Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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000
FXUS66 KMTR 250509
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
909 PM PST WED DEC 24 2014

...LOCALLY BLUSTERY CONDITIONS NEAR THE COAST AND IN THE HILLS TONIGHT
THROUGH CHRISTMAS MORNING...
...MUCH COOLER WEATHER ON CHRISTMAS DAY AND ON INTO THE WEEKEND...

.SYNOPSIS...GUSTY NORTHWEST WINDS BEHIND A DEPARTING COLD FRONT
WILL CONTINUE ALONG THE COAST AND IN THE HILLS ON WEDNESDAY NIGHT.
WINDS WILL SLOWLY SUBSIDE ON CHRISTMAS DAY. OTHERWISE CHRISTMAS
DAY WILL BE DRY AND COOL. DRY WEATHER IS EXPECTED TO CONTINUE
THROUGH NEXT WEEK. SOME OF THE COLDEST TEMPERATURES SO FAR THIS
SEASON ARE EXPECTED BY FRIDAY NIGHT WHEN OVERNIGHT LOWS ARE
FORECAST TO BE AT OR SLIGHTLY BELOW FREEZING IN THE INLAND
VALLEYS.

&&

.DISCUSSION...AS OF 9:05 PM PST WEDNESDAY...A FAST-MOVING COLD
FRONT SWEPT FROM NORTH TO SOUTH ACROSS OUR REGION THIS AFTERNOON.
RAIN RATES WERE BRIEFLY HEAVY IN SOME LOCATIONS AS THE FRONT MOVED
THROUGH. HOWEVER...RAIN DURATION WAS VERY SHORT AND SO RAINFALL
TOTALS WERE MOSTLY LESS THAN A TENTH OF AN INCH. ISOLATED POST-
FRONTAL RAIN SHOWERS ENDED ACROSS THE NORTHERN PORTION OF THE AREA
BY SUNSET AND A FORECAST UPDATE EARLY THIS EVENING INCLUDED
REMOVAL OF ALL MENTION OF PRECIP ACROSS MOST OF THE SF BAY AREA
THIS EVENING. BY MID-EVENING...SHOWER ACTIVITY HAD ENDED ACROSS THE
ENTIRE FORECAST AREA.

BLUSTERY CONDITIONS DEVELOPED BEHIND THE DEPARTING COLD FRONT.
NORTHWEST WINDS HAVE BEEN LOCALLY STRONG AND GUSTY SINCE LATE
AFTERNOON WITH GUSTS IN EXCESS OF 40 MPH OBSERVED IN THE HILLS AND
NEAR THE COAST. BY MID EVENING...WINDS WERE BEGINNING TO SUBSIDE
ALONG THE COAST...BUT CONTINUE TO GUST IN EXCESS OF 40 MPH IN THE
HILLS. ISOLATED RIDGE TOPS WILL LIKELY CONTINUE TO SEE GUSTS AT OR
NEAR WIND ADVISORY CRITERIA (45 MPH) THROUGH THE NIGHT...BUT
WINDY CONDITIONS ARE NOT EXPECTED TO BE WIDESPREAD ENOUGH FOR
ISSUANCE OF WIND ADVISORIES. NORTHERLY WINDS WILL GRADUALLY
SUBSIDE ON CHRISTMAS DAY...ESPECIALLY AT LOWER ELEVATIONS...BUT
REMAIN LOCALLY GUSTY IN THE HILLS THROUGH THURSDAY NIGHT.

CHRISTMAS DAY IS FORECAST TO BE MOSTLY SUNNY...DRY AND COOL. DRY
CONDITIONS ARE THEN EXPECTED TO PERSIST THROUGH THE WEEKEND AND
WELL INTO NEXT WEEK AS THE SYNOPTIC PATTERN REMAINS AMPLIFIED AND
QUASI-STATIONARY WITH AN UPPER RIDGE HOLDING FIRM OFF THE WEST
COAST OF NORTH AMERICA.

