Graphic for MPD #0892

MESOSCALE PRECIPITATION DISCUSSION 0892...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
808 AM EDT THU OCT 19 2017

CORRECTED FOR VALID TIME

AREAS AFFECTED...AREAS AFFECTED...WESTERN WA...WESTERN OR

CONCERNING...HEAVY RAINFALL

VALID 190530Z - 191730Z

SUMMARY...HEAVY RAINS WILL CONTINUE OVERNIGHT AND WELL INTO
THURSDAY FOR THE COASTAL RANGES OF THE PACIFIC NORTHWEST.

DISCUSSION...A WELL-DEFINED ATMOSPHERIC RIVER CONTINUES TO BRING
HEAVY RAINFALL TO WESTERN WA AS A DEEP LOW PRESSURE TROUGH OVER
THE GULF OF AK SENDS A COLD FRONT GRADUALLY TOWARDS THE PACIFIC
NORTHWEST AND ALONG WITH A PLUME OF ENHANCED DEEP LAYER MOISTURE.
THE LATEST BLENDED-TPW IMAGERY SHOWS A POOL OF 1.2 TO 1.3 INCH
PWATS AIMING RIGHT INTO THE COASTAL RANGES OF WESTERN WA AT THIS
TIME...AND THIS SW/NE AXIS OF DEEPER MOISTURE IS SLOWLY SINKING
SOUTH WITH TIME. THE LATEST CIRA-LPW DATA IS SHOWING SOME
RELATIVELY FOCUSED MOISTURE IN THE 500/300 MB LAYER WHICH IS
LIKELY HELPING TO CONTRIBUTE TO MORE EFFICIENT RAINFALL PROCESSES.

THE COLD FRONT WILL SLOWLY SETTLE SOUTH DOWN ACROSS SOUTHWEST WA
AND INTO WESTERN OR THROUGH EARLY TO MID-MORNING ON THURSDAY...AND
THEN INTO SOUTHWEST OR BY MID-AFTERNOON. THE HIRES MODEL CONSENSUS
SUPPORTS A CONTINUATION OF A 40 TO 50 KT SOUTHWESTERLY LOW LEVEL
JET INTO THE COASTAL RANGES THROUGH THIS PERIOD WHICH WILL ENHANCE
THE MOISTURE TRANSPORT AND FOSTER OROGRAPHICALLY ENHANCED
RAINFALL. IT IS LIKELY THAT SUFFICIENTLY STRONG SURFACE
CONVERGENCE WITH THE FRONT ALONG WITH SOME RIGHT ENTRANCE REGION
JET DYNAMICS ASSOCIATED WITH 130+ KT 250 MB CORE WILL SUSTAIN A
SOLID AXIS OF MODERATE TO HEAVY RAIN...WITH SOME PERIODIC RAINFALL
RATES REACHING CLOSE TO A 0.50 INCH/HR. THIS WILL MAINLY BE FOR
THE IMMEDIATE SOUTHWEST FACING SLOPES OF THE CASCADES AND ALSO THE
COASTAL RANGES.

THE HIRES MODEL CONSENSUS FROM 00Z SUPPORTS AS MUCH AS 2 TO 4
INCHES OF RAIN THROUGH MID-AFTERNOON THURSDAY WITH ISOLATED
HEAVIER TOTALS. SOME ISOLATED RUNOFF PROBLEMS CANNOT BE RULED OUT
AS A RESULT.

ORRISON

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

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

LAT...LON   48832188 48752143 47822137 46692147 45272167
            44562189 43892223 43322295 42602350 42052382
            42342473 44612441 46622452 47772447 48182399
            48162326 47772285 47772241 47872212 48212193
            48562210


Last Updated: 808 AM EDT THU OCT 19 2017