MESOSCALE PRECIPITATION DISCUSSION 0010
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
916 PM EST SUN FEB 08 2015
 
AREAS AFFECTED...PORTIONS OF THE SIERRA NEVADA IN CA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 090215Z - 090745Z
 
SUMMARY...A BAND OF HEAVY RAINFALL WITH EMBEDDED THUNDERSTORMS IS
MOVING INTO AN AREA OF THE SIERRA NEVADA WITH RECENT SNOWFALL AND
BURN SCARS.  FLASH FLOODING IS CONSIDERED POSSIBLE HERE.

DISCUSSION...A BAND OF HEAVY RAINFALL WITH EMBEDDED THUNDERSTORMS
IS MOVING INTO THE SIERRA NEVADA FROM THE CENTRAL VALLEY OF CA,
WITH SHOWERS AND SHALLOW CONVECTION NOTED ON RADAR ALONG THE SPINE
OF THE SIERRA NEVADA ON EITHER SIDE OF THE LINE.  RECENT HOURLY
RAIN RATES WITHIN THIS BAND ARE 0.50-0.60" PER MESONET
OBSERVATIONS. ANOMALOUSLY MOIST AIR -- 2.5 TO 3 SIGMAS ABOVE THE
NORM FOR EARLY FEBRUARY -- WITH PRECIPITABLE WATER VALUES OF 1.30"
PER RECENT GPS ESTIMATES IS BRING DRAWN IN BY 50-60 KNOTS OF 700
HPA INFLOW FROM THE SOUTHWEST.  POCKETS OF 500+ J/KG CAPE ALSO LIE
IN THE CENTRAL VALLEY, WHICH IS ALLOWING FOR THE THUNDERSTORM
DEVELOPMENT.  THIS DEGREE OF INFLOW IS CLOSE TO THE MAGNITUDE OF
THE MEAN 850-400 HPA WIND AND SHOULD AID PRECIPITATION EFFICIENCY.
 ANOTHER FACTOR IS THE HIGH WET BULB ZEROES IN THIS REGION, LYING
ROUGHLY 9000 FEET ABOVE SEA LEVEL.  THIS IS QUITE HIGH FOR THE
REGION, AND ALONG WITH THE MOIST UPSLOPE FLOW, SHOULD LEAD TO WARM
RAIN PROCESSES BEING AT PLAY. 

RECENT MESOSCALE QPF GUIDANCE IS AGREEABLE AND SUGGESTS 2-3" OF
RAINFALL COULD OCCUR OVER THE NEXT SEVERAL HOURS, WITH LOCALLY
HIGHER AMOUNTS.  THE PRESENT PRECIPITABLE WATER VALUES SUGGEST 1"
AN HOUR RAIN RATES ARE A DISTINCT POSSIBILITY.  THIS TYPE OF RAIN
FALLING ON BURN SCARS ACROSS THE REGION (CAUSED BY WILDFIRES
WITHIN A REGION OF LONG TERM DROUGHT) AND A FRESH SNOW PACK
DEPOSITED RECENTLY BELOW 9000 FEET ABOVE SEA LEVEL COULD CAUSE
FLASH FLOOD ISSUES.  OVER THE NEXT SEVERAL HOURS, LOW-LEVEL
INFLOW/BOUNDARY LAYER MOISTURE CONVERGENCE ACROSS THE REGION IS
FORECAST TO WEAKEN, AVAILABLE MOISTURE IS EXPECTED TO DWINDLE, AND
AVAILABLE CAPE SHOULD EXHAUST PER RECENT RAP RUNS IN THE WAKE OF A
COLD FRONT PROGRESSING THROUGH THE REGION.

ROTH

ATTN...WFO...HNX...REV...STO...

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

LAT...LON   40092113 39442008 38761966 37591895 36861866 
            36621867 36191899 37131981 37952071 39032110 
            39902148