Graphic for MPD #0012
 
MESOSCALE PRECIPITATION DISCUSSION 12
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1007 PM EST SUN JAN 8 2017
 
AREAS AFFECTED...SOUTH-CENTRAL CALIFORNIA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 090306Z - 091506Z
 
SUMMARY...THE MAIN ATMOSPHERIC RIVER PLUME WILL NOW BEGIN SHIFTING
FARTHER TOWARDS THE SOUTHEAST OVERNIGHT.  THE DEEP MOISTURE FLUX
ALONG WITH SOME INSTABILITY WILL SUPPORT RAINFALL RATES OF 0.5 TO
LOCALLY 1 INCH PER HOUR WITH FLASH FLOODING POSSIBLE IN BURN SCAR
AND OTHER SUSCEPTIBLE AREAS.

DISCUSSION...A DEEP SURGE OF PACIFIC MOISTURE IS ADVECTING TOWARDS
THE SOUTH-CENTRAL CALIFORNIA COAST WITH A SUBTROPICAL CONNECTION. 
PRECIPITABLE WATER STANDARDIZED ANOMALIES APPROACHING +3 ARE
CURRENTLY INDICATED BY THE GEFS MEAN, WITH A PLUME OF 1.25 TO 1.50
INCH PWS SUGGESTED BY THE LATEST RAP GUIDANCE DIRECTED TOWARDS THE
COAST NEAR SANTA BARBARA DURING THE OVERNIGHT PERIOD.  A PROLONGED
FETCH OF 35 TO 50 KNOT 850MB FLOW ORIENTED ORTHOGONAL TO THE
TERRAIN, ALONG WITH THE ANOMALOUS PWS, WILL BE QUITE FAVORABLE FOR
PERIODS OF HEAVY RAINFALL.  ALTHOUGH THIS IS A SLIGHT DECREASE
COMPARED TO WHAT WAS OBSERVED EARLIER ON SUNDAY, IT IS STILL
SIGNIFICANT.  THE PRESENCE OF MODEST 100-250 J/KG MUCAPE OFFSHORE
MAY SUPPORT SOME CONVECTIVE ELEMENTS WITHIN THIS PLUME OF
MOISTURE, WHERE RATES COULD REACH ONE INCH PER HOUR WITH FLASH
FLOODING POSSIBLE.  A FAVORABLE CYCLONICALLY CURVED UPPER LEVEL
JET STRUCTURE WITH RIGHT ENTRANCE DYNAMICS AND POSITIVE VORTICITY
ADVECTION WILL AID IN SUSTAINING THE ASCENT AND HEAVY RAIN.     

AN AGGRAVATING FACTOR IN THE FLOODING POTENTIAL WITH THIS EVENT
WILL BE THE ABNORMALLY HIGH SNOW LEVELS ACROSS THE SIERRA NEVADA
RANGE, APPROACHING 9000 TO 10000 FEET BEFORE THE COLD FRONT PASSES
THROUGH AROUND 12Z MONDAY.  HEAVY RAIN FALLING OVER A DENSE SNOW
COVER FROM THE EVENT LAST WEEK WILL LEAD TO SOME SNOW MELT THAT
WILL LOCALLY ENHANCE RUN-OFF PROBLEMS AND THUS THE POSSIBILITY OF
LOCALIZED FLASH FLOODING DOWNSTREAM OF THESE AREAS.

THE LATEST HI-RES GUIDANCE IS INDICATING 2 TO LOCALLY 4 INCHES OF
RAINFALL BY 15Z MONDAY, WITH SOME ADDITIONAL RAINFALL AFTER THIS
TIME.  THE HIGHEST AMOUNTS ARE EXPECTED FOR THE SOUTHERN COASTAL
RANGES, TRANSVERSE RANGES, AND THE WESTERN SLOPES OF THE SIERRA
NEVADA.  THE PLACES WITH GREATEST RUN-OFF CONCERNS WOULD BE RECENT
BURN-SCAR AREAS AND THOSE LOCATIONS THAT RECEIVED APPRECIABLE
RAINFALL OVER THE PAST COUPLE OF DAYS.

HAMRICK

ATTN...WFO...HNX...LOX...MTR...REV...STO...

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

LAT...LON   40072111 40032072 39412028 38751983 38081947 
            37481906 37021881 36551844 35911819 35181813 
            34581813 34161839 34001898 33871974 33902038 
            34562080 35182097 35822157 36362190 36632169 
            36402126 36132068 36382001 36821983 37401997 
            37872024 38742076 39322097 39822125 


Last Updated: 1007 PM EST SUN JAN 08 2017