FXUS66 KMTR 102348
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
350 PM PST THU DEC 10 2009

.DISCUSSION...AS OF 3:30 PM PST THURSDAY...FORECAST FOCUS IS ON SHORT
TERM LIGHT RAIN OVER THE NEXT 36 HOURS THEN POTENTIAL FOR MODERATE
TO HEAVY RAIN EVENT ON SATURDAY.

IN THE SHORT TERM...LIGHT SHOWERS ARE PASSING FROM SOUTH TO NORTH
ACROSS THE REGION AT THIS HOUR. ORGANIZED RAIN BAND WEST OF BIG SUR
IS ABOUT TO PASS OVER THE MONTEREY PENINSULA...REACHING THE SOUTH
BAY AND GREATER SF BAY AREA FOR THE SECOND HALF OF THE EVENING
COMMUTE. RAIN TOTALS OVERNIGHT SHOULD AVERAGE FROM A FEW TENTHS TO
A QUARTER INCH. MODERATE RAIN NOTED LAST HOUR AT SAN LUIS OBISPO
WITH THIS BOUNDARY. TWO LIGHTNING STRIKES HAVE BEEN OBSERVED ABOUT
150NM WEST OF MONTEREY BAY THIS AFTERNOON...CLOSER TO THE CENTER OF
THE LOW WITH VISIBLE SATELLITE SHOWING GOOD VERTICAL CLOUD GROWTH.
FOR NOW HAVE KEPT THE MENTION OF T-STORMS CONFINED TO THE SOUTHERN
COASTAL WATERS FOR TONIGHT.

STEADY RAINS SHOULD EXIT TO OUR NORTH BY SUNRISE FRIDAY BUT BOTH THE
NAM AND GFS MODELS ARE CONSISTENT IN MORE LIGHT RAIN RE-DEVELOPING BY
FRIDAY AFTERNOON ACROSS THE REGION. THE SYNOPTIC ENVIRONMENT WILL
FEATURE A MOIST SOUTHWEST FLOW WITH RAIN BEING GENERATED IN A WARM-
FRONTAL...ISENTROPIC UPGLIDE ENVIRONMENT. EXPECT ANOTHER ROUND OF
LIGHT TO MODERATE RAIN THEN LATER FRIDAY AFTERNOON AND EVENING WITH
THE POTENTIAL FOR THE SANTA CRUZ MOUNTAINS AND MONTEREY COAST TO SEE
HIGHER AMOUNTS DUE TO FAVORED OROGRAPHICS...WHERE STEADY RAINS CAN
FALL ALL DAY IN THE MOIST ONSHORE FLOW.

ONE CHANGE WITH THIS WETTER PATTERN WILL BE MUCH WARMER NIGHTS WITH
OVERNIGHT LOWS GENERALLY STAYING IN THE 40S WITH SMALL DIURNAL
VARIATIONS...WITH AFTERNOON HIGHS IN THE 50S.

MAIN ATTENTION WILL THEN SHIFT TO THE SATURDAY COLD FRONT. THE
TIMING ON THIS HAS SLOWED SLIGHTLY WITH MODELS NOW BRINGING THE MAIN
COLD FRONTAL BOUNDARY THROUGH SATURDAY AFTERNOON. A SEVERAL HOUR
WINDOW OF MODERATE TO HEAVY RAIN WILL BE POSSIBLE ACROSS MUCH OF
THE CWA WITH SOME PRETTY HEFTY QPF POSSIBLE...ESPECIALLY IN THE
HILLS WITH TOTALS IN EXCESS OF 2 INCHES. WILL ALSO HAVE TO MONITOR
WIND POTENTIAL AHEAD OF AND BEHIND THE COLD FRONT. T-STORMS APPEAR
POSSIBLE AS WELL WITH COLD CORE DYNAMIC SYSTEM. THIS WILL BE
EVALUATED OVER THE NEXT TWO DAYS AS WELL.

SHOWERS SHOULD GRADAULLY TAPER OFF BY SUNDAY AFTERNOON IN COOL NW
FLOW. CURRENT TRENDS LOOK DRIER FOR THE START OF NEXT WEEK WITH
RIDGE DEVELOPING.

&&

.AVIATION...AS OF 3:50 PM PST THURSDAY...STEADY RAIN BAND IS OVER
KMRY AS OF 00Z. IT WILL MOVE NORTHEASTWARD TOWARDS THE 3 MAJOR BAY
AREA TERMINALS THRU THE EVENING HOURS. CURRENT EASTERLY WINDS AT
BAY AREA TERMINALS EXPECTED TO TREND SOUTHEAST IN DIRECTION THIS
EVENING. RAIN WILL BE FAIRLY LIGHT BUT STEADY WITH CIGS IN THE 3-4K
RANGE EXPECTED OVERNIGHT. MAIN IDEA IS TO EXPECT WET RUNWAYS WITH
LIGHT SE WIND FLOW.

VICINITY OF KSFO...EXPECT STEADY LIGHT RAIN THRU MOST OF THE NIGHT
WITH CIGS IN THE 3-4K RANGE. CURRENT EAST WINDS FORECAST TO SHIFT
MORE SOUTHEAST FOR MUCH OF THE EVENING AND OVERNIGHT HOURS. WET
RUNWAYS WITH CONTINUED LIGHT SE WINDS AND SHOWER CHANCES FOR FRIDAY
MORNING. MAY BE A BREAK IN THE WET WX FOR A TIME MIDDAY FRIDAY BUT
THEN FORECAST TO REDEVELOP AGAIN LATER FRIDAY AFTERNOON AND EVENING.

KSFO BRIDGE APPROACH...SAME AS KSFO VICINITY.

MRY BAY AREA TERMINALS...STRONG SE WINDS AT KSNS THIS EVENING WITH
LIGHTER SE WINDS FOR KMRY. STEADY LIGHT RAIN THRU 06Z THIS EVENING
WITH CIGS 3-5K. MORE SE WINDS WITH WET RUNWAYS AND CONTINUED -SHRA
FOR MUCH OF FRIDAY WITH BEST CHANCE AT A BREAK DURING THE MIDDLE OF
THE DAY WHEN WERE BETWEEN SYSTEMS.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...PT ARENA TO PIGEON PT 10 TO 60 NM OFFSHORE
                ...PIGEON PT TO PT PIEDRAS BLANCAS 10 TO 60 NM
                ...PT PINOS TO PT PIEDRAS BLANCAS TO 10 NM

$$

PUBLIC FORECAST: RWW
AVIATION/MARINE: RWW

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO