MESOSCALE PRECIPITATION DISCUSSION 0007
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM EST FRI FEB 06 2015
 
AREAS AFFECTED...SOUTHWEST OR & NORTHWEST CA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 060757Z - 061357Z
 
SUMMARY...A BAND OF HEAVY RAIN SHOULD LEAD TO RAINFALL RATES
INCREASING FURTHER OVER THE NEXT SEVERAL HOURS.  HOURLY RAIN RATES
UP TO 1" COULD CAUSE FLASH FLOODING, WITH ROCK AND MUD SLIDES
POSSIBLE.

DISCUSSION...A COLD FRONT IS SLOWLY EDGING TOWARDS THE COAST FROM
THE EASTERN PACIFIC, WITH LOW- TO MID-LEVEL FRONTOGENESIS
REMAINING OVER THE REGION PER THE 00Z NAM GUIDANCE.  A FRESH SURGE
OF MOISTURE ASSOCIATED WITH A CLOUD BAND WITH COOLING TOPS WORKED
INTO THE REGION AROUND 06Z, WITH A FEW MESONET SITES REPORTING
HOURLY RAIN RATES OVER 0.6" ACROSS NORTHWEST CA SINCE THEN --
SOILS ARE SATURATING.  MOISTURE ACROSS THE REGION CONTINUES TO
INCREASE DUE TO INCREASING BOUNDARY LAYER MOISTURE CONVERGENCE. 
PRECIPITABLE WATER VALUES OF 1-1.25" NEAR THE COAST ARE NEAR THE
99TH PERCENTILE OR ABOUT 2.5 SIGMAS ABOVE THE AVERAGE FOR EARLY
FEBRUARY.  INFLOW AT 850 HPA REMAINS 65-70 KTS, SOMEWHAT EXCEEDING
THE 850-400 MEAN WINDS ACROSS THE REGION, LEADING TO PRECIPITATION
EFFICIENCY.  CAPE VALUES NEAR AND OFFSHORE ARE IN THE 100-300 J/KG
RANGE PER THE SPC MESOANALYSIS TOOL, SOMEWHAT HIGHER THAN SEEN
EARLIER IN THE EVENING.

THE MESOSCALE QPF GUIDANCE CALLS FOR RAINFALL RATES TO INCREASE
FURTHER OVER THE NEXT SEVERAL HOURS AS THE FRONT ATTEMPTS LANDFALL
AND THE LOW-LEVEL FLOW EDGES MORE SOUTH-SOUTHWESTERLY -- ISOLATED
THUNDERSTORMS ARE POSSIBLE CONSIDERING THE AVAILABLE INSTABILITY. 
A SECOND DISTURBANCE ON SATELLITE IS POISED TO MOVE INTO THE
REGION AROUND 14-15Z, WHICH COULD LEAD TO ANOTHER ENHANCEMENT OF
RAIN RATES TOWARDS SUNRISE.  THE 00Z SSEO NEIGHBORHOOD
PROBABILITIES INDICATE AN INCREASING CHANCE OF EXCEEDING THREE
HOUR FLASH FLOOD GUIDANCE VALUES ACROSS THE REGION OVER THE NEXT
SEVERAL HOURS, WITH A COUPLE POCKETS OVER 50% INDICATED. 
CONSIDERING THE AVAILABLE MOISTURE AND RADAR TRENDS, HOURLY RAIN
RATES UP TO 1" COULD CAUSE FLASH FLOODING AND ASSOCIATED MUD AND
ROCK SLIDES.  THE EXPECTED RAINFALL MAGNITUDE REMAINS NEAR THE
BORDER OF A FLOOD AND FLASH FLOOD EVENT.

ROTH

ATTN...WFO...EKA...MFR...MTR...STO...

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

LAT...LON   43242445 43172387 42802348 42102323 41502291 
            41632206 41472157 40972172 40582215 39952246 
            39822251 39332248 38752262 38402316 38592365 
            38962389 39372400 39742404 40352455 41312433 
            42372465 42912459