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

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS66 KMTR 260532
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
932 PM PST THU DEC 25 2014

...MUCH COOLER TEMPERATURES EXPECTED TONIGHT AND FRIDAY NIGHT WITH
FROST IN THE VALLEYS...

.SYNOPSIS...MOST LOCATIONS WILL SEE THEIR COLDEST TEMPERATURES SO
FAR THIS SEASON OVER THE NEXT TWO NIGHTS...WITH OVERNIGHT LOWS
FORECAST TO BE AT OR SLIGHTLY BELOW FREEZING IN THE INLAND VALLEYS
ALONG WITH SOME LATE NIGHT AND MORNING FROST. OTHERWISE...DRY
WEATHER IS EXPECTED TO PERSIST INTO AT LEAST THE BEGINNING OF NEXT
WEEK.

&&

.DISCUSSION...AS OF 8:50 PM PST THURSDAY...CHRISTMAS DAY WAS A
SUNNY AND BREEZY DAY WITH GUSTY NORTHERLY WINDS. HIGH
TEMPERATURES WERE MOSTLY IN THE 50S....AND WITHIN A FEW DEGREES OF
NORMAL. NORTHERLY WINDS HAVE BEEN GRADUALLY SUBSIDING AT MOST
LOWER ELEVATION LOCATIONS SINCE SUNSET...AND WINDS NEAR SEA LEVEL
WILL CONTINUE TO TREND DOWNWARD OVERNIGHT. AT HIGHER
ELEVATIONS...WIND GUSTS AS HIGH AS 30 MPH CONTINUE ACROSS THE
RIDGE TOPS AND THESE GUSTY CONDITIONS ARE EXPECTED TO CONTINUE IN
THE HILLS OVERNIGHT AND INTO FRIDAY MORNING.

THE AIRMASS THAT SWEPT INTO OUR AREA FROM THE NORTH LAST NIGHT AND
TODAY IS MUCH DRIER THAN WHAT OUR REGION HAS SEEN IN QUITE SOME
TIME. EVENING DEWPOINTS ARE MOSTLY IN THE UPPER 20S AND 30S...AND
AS MUCH AS 15 DEGREES BELOW WHAT THEY WERE 24 HOURS PRIOR. THIS
COOL AND DRY AIRMASS...ALONG WITH CLEAR SKIES...WILL RESULT IN
RAPID COOLING NEAR THE SURFACE ONCE WINDS SUBSIDE LATER TONIGHT.
TEMPERATURES ARE EXPECTED TO DROP TO NEAR FREEZING IN THE INLAND
VALLEYS BY SUNRISE FRIDAY MORNING...AND SLIGHTLY BELOW FREEZING IN
THE WIND-SHELTERED VALLEYS. PATCHY FROST IS LIKELY EARLY ON
FRIDAY FOR MANY INLAND VALLEY LOCATIONS.

FRIDAY WILL BE A DAY MUCH LIKE TODAY...EXCEPT FOR LESS WIND. THE
AIRMASS WILL REMAIN COOL AND DRY GOING INTO FRIDAY NIGHT. AND WITH
LESS WIND ON FRIDAY NIGHT...OVERNIGHT LOWS ARE EXPECTED TO BE A
FEW DEGREES COLDER THAN TONIGHT. IN FACT...FRIDAY NIGHT WILL
PROBABLY BE THE COLDEST NIGHT OF THE SEASON THUS FAR WITH THE
COLDEST INLAND VALLEYS SEEING TEMPERATURES DIP INTO THE UPPER 20S.
WIDESPREAD FROST IS LIKELY ACROSS INLAND AREAS LATE FRIDAY NIGHT
AND EARLY SATURDAY MORNING AND THERE MAY EVEN BE SOME PATCHY FROST
IN LOW LYING AREAS NEAR THE COAST AND BAYS. FORECAST LOW
TEMPERATURES FOR THE INLAND VALLEYS ON FRIDAY NIGHT ARE CLOSE TO
THE CRITERIA FOR FREEZE WARNINGS...BUT THESE COLD TEMPERATURES ARE
NOT EXPECTED TO PERSIST LONG ENOUGH...OR COVER A LARGE ENOUGH
AREA...TO WARRANT FREEZE WARNINGS. HAVE ELECTED INSTEAD TO COVER
THE COLD WEATHER SITUATION WITH A HAZARDOUS WEATHER OUTLOOK.

