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

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000
FXUS66 KMTR 290026
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
426 PM PST SUN DEC 28 2014

...A STRONG...COLD AND DRY STORM SYSTEM REMAINS ON TRACK FOR TUESDAY
BRINGING GUSTY WINDS AND COLD TEMPERATURES TO THE AREA FROM
TUESDAY AFTERNOON THROUGH WEDNESDAY...

.SYNOPSIS...DRY SEASONAL WEATHER IS EXPECTED THROUGH MONDAY AS
HIGH PRESSURE REMAINS POSITIONED OVER THE AREA. ON TUESDAY A
STRONG...COLD AND DRY STORM SYSTEM WILL MOVE THROUGH THE REGION
BRINGING WITH IT STRONG WINDS AND COLD OVERNIGHT TEMPERATURES.
WINDS WILL DISSIPATE WEDNESDAY EVENING BUT THE COLDEST
TEMPERATURES ARE EXPECTED WEDNESDAY NIGHT.

&&

.DISCUSSION...AS OF 2:58 PM PST SUNDAY...MOSTLY SUNNY SKIES AND
LIGHT WINDS ARE BEING REPORTED ACROSS THE FORECAST ARE THIS
AFTERNOON. ALTHOUGH IT IS SUNNY OUTSIDE...THE AIR IS A BIT CHILLY
WITH MOST AREAS REPORTING CURRENT TEMPERATURES IN THE MID TO UPPER
50S. OVERNIGHT LOWS WILL ONCE AGAIN FALL INTO THE MID TO UPPER 30S
INLAND WITH UPPER 30S TO MID 40S ALONG THE COAST AND IN THE SAN
FRANCISCO BAY AREA. EXPECT SIMILAR CONDITIONS ON MONDAY.

THE WEATHER STORY OF THE WEEK CONTINUES TO BE A COLD DRY STORM
SYSTEM EXPECTED TO ARRIVE ON TUESDAY. THE 1800Z RUNS OF THE
GFS40...NAM12 AND THE 1200Z ECMWF HAVE ALL INITIALIZED WELL WITH
THE CURRENT SYNOPTIC PATTERN AND ARE IN GOOD AGREEMENT THROUGH THE
NEXT 84 HOURS. THE TRACK OF THIS STORM WILL FORCE COLD DRY AIR
INTO OUR AREA WITH THE GREATEST IMPACT BEING STRONG WINDS OVER THE
NORTH BAY MOUNTAINS...EAST BAY HILLS AND SANTA CRUZ MOUNTAINS.

IN ADDITION TO THE STRONG BRISK WINDS COLD OVERNIGHT TEMPERATURES
ARE ALSO ANTICIPATED TUESDAY NIGHT AND WEDNESDAY NIGHT. WEDNESDAY
NIGHT IS EXPECTED TO BE THE COLDER OF THE TWO NIGHTS WITH WIDE
SPREAD FREEZING AND BELOW FREEZING TEMPERATURES EXPECTED. THESE
COLD TEMPERATURES MAY EVEN IMPACT THE SAN FRANCISCO BAY URBAN
CORRIDOR. SNOW LEVELS ARE ANTICIPATED TO FALL TO 2500 TO 3000
FEET...SO ANY PRECIPITATION THAT DOES FALL WILL SNOW IN THE
MOUNTAINS.

IN TERMS OF THE WIND THE 1800Z NAM12 IS SHOWING 35 TO 40 KT WINDS
AT 925MB OVER THE NORTH BAY MOUNTAINS AND EAST BAY HILLS. THE
1800Z GFS40 IS FORECASTING 40 TO 45 KTS OVER THE SAME LOCATION.
THESE WINDS ARE SLIGHTLY LIGHTER THAN PREVIOUS MODEL RUNS...BUT
THE MID DAY MODEL RUNS OFTEN DIFFER FROM THE 0000Z AND 1200Z MODEL
RUNS SINCE THE 0000Z AND 1200Z RUNS INCLUDE UPPER AIR SOUNDINGS
AND THE MID DAY RUNS DO NOT.

CROSS SECTIONAL ANALYSIS PERFORMED WITH THE 1200Z RUN OF THE GFS40
AND NAM12 SHOW PLENTY OF WIND WITH STRONG DOWNWARD MOTION UP TO 20
UBARS OF OMEGA. THIS ANALYSIS PROVIDES ME WITH A HIGH LEVEL OF
CONFIDENCE THAT THE NORTH BAY MOUNTAINS AND EAST BAY HILLS WILL
SEE SUSTAINED WIND SPEED IN THE ADVISORY LEVEL OF 35 TO 40 MPH
WITH WARNING LEVEL GUSTS UP TO 70 MPH. IN ADDITION...EARLIER IN
THE SEASON OUR PARTNERS MADE US AWARE OF THE POOR CONDITION THAT
THE DROUGHT HAS LEFT TREES IN IN THIS AREA AND THEIR
SUSCEPTIBILITY TO WIND. THIS INFORMATION SUGGESTS THAT A LARGE
NUMBER OF TREES MAY BE BLOWN DOWN BY THESE STRONG WINDS.
THEREFORE...WE HAVE ISSUED A HIGH WIND WATCH VALID FROM 1800Z
TUESDAY THROUGH 0000Z THURSDAY (WEDNESDAY AFTERNOON).

&&

.AVIATION...AS OF 4:30 PM PST SUNDAY...WEAK ONSHORE FLOW HAS
DEVELOPED. THIS WILL BRING SOME LIGHT FOG TO STS BUT OTHERWISE IT
WILL REMAIN CLEAR FOR THE REST OF THE AREA THROUGH MONDAY.

VICINITY OF KSFO...VFR. WINDS 10KT OR LESS.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...VFR.

&&

.MARINE...AS OF 4:30 PM PST SUNDAY...LOOK FOR INCREASING NORTH
WINDS THIS AFTERNOON AS A HIGH AMPLITUDE RIDGE SHIFTS EAST ALONG
THE PACIFIC COAST. WINDS UP TO 20KT POSSIBLE OVER THE OUTER WATERS
FOR TOMORROW. WIND INCREASE FURTHER AND VEER TO THE NORTHEAST BY
TUESDAY AS AN ENERGETIC AIRMASS INVADES FROM THE ARCTIC. A PERIOD
OF STEEP FRESH NORTH SWELL INVADES THE COASTAL WATERS TUESDAY INTO
WEDNESDAY.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...NONE.

&&

$$

PUBLIC FORECAST: LARRY
AVIATION: W PI
MARINE: DRP

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