Half Moon Bay CA WX RSS feed

Area Forecast Discussion

FXUS66 KMTR [Monterey CA] 221805 AFDMTR ∨

FXUS66 KMTR 221805
AFDMTR [HEAD]

National Weather Service San Francisco Bay Area 11:05am PDT Thu Oct 22 2020 ∨

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1105 AM PDT THU OCT 22 2020 [HEAD]

Synopsis. Moderate offshore wind event is developing and offshore winds will spread over the Bay Area Hills today ushering in a much drier airmass while temperatures remain seasonably warm. A second burst of moderate offshore winds in the hills tonight while low clouds and fog will return to the coast. Winds turn onshore Friday leading to a noted cooling trend into Saturday. A dry cold front over Nevada on Sunday will keep temperatures near normal and allow for another round of strong winds Sunday night into Monday as a very dry airmass settles over the state. Warming trend starts next week with sunny and warm afternoons but some of the coldest nights so far this fall as interior valleys cool into the 30s at night. ∨

.SYNOPSIS...MODERATE OFFSHORE WIND EVENT IS DEVELOPING AND
OFFSHORE WINDS WILL SPREAD OVER THE BAY AREA HILLS TODAY USHERING
IN A MUCH DRIER AIRMASS WHILE TEMPERATURES REMAIN SEASONABLY WARM.
A SECOND BURST OF MODERATE OFFSHORE WINDS IN THE HILLS TONIGHT
WHILE LOW CLOUDS AND FOG WILL RETURN TO THE COAST. WINDS TURN
ONSHORE FRIDAY LEADING TO A NOTED COOLING TREND INTO SATURDAY.
A DRY COLD FRONT OVER NEVADA ON SUNDAY WILL KEEP TEMPERATURES
NEAR NORMAL AND ALLOW FOR ANOTHER ROUND OF STRONG WINDS SUNDAY
NIGHT INTO MONDAY AS A VERY DRY AIRMASS SETTLES OVER THE STATE.
WARMING TREND STARTS NEXT WEEK WITH SUNNY AND WARM AFTERNOONS BUT
SOME OF THE COLDEST NIGHTS SO FAR THIS FALL AS INTERIOR VALLEYS
COOL INTO THE 30S AT NIGHT. [DISC]

Discussion. As of 09:10am PDT Thursday… the ongoing forecast for today remains on track as we are seeing an increase in northeasterly winds across the northern portion of the Santa Cruz Mountains. Additionally, wind gusts of 30–45 mph and humidity values in the 15–25% range persist over the Diablo Range with slightly weaker winds in the North Bay mountains. Thus, will continue with the ongoing Red Flag Warnings in place. Meanwhile, a much deeper marine layer along the Central Coast resulted in widespread stratus along the coast from Point Reyes [San Francisco CA] southward and well inland into the Salinas Valley. That said, no changes are anticipated this morning. Please see the previous forecast discussions below and be on the lookout for updates by this afternoon as we Hone in on the details related to our next offshore wind event from Sunday into early next week. ∨

.DISCUSSION...AS OF 09:10 AM PDT THURSDAY...THE ONGOING FORECAST
FOR TODAY REMAINS ON TRACK AS WE ARE SEEING AN INCREASE IN
NORTHEASTERLY WINDS ACROSS THE NORTHERN PORTION OF THE SANTA CRUZ
MOUNTAINS. ADDITIONALLY, WIND GUSTS OF 30 TO 45 MPH AND HUMIDITY
VALUES IN THE 15-25% RANGE PERSIST OVER THE DIABLO RANGE WITH
SLIGHTLY WEAKER WINDS IN THE NORTH BAY MOUNTAINS. THUS, WILL
CONTINUE WITH THE ONGOING RED FLAG WARNINGS IN PLACE. MEANWHILE, A
MUCH DEEPER MARINE LAYER ALONG THE CENTRAL COAST RESULTED IN
WIDESPREAD STRATUS ALONG THE COAST FROM POINT REYES SOUTHWARD AND
WELL INLAND INTO THE SALINAS VALLEY. THAT SAID, NO CHANGES ARE
ANTICIPATED THIS MORNING. PLEASE SEE THE PREVIOUS FORECAST
DISCUSSIONS BELOW AND BE ON THE LOOKOUT FOR UPDATES BY THIS
AFTERNOON AS WE HONE IN ON THE DETAILS RELATED TO OUR NEXT
OFFSHORE WIND EVENT FROM SUNDAY INTO EARLY NEXT WEEK. [DISC]

Previous discussion… as of 3:35am PDT Thursday. No changes to ongoing red flags. Forecast is complicated and full of nuance. Offshore wind event is perhaps delayed slightly but north winds are making their way down the state at this time. The Knoxville Creek RAWS [Remote Automated Weather Station] is often our first signal that winds are approaching and the last observations shows north winds gusting to 21 mph. Latest mesoscale [medium-scale (km to 10s of km)] models bring burst of northeast winds over the North and East Bay hills starting soon through mid-morning. Current pattern is supported by a strong 8 mb northerly gradient down the coast while the SFO [San Francisco CA]-Winnemucca [NW Nevada] is strengthening to 6.5 as the main upper trough is digging into the northern Rockies. In general the trend for this event appears to be showing a weakening trend in terms of winds compared to what was forecast a few days ago. Nonetheless will keep all current Red Flag headlines in place for now. Latest fuels analysis continues to show many regions of the Bay Area at historically dry fuels for this date. History is not on our side as we are close the Anniversary date of last years kincade fire and the Oakland Hills firestorm of 1991. Other complicating factor is a shallow southerly surge that has moved up the Central Coast and pushing a sliver of fog up towards Half Moon Bay. This shallow layer will bring cooling to the Monterey Bay region with higher humidity. Will be interesting to watch that finger of fog this morning as the offshore winds hit the Santa Cruz Mountains around sunrise and then drop down towards the ocean. Latest NAM [North American Meso (formerly Eta) model] model shows the offshore winds Winning out and eroding the coastal fog layer. However its possible the winds ride over the top and the surge continues northwards towards Ocean Beach and the Golden Gate Bridge, best estimate at this time is it won't make it much past pillar point this morning. ∨

.PREV DISCUSSION...AS OF 3:35 AM PDT THURSDAY...NO CHANGES TO
ONGOING RED FLAGS. FORECAST IS COMPLICATED AND FULL OF NUANCE.
OFFSHORE WIND EVENT IS PERHAPS DELAYED SLIGHTLY BUT NORTH WINDS
ARE MAKING THEIR WAY DOWN THE STATE AT THIS TIME. THE KNOXVILLE
CREEK RAWS IS OFTEN OUR FIRST SIGNAL THAT WINDS ARE APPROACHING
AND THE LAST OBS SHOWS NORTH WINDS GUSTING TO 21 MPH. LATEST
MESOSCALE MODELS BRING BURST OF NORTHEAST WINDS OVER THE NORTH AND
EAST BAY HILLS STARTING SOON THROUGH MID-MORNING. CURRENT PATTERN
IS SUPPORTED BY A STRONG 8 MB NORTHERLY GRADIENT DOWN THE COAST
WHILE THE SFO-WMC IS STRENGTHENING TO 6.5 AS THE MAIN UPPER TROUGH
IS DIGGING INTO THE NORTHERN ROCKIES. IN GENERAL THE TREND FOR
THIS EVENT APPEARS TO BE SHOWING A WEAKENING TREND IN TERMS OF
WINDS COMPARED TO WHAT WAS FORECAST A FEW DAYS AGO. NONETHELESS
WILL KEEP ALL CURRENT RED FLAG HEADLINES IN PLACE FOR NOW. LATEST
FUELS ANALYSIS CONTINUES TO SHOW MANY REGIONS OF THE BAY AREA AT
HISTORICALLY DRY FUELS FOR THIS DATE. HISTORY IS NOT ON OUR SIDE
AS WE ARE CLOSE THE ANNIVERSARY DATE OF LAST YEARS KINCADE FIRE
AND THE OAKLAND HILLS FIRESTORM OF 1991. OTHER COMPLICATING FACTOR
IS A SHALLOW SOUTHERLY SURGE THAT HAS MOVED UP THE CENTRAL COAST
AND PUSHING A SLIVER OF FOG UP TOWARDS HALF MOON BAY. THIS SHALLOW
LAYER WILL BRING COOLING TO THE MONTEREY BAY REGION WITH HIGHER
HUMIDITY. WILL BE INTERESTING TO WATCH THAT FINGER OF FOG THIS
MORNING AS THE OFFSHORE WINDS HIT THE SANTA CRUZ MOUNTAINS AROUND
SUNRISE AND THEN DROP DOWN TOWARDS THE OCEAN. LATEST NAM MODEL
SHOWS THE OFFSHORE WINDS WINNING OUT AND ERODING THE COASTAL FOG
LAYER. HOWEVER ITS POSSIBLE THE WINDS RIDE OVER THE TOP AND THE
SURGE CONTINUES NORTHWARDS TOWARDS OCEAN BEACH AND THE GOLDEN GATE
BRIDGE, BEST ESTIMATE AT THIS TIME IS IT WONT MAKE IT MUCH PAST
PILLAR POINT THIS MORNING. [DISC]

