MESOSCALE PRECIPITATION DISCUSSION 0007
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1028 AM EST TUE JAN 12 2016
 
AREAS AFFECTED...WESTERN OREGON 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 121525Z - 122100Z
 
SUMMARY...RAINFALL RATES WILL BE INCREASING OVER THE OREGON
COASTAL RANGES THROUGH EARLY AFTERNOON.

DISCUSSION...COOLING CLOUD TOPS ARE SEEN IN IR SATELLITE IMAGERY
OFFSHORE THE WEST COAST IN ASSOCIATION WITH A DEVELOPING LOW
CENTER NEAR 39N 133W. THIS IS BEING FOSTERED BY A 130 KT 250 MB
JET MAX LIFTING NORTHEAST OUT OF THE BASE OF THE BROADER UPPER
TROUGH THAT EXTENDS SOUTH OF THE GULF OF AK.

THIS ENERGY WILL BE ENCROACHING ON THE OREGON COASTAL RANGES OF
OREGON THROUGH EARLY AFTERNOON AS THE SURFACE WAVE LIFTS NORTHEAST
ALONG A WELL-DEFINED FRONTAL ZONE...AND THIS WILL ENHANCE THE
ONSHORE FLOW INTO THE TERRAIN WITH TIME.

THE HIRES GUIDANCE SHOWS A SOUTHWESTERLY LOW LEVEL JET INCREASING
TO 50 TO 60 KTS BY 18Z JUST OFFSHORE THE OREGON COAST...AND THIS
WILL BE AFFORDING 850 MB MOISTURE FLUX ANOMALIES OF UP TO 4
STANDARD DEVIATIONS ABOVE NORMAL. THE GUIDANCE SHOWS AN AXIS OF 1
TO 1.25 INCH PWATS ADVECTING NORTHEAST JUST AHEAD OF THE SURFACE
WAVE AND FRONTAL ZONE...AND THIS WILL GRADUALLY ENHANCE THE
RAINFALL RATES INTO THE COASTAL RANGES WITHIN THE LARGER SCALE AND
BROAD WARM AIR ADVECTION PATTERN.

THE LOW LEVEL FLOW WILL TEND TO BECOME A BIT MORE PARALLEL TO THE
COASTAL TERRAIN WITH TIME AS THE FRONT APPROACHES AND THUS THE
OROGRAPHIC FORCING/UPSLOPE COMPONENT WILL TEND TO BE MITIGATED
SOMEWHAT. HOWEVER...EXPECT SOUTHWEST FACING SLOPES OF ESPECIALLY
SOUTHWEST OREGON TO SEE HEAVY RAINFALL RATES THIS AFTERNOON. A
1420Z AMSU PASS ALREADY SHOWS RAIN RATES APPROACHING 0.50
INCHES/HR OFFSHORE TO THE EAST OF THE DEVELOPING LOW CENTER...AND
THE LAST COUPLE RUNS OF THE HRRR SUGGEST THESE RATES ARRIVING
ACROSS COASTAL AREAS OF SOUTHWEST OREGON IN THE 18Z TO 21Z TIME
FRAME.

ORRISON

ATTN...WFO...EKA...MFR...PQR...

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

LAT...LON   45892391 45832329 44322328 42472353 42042379 
            41952420 42252445 42842452 43702424 44842410