MESOSCALE PRECIPITATION DISCUSSION 0659
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
102 AM EST THU NOV 19 2015
 
AREAS AFFECTED...WESTERN OR 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 190600Z - 191800Z
 
SUMMARY...SURGE OF PACIFIC MOISTURE ASSOCIATED WITH A SURFACE LOW
WILL BRING MODERATE TO LOCALLY HEAVY RAINS TO WESTERN OR THIS
MORNING.

DISCUSSION...THE LATEST WV AND IR SATELLITE IMAGERY SHOWS ANOTHER
ATMOSPHERIC RIVER BEGINNING TO EDGE INTO THE PACIFIC
NORTHWEST...WITH THE NOSE OF IT POISED TO MOVE INLAND ACROSS
WESTERN OR OVERNIGHT AND THROUGH THE MORNING HOURS OF THURSDAY.
THIS IS BEING FACILITATED BY AN UPPER LEVEL JET STREAK OF 100-120
KTS THAT IS SLIDING ACROSS FAR SOUTHERN CANADA AND DOWN THROUGH
NORTHERN WA AND NORTHERN ID. THIS JET ENERGY IS ALSO FOSTERING
SURFACE LOW PRESSURE OFFSHORE WHICH QUICKLY MOVING EAST TOWARD THE
OR COASTLINE.  

STRONG WARM ADVECTION WILL ALLOW AT LEAST MODERATE RAIN TO
OVERSPREAD WESTERN OR OVERNIGHT...WITH LOCALLY HEAVY RAINS
ARRIVING TOWARD 12Z AS SURFACE LOW PRESSURE ARRIVES AND MOVES
INLAND. THE LATEST HRRR CONFIRMS THIS LINE OF THINKING AND SHOWS
AS MUCH AS 1 TO 1.5 INCHES OF RAIN OVER THE COASTAL RANGES AND
PORTIONS OF THE WESTERN SLOPES OF THE CASCADES. HEAVIER RAINFALL
IS EXPECTED JUST AFTER 12Z AND ESPECIALLY OVER THESE
OROGRAPHICALLY FAVORED AREAS WITH ADDITIONAL AMOUNTS LOCALLY UP TO
2 INCHES THROUGH 18Z. A WESTERLY 850 MB JET OF 40 TO 50
KTS...COUPLED WITH A PLUME OF 1.25 INCH PWATS AND LARGE SCALE 250
MB RIGHT-ENTRANCE REGION JET DYNAMICS WILL SUPPORT THESE HEAVIER
TOTALS.

A 0520Z AMSU PASS SHOWS RAIN RATES OF 0.25 TO 0.40 INCHES/HR
ALREADY JUST OFFSHORE AHEAD OF THE WARM FRONT. THESE RATES ARE
LIKELY TO EXCEED 0.50 INCHES/HR OVER THE COASTAL RANGES AND
EVENTUALLY THE WESTERN SLOPE OF THE CASCADES DUE TO STRONG
OROGRAPHIC FORCING. WILL CONTINUE TO MONITOR.

ORRISON

ATTN...WFO...MFR...PDT...PQR...

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

LAT...LON   46232337 46152252 45942204 45412161 44792157 
            44022175 43332187 42842200 42402265 42322332 
            42482397 42842427 43522431 44002433 44632426 
            45532414 46032391