The offshore winds will keep temperatures warm with lots of 80s across the region. The northeast winds will dry the boundary layer through the day with humidity values lowering for all locations away from the coast, keeping the fire danger high, even in many of the valleys where winds will be light. ∨

THE OFFSHORE WINDS WILL KEEP TEMPERATURES WARM WITH LOTS OF 80S
ACROSS THE REGION. THE NORTHEAST WINDS WILL DRY THE BOUNDARY LAYER
THROUGH THE DAY WITH HUMIDITY VALUES LOWERING FOR ALL LOCATIONS
AWAY FROM THE COAST, KEEPING THE FIRE DANGER HIGH, EVEN IN MANY OF
THE VALLEYS WHERE WINDS WILL BE LIGHT. [DISC]

Offshore flow to stay in place tonight for the Bay Area while the Central Coast will be cooler and cloudier as a weak low west of Big Sur will impact the weather for locations south of Santa Cruz. ∨

OFFSHORE FLOW TO STAY IN PLACE TONIGHT FOR THE BAY AREA WHILE THE
CENTRAL COAST WILL BE COOLER AND CLOUDIER AS A WEAK LOW WEST OF
BIG SUR WILL IMPACT THE WEATHER FOR LOCATIONS SOUTH OF SANTA CRUZ. [DISC]

Red Flag Warnings set to expire at 8am Friday and all indications show a return of onshore winds through the day with rapid increases of humidity near the coast and bay as well as the Santa Cruz Mountains while humidity relief will be slower for the North and East Bay hills. ∨

RED FLAG WARNINGS SET TO EXPIRE AT 8 AM FRIDAY AND ALL INDICATIONS
SHOW A RETURN OF ONSHORE WINDS THROUGH THE DAY WITH RAPID
INCREASES OF HUMIDITY NEAR THE COAST AND BAY AS WELL AS THE SANTA
CRUZ MOUNTAINS WHILE HUMIDITY RELIEF WILL BE SLOWER FOR THE NORTH
AND EAST BAY HILLS. [DISC]

Saturday morning could start out with extensive marine stratus covering much of the Bay Area as the low west of Big Sur will keep onshore winds in place with plenty of low level moisture. The combination of clouds, onshore breezes and cooler temps aloft will bring noted cooling for Saturday with highs generally upper 60s and lower 70s regionwide. ∨

SATURDAY MORNING COULD START OUT WITH EXTENSIVE MARINE STRATUS
COVERING MUCH OF THE BAY AREA AS THE LOW WEST OF BIG SUR WILL KEEP
ONSHORE WINDS IN PLACE WITH PLENTY OF LOW LEVEL MOISTURE. THE
COMBINATION OF CLOUDS, ONSHORE BREEZES AND COOLER TEMPS ALOFT WILL
BRING NOTED COOLING FOR SATURDAY WITH HIGHS GENERALLY UPPER 60S AND
LOWER 70S REGIONWIDE. [DISC]

Another potent shortwave drops into the northern Rockies on Sunday. This will set the stage for another potentially strong offshore wind event. This set-up looks different. The air over the Great Basin will be very cold as a back door cold front drops down the Sierra. North to northeast winds will sweep over the region as early as Sunday afternoon but especially Sunday night into Monday. Strong cold advection will bring a favorable stability profile to allow strong winds aloft to mix down into the valleys so it may not just be wind in the usual North and East Bay hills. Will need to consider Fire Weather Watches as well as potential for High Wind Watches. Still far enough out to keep significant model differences in play with the ECMWF [European Center for Medium-Range Weather Forecasts model] generally farther west and winder. However, no models bring any precipitation to the Bay Area while portions of the Sierra could see some showers. ∨

