MESOSCALE PRECIPITATION DISCUSSION 0738
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
536 AM EDT SAT OCT 15 2016
 
AREAS AFFECTED...NRN CA/WRN OR 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 150933Z - 152130Z
 
SUMMARY...A RAPIDLY STRENGTHENING CYCLONE WILL APPROACH THE
PACIFIC NORTHWEST COAST LATE THIS MORNING AND WILL BRING A PERIOD
OF HEAVY RAINFALL RATES STARTING BETWEEN 16-18Z TO THE OR
COASTLINE AND NRN CA. THE GREATEST RAINFALL ACCUMULATIONS ARE
EXPECTED FROM SWRN OR INTO NRN CA WHERE 3-5 INCHES OF RAIN IS
EXPECTED THROUGH 22Z.

DISCUSSION...09Z GOES WEST WATER VAPOR AND INFRARED IMAGERY SHOWED
A RAPIDLY DEEPENING MID-UPPER LEVEL TROUGH LOCATED NEAR 43N
137W...WITH AN EXPANDING AREA OF COOLING CLOUD TOPS AHEAD OF A
STRENGTHENING SURFACE LOW...ESTIMATED TO BE NEAR 42N 132W. A 0614Z
AMSU PASS PLACED A LARGE AREA OF 0.50 TO 0.75 IN/HR RAINFALL RATES
WITHIN THE COLDEST CLOUD TOPS WHICH HAVE SINCE MOVED ENEWD.
SATELLITE DERIVED TPW IMAGERY SHOWED A SWATH OF 1.4 INCH
PRECIPITABLE WATER VALUES JUST AHEAD OF THE SURFACE COLD FRONT.

GLOBAL AND SHORT TERM MODELS ARE IN GOOD AGREEMENT WITH THE TRACK
OF THE LOW TO ROUGHLY 200 MI WEST OF PDX BY 18Z. WHILE THERE ARE
CNTRL PRESSURE DIFFERENCES IN THE GUIDANCE...THEY ARE UNANIMOUS
WITH RAPID DEEPENING OF THE LOW AND DEVELOPMENT OF AN OCCLUDED
FRONT WITH THE TRIPLE POINT OFF OF THE SRN OR COAST BY 18Z. WHILE
THE STRONGEST 850-700 MB WINDS...70-80 KTS... ARE EXPECTED ALONG
AND NORTH OF THE TRIPLE POINT...PRECIPITABLE WATER VALUES MAY ONLY
BE NEAR AN INCH FROM CNTRL OR TO NWRN WA. HOWEVER...THE
COMBINATION OF STRENGTHENING UPPER LEVEL
DIVERGENCE/DIFFLUENCE...FORECAST 250-750 J/KG MUCAPE AND STRONG
SURFACE CONVERGENCE WILL LIKELY PRODUCE A SQUALL ALONG THE SURFACE
FRONT WITH BRIEF BUT INTENSE RAINFALL RATES. GIVEN THE SLY
ORIENTATION TO THE LOW LEVEL FLOW...OROGRAPHIC ENHANCEMENT SHOULD
BE LIMITED TO ANY SLOPES FACING S OR SSW BUT BRIEF DURATION RATES
OVER 0.50 IN/HR WILL BE POSSIBLE.

SOUTH OF THE TRIPLE POINT...PRECIPITABLE WATER VALUES OF 1.0 TO
1.3 INCHES ARE EXPECTED TO REACH THE SWRN OR TO NWRN CA COAST
ALONG WITH 60-70 KT 850-700 MB WINDS FROM THE SSW. THE STRONG
MOISTURE FLUX WILL FOCUS GREATEST INTO THE COASTAL RANGES AND
KLAMATH/CASCADE RANGES OF NRN CA. GIVEN THE GREATER VALUES OF
MOISTURE AND SLIGHTLY LONGER DURATION OF FLUX INTO THESE
AREAS...RAINFALL TOTALS OF 3-5 INCHES ARE FORECAST WHICH COULD
CAUSE FLOODING ISSUES GIVEN HEAVY RAINFALL WHICH FELL OVER THE
PAST 24-36 HOURS.

OTTO

ATTN...WFO...EKA...MFR...PDT...PQR...REV...SEW...STO...

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

LAT...LON   47872382 47812313 47852197 47662142 46482110 
            45162156 44312164 41672173 40562127 39912162 
            40292241 38862326 38942407 40102473 42232502 
            44532432 47372452