MESOSCALE PRECIPITATION DISCUSSION 0666
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1052 PM EST SUN DEC 06 2015
 
AREAS AFFECTED...SW WASHINGTON TO NWRN/WRN OREGON 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 070351Z - 071430Z
 
SUMMARY...THE FOCUS OF THE HEAVIEST RAIN WILL BE SHIFTING SOUTH
OVERNIGHT INTO THE COASTAL RANGES AND CASCADES OF CNTRL/NRN
OREGON. RAINFALL RATES UP TO 0.50 IN/HR ARE EXPECTED TO LEAD TO 12
HR TOTALS OF 4-5 INCHES FOR FAVORED SOUTHWEST FACING SLOPES.

WATER VAPOR IMAGERY OVER THE PAST SEVERAL HOURS HAS SHOWN A
SHORTWAVE NEAR THE NRN TIP OF VANCOUVER ISLAND AND ITS ASSOCIATED
NEGATIVELY TILTED TROUGH AXIS SWINGING INTO BRITISH COLUMBIA. AN
AMSU PASS NEAR 00Z INDICATED RAIN RATES OFFSHORE ONLY AVERAGING
BETWEEN 0.10 - 0.20 IN/HR JUST WEST OF THE OREGON COAST.
HOWEVER...WIDE VIEW OF BLENDED TPW LOOP SHOWS THE CORE OF AN
EXTENSIVE ATMOSPHERIC RIVER...WITH A DIRECT CONNECTION TO THE WEST
PACIFIC OFF OFF SOUTHEAST ASIA...WAS NEARING THE COAST OF OREGON.
PRECIPITABLE WATER VALUES SHOULD INCREASE TO BETWEEN 1.00 AND 1.25
INCHES ALONG THE OREGON COAST BY 12Z.

AS THE SHORTWAVE NEAR VANCOUVER CONTINUES MOVING EAST
OVERNIGHT...A COLD FRONT AT THE SURFACE WILL MOVE INLAND ACROSS
WASHINGTON WITH THE CORE OF STRONGEST 850-700 MB FLOW SETTING UP
ACROSS THE CNTRL OREGON COAST...BETWEEN TILLAMOOK AND COOS
COUNTIES. THE MAGNITUDE OF THESE WINDS IS FORECAST TO RANGE
BETWEEN 50-60 KTS...PER COMPARISON OF GFS/RAP MODELED WINDS TO
VAD-WIND PLOTS. AS THE COLD FRONT MOVES INLAND...THE FETCH OF
THESE LOW LEVEL WINDS WILL ALSO INCREASINGLY VEER TOWARD THE
SOUTHWEST. ACCORDING TO WATER VAPOR IMAGERY...THE NEXT APPRECIABLE
SHORTWAVE IS LOCATED BACK TO THE WEST NEAR 45N/135W...WHICH MEANS
FORCING FOR RAINFALL WILL BE FOCUSED PRIMARILY THROUGH LOW LEVEL
MOISTURE TRANSPORT INTO THE OROGRAPHICALLY FAVORED SLOPES OF THE
COASTAL RANGES AND CASCADES...WITH THE AID OF DIFFLUENT FLOW ALOFT
FROM AN 140-150 KT JET CORE IDENTIFIED THROUGH GOES HD WINDS
MOVING EAST FROM 140W. A CONSENSUS OF HI-RES MODELS SHOWS
AGREEMENT ON RAINFALL TOTALS AND LOCATION THROUGH 1430Z.

OTTO

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

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

LAT...LON   47072173 47072128 46902107 46572111 46222132 
            45892154 45292164 44722169 43852177 43262214 
            43012278 43102346 43462455 44822425 46202430 
            46682381 46902318 47032239