ANOTHER POTENT SHORTWAVE DROPS INTO THE NORTHERN ROCKIES ON
SUNDAY. THIS WILL SET THE STAGE FOR ANOTHER POTENTIALLY STRONG
OFFSHORE WIND EVENT. THIS SET-UP LOOKS DIFFERENT. THE AIR OVER THE
GREAT BASIN WILL BE VERY COLD AS A BACK DOOR COLD FRONT DROPS DOWN
THE SIERRA. NORTH TO NORTHEAST WINDS WILL SWEEP OVER THE REGION AS
EARLY AS SUNDAY AFTERNOON BUT ESPECIALLY SUNDAY NIGHT INTO MONDAY.
STRONG COLD ADVECTION WILL BRING A FAVORABLE STABILITY PROFILE TO
ALLOW STRONG WINDS ALOFT TO MIX DOWN INTO THE VALLEYS SO IT MAY
NOT JUST BE WIND IN THE USUAL NORTH AND EAST BAY HILLS. WILL NEED
TO CONSIDER FIRE WX WATCHES AS WELL AS POTENTIAL FOR HIGH WIND
WATCHES. STILL FAR ENOUGH OUT TO KEEP SIGNIFICANT MODEL
DIFFERENCES IN PLAY WITH THE ECMWF GENERALLY FARTHER WEST AND
WINDER. HOWEVER, NO MODELS BRING ANY PRECIP TO THE BAY AREA WHILE
PORTIONS OF THE SIERRA COULD SEE SOME SHOWERS. [DISC]

After the winds ease on Monday, lingering northeast flow will allow temps to warm quickly back into the 70s and lower 80s given the very dry airmass. However some of the coldest night so far this fall are likely with 30s for the valleys of the North Bay and Central Coast likely Tuesday–Thursday of next week as the thermometer gets long with mild days and cool nights. Tranquil high pressure looks to be in the cards all of next week through Halloween with no precipitation forecast. ∨

AFTER THE WINDS EASE ON MONDAY, LINGERING NORTHEAST FLOW WILL
ALLOW TEMPS TO WARM QUICKLY BACK INTO THE 70S AND LOWER 80S GIVEN
THE VERY DRY AIRMASS. HOWEVER SOME OF THE COLDEST NIGHT SO FAR
THIS FALL ARE LIKELY WITH 30S FOR THE VALLEYS OF THE NORTH BAY AND
CENTRAL COAST LIKELY TUE-THURSDAY OF NEXT WEEK AS THE THERMOMETER
GETS LONG WITH MILD DAYS AND COOL NIGHTS. TRANQUIL HIGH PRESSURE
LOOKS TO BE IN THE CARDS ALL OF NEXT WEEK THROUGH HALLOWEEN WITH
NO PRECIP FORECAST. [DISC]

Aviation. As of 11:05am PDT Thursday… for the 18Z [11am PDT] TAFs [Terminal Aerodrome Forecasts]. Mostly VFR [Visual Flight Rules] conditions except for lingering stratus at coastal terminals around Monterey Bay and into the Salinas Valley. Southerly surge has pushed stratus up the coast to Sonoma County and is continuing northward. No inland penetration expected around SF Bay Area today. VFR [Visual Flight Rules] continuing through the day, except around Monterey Bay which looks to hold onto IFR [Instrument Flight Rules]/MVFR [Marginal Visual Flight Rules] skies through early afternoon, and possibly throughout the day. Winds light and variable, except for some gusty northerly winds in the East Bay affecting KLVK [Livermore CA]. Winds shoud be predominantly onshore and moderate this afternoon, with breezier conditions through coastal gaps. Overnight, strong northerly winds aloft expected in North Bay. Low-level wind shear included in KAPC [Napa CA] TAF [Terminal Aerodrome Forecast] from 04Z [9pm PDT] at 2000 ft/25 kt [29 mph]. Will continue to monitor for updates. ∨

