FXUS66 KMTR 081150
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
350 AM PST TUE DEC 8 2009

.DISCUSSION...AS OF 3:30 AM PST TUESDAY...EARLY MORNING TEMPERATURES
ARE RUNNING IN THE 20S INLAND AND IN THE 30S ALONG THE COAST AND
IN THE GREATER SFO BAY AREA.

THE UPPER LEVEL TROUGH OVER THE GREAT BASIN THAT HAS BROUGHT THE
ARCTIC AIRMASS TO THE AREA WILL MOVE EASTWARD TODAY. THIS WILL ALLOW
THE AIRMASS TO SLOWLY WARM UP. HOWEVER WITH WINDS BEING VERY LIGHT...
IT WILL TAKE TIME TO MIX OUT THE COLD AIR OVER THE DISTRICT. AS A
RESULT TEMPERATURES WILL ONLY WARM A COUPLE OF DEGREES TODAY AND
TONIGHT. OVERNIGHT LOWS TONIGHT COULD STILL DROP INTO THE UPPER 20S
IN THE INLAND VALLEYS BUT DURATIONS OF SUBFREEZING TEMPERATURES WILL
BE SHORTER...PROBABLY A FEW HOURS OR LESS. A FREEZE WARNING MAY
STILL NEED TO BE ISSUED FOR THE INTERIOR FOR ONE MORE NIGHT. FROST
ADVISORY MAY NOT BE NEEDED TONIGHT FOR THE COASTAL AREAS AS
TEMPERATURES SHOULD STAY ABOVE THE CRITERIA.

MORE SIGNIFICANT WARMING IS EXPECTED WEDNESDAY AS LIGHT SOUTHERLY
FLOW DEVELOPS AHEAD OF THE NEXT SYSTEM. THIS SYSTEM IS UNDERCUTTING
THE BLOCKING HIGH OVER ALASKA AND IS APPROACHING FROM THE WEST.
THIS SYSTEM SPLITS AS IT APPROACHES THE COAST SO ONLY LIGHT AMOUNTS
OF PRECIPITATION IS EXPECTED. LATEST NAM NOW KEEPS ALL OF THE PRECIP
FROM THE MRY BAY AREA SOUTH WHILE THE GFS AND ECMWF PRECIP TO THE
ENTIRE DISTRICT. THE FORECAST CALLS FOR A HIGHER CHANCE OF RAIN IN
THE SOUTHERN PART OF THE CWA AND LESS CHANCES IN THE NORTH THURSDAY.
LATEST NAM AND GFS BRINGS A WEAK SECONDARY SYSTEM TO THE AREA ON
FRIDAY SO WILL KEEP IN A CHANCE OF RAIN FOR FRIDAY.

THE MODELS SHOW A STRONGER STORM MOVING INTO THE AREA ON SATURDAY
WITH RAIN BEGINNING AS EARLY AS FRIDAY NIGHT. THIS STORM COULD HAVE
SOME OROGRAPHICALLY ENHANCED RAINFALL AS IT WILL BE ACCOMPANIED BY A
MODERATE SOUTHERLY FLOW AHEAD OF THE SYSTEM. RAIN IS LIKELY SATURDAY
WITH A CHANCE FOR RESIDUAL RAIN OR SHOWERS INTO SUNDAY.

LOOKING FURTHER AHEAD...MODELS SUGGEST A REX BLOCK PATTERN DEVELOPING
OVER THE CENTRAL PACIFIC NEXT WEEK WITH AN UPPER LEVEL CUTOFF LOW
FORMING SOUTH OF THE BLOCKING HIGH. THIS WILL ALLOW A RIDGE TO BUILD
OVER THE AREA FOR DRYING CONDITIONS FOR AT LEAST THE FIRST PART OF
NEXT WEEK.

&&

.AVIATION...AS OF 3:50 AM PST TUESDAY...CLEAR SKIES CONTINUE ACROSS
THE REGION THIS MORNING WITH THE POSSIBILITY OF FOG BECOMING MORE
AND MORE FAINT. HOWEVER HAVE MAINTAIN A LOW CONFIDENCE TEMPO GROUP
FOR VLIFR CONDITIONS FOR THE SLIGHT CHANCE OF DEVELOPING AROUND
SUNRISE. LIGHT AND VARIABLE WINDS WILL PERSIST THROUGH THE MORNING
THEN BECOMING WEST TO NORTHWEST THIS AFTERNOON.

VICINITY OF KSFO...CLEAR SKIES AND LIGHT AND VARIABLE WINDS
ANTICIPATED THROUGH THE MORNING HOURS. WINDS WILL BECOMING WEST
TO NORTHWEST LATER THIS AFTERNOON.

KSFO BRIDGE APPROACH...SAME AS SFO.

MRY BAY AREA TERMINALS...CLEAR SKIES AND LIGHT AND VARIABLE WINDS
ANTICIPATED THROUGH THE MORNING HOURS. WINDS WILL BECOMING WEST
TO NORTHWEST LATER THIS AFTERNOON.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
    .THRU 9 AM...FREEZE WARNING FOR VALLEY ZONES AND N BAY MOUNTAINS.
              ...FROST ADVISORY FOR COAST AND BAYSIDE ZONES

$$

PUBLIC FORECAST: W PI
AVIATION/MARINE: CW

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO