Graphic for MPD #0074

MESOSCALE PRECIPITATION DISCUSSION 0074
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1101 PM EDT FRI MAR 17 2017

AREAS AFFECTED...COASTAL RANGES & CASCADES OF OR/WA

CONCERNING...HEAVY RAINFALL

VALID 180300Z - 181500Z

SUMMARY...DUAL MOISTURE CHANNELS AND STRONG ONSHORE FLOW ARE
EXPECTED TO COMBINE FORCES AND LEAD TO HOURLY RAIN RATES OF 0.5"+
AND LOCAL AMOUNTS OF 3"+ THROUGH 15Z.

DISCUSSION...PACIFIC MOISTURE IS HEADING INTO THE REGION AHEAD OF
A DEEP CYCLONE NEAR 40N 134W.  WATER VAPOR IMAGERY REVEALS A
BROADLY DIVERGENT PATTERN ALOFT AHEAD OF THE UPPER TROUGH. 
PRECIPITABLE WATER VALUES OF 0.7-1" HAVE BEEN SEEN WITHIN RECENT
GPS INFORMATION.  INFLOW AT 850 HPA IS CONVERGENT OUT OF THE
SOUTH-SOUTHWEST IN THE 35-50 KT RANGE PER RECENT VAD WIND
PROFILES.  TWO MOISTURE CHANNELS WERE NOTED ON SATELLITE IMAGERY
AND WITHIN THE PRECIPITABLE WATER FIELD -- ONE JUST OFFSHORE THE
COAST NEAR THE OR/CA BORDER WHICH ORIGINATED FROM THE PREVIOUS
SYSTEM THAT MOVED INTO THE WEST AND THE OTHER IN THE FORM OF A
PINEAPPLE CONNECTION HEADING TOWARDS THE OLYMPIC PENINSULA JUST
AHEAD OF A SYSTEM APPROACHING THE PACIFIC NORTHWEST.

THE MESOSCALE GUIDANCE SHOWS INFLOW AT 850 HPA WITHIN A
UNIDIRECTIONAL FLOW REGIME REACHING 70 KTS ACROSS WA AND 60 KTS
ACROSS PORTIONS OF OR, WHICH EVEN WITHIN AN ENVIRONMENT WITH
ESSENTIALLY NO INSTABILITY SHOULD BE CAPABLE OF GENERATING HOURLY
RAIN RATES NEAR OR EXCEEDING 0.5".  THE SNOW LEVEL SHOULD BE IN
THE 7000-8500 FT ELEVATION RANGE ACROSS OR AND RISE TO ~5500 FEET
WITHIN THE TERRAIN OF WESTERN WA.  THE MESOSCALE GUIDANCE AGREES
ON HOURLY RAIN RATES REACHING 0.5" AND ADVERTISES LOCAL AMOUNTS OF
3"+ THROUGH 15Z ACROSS THE OLYMPICS AND CASCADES OF WA WHERE
BETTER BOUNDARY LAYER MOISTURE CONVERGENCE IS EXPECTED. MORE
SPOTTY COVERAGE OF HIGHER AMOUNTS IS EXPECTED ACROSS THE CASCADES
OF OR AND THE OR COASTAL RANGES, WITH THE EMPHASIS IN HIGHER
AMOUNTS NEAR BROOKINGS WITHIN THE SOUTHERN MOISTURE BAND.

ROTH

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

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

LAT...LON   48372498 48372432 48292347 48252304 46512312
            46672235 48022231 48252192 48102088 46732108
            46012146 45432149 45102160 43972175 43402290
            42862355 42382349 41592365 41882451 43502447
            46052413


Last Updated: 1101 PM EDT FRI MAR 17 2017