Flash Flood Guidance
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000
AWUS01 KWNH 171950
FFGMPD
ORZ000-WAZ000-180748-

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

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

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

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

LAT...LON   48422448 48202370 48082294 47892260 47592263
            47232287 46782279 46502283 46042317 45552322
            44182337 44102304 44302292 44532290 45002278
            45472237 46012258 46312249 46532205 46362147
            46012141 45662158 45222143 44832160 44292156
            44062143 43732174 43582251 43582320 43732388
            44252421 45162415 46372417 46962428 47692468
            48272476



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