MESOSCALE PRECIPITATION DISCUSSION 0795
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
317 PM EST WED DEC 14 2016
 
AREAS AFFECTED...SOUTHWESTERN OREGON/NORTHWESTERN CALIFORNIA... 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 142015Z - 150415Z
 
SUMMARY...MODERATE TO LOCALLY HEAVY RAINFALL SHOULD CONTINUE
ACROSS NORTHWESTERN CALIFORNIA/SOUTHWESTERN OREGON GIVEN THE
FAVORABLE ATMOSPHERIC RIVER SETUP. WHILE HOURLY RATES HAVE
GENERALLY REMAINED UNDER 0.40 INCHES...THE LONG DURATION OF THIS
EVENT SHOULD LEAD TO SOME LOCALIZED HYDROLOGIC EFFECTS GIVEN THE
REGION HAS BEEN WET THIS MONTH.

DISCUSSION...THE 20Z SURFACE ANALYSIS SHOWED A WAVY FRONTAL
BOUNDARY EXTENDING SOUTHWEST TO NORTHEAST WHILE INTERSECTING THE
COASTAL CALIFORNIA/OREGON BORDER. BLENDED-TPW IMAGERY DEPICTED A
WELL-DEFINED MOISTURE PLUME WITH ORIGINS FROM THE SUBTROPICAL
PACIFIC GENERALLY STRADDLING THE DEPICTED SURFACE BOUNDARY.
GENERAL PWAT VALUES REMAIN IN THE 1 TO 1.25 INCH RANGE PER AMSU
SATELLITE DATA IN CONJUNCTION WITH THE LATEST RAP OBJECTIVE
ANALYSIS. THIS ENHANCED TROPOSPHERIC MOISTURE IS BEING DIRECTED BY
A POWERFUL LOW/MID-LEVEL SOUTH-SOUTHWESTERLY JET TOWARD THE
COASTAL RANGES. VAD-WIND PROFILER DATA FROM THE KMAX RADAR
INDICATED 60 TO 70 KNOTS OF SOUTH-SOUTHWESTERLY FLOW AS LOW AS 8
TO 10 KFT. THIS STRONG UPSLOPE REGIME WILL LEAD TO SEVERAL INCHES
OF RAINFALL ACROSS THE SOUTHWESTERN SLOPES OF THE COASTAL RANGES.
OF COURSE THIS WILL ENHANCE THE POTENTIAL FOR HYDROLOGIC ISSUES
GIVEN THE REGION HAS SEEN ABOVE NORMAL PRECIPITATION THIS MONTH.

OVERALL...THE FORECAST SUGGESTS THE HEAVIEST RAINFALL SHOULD
GRADUALLY SINK SOUTHWARD AS THE SURFACE BOUNDARY INCHES CLOSER TO
THE COAST. THERE IS A UNANIMOUS SIGNAL IN THE HIGH-RESOLUTION
GUIDANCE FAVORED 2 TO 4 INCHES OF RAINFALL THROUGH 06Z. GIVEN
OBSERVED 6-HOUR AMOUNTS IN THE 2 TO 2.50 INCH RANGE ALONG THE
SOUTHWESTERN OREGON COAST...SUCH FORECASTS APPEAR QUITE
REASONABLE.  

RUBIN-OSTER

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

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

LAT...LON   43582302 43512235 42932228 42482298 42042306 
            41292285 40472318 40192392 40682459 41432493 
            42522482 43102432 43302353