FXUS66 KMTR 230020
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
420 PM PST TUE DEC 22 2009

.DISCUSSION...AS OF 3:00 PM PST TUESDAY...FORECAST FOCUS IS ON COOL
OVERNIGHT TEMPS...OTHERWISE DRY WITH MILD AFTERNOONS THE REST OF THE
WEEK INCLUDING XMAS DAY.

IN THE SHORT TERM...BREEZY CONDITIONS CONTINUE ACROSS THE AREA THIS
AFTERNOON WITH GUSTS OF 20-30 MPH SHOWING UP AT MOST OF THE
AIRPORTS. UP IN THE HILLS GUST OF 30-35 MPH ARE COMMON BUT FOR THE
MOST PART WINDS ARE STAYING BELOW ADVISORY CRITERIA. WIND IS BEING
GENERATED ON THE BACKSIDE OF YESTERDAYS TROUGH THAT IS NOW DOWN
OVER ARIZONA. GRADIENTS ARE IMPRESSIVE WITH 8 MB DOWN THE COAST FROM
SFO TO SANTA BARBARA AND OVER 18 MB ONSHORE FROM SFO TO LAS VEGAS.
WINDS SHOULD SLOWLY EASE IN THE VALLEYS TONIGHT BUT STAY STEADY OR
SLIGHTLY INCREASE IN THE HILLS AND VEER NORTHEAST AS NIGHT-TIME
INVERSIONS SET-UP. TEMPS WILL BE CHILLY TONIGHT BUT 2 PM DEWPOINTS
IN THE 30-35 DEGREE RANGE SUGGEST NO WIDESPREAD FREEZE CONDITIONS
EXPECTED FOR TONIGHT. AS WINDS EASE WOULD EXPECT DEWPOINTS TO DROP
INTO THE UPPER 20S...WITH CURRENT FORECAST INDICATING LOWS NEAR
FREEZING IN THE NORTH AND EAST BAY VALLEYS WITH TEMPS INTO THE MID
30S AROUND THE BAYS AND COAST. SO COOLER THAN THE LAST SEVERAL DAYS
BUT NOT AS COLD AS THE EARLY DECEMBER COOL PERIOD.

THE ABOVE COMBINATION OF DRY AIRMASS AND WINDS ALOFT SHOULD PRECLUDE
MUCH VALLEY FOG TONIGHT AND THE CENTRAL VALLEY OFFICES ARENT
EXPECTING TULE FOG. WITH EACH PROGRESSIVE NIGHT VALLEY FOG MAY
BECOME MORE PREVALENT AS THE PATTERN BECOMES STAGNANT. OVERALL THE
SYNOPTIC PATTERN WILL FEATURE BUILDING HIGH PRESSURE WEDS THROUGH
FRIDAY WITH SUNNY AND SEASONABLE AFTERNOONS THROUGH THE END OF THE
WEEK. QUIET TRAVEL WX EXPECTED STATEWIDE ALTHOUGH WILL HAVE TO
MONITOR FOR OVERNIGHT DENSE FOG POTENTIAL AS THE WEEK WEARS ON.

NEXT BIG FORECAST CHALLENGE DEALS WITH RAIN CHANCES LATER SATURDAY
INTO SUNDAY. THE LATEST EURO MODEL IS MUCH WETTER BRINGING RAIN TO
NEARLY OUR ENTIRE CWA BY LATER SATURDAY AFTERNOON WITH PERIODS OF
RAIN CONTINUING RIGHT THROUGH SUNDAY. THE OPERATIONAL RUNS OF THE
12 AND 18Z GFS ARE MUCH DRIER. HOWEVER THE GFS ENSEMBLES AND THE
CANADIAN MODEL WOULD ARGUE FOR AT LEAST SOME CHANCE OF RAIN. HAVE
INCREASED POPS FOR THE LATE SATURDAY PERIOD TO ABOVE CLIMO AND THEN
TRENDED THE INHERITED POPS FOR SATURDAY NIGHT INTO SUNDAY HIGHER AS
WELL.

CONFIDENCE IS PRETTY LOW AS THE EURO HAS LEAD US ASTRAY AS OF LATE.
THE MAIN NORTH AMERICAN PATTERN WILL FEATURE AN ANOMALOUS LOW OVER
THE CENTRAL US SO THERE IS REASON TO BELIEVE THE DRIER GFS
SOLUTIONS. WILL CONTINUE TO MONITOR.

IN FOLLOWING THE EURO SOLUTIONS ANY STEADY RAIN WOULD TAPER TO
SHOWERS BY SUNDAY NIGHT INTO EARLY MONDAY. FORECAST LOOKS DRY FOR
MOST OF MONDAY INTO THE FIRST HALF OF TUESDAY. THEN LATER TUESDAY
THROUGH WEDS THERE CONTINUES TO BE BETTER OVERALL MODEL AGREEMENT
IN BRINGING ANOTHER MODERATE STRENGTH STORM ONSHORE WITH RAIN FOR THE
BAY AREA AND SNOW IN THE MOUNTAINS.

&&

.AVIATION...AS OF 4:20 PM TUESDAY...GUSTY WINDS WILL PREVAIL UNTIL
04Z-05Z THIS EVENING AS COLD DRY NORTHWESTERLY FLOW CONTINUES TO
STREAM INTO THE REGION. CLEAR SKIES AND VFR CONDITIONS WILL
CONTINUE THROUGH TONIGHT.

VICINITY OF KSFO...VFR CONDITIONS WILL CONTINUE THROUGH TONIGHT.
NW WINDS WILL BE SUSTAINED IN THE TEENS TO 20 KT WITH OCCASIONAL
GUSTS TO 30 KT UNTIL 05Z TONIGHT.

KSFO BRIDGE APPROACH...SAME AS KSFO.

MRY BAY AREA TERMINALS...VFR CONDITIONS WILL CONTINUE THROUGH
TONIGHT. NW WINDS OF 10 TO 20 KT WITH HIGHER GUSTS POSSIBLE AT
KMRY UNTIL AROUND 04Z THIS EVENING.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
   .TNGT..SCA...PT ARENA TO PIGEON PT 0-60 NM AND MRY BAY
       ...SCA...ROUGH BAR
       ...GALE WARNING...PIGEON PT TO PT PIEDRAS BLANCAS 0-60 NM

$$

PUBLIC FORECAST: RWW
AVIATION/MARINE: CW

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO