000
FXUS66 KMTR 071114
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
315 AM PST WED JAN 7 2009
.UPDATE...AS OF 3:15 AM PST WEDNESDAY...CONCORD JUST DROPPED DOWN TO
A QUARTER MILE OF VISIBILITY SO A DENSE FOG ADVISORY HAS BEEN
ISSUED FOR THE EAST BAY VALLEYS THROUGH 9 AM.
.DISCUSSION...AS OF 2:45 AM PST WEDNESDAY...MAIN FORECAST CONCERNS
ARE FOR FOG THIS MORNING...FOLLOWED BY HOW MUCH RAIN TO EXPECT ON
THURSDAY...AND FINALLY IF ANYTHING STORMS ARE ON THE HORIZON FOR NEXT
WEEK.
SIMILAR TO YESTERDAY MORNING A FEW POCKETS OF FOG ARE AROUND THE CWA
THIS MORNING. AT THIS TIME ONLY LIVERMORE HAS DROPPED DOWN TO A
QUARTER OF A MILE -- OR DENSE CRITERIA -- WITH CONCORD NOW DOWN TO
HALF A MILE. WE MAY ISSUE A DENSE FOG ADVISORY FOR THE EAST BAY
VALLEYS THIS MORNING IF CONCORD DOES DROP FURTHER. CHP PAGE
CURRENTLY DOES NOT HAVE FOG RELATED INCIDENTS AROUND THE BAY SO AT
THIS TIME IT DOES NOT APPEAR TO BE CAUSING ANY ISSUES. OUTSIDE OF
THE FOG THIS MORNING...NOT A LOT TO TALK ABOUT FOR THE WEATHER
TODAY AS WE WILL SEE DRY CONDITIONS NORTH TO SOUTH WITH HIGHS 3 TO 6
DEGREES WARMER THAN YESTERDAY FOR THE SOUTHERN HALF OF THE CWA. FOR
THE NORTHERN HALF THE TEMPERATURE INCREASE WILL BE JUST A BIT SMALLER
MOSTLY DUE TO MORE CLOUD COVER.
BY VERY LATE TONIGHT THE FINAL SYSTEM FOR QUITE AWHILE WILL START TO
PUSH INTO THE CWA FROM THE NORTH. THE BIG QUESTION WITH THIS SYSTEM
IS NOT WE WOULD GET MUCH RAIN OUT OF IT -- AMOUNTS STILL LOOK VERY
LIGHT -- BUT RATHER...HOW WIDESPREAD THE LIGHT RAINFALL WOULD BE.
PREVIOUS AFD DID MENTION THE LOCAL NAM ENSEMBLES WHICH PAINTED THE
MOST BULLISH SCENARIO ACROSS OUR AREA. AS SUSPECTED..THE POORER
PERFORMANCE OF THE NAM APPEARS TO BE REARING ITS UGLY HEAD AGAIN
WITH ALL OF THE ENSEMBLES DURING THE SHIFT TONIGHT TRENDING MUCH
DRIER TOWARD THE GFS/ECMWF SOLUTIONS. AFTER TAKING A LOOK AT THE
LATEST SREF WHICH SHOWS OVER AN 80 PERCENT CHANCE OF ONE HUNDREDTH
IN THE TWELVE HOUR BLOCK FOR THE FAR NORTH BAY WITH MUCH LOWER
PROBABILITIES BY THE TIME YOU GET SOUTH OF SAN FRANCISCO...THE POP
GRIDS FOR THE NORTHERN HALF OF THE CWA WERE LEFT MOSTLY ALONE WHICH
MEANS A 60 TO 80 PERCENT CHANCE OF MEASURABLE RAINFALL THERE. FOR THE
SOUTHERN HALF...POPS WERE LOWERED AS ALL OF THE GUIDANCE HAS FALLEN
INTO PLACE WITH VERY LOW CHANCES OF RAIN. IN FACT...THE NAM GUIDANCE
FOR MONTEREY AND SALINAS IS BARELY IN THE DOUBLE DIGITS. THE SAN JOSE
METRO DOES NOT FARE MUCH BETTER WITH AROUND A 20 IN THE GUIDANCE.
THERE IS STILL AN OUTSIDE SHOT OF RAIN DOWN TO MONTEREY COUNTY SO A
SLIGHT CHANCE WAS LEFT IN FOR MOST OF OUR AREA. TIMING OF THE RAIN IS
ONE BRIGHT SPOT FOR COMMUTERS TOMORROW AS IT NOW LOOKS LIKE IT WILL
NOT MAKE IT TO THE SF BAY METRO UNTIL AFTER THE MORNING RUSH.
FINALLY...QPF TOTALS LOOK EXTREMELY LIGHT WITH ONLY UP TO TWO TENTHS
OVER THE NORTH BAY MOUNTAINS...JUST UP TO A TENTH OF AN INCH FOR ALL
CITIES FROM SF BAY TO THE NORTH...AND ONLY A TRACE TO FIVE
HUNDREDTHS FOR SAN JOSE SOUTHWARD. THE BURN AREAS LOOK TO BE IN THE
CLEAR FOR ANY DEBRIS FLOW CONCERNS. EVEN WITHOUT MUCH RAIN...THE
INCREASE IN CLOUD COVER WILL HELP TO DROP HIGHS A FEW DEGREES ON
THURSDAY.
THE SYSTEM WILL SWEEP THROUGH QUICKLY ON THURSDAY AND SHOULD BE
OUT OF HERE BY THAT EVENING. BEHIND THE FRONT 500 MB HEIGHTS
CONTINUE TO BE FORECAST TO GREATLY INCREASE THROUGH THE END OF NEXT
WEEK WHILE TEMPERATURES AT 850 MB INCREASE UP TO 18C AT LEAST INTO
TUESDAY. STILL LOOKS LIKE THE SOUTHERN THIRD OF THE CWA WILL HAVE THE
BEST CHANCE FOR WARM TO VERY WARM HIGHS FROM SUNDAY TO TUESDAY. FOR
THE REST OF THE AREA...THIS TYPE OF SETUP OFTEN LEAVES THAT AREA WITH
ONLY A LIMITED INCREASE IN TEMPERATURES. FINALLY...IT STILL APPEARS
THAT THURSDAY WILL REPRESENT THE END OF OUR RAIN CHANCES FOR QUITE
SOME TIME. ALL ENSEMBLES FROM GFS TO ECMWF TO CANADIAN/GEM DO NOT
BRING ANY MAJOR STORMS TO OUR AREA AT LEAST THROUGH THE END OF NEXT
WEEK. CPC 8 TO 14 DAY FORECAST WHICH GOES THROUGH JANUARY 20TH ALSO
SHOWS BELOW NORMAL PRECIPITATION.
&&
.AVIATION...AS OF 10:00 PM PST TUESDAY...LOW-LEVEL MOISTURE IN THE
FORM OF STRATUS LIES ALONG THE SAN FRANCISCO PENINSULA AND INTRUDES
INTO SAN FRANCISCO BAY AT 06Z POST TIME. N-S PRESSURE GRADIENTS
ALONG THE COAST ABOUT 2.5MB IN COMBINATION WITH CLOSE ON-SHORE
PRESSURE GRADIENTS VERY WEAKLY OFFSHORE. BKN-OVC011-013 AROUND
S.F.BAY AND EXPECTED TO PERSIST THROUGH MOST OF S.F.BAY THROUGH THE
NIGHT WITH VERY LIMITED INLAND PENETRATION BEYOND THE BAY. KSJC
LIKELY TO BE INFLUENCED BY LOW STRATUS AND FOG DUE TO RADIATIONAL
EFFECTS. MONTEREY STRATUS HAS MOVED FARTHER OFFSHORE AND WITH LIGHT
SOUTHEAST DRAINAGE FLOW AT KMRY AND SIMILAR FLOW EXPECTED TO DEVELOP
AT KSNS...FORECAST FOR STRATUS DECK AMENDED FOR PRIMARILY CLEAR SKIES
DURING THE EVENING. HOWEVER...RADIATIONAL FOG DEVELOPMENT LIKELY TO
BRING SOME DEGRADATION IN VSBYS BY 12Z FOR KMRY AND IFR CIG/MVFR
VSBY KSNS. EXPECT THOSE TERMINALS TO RETURN TO UNRESTRICTED
CIG/VSBY BY 18Z. WINDS RELATIVELY LIGHT OVERNIGHT WITH CLEARING
S.F.BAY TERMINALS BY 18Z. DO NOT EXPECT BUT MINIMAL STRATUS ON-SHORE
WEDNESDAY EVENING/THURSDAY MORNING AS WINDS VEER TO SOUTHEAST AHEAD
OF WEAK ONCOMING THURSDAY FRONTAL SYSTEM.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.TDA...DENSE FOG ADVISORY FOR EAST BAY VALLEYS UNTIL 9 AM.
&&
$$
PUBLIC FORECAST: BELL
AVIATION/MARINE: GUDGEL/CW
NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO
