Flash Flood Guidance
Issued by NWS

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606
AWUS01 KWNH 201012
FFGMPD
CAZ000-201600-

MESOSCALE PRECIPITATION DISCUSSION 0028...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
512 AM EST FRI JAN 20 2017

CORRECTED FOR CONCERNING LINE FROM HEAVY RAINFALL TO FLASH
FLOODING POSSIBLE

AREAS AFFECTED...COASTAL CENTRAL CALIFORNIA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 201000Z - 201600Z

SUMMARY...STRONG VERTICAL ASCENT WITH LOW BUT SUFFICIENT
INSTABILITY AND MOISTURE MAY SUPPORT CONVECTIVELY INDUCED SHORT
DURATION HIGH INTENSITY RAINFALL THAT MAY POSE FLASH FLOODING
CONCERN ALONG THE CA COAST THIS MORNING.

DISCUSSION...GOES-W WV LOOP SHOWS STRONG HEIGHT FALLS/DARKENING
JUST OFF THE NW CA COASTLINE AT THIS TIME ALONG THE LEFT EXIT OF
150KT JET.  THIS DARKENING/LEFT EXIT REGION HAS STRONG DPVA SIGNAL
WITH SIGNIFICANT TRANSVERSE BANDING AND CONVECTIVE ELEMENTATION
GROWING IN GOES-W IR FROM CAPE MENDOCINO TOWARD SAN FRANCISCO BAY
AREA.  EIR ALSO DENOTES A MODESTLY WIDE SW-NE ORIENTED HAZY/MILKY
BAND ASSOCIATED WITH THE LOW LEVEL MOISTURE.  BLENDED TPW SUGGESTS
DEEPEST MST (ABOVE 1.0") REMAINS WELL OFFSHORE WHICH MATCHES
CURRENT LOW TDS SEEN ALONG THE COAST AT THIS TIME.  BLENDED
LAYERED TPW SUGGEST 850-700MB VALUES REMAIN BELOW .3" ALONG THE
COAST FURTHER SUPPORTING THE LOWER LEVEL DRYNESS.  STILL WITH
VIGOROUS HEIGHT FALLS/DPVA AND MILD CAA ALOFT TO STEEPEN LAPSE
RATES WILL SUPPORT MUCAPES TO 250 J/KG...ALLOWING FOR SOME
VERTICAL GROWTH/CONVECTIVE EXPANSION THAT WILL BE MAXIMIZED ALONG
THE RAPIDLY ADVANCING COLD FRONT.

STILL HI-RES CAMS ARE SUPPORTIVE OF THIS NARROW LINE OF EXPANDING
CONVECTION REACHING S MENDOCINO/N SONOMA COUNTY JUST AHEAD OF THE
SFC TRIPLE POINT AND UPPER LEVEL VORT CENTER AROUND 11-12Z...AND
WILL SLIDE SOUTHEASTWARD WITHIN THE LEFT EXIT OF THE JET ACROSS
MARIN TO SANTA CRUZ FROM 12-14Z...WITH RATES UP TO .75"/HR
PARTICULARLY IN AREAS AIDED BY OROGRAPHIC ASCENT.  THIS COULD
POTENTIALLY LEAD TO RAINFALL TOTALS OF 1.5-2" IN 2-3 HRS POSING
LOCALIZED FLASH FLOODING CONCERNS THROUGH THE EARLY MORNING HOURS
PARTICULARLY GIVEN WET ANTECEDENT CONDITIONS.

GALLINA

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...LOX...MTR...STO...

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

LAT...LON   38802228 38282177 37562151 36732122 35702038
            35412007 35082006 35002048 35122076 35432117
            35882157 36272201 36592215 36862224 37292262
            37762267 37982307 38312326 38522350 38702348
            38772284



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