ALONG WITH MUCH COOLER AIR MOVING INTO THE AREA THIS EVENING...A
MUCH DRIER AIRMASS WILL SWEEP FROM NORTH TO SOUTH ACROSS OUR
REGION ON CHRISTMAS DAY. THIS COOL AND DRY AIRMASS WILL SET THE
STAGE FOR THE COLDEST TEMPS OF THE SEASON ONCE WINDS SUBSIDE BY
LATE THIS WEEK. OVERNIGHT LOWS ARE FORECAST TO DROP TO AROUND
FREEZING IN THE INLAND VALLEYS BY LATE THURSDAY NIGHT AND PATCHY
FROST IS LIKELY IN THOSE AREAS EARLY FRIDAY MORNING. TEMPERATURES
ARE EXPECTED TO BE EVEN COLDER ON FRIDAY NIGHT WHEN LOWS WILL DIP
INTO THE UPPER 20S IN THE COLDEST INLAND VALLEYS. FRIDAY NIGHT`S
TEMPERATURES ARE FORECAST TO FALL JUST SHY OF WHAT WOULD JUSTIFY
ISSUANCE OF FREEZE WARNINGS FOR THE INLAND VALLEYS. SO HAVE OPTED
INSTEAD TO GET THE WORD OUT ABOUT THESE UPCOMING COLD TEMPS WITH
A SPECIAL WEATHER STATEMENT AND HAZARDOUS WEATHER OUTLOOK.

MINIMUM TEMPERATURE GRIDS WERE UPDATED THIS
EVENING...ESPECIALLY FOR FRIDAY NIGHT WHEN MINIMUMS WERE ADJUSTED
DOWNWARD ACROSS MOST INLAND AREAS.

TEMPERATURES WILL WARM SLIGHTLY BY LATE IN THE WEEKEND AS THE
UPPER RIDGE OVER THE EASTERN PACIFIC EDGES INLAND OVER CA. BUT
THEN A DRY SHORTWAVE TROUGH DROPPING SOUTH OUT OF WESTERN CANADA
IS EXPECTED TO BRING A REINFORCING SHOT OF COLD AIR INTO OUR
REGION BY LATE MONDAY OF NEXT WEEK. THE 00Z GFS IS ESPECIALLY
BULLISH WITH THIS WEATHER FEATURE...CARVING OUT A COLD UPPER
TROUGH ACROSS NEVADA AND EASTERN CA BY LATE MONDAY NIGHT AND
PLUNGING 850 MB TEMPS DOWN AS LOW AS MINUS 2 DEG C. IF THE GFS
WERE TO VERIFY...NIGHTTIME TEMPS WOULD BE EVEN COLDER BY THE
MIDDLE OF NEXT WEEK THAN WHAT IS EXPECTED ON FRIDAY NIGHT. THE
ECMWF DIGS THE COLD UPPER TROUGH FARTHER TO THE EAST EARLY NEXT
WEEK...A SOLUTION WHICH WOULD RESULT IN LESS FRIGID CONDITIONS
COMPARED TO THE GFS. THE SPECIAL WEATHER STATEMENT MENTIONS THE
POTENTIAL FOR MORE FREEZING NIGHTS NEXT WEEK.

ON THING TO CONSIDER...CONTINUED WARMER THAN NORMAL SEA SURFACE
TEMPERATURES ALONG THE COAST MAY ACT TO LOCALLY MODIFY THE COLD
AIRMASS AND RESULT IN SOMEWHAT MORE MILD OVERNIGHT LOWS ALONG THE
IMMEDIATE COAST THAN WHAT IS FORECAST BY MOS GUIDANCE.

&&

.AVIATION...AS OF 4:30 PM PST WEDNESDAY...FAST MOVING COLD FRONTAL
BAND PASSED BY THE NWS OFFICE IN MONTEREY WITH SOME LIGHT RAIN AND
GUSTY WINDS. KMUX RADAR IS NOT SHOWING MUCH REFLECTIVITIES ALONG
THIS PART OF THE COLD FRONT HERE AS THE RADAR BEAM AT 5900 FEET IS
OVER THE TOP OF THE PRECIPITATION. NARROW BAND OF MODERATE TO BRIEFLY
HEAVY RAIN SHOWERS EXTEND ENE TO NORTHERN SAN BENITO COUNTY. THE
COLD FRONT WILL CONTINUE TO PRESS SOUTHEASTWARD THIS EVENING WITH
RAPIDLY DRYING WEATHER BEHIND THE FRONTAL SYSTEM. GUSTY W-NW WINDS
WILL CONTINUE AT LEAST INTO THE EARLY EVENING HOURS BEFORE SURFACE
WIND DE-COUPLING BECOMES INCREASINGLY PROBABLE IN VALLEY LOCATIONS
AND LESS PROBABLE OVER THE HILLS AND MTNS. NOT LIKELY TO HAPPEN
THIS EVENING BUT WILL MONITOR FOR SLIGHT PROBABILITY OF LOW LEVEL
WIND SHEAR (LLWS) AT AREA TERMINALS. SUFFICIENT ATMOSPHERIC MIXING IS
FORECAST TONIGHT WHICH WILL PRECLUDE LATE NIGHT/EARLY MORNING FOG
DEVELOPMENT THAT IS DEPENDENT UPON LIGHT WINDS AND A STABLE AIR
MASS. GUSTY N-NW LOW LEVEL WINDS WILL CONTINUE THROUGH THURSDAY
AND THURSDAY NIGHT RESULTING IN CONTINUED DRY WEATHER AND VFR
CONDITIONS.

VICINITY OF KSFO...RECENT 5 MIN ASOS OBS FROM KSFO INDICATE PEAK
WEST WIND GUSTS TO 37 KNOTS. ISSUED AN AIRPORT WEATHER WARNING FOR
WINDS VALID TIL 04Z (8 PM PST). W-NW SURFACE TO LOW LEVEL WINDS
ARE LINKED WITH WIND GUSTS TO 37 KNOTS AND 39 KNOTS HALF MOON BAY
AND SAN FRANCISCO BUOYS RESPECTIVELY. WILL TAKE A FEW HOURS FOR
W-NW WIND TO VEER TO STRONGER NORTHERLY DIRECTION BY WHICH TIME
ANTICIPATE THE KSFO SURFACE WINDS TO TAPER OFF SOME.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...COLD FRONT IS SWEEPING BY HEADING
OFF TO THE SE AT QUICK PACE. CLEARING WILL MOVE INTO THE REGION
DURING THE EVENING. GUSTY W-NW WINDS WILL CONTINUE AT LEAST INTO
THE EARLY EVENING.

&&

.MARINE...AS OF 09:58 AM PST WEDNESDAY...A SWIFTLY APPROACHING
STORM WILL SWEEP ACROSS THE REGION LATER TODAY. THIS WILL RESULT
IN STRONG NORTH TO NORTHWEST WINDS OVER THE COASTAL WATERS LATE
THIS AFTERNOON AND INTO THURSDAY. SUSTAINED GALE FORCE WINDS WITH
OCCASIONAL STORM FORCE GUSTS ARE POSSIBLE OVER THE OUTER WATERS.
FOR THE COASTAL WATERS... EXPECT SMALL CRAFT WINDS WITH OCCASIONAL
GALE FORCE GUSTS.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...SF BAY NORTH OF THE BAY BRIDGE
             SCA...SF BAY SOUTH OF THE BAY BRIDGE
             SCA...PIGEON PT TO PT PINOS 0-10 NM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
             GLW...PT ARENA TO PT REYES 10-60 NM
             GLW...PT REYES TO PIGEON PT 10-60 NM
             GLW...PIGEON PT TO PT PINOS 10-60 NM
             SCA...PT ARENA TO PT REYES 0-10 NM
             SCA...PT REYES TO PIGEON PT 0-10 NM
             SCA...ROUGH BAR ADVISORY FOR SF BAR
             GLW...PT PINOS TO PT PIEDRAS BLANCAS 10-60 NM
             SCA...MONTEREY BAY UNTIL 4 AM

&&

$$

PUBLIC FORECAST: DYKEMA
AVIATION: CANEPA
MARINE: W PI

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