MESOSCALE PRECIPITATION DISCUSSION 0081
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
630 AM EST SAT MAR 12 2016
 
AREAS AFFECTED...SOUTHWEST OR...NORTHWEST CA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 121129Z - 121629Z
 
SUMMARY...SHALLOW CONVECTION WILL BRING BRIEF HEAVY RAIN RATES
FOLLOWED BY MOIST ONSHORE FLOW AS A COLD FRONT ARRIVES. GIVEN
RECENT HEAVY RAINS...THE REGION MAY BE MORE PRONE TO RAPID SURFACE
RUNOFF / FLOODING / FLASH FLOODING.

DISCUSSION...OBSERVATIONAL TRENDS AT 11Z SHOWED INCREASING
PRECIPITATION INTENSITY JUST OFFSHORE OF SW OR / NW CA. CLUSTERS
OF LIGHTNING WERE DETECTED WITHIN A NARROW WEDGE-SHAPED SATELLITE
SIGNATURE OFF OF OREGON...INDICATIVE OF STRONGLY FORCED ASCENT
ALONG AN ARRIVING COLD FRONT. THE UPSTREAM ENVIRONMENT WAS VERY
COLD ALOFT WITH A VERY BROAD AREA OF OPEN CELL CONVECTION BEHIND
THE LEADING LINE. RADAR IMAGERY FROM KBHX IN NORTHWEST CA DETECTED
A BROKEN LINE OF SHALLOW CONVECTION...STRONG ECHOES UP THROUGH 12
KFT...FORMING OFFSHORE OF CALIFORNIA WITH MOTION TO THE
EAST-NORTHEAST. PRECIPITABLE WATER VALUES WERE NOT PARTICULARLY
HIGH...BUT WILL EXCEED 0.50 INCHES JUST ONSHORE...AND MAY SPIKE TO
NEAR 0.75 INCHES BRIEFLY WITHIN THE NARROW ZONE OF STRONG ASCENT.
OBSERVED 00Z SOUNDINGS AS WELL AS RAP FORECAST SOUNDINGS INDICATE
STEEP LAPSE RATES AND SUFFICIENT INSTABILITY TO SUSTAIN CONVECTION
JUST INLAND FROM THE COAST...SUPPORTING HOURLY RAIN RATES THAT
SHOULD PUSH ABOVE 0.50 INCHES FOR A BRIEF TIME...THEN FOLLOWED BY
SCATTERED SHALLOW CONVECTION AND MORE OROGRAPHICALLY FORCED
POST-FRONTAL PRECIPITATION LATER THIS MORNING. 

THERE IS A GOOD MODEL CONSENSUS FOR THIS REGION TO SEE 0.50 TO
1.25 INCH AREAL AVERAGE RAINFALL THROUGH 16Z FROM SOUTHWEST OREGON
DOWN TO MENDOCINO CA AND INLAND TO REDDING/SHASTA. MUCH OF THE
AREA HAD RECEIVED 2 TO 4 TIMES THE CLIMATOLOGICAL RAINFALL VALUES
OVER THE PAST 7 DAYS...SUCH THAT ALL MANNER OF FLOODING / FLASH
FLOODING MAY OCCUR DEPENDING ON THE LOCAL SCALE HYDROLOGY. 

BURKE

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

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

LAT...LON   44382412 44152350 43142346 42532348 42372346 
            42072348 41852345 41742324 41662316 41492317 
            41392321 41292333 41192340 40982342 40802333 
            40792306 40882285 41012258 41162237 41152198 
            40992175 40782176 40582228 40432288 40232313 
            39982316 39592314 39252365 39412400 40602461 
            42972512