MESOSCALE PRECIPITATION DISCUSSION 0752
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
455 PM EDT MON OCT 24 2016
 
AREAS AFFECTED...TERRAIN OF NORTHERN CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 242053Z - 250853Z
 
SUMMARY...A FRONTAL ZONE MOVING THROUGH THE REGION COULD PRODUCE
HOURLY RAIN RATES OF 0.5" AND LOCAL AMOUNTS EXCEEDING 3" INTO THE
OVERNIGHT HOURS AS THE FRONT SLOWS TO A CRAWL NEAR THE BAY
AREA/NORTHERN SIERRA NEVADA TONIGHT.

DISCUSSION...SATELLITE IMAGERY AND SURFACE OBSERVATIONS REVEAL A
968 HPA CYCLONE CENTERED NEAR 46N 132W.  TO ITS SOUTHEAST, A
NARROW PLUME OF MOISTURE IS FOCUSED NEAR THE SYSTEM'S FRONTAL ZONE
INTO NORTHERN CA.  PRECIPITABLE WATER VALUES WITHIN THE PLUME ARE
IN THE 1.1" RANGE NEAR SEA LEVEL AND 0.5-0.75" AT ELEVATION -- A
TYPICAL MOISTURE PLUME FOR THIS TIME OF THE YEAR THOUGH 1-2 SIGMAS
ABOVE THE MEAN FOR LATE OCTOBER.  INFLOW AT 850 HPA IS ROUGHLY 30
KTS FROM THE SOUTH-SOUTHWEST AND 50-60 KTS AT 700 HPA PER VAD WIND
PROFILES.  SPC MESOANALYSES SHOW 100+ J/KG OF MUCAPE NEAR THE
COAST, WHICH APPEARS TO BE AUGMENTING HOURLY RAIN RATES.  THE
WESTERN MESONET HAVE REVEALED 0.25-0.4" HOURLY RAIN TOTALS AS OF
LATE.  FOR THE MOMENT, THE FREEZING LEVEL IS HIGH ENOUGH THAT ONLY
THE TALLEST PEAKS MIGHT BE SNOWING.

THE DEGREE OF 700 HPA INFLOW, INSTABILITY, AND AVAILABLE MOISTURE
SUPPORT THE IDEA THAT HOURLY RAIN RATES COULD REACH 0.5".  A
SHORTWAVE UPSTREAM NEAR 127W LONGITUDE IS EXPECTED TO SLIGHTLY
INCREASE THE HOURLY RATES UNTIL IT MOVES INLAND IN 4-8 HOURS.  THE
PLUME SHOULD REMAIN JUST AHEAD OF THE COOLING ALOFT THAT SNOW
SHOULD BE MINIMAL ON THE BACK SIDE OF THE PRECIPITATION BAND
ACROSS THE SHASTA/SISKIYOU MOUNTAIN RANGES.  THEREAFTER, A SECOND
STRONG SHORTWAVE MOVING BY 37N 148W AT THIS TIME IS EXPECTED TO
ROUND THE BASE OF THE DEEP CYCLONE OFFSHORE THE NORTHWEST, WHICH
SHOULD HOLD UP PROGRESSION OF THE FRONTAL BAND/MOISTURE PLUME AS
IT ENTERS THE SAN FRANCISCO BAY AREA.  THE MESOSCALE GUIDANCE
SUGGESTS LOCAL AMOUNTS OF 3"+ IN THE NORTHERN SIERRA NEVADA AND
1.5-2.5" IN THE COASTAL RANGES THROUGH 09Z.  THESE RAIN RATES
COULD BECOME PROBLEMATIC IN AREAS WITH BURN SCARS, STEEP TERRAIN
WHERE ROCK SLIDES ARE POSSIBLE, AND IN AREAS WITH MORE SENSITIVE
RIVERS OR STREAMS.  THE IMPACTS DUE TO BURN SCARS COULD BE MORE
SIGNIFICANT NEAR AND SOUTH OF THE KLAMATH NATIONAL FOREST AND
NORTHEAST TO NORTH OF SANTA ROSA AND NAPA CA PER WRH DETAILED
HAZARDS INFORMATION FROM 2014 ONWARD.  INFORMATION WITHIN THIS
MESSAGE WAS COORDINATED WITH THE STO AND REV FORECAST OFFICES.

ROTH

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

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

LAT...LON   41482195 41312153 40932163 40562125 40272114 
            39952070 39262038 39132063 39732166 40712238 
            40372283 38922255 38172244 37702249 37902293 
            38172330 38752383 39732398 40202432 40562432 
            41312385 41252264 
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