MESOSCALE PRECIPITATION DISCUSSION 0734
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
738 AM EDT THU OCT 13 2016
 
AREAS AFFECTED...MTS OF WESTERN OR, WESTERN WA, & FAR NW CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 131138Z - 132338Z
 
SUMMARY...DISTURBANCES RIDING NEAR THE POLAR JET SHOULD KEEP HEAVY
RAINFALL IN THE OFFING ACROSS THE MOUNTAINS OF WESTERN WA, WESTERN
OR, AND EVENTUALLY NORTHWEST CA THROUGH THIS AFTERNOON.  HOURLY
RAIN RATES OF 0.5-0.8" ARE POSSIBLE, WHICH COULD LEAD TO ISSUES IN
BURN SCARS AND MORE SENSITIVE RIVER BASINS.

DISCUSSION...SATELLITE IMAGERY REVEALS TWO MAIN SURGES OF RAINFALL
WITHIN AN ATMOSPHERIC RIVER -- ONE CURRENTLY ASHORE WESTERN WA AND
A SECOND SURGE AHEAD OF A SHORTWAVE APPROACHING 140W LONGITUDE. 
BROAD DIVERGENCE IS SEEN ACROSS THE WHOLE AREA, WHICH IS EAST OF A
BROAD GYRE LOCATED IN THE NORTHEAST PACIFIC OCEAN.  MUCAPES NEAR
THE WA COAST ARE CURRENTLY ~ 100 J/KG, WITH HIGHER VALUES SHOWN
OFFSHORE IN SPC MESOANALYSES.  THE LIGHTNING DETECTION NETWORK
AGREES WITH THIS ASSESSMENT, AS LIGHTNING HAS BEEN WITNESSED AS
FAR EAST AS 129W LONGITUDE OFFSHORE WESTERN WA.  LIGHTNING IS
ESPECIALLY NUMEROUS AHEAD OF THE SECOND UPPER DISTURBANCE BETWEEN
40-41N AND 139-140W WHERE SATELLITE DERIVED RAIN RATES ARE NEAR
0.5" AN HOUR.  PRECIPITABLE WATER VALUES ARE RISING, WITH GPS
VALUES NEAR 1.25" FROM NORTHWEST CA UP THE COAST TO QUILLAYUTE,
AND 0.75"+ VALUES IN THE CASCADES OF NORTHERN OR AND WA.  LOW
LEVEL INFLOW OF 25-45 KTS IS SEEN IN AREA VAD WIND PROFILES.

LOW-LEVEL INFLOW WITH THE FIRST BATCH OF HEAVY RAINFALL IS
EXPECTED TO DECREASE BY 15Z DOWN TO 25-35 KTS.  HOWEVER, WITH
INSTABILITY FORECAST TO SLOWLY INVADE FROM THE NORTHEAST PACIFIC
WITHIN RAP/SREF MEAN MASS FIELDS, IT IS POSSIBLE THAT WESTERN WA
IS NOT OFF THE HOOK FOR HEAVY RAINFALL DURING THE DAY TODAY. 
LOW-LEVEL INFLOW SHOULD RAMP UP ACROSS SOUTHWEST OR/FAR NORTHWEST
CA AFTER 18Z AHEAD OF THE SECOND DISTURBANCE, NEARLY DOUBLING TO
80 KTS BY 23Z.  THE MAIN FOCUS FOR HOURLY RAIN RATES OF 0.5-0.8"
IS EXPECTED TO LIE IN THE COASTAL RANGES OF OR AND THE CASCADES
NEAR THE WA/OR BORDER.  THE MESOSCALE/CAM GUIDANCE SHOWS THE MOST
COHESIVE SIGNAL HERE FOR LOCAL AMOUNTS IN THE 3-5" RANGE THROUGH
23Z.  THIS DEGREE OF RAINFALL COULD BE PROBLEMATIC FOR AREAS WITH
BURN SCARS AND MORE SENSITIVE RIVER BASINS ACROSS THE REGION.  

ROTH

ATTN...WFO...EKA...MFR...OTX...PDT...PQR...SEW...

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

LAT...LON   49132113 48502072 47032094 45522148 44122156 
            44002164 43252275 43512306 43972338 43532370 
            42562360 41702347 41572349 41422391 42162445 
            43062458 44192419 45922407 47572439 48292465 
            48382439 47982311 47642297 46982335 46172324 
            45912320 45012327 44492302 45622268 46412267 
            46882228 47842210 48572236 48822221 49042159