MESOSCALE PRECIPITATION DISCUSSION 0006
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
941 PM EST THU FEB 05 2015
 
AREAS AFFECTED...SOUTHWEST OR & NORTHWEST CA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 060241Z - 060801Z
 
SUMMARY...INCREASINGLY HEAVY RAINFALL IS EXPECTED ACROSS THIS
REGION, MAINLY WITHIN A FRONTOGENETIC BAND IN THE LOW- TO
MID-LEVELS OF THE TROPOSPHERE.  FLASH FLOODING, WITH MUD AND ROCK
SLIDES, ARE POSSIBLE IN THIS REGION AFTER 06Z.

DISCUSSION...THE WARM CONVEYOR BELT OF A CYCLONE ACROSS THE
NORTHEAST PACIFIC IS RELATIVELY STATIONARY NEAR THE COAST OF
NORTHWEST CA AND SOUTHWEST OR.  WITHIN THE WARM CONVEYOR BELT, AN
AREA OF 850-600 HPA FRONTOGENESIS WAS NOTED BY THE 18Z NAM RUN. 
RAINFALL AMOUNTS SO FAR TO THE SOUTH OF EUREKA HAVE EXCEEDED 3" SO
FAR TODAY PER MESONET REPORTS, SATURATING SOILS IN THE REGION. 
PRECIPITABLE WATER VALUES ARE 1-1.25", NEAR THE 99TH PERCENTILE,
OR 2.5 SIGMAS ABOVE THE AVERAGE,  FOR EARLY FEBRUARY.  THE LATEST
SPC MESOANALYSIS AND RAP RUNS INDICATE CAPES > 100 J/KG JUST OFF
THE COAST AND 500+ J/KG WELL OFFSHORE CLOSER TO THE 130TH
MERIDIAN, NEAR THE NEXT SURGE OF MOISTURE.  SEA SURFACE
TEMPERATURE ANOMALIES OF 1-2 DEGREES CELSIUS JUST OFFSHORE
COMBINED WITH THE AVAILABLE DYNAMICS ARE AIDING THE MINIMAL
AVAILABLE CAPE.  INFLOW AT 850 HPA IS CLOSE TO 65 KTS, JUST
EXCEEDING THE MAGNITUDE OF THE 850-400 HPA MEAN FLOW, WHICH SHOULD
LEAD TO PRECIPITATION EFFICIENCY. 

SAB/NESDIS INDICATES HOURLY RAIN RATES OF 0.50" WITHIN THE NEXT
SURGE/WAVE OF MOISTURE, WHICH WOULD MAGNIFY ONCE IT MOVES ASHORE
AND INTERACTS WITH LOCAL TOPOGRAPHY.  WHILE WET BULB FREEZING
LEVELS ARE ~6500 FEET PER REGIONAL SOUNDINGS, THE MOIST UPSLOPE
FLOW REGIME INTO THE TOPOGRAPHY SHOULD MIMIC WARM RAIN PROCESSES
IN THIS REGION.  COMBINED WITH THE AVAILABLE MOISTURE, HOURLY RAIN
RATES OF 1"+ IN UPSLOPE AREAS ARE POSSIBLE ONCE THE NEXT SURGE
MOVES INLAND, WHICH WOULD BE PROBLEMATIC WITHIN THE RUGGED TERRAIN
OF THE REGION.  BURN SCARS WITHIN THIS REGION CAUSED BY LONG
DURATION DROUGHT WOULD ALSO HEIGHTEN THE RISK OF FLOODING/FLASH
FLOODING.  THE LATEST MESOSCALE QPF GUIDANCE INDICATES THAT
PRECIPITATION INTENSITY SHOULD INCREASE BY 07Z, AIDED BY AN
INCREASE IN BOUNDARY LAYER MOISTURE CONVERGENCE PER RECENT RAP
RUNS.  THIS APPEARS TO BE A BORDERLINE FLOOD/FLASH FLOOD EVENT,
WHICH COULD LEAD TO MUD AND ROCK SLIDES.

ROTH

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

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

LAT...LON   43032421 42402324 42222266 41922304 41782292 
            41942233 41832157 41642128 41212122 40992165 
            40702235 40422260 39372251 39262253 38722272 
            38802297 38572319 39072393 39622391 40032424 
            40402455 41092428 41712432 42632461