000
FXUS66 KMTR 300546
AFDMTR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
1045 PM PDT FRI AUG 29 2008
.DISCUSSION...AS OF 8:00 PM PDT...WIND EVENT LIKELY FOR
SUNDAY EVENING THROUGH TUESDAY MORNING ESPECIALLY FOR HIGHER
ELEVATIONS.
THE SEABREEZE FINALLY KICKED IN ACROSS MANY PORTIONS OF THE
DISTRICT TODAY AND TEMPERATURES HAD DROPPED ACCORDINGLY. THE 24 HOUR
CHANGE PRODUCT SHOWS MANY SPOTS ARE RUNNING AROUND 10 DEGREES
COOLER THAN THIS TIME YESTERDAY. ALL OF THE HEAT RELATED PRODUCTS
WERE ALLOWED TO EXPIRE AROUND 6 PM AS EVERYONE DROPS BACK BELOW
ADVISORY CRITERIA. SURFACE GRADIENT PATTERN SHOWS THAT THE ONSHORE
COMPONENT HAS REALLY STARTED TO RAMP UP AND IS APPROACHING 3 MB.
WITH THE FOG PRODUCT SHOWING LOW CLOUDS JUST OFF THE COAST AND IN
BOTH BAYS PLUS THE MARINE LAYER BASED OFF THE FORT ORD PROFILER HAS
RETURNED AND GONE TO OVER 1000 FEET IN LESS THAN 2 HOURS. ALL SIGNS
POINT TO THE RETURN OF PATCHY FOG AND LOW CLOUDS TONIGHT...
SOMETHING THAT WE HAVE HAD A NICE BREAK FROM AS OF LATE. THE
N-S GRADIENT HAS A VERY ROBUST VALUE OF 5.9 MB FROM THE NORTH WHICH
SHOULD BE ENOUGH TO KEEP IT FROM EXTENDED VERY FAR THROUGH SF BAY.
THE HOT WEATHER WE HAD TODAY WILL TAKE A BREAK AS THE RIDGE OF HIGH
PRESSURE THAT HAD BEEN OVERHEAD MOVES WELL TO THE EAST WHILE A
SIGNIFICANT TROUGH MOVES INTO NORTHERN CALIFORNIA AND CONTINUES TO
THE GREAT BASIN. ALL OF THE MODELS ARE IN GOOD AGREEMENT WITH THE
TIMING...STRENGTH...AND LOCATION OF THE TROUGH SO CONFIDENCE IN THE
SUNDAY THROUGH TUESDAY PORTION OF THE FORECAST IS HIGH. WHAT MAKES
THIS PARTICULARLY WORTH KEEPING AN EYE ON IS THE ANOMALY CHARTS
SHOW STANDARD DEVIATIONS OF BETWEEN -3.5 AND -5 ON BOTH THE 850 MB
AND 500 MB CHARTS. IF THE TROUGH IS ABLE TO STRENGTHEN TO A -5 WHEN
IT GETS TO THE GREAT BASIN...WE WOULD HAVE A VERY STRONG WIND EVENT
ON OUR HANDS ESPECIALLY FROM THE EAST AND NORTH BAY HILLS PLUS THE
DIABLO RANGE. THEREFORE...A FIRE WEATHER WATCH WILL BE ISSUED FOR
THOSE ZONES. A BIGGER QUESTION MARK IS HOW MUCH OF THE WIND WILL
TRANSFER DOWN TO THE SURFACE. ALTHOUGH THE NAM HAS STRONG WINDS AT
925 MB IT DOES NOT BRING MUCH OF THAT DOWN TO THE SURFACE WHICH
WOULD SUGGEST THAT THE EVENT MAY BE CONFINED TO HIGHER ELEVATIONS...
N-S VALLEYS...AND AREAS PRONE TO DOWNSLOPING FROM THE NORTH.
WE WILL LIKELY BE ISSUING WIND ADVISORIES AS THE EVENT GETS CLOSER
FOR AT LEAST THE HILLS. BY LATE TUESDAY CALMER CONDITIONS SHOULD
RETURN AS THE TROUGH MOVES WELL TO THE EAST WHILE A RIDGE BUILDS
ALONG THE COAST.
&&
.FIRE WEATHER...AS OF 8:00 PM PDT FRIDAY...A FIRE WEATHER WATCH IS
IN EFFECT FROM SUNDAY EVENING THROUGH TUESDAY MORNING FOR THE NORTH
AND EAST BAY HILLS PLUS DIABLO RANGE.