THE AIRMASS OVER OUR AREA WILL GRADUALLY WARM OVER THE WEEKEND AND
RESULT IN SLIGHT MODERATION OF NIGHTTIME TEMPERATURES ON SATURDAY
NIGHT AND SUNDAY NIGHT. BUT PATCHY FROSTY CONDITIONS WILL LIKELY
CONTINUE IN THE COLDEST INLAND VALLEYS.

REINFORCING SHOTS OF COLD AIR ARE FORECAST TO ARRIVE ACROSS OUR
REGION EARLY NEXT WEEK AS A COUPLE OF SHORTWAVE TROUGHS DROP SOUTH
OUT OF BRITISH COLUMBIA. THE FIRST SHORTWAVE IS FORECAST TO SLIDE
INLAND WELL TO OUR EAST BY LATE SUNDAY. THE SECOND WAVE IS
THEN FORECAST TO DROP DUE SOUTH AND CARVE OUT A SHARP TROUGH OVER
CA AND NV...EVENTUALLY FORMING A CUTOFF LOW OVER SOUTHERN
NV/CENTRAL CA BY LATE TUESDAY. THE 12Z ECMWF FORECASTS SOME
SCATTERED LIGHT PRECIP WITH THIS SECOND COLD SYSTEM ON MONDAY
NIGHT AND TUESDAY MORNING. IF PRECIP WOULD DEVELOP...SNOW LEVELS
WOULD BE VERY LOW. THE 00Z GFS INDICATES THIS SYSTEM WILL GENERATE
NO PRECIP IN OUR AREA. IN ANY CASE...GIVEN THE TRAJECTORY OF THIS
SYSTEM ANY PRECIP WILL LIKELY BE ISOLATED AND VERY LIGHT. THE
PRIMARY IMPACTS OF THIS SYSTEM EARLY NEXT WEEK WILL BE ANOTHER
ROUND OF BLUSTERY CONDITIONS FROM LATE MONDAY THROUGH TUESDAY
NIGHT...ESPECIALLY IN THE HILLS...AND THEN MORE COLD NIGHTS WITH
FREEZING TEMPS ONCE AGAIN IN THE VALLEYS BY MONDAY NIGHT OR
TUESDAY NIGHT.

THE SYNOPTIC PATTERN SETTING UP BY EARLY NEXT WEEK...WITH A
PERSISTENT HIGH AMPLITUDE RIDGE JUST OFF THE WEST COAST...IS VERY
MUCH LIKE THE PATTERN THAT DOMINATED LAST DECEMBER WHEN OUR AREA
SAW ALMOST NO PRECIP AND MANY COLD NIGHTS.

&&

.AVIATION...AS OF 9:30 PM PST CHRISTMAS DAY...CLEAR SKIES WILL
PREVAIL THROUGH THE FORECAST PERIOD AS A DRY AIRMASS SETTLES IN
OVER THE REGION. MODERATE NORTH WINDS WILL CONTINUE THROUGH LATE
TONIGHT THEN DIMINISH OVERNIGHT.

VICINITY OF KSFO...VFR. MODERATE NORTH WINDS WILL CONTINUE
THROUGH LATE TONIGHT THEN DIMINISH OVERNIGHT.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS... VFR.

&&

.MARINE...AS OF 9:00 PM PST CHRISTMAS DAY...THE GRADIENT ACROSS
THE REGION WILL GRADUALLY WEAKEN OVERNIGHT RESULTING IN LIGHTER
WINDS ACROSS THE COASTAL WATERS. THE STRONGEST WINDS WILL REMAIN
OVER THE NORTHERN OUTER WATERS THROUGH FRIDAY. MODERATE NORTHWEST
SWELL WILL GRADUALLY DIMINISH THROUGH THE WEEKEND AND INTO EARLY
NEXT WEEK.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TNGT...SCA...PT ARENA TO PT REYES 10-60 NM
             SCA...PT REYES TO PIGEON PT 10-60 NM
             SCA...PT REYES TO PIGEON PT 0-10 NM UNTIL MIDNIGHT
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM UNTIL MIDNIGHT
             SCA...PT ARENA TO PT REYES 0-10 NM UNTIL 3 AM
             SCA...PIGEON PT TO PT PINOS 10-60 NM UNTIL 3 AM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 10-60 NM UNTIL 3 AM

&&

$$

PUBLIC FORECAST: CW
AVIATION: CW
MARINE: W PI

VISIT US AT WEATHER.GOV/SANFRANCISCO

FOLLOW US ON FACEBOOK, TWITTER, AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSBAYAREA
WWW.TWITTER.COM/NWSBAYAREA
WWW.YOUTUBE.COM/NWSBAYAREA





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.