MESOSCALE PRECIPITATION DISCUSSION 0673
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
205 AM EST THU DEC 10 2015
 
AREAS AFFECTED...WESTERN TO SOUTHWESTERN OR/NORTHWESTERN CA... 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 100705Z - 101405Z
 
SUMMARY...AN IMPRESSIVE MOISTURE SURGE AND ACCOMPANYING MID-LEVEL
FORCING WILL MOVE ONSHORE SPREADING HEAVY RAINFALL TO THE KLAMATH
MOUNTAIN RANGE DOWN INTO THE COASTAL RANGES OF NORTHWESTERN CA.
THE LATEST AMSU SATELLITE DATA SUGGESTED 0.50 TO 0.75 INCH HOURLY
AMOUNTS WERE FALLING WITHIN THE CONVECTIVE BANDS. EXPECT LOCAL
OROGRAPHIC EFFECTS TO AUGMENT SUCH AMOUNTS WITH LOCALIZED AREAS
POSSIBLY REACHING RATES APPROACHING AN INCH. EXPECT LOCALIZED
HYDROLOGIC ISSUES...PARTICULARLY IN AREAS WHICH RECEIVED HEAVY
RAINFALL EARLIER IN THE WEEK.

DISCUSSION...WATER VAPOR IMAGERY SHOWED A WELL-DEFINED
NEGATIVELY-TILTED UPPER TROUGH APPROACHING 130W LONGITUDE. RECENT
LIGHTNING DATA INDICATED A BULK OF THE ACTIVITY WAS WELL TO THE
NORTH CLOSER TO THE UNSTABLE AIR IN THE VICINITY OF THE UPPER LOW.
IT IS QUITE THE DYNAMIC UPPER TROUGH WITH 500-MB WINDS OBSERVED IN
THE 140 TO 160 KNOT RANGE WITHIN THE CORE OF STRONGER HEIGHT
FALLS. THE LATEST AMSU PASS SHOWED 0.50 TO 0.75 INCH HOURLY RATES
WITHIN THE CORRIDOR OF HEAVIER RAINFALL WHICH SHOULD INCREASE AS
OROGRAPHICS COME INTO PLAY ACROSS SOUTHWESTERN OR/NORTHWESTERN CA.
THE OVERALL SETUP IS QUITE IMPRESSIVE WITH THE INTEGRATED VAPOR
TRANSPORT NEARING THE 99TH PERCENTILE AND THE U-COMPONENT OF THE
LOW/MID-LEVEL WINDS NEAR THE MAXIMA FOR MID-DECEMBER. STRONG
OROGRAPHIC LIFT IN THIS SETUP WILL SUPPLY A PERIOD OF
MODERATE/HEAVY RAINFALL ALONG THE WINDWARD SLOPES OF THE KLAMATH
RANGES DOWN INTO THE COASTAL RANGES OF NORTHERN CA. BASED ON THE
PAST WEEK OF RAINFALL RELATIVE TO CLIMATOLOGY...MUCH OF
SOUTHWESTERN OR HAS SEEN 200 TO 300 PERCENT ABOVE NORMAL
SUGGESTING SOILS ARE RATHER SATURATED. THIS WOULD BE THE AREA OF
STRONGEST IMPACTS DURING THE NEXT SEVERAL HOURS. HIGH-RESOLUTION
GUIDANCE ARE UNANIMOUS FOCUSING THE HEAVIEST RAINFALL WITHIN THE
COMPLEX TERRAIN WHICH AGREES WITH CURRENT SATELLITE TRENDS.

RUBIN-OSTER

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

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

LAT...LON   44342408 43852375 43582370 42842370 42402362 
            42052354 41972340 41752315 41582288 41262269 
            41052271 40842289 40782307 40632315 40502310 
            40352297 40112274 39782262 39372262 39092306 
            39272366 39792410 40482449 41432433 42382455 
            42582467 43562472 44292460