Graphic for MPD #0009
 
MESOSCALE PRECIPITATION DISCUSSION 9
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1258 AM EST SUN JAN 8 2017
 
AREAS AFFECTED...CENTRAL CALIFORNIA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 080557Z - 081757Z
 
SUMMARY...A LONG DURATION HEAVY PRECIPITATION EVENT IS IN PROGRESS
WITH WIDESPREAD HEAVY RAINFALL EXPECTED ACROSS CENTRAL CALIFORNIA
THROUGH SATURDAY NIGHT. THE DEEP MOISTURE FLUX ALONG WITH SOME
INSTABILITY WILL SUPPORT RAINFALL RATES OF 0.5 TO 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 CENTRAL CALIFORNIA COAST WITH A SUBTROPICAL CONNECTION. 
MOISTURE FLUX STANDARDIZED ANOMALIES ON THE ORDER OF +6 ARE
INDICATED BY THE GEFS MEAN, WITH A PLUME OF 1.3 TO 1.5 INCH PWS
SUGGESTED BY THE LATEST RAP GUIDANCE OVER THE CENTRAL CALIFORNIA
COAST DURING THE OVERNIGHT PERIOD.  A PROLONGED FETCH OF 45 TO 60
KNOT 850MB FLOW ORIENTED ORTHOGONAL TO THE TERRAIN, ALONG WITH THE
ANOMALOUS PWS, WILL BE QUITE FAVORABLE FOR PERIODS OF HEAVY
RAINFALL.  THE PRESENCE OF 250-500 J/KG MUCAPE OFFSHORE WILL
SUPPORT SOME CONVECTIVE ELEMENTS WITHIN THIS PLUME OF MOISTURE,
WHERE RATES COULD REACH ONE INCH PER HOUR WITH FLASH FLOODING
POSSIBLE.  A FAVORABLE UPPER LEVEL JET STRUCTURE WITH A LARGE
REGION OF DIVERGENCE ALOFT WILL AID IN SUSTAINING THE ASCENT AND
HEAVY RAIN.   THE HEAVIEST RAINFALL TOTALS ARE EXPECTED FOR THE
COASTAL MOUNTAINS SOUTH OF SAN FRANCISCO, AND THE WESTERN SLOPES
OF THE CENTRAL SIERRA NEVADA.  

AN AGGRAVATING FACTOR IN THE FLOODING POTENTIAL WITH THIS EVENT
WILL BE THE RISING SNOW LEVELS ACROSS THE SIERRA NEVADA RANGE,
APPROACHING 9000 FEET.  HEAVY RAIN FALLING OVER A DENSE SNOW COVER
FROM THE EVENT A FEW DAYS AGO 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 3 TO LOCALLY 6 INCHES OF
RAINFALL BY 18Z SUNDAY, WITH ADDITIONAL RAINFALL AFTER THIS TIME. 
THE HIGHEST AMOUNTS ARE EXPECTED FOR THE COASTAL MOUNTAINS SOUTH
OF SAN FRANCISCO, 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 ON SATURDAY.

HAMRICK

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

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

LAT...LON   40202144 40132086 39552030 39182009 38701980 
            38291958 37871945 37561929 37291906 37001885 
            36691862 36321833 36161821 35841819 35761860 
            36511912 37111980 37362053 37172103 36742130 
            36222119 35782088 35532113 35932173 36442213 
            36922244 37462275 38062320 38642349 39062333 
            39332285 39102206 39202150 39822165 


Last Updated: 1258 AM EST SUN JAN 08 2017