MESOSCALE PRECIPITATION DISCUSSION 0021
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
249 PM EST TUE JAN 17 2017
 
AREAS AFFECTED...WA/OR COASTAL RANGES/CASCADES... 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 171948Z - 180748Z
 
SUMMARY....AN IMPRESSIVE ATMOSPHERIC RIVER SET UP IS IN PLACE WITH
DEEP SUBTROPICAL MOISTURE EXTENDING BACK INTO THE CENTRAL PACIFIC.
THIS COUPLED WITH 60-70 KNOT SOUTH-SOUTHWESTERLY FLOW WILL AID IN
IMPRESSIVE RAINFALL ACROSS THE OROGRAPHICALLY FAVORED REGIONS.
EXPECT HOURLY RATES TO APPROACH OR EVEN EXCEED 0.50 INCHES DURING
THE HEIGHT OF THE EVENT.

DISCUSSION...WATER VAPOR IMAGERY AND 500-MB HEIGHT FIELDS SHOWED A
LONGWAVE TROUGH ANCHORING THE CENTRAL/EASTERN PACIFIC. AN EMBEDDED
SHORTWAVE CURRENTLY MOVING ACROSS 135W HAS AMPLE MOISTURE SUPPORT
PER RECENT AMSU SATELLITE PASSES. 1.50 TO 2 INCH PWATS ARE
CURRENTLY BEING ANALYZED WITHIN THIS ATMOSPHERIC RIVER WITH RECENT
HOURLY RATES BETWEEN 0.25 TO 0.50 INCHES. ADDITIONALLY...THE AR
DETECTION TOOL SHOWED INTEGRATED VAPOR TRANSPORT VALUES EXCEEDING
1250 KG/M/S. ALL OF THIS ACTIVITY WILL SHIFT NORTHEASTWARD DURING
THE NEXT 4 HOURS. MOST OF THE GUIDANCE SUPPORT THIS MORE ENHANCED
PRECIPITATION TO ARRIVE JUST BEFORE 00Z AND CONTINUING THROUGHOUT
THE REMAINDER OF THE MPD ISSUANCE. GIVEN THE IMPRESSIVE LOW-LEVEL
SOUTHWESTERLY FLOW IMPINGING ON THE COASTAL RANGES AND
CASCADES...WOULD EXPECT HOURLY RATES TO RAMP UP POSSIBLY EXCEEDING
0.50 INCHES. THIS IS FAIRLY CONSISTENT AMONG THE HIGH-RESOLUTION
SOLUTIONS...PARTICULARLY THE LAST FEW RUNS OF THE HRRR. IN TERMS
OF IMPACTS...MUCH OF THE HEAVIEST PRECIPITATION THE PAST TWO WEEKS
HAS BEEN OVER WESTERN OR WHICH IS WHERE SOME ISOLATED HYDROLOGIC
ISSUES MAY OCCUR.


RUBIN-OSTER

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

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

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            48272476