MESOSCALE PRECIPITATION DISCUSSION 0670
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
728 PM EST TUE DEC 08 2015
 
AREAS AFFECTED...WA...OR 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 090020Z - 090720Z

...CORRECTED SPELLING...
 
SUMMARY...THERE IS HIGH CONFIDENCE IN AREAL AVERAGE RAINFALL 2 TO
4 INCHES OVERNIGHT...CENTERING ON THE AREA FROM MOUNT RAINIER TO
MOUNT HOOD AND WESTWARD TO THE NORTHWEST OREGON COAST. THIS WILL
COMPOUND ONGOING FLOODING.

DISCUSSION...AFTER DIALOGUE WITH NESDIS...IT WOULD APPEAR THE
SUPPLY OF MOISTURE AND ASSOCIATED RAIN RATES ARE NEARLY STEADY
STATE...WITH A RIVER OF TPW 1.0 TO 1.25 INCHES EXTENDING FROM THE
COAST WELL BACK INTO THE PACIFIC. AMSU SATELLITE PASSES CONTINUED
TO INDICATE HOURLY RAIN RATES OFFSHORE PEAKING AT ABOUT 0.30
INCHES. WHEN BROUGHT ONSHORE AND ENCOUNTERING
TERRAIN...OBSERVATIONS HAD CONTINUALLY SHOWN HOURLY RAIN RATES
PUSHING ABOVE 0.50 INCHES ALONG FAVORED SLOPES. THE PATTERN WAS
ADJUSTING...HOWEVER...TOWARD ORGANIZATION OF A STRONGER AND MORE
LASTING FRONTAL WAVE THAT WILL EVENTUALLY PUSH THROUGH THE
REGION...BUT NOT BEFORE SPURRING AN INCREASE OF MOISTURE TRANSPORT
LATE THIS EVENING.

RAPIDLY MOVING CIRRUS...ASSOCIATED WITH A 150 KT JET STREAK...WAS
OBSERVED CROSSING THE ATMOSPHERIC RIVER AT AN ANGLE AROUND 140 DEG
WEST. THIS WILL FURTHER THE DEVELOPMENT OF A FRONTAL WAVE THAT WAS
ALREADY EVIDENCED DOWNSTREAM PER CONVECTIVE CLOUD STRUCUTRE AND
SOME LIGHTNING AROUND 47 N / 136 W PER GLD360 MOCKED UP GOES-R
LIGHTNING DENSITY PRODUCT. THOUGH LIGHTNING WAS NOT OBSERVED IN
THE RIVER ITSELF...RAIN RATES WILL BE ENHANCED TOWARD 03-07Z AS
850-700 MB SOUTHWESTERLY FLOW INCREASES AGAIN TO 65 KNOTS OVER
WESTERN WA/OR. HI-RES MODELS ARE UNANIMOUS IN FORECASTING 2 TO 4
INCHES...LOCALLY 5...IN THE 12 HOURS THROUGH 12Z. HOURLY RATES IN
THE WRF-ARW PEAK AT JUST ABOVE 0.75 INCH PER HOUR IN THE MOST
STRONGLY FAVORED WSW-FACING SLOPES.

ALTHOUGH THE REGION IS ACCUSTOMED TO WET WEATHER AND
FLOODING...RECENT EVENTS HAVE BEEN EXCEPTIONAL...WITH OBSERVED
7-DAY TOTALS RUNNING 10-20 INCHES...IN SOME CASES MORE THAN 8
INCHES ABOVE AVERAGE FOR EARLY DECEMBER.

BURKE

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

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

LAT...LON   48822142 48632075 48032075 46642100 44652170 
            44272260 43922428 46692447 47722409 48052320 
            47572251 48482187