MESOSCALE PRECIPITATION DISCUSSION 0654
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
903 PM EST TUE NOV 17 2015
 
AREAS AFFECTED...COASTAL RANGES OF OR & THE CASCADES OF WA/OR 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 180200Z - 180800Z
 
SUMMARY...HOURLY RAIN RATES ARE EXPECTED TO FADE OVER THE NEXT
SEVERAL HOURS AS A SHORTWAVE MOVES AWAY FROM THE REGION.  HOURLY
RAIN RATES > 0.50" AN HOUR ARE POSSIBLE OVER THE NEXT FEW HOURS.

DISCUSSION...A SHORTWAVE MOVING EASTWARD ALONG THE WA/BRITISH
COLUMBIA BORDER HAS KEPT THE HIGHEST HOURLY RAIN RATES STEADY IN
THE 0.5-1.2" RANGE UNDER ITS BASE ACROSS THE TERRAIN OF NORTHWEST
OR AND THE WASHINGTON CASCADES PER MESOWEST OBSERVATIONS.  THE
SALEM OR SOUNDING SHOWED NO INVERSIONS/ISOTHERMAL LAYERS THAT
WOULD OTHERWISE ACT AS A CAP ON RAIN RATES.  PRECIPITABLE WATER
VALUES (PWS) OF 1-1.2" LIE ACROSS THE REGION, PER GPS VALUES. 
MUCAPES IN THE 100-300 J/KG ARE ADVERTISED NEAR THE OLYMPIC
PENINSULA OF WA BY THE LATEST SPC MESOANALYSIS, THOUGH THIS
INSTABILITY HAS BEEN REALIZED AS LIGHT/MODERATE RAIN SINCE PWS IN
THAT AREA ARE FALLING UNDER 0.60".  

RECENT SATELLITE IMAGERY REVEALS WARMING CLOUD TOPS ACROSS THE
REGION WHILE THE HIGHER RAIN RATES FROM MICROWAVE IMAGERY HAVE
SHOWN A REDUCTION IN AMOUNTS AND COVERAGE OVER THE LAST SEVERAL
HOURS.  THE ABOVE INDICATES THAT THE BEGINNING OF THE EXPECTED
FADE IN HEAVY RAINFALL SHOULD OCCUR SHORTLY.  AS THE SHORTWAVE
NEAR THE INTERNATIONAL BORDER CONTINUES MOVING EASTWARD, LOW-LEVEL
INFLOW OFF THE PACIFIC SHOULD SLOWLY LESSEN OVER THE NEXT SEVERAL
HOURS, AND BECOME DECOUPLED FROM THE AVAILABLE MOISTURE PLUME
WHICH SHIFTS SOUTH IN TANDEM WITH THE COLD FRONT WITH TIME TOWARDS
NORTHERN CA.  RAP FORECASTS SHOW PWS FALLING TO <= 1" ACROSS
WESTERN OR FROM 06Z ONWARD, WHICH IS LIKELY WHEN HOURLY RAIN RATES
SHOULD FALL BELOW 0.50" WITHIN FAVORED AREAS OF TERRAIN.  THE CAM
GUIDANCE GENERALLY ADVERTISES ANOTHER 2" OF RAIN LOCALLY, WHICH
SHOULD OCCUR PRIMARILY OVER THE NEXT 3-4 HOURS.  THE 18Z SSEO
NEIGHBORHOOD PROBABILITIES SUGGEST HEAVY RAIN CONCERNS OVER THE
REGION SHOULD END AROUND 08Z, WHICH WAS USED AS THE HORIZON OF
THIS MPD.

THIS INFORMATION WAS COORDINATED WITH SAB/ NESDIS.

ROTH

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

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

LAT...LON   48982082 48982064 48752052 48552052 47392046 
            46632091 46372089 45962087 44742134 43632167 
            42462074 42452119 42702176 42182234 42532297 
            42272308 41842291 40952364 41392458 43152467 
            44962425 46672393 46662319 46322283 46832235 
            48672188