FIRE WEATHER CONDITIONS WILL CONTINUE TO IMPROVE THROUGH SUNDAY
MORNING AS AN ONSHORE FLOW RETURNS TO THE AREA ALONG WITH HIGHER
RELATIVE HUMIDITIES.
CONDITIONS ARE EXPECTED TO WORSEN BY SUNDAY AFTERNOON AS A TROUGH
MOVES INTO NORTHERN CALIFORNIA SUNDAY EVENING WHICH WILL CAUSE GUSTY
SOUTHWESTERLY WINDS IN MANY SPOTS. AT THIS TIME...THIS TROUGH APPEARS
TO BE STRONG AND UNUSUALLY FAR TO THE SOUTH FOR THIS TIME
OF YEAR WHICH MAKES IT PARTICULARLY CONCERNING GIVEN ALL OF THE
FUELS THROUGH OUR AREA. AS THE TROUGH MOVES TO THE GREAT BASIN ON
MONDAY...NORTHERLY WINDS WILL STREAM DOWN THE BACK OF IT AND THROUGH
CALIFORNIA. EVEN THOUGH TEMPERATURES WILL BE COOLER THAN WHAT WE HAD
RECENTLY AND HUMIDITY VALUES WILL BE HIGHER...HIGHER ELEVATION
LOCATIONS SUCH AS THE NORTH AND EAST BAY HILLS PLUS DIABLO RANGE WILL
LIKELY SEE VERY GUSTY CONDITIONS WHICH SHOULD REACH ADVISORY
CRITERIA. THIS WILL CAUSE A DANGEROUS FIRE WEATHER SITUATION THAT
WILL LIKELY FACILITATE UPGRADING THE FIRE WEATHER WATCH TO A RED FLAG
WARNING AS THE EVENT GETS CLOSER. ALL PERSONS IN THE FIRE COMMUNITY
SHOULD CLOSELY MONITOR THE FORECASTS OVER THE NEXT COUPLE OF DAYS.
WINDS WILL START TO DIMINISH BY EARLY TUESDAY MORNING AND BE MUCH
LIGHTER BY TUESDAY AFTERNOON AS THE TROUGH HEADS WELL TO THE EAST.
&&
.AVIATION...AS OF 10:45 PM PDT FRIDAY...AN APPROACHING UPPER LEVEL
TROUGH IS TRIGGERING A RAPID DEEPENING OF THE MARINE LAYER THIS
EVENING AS WELL AS INCREASING ONSHORE FLOW. IFR CIGS HAD ALREADY
DEVELOPED AT KMRY BY 04Z AND SHOULD DEVELOP AT KSFO AND KOAK BY 09Z.
CLEARING AT KSFO ON SATURDAY MORNING IS A DIFFICULT CALL. THE SFO-
SAC GRADIENT IS TRENDING STRONGER ONSHORE AND THE MARINE LAYER SHOULD
CONTINUE TO DEEPEN OVERNIGHT. THESE FACTORS POINT TO RELATIVELY LATE
CLEARING ON SATURDAY...NOT UNTIL 18Z OR LATER. HOWEVER...THE N-S
GRADIENT IS INCREASING AND THIS MAY RESULT IN EARLIER CLEARING THAN
EXPECTED. BEST ESTIMATE OF CLEARING AT KSFO ON SATURDAY IS 18Z.
&&
.CLIMATE...HERE ARE SELECTED HIGH TEMPERATURES DURING OUR RECENT
HEATWAVE.
.CITY....................AUG 27....AUG 28...AUG 29
SANTA ROSA................99.......101.......98
PETALUMA.................102.......107......103
SAN FRANCISCO CITY........83........80.......81
CONCORD...................98.......102......103
LIVERMORE................102.......104.......89
LOS GATOS.................99.......103......102
SAN JOSE..................95.......101.......98
MORGAN HILL...............98.......102......103
HOLLISTER.................97........98.......99
PINNACLES................105.......112......113
OAKLAND DOWNTOWN..........88........88.......85
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.TNGT..SCA.....PT ARENA TO PIGEON PT 20-60 NM...PT ARENA
TO PT REYES OUT 20 NM...AND SF BAY.
.FIRE WEATHER WATCH FOR THE NORTH BAY AND EAST BAY HILLS
(ZONES 507 AND 511) SUNDAY EVENING THROUGH TUESDAY
MORNING.
$$
PUBLIC FORECAST: BELL
AVIATION/MARINE: DYKEMA
FIRE WEATHER: BELL
CLIMATE: JOROS/BELL
NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO
