TO
0.60 IN/HR ONCE INLAND. THIS WOULD BE CONSISTENT WITH WHAT HAS
BEEN OBSERVED OVER THE PAST SEVERAL HOURS ACROSS THE NRN OREGON
COASTAL RANGES AND THE SRN WASHINGTON CASCADES. 

REGIONAL RADAR IMAGERY OVER THE PAST COUPLE OF HOURS HAS SHOWN AN
UPTICK IN REFLECTIVITY ACROSS THE N-CNTRL OREGON COAST DUE TO THE
ADVANCING COLD FRONT WHICH WILL BE SENDING THE CORE OF THE HIGHEST
PRECIPITABLE WATER VALUES SOUTHWARD DOWN THE OREGON COAST THROUGH
13Z. 850-700 MB FLOW OF 50-60 KTS...OBSERVED AT KRTX VAD WIND
PROFILE...IS MATCHED BY THE 06Z RAP...AND IS FORECAST TO CONTINUE
JUST AHEAD OF THE FRONT ALLOWING A CONTINUATION OF HOURLY RAIN
RATES OF 0.5 TO 0.6 IN/HR WITHIN HEAVIER BANDS. HOWEVER...THE
DURATION OF THESE HEAVY BANDS WILL BE LIMITED TO 2-3 HOURS OVER
ANY GIVEN LOCATION AS THE ENTIRE HEAVY RAINFALL AXIS WILL BE
MOVING SOUTH. THERE MAY BE SOME ENHANCEMENT AS THE CORE OF A 150+
KT UPPER LEVEL JET NEARS THE COAST BUT 6 HOUR RAINFALL TOTALS
SHOULD BE LIMITED TO BETWEEN 1.5 - 2.5 INCHES THROUGH ABOUT 13Z
WITH PERHAPS VERY LOCALIZED VALUES OF 3 INCHES ACROSS FAVORED
UPSLOPE LOCATIONS.

OTTO

ATTN...WFO...EKA...MFR...PDT...PQR...SEW...

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

LAT...LON   46782181 46612141 46152135 45392148 44622173 
            43982171 43382195 42712206 42532249 42532324 
            41682349 41452392 41612442 42262471 43362473 
            44332440 45632419 45972392 46112342 46172285 
            46282255