.AVIATION...AS OF 11:05 AM PDT THURSDAY...FOR THE 18Z TAFS. MOSTLY
VFR CONDITIONS EXCEPT FOR LINGERING STRATUS AT COASTAL TERMINALS
AROUND MONTEREY BAY AND INTO THE SALINAS VALLEY. SOUTHERLY SURGE
HAS PUSHED STRATUS UP THE COAST TO SONOMA COUNTY AND IS CONTINUING
NORTHWARD. NO INLAND PENETRATION EXPECTED AROUND SF BAY AREA
TODAY. VFR CONTINUING THROUGH THE DAY, EXCEPT AROUND MONTEREY BAY
WHICH LOOKS TO HOLD ONTO IFR/MVFR SKIES THROUGH EARLY AFTERNOON,
AND POSSIBLY THROUGHOUT THE DAY. WINDS LIGHT AND VARIABLE, EXCEPT
FOR SOME GUSTY NORTHERLY WINDS IN THE EAST BAY AFFECTING KLVK.
WINDS SHOUD BE PREDOMINANTLY ONSHORE AND MODERATE THIS AFTERNOON,
WITH BREEZIER CONDITIONS THROUGH COASTAL GAPS. OVERNIGHT, STRONG
NORTHERLY WINDS ALOFT EXPECTED IN NORTH BAY. LLWS INCLUDED IN
KAPC TAF FROM 04Z AT 2000FT/25KT. WILL CONTINUE TO MONITOR FOR
UPDATES. [AVIA]

Vicinity of KSFO [San Francisco CA]… VFR [Visual Flight Rules] throughout the TAF [Terminal Aerodrome Forecast] period. Light to calm wind becoming northwest 10–15 knots [12–17 mph] in the afternoon and evening. ∨

VICINITY OF KSFO...VFR THROUGHOUT THE TAF PERIOD. LIGHT TO CALM
WIND BECOMING NORTHWEST 10-15 KNOTS IN THE AFTERNOON AND EVENING. [AVI2]

SFO [San Francisco CA] bridge approach… similar to KSFO [San Francisco CA]. ∨

SFO BRIDGE APPROACH...SIMILAR TO KSFO. [AVI2]

Monterey Bay terminals… IFR [Instrument Flight Rules]/MVFR [Marginal Visual Flight Rules] with stratus lingering. Lifting to VFR [Visual Flight Rules] at KSNS [Salinas CA] by around 19Z [12pm PDT]. Clouds may linger throughout the day at KMRY [Monterey CA]. Light and variable winds becoming west to northwest near 10 knots [12 mph] in the afternoon. Return of stratus overnight with possible patchy fog in coastal areas. IFR [Instrument Flight Rules]/LIFR [Low Instrument Flight Rules] overnight into mid-morning. ∨

MONTEREY BAY TERMINALS...IFR/MVFR WITH STRATUS LINGERING. LIFTING
TO VFR AT KSNS BY AROUND 19Z. CLOUDS MAY LINGER THROUGHOUT THE DAY
AT KMRY. LIGHT AND VARIABLE WINDS BECOMING WEST TO NORTHWEST NEAR
10 KNOTS IN THE AFTERNOON. RETURN OF STRATUS OVERNIGHT WITH
POSSIBLE PATCHY FOG IN COASTAL AREAS. IFR/LIFR OVERNIGHT INTO
MID-MORNING. [AVI2]

Fire weather. As of 4:03am PDT Thursday… no changes to current round of red flags. Northerly gradient is around 8 mb with 7 mb offshore from the deserts. First shot of winds just now starting to show up with northeast gusts to 25 mph from Napa Hills down to Diablo. Event is perhaps slightly delayed but winds will pick-up and become more widespread through midday. Humidity values generally 20–40% in the hills but will rapidly dry through the day. Would categorize event as moderate in strength but dryness of fuels is concerning. ERC [Energy Release Component] charts updated as of October 20th show the North Bay region at record dry levels for this date. Rule of thumb is if you throw a weather event (ie wind plus low humidity) on top of record dry fuels the chance for large fires goes up dramatically. Any bursts of wind will be of concern. ∨

.FIRE WEATHER...AS OF 4:03 AM PDT THURSDAY...NO CHANGES TO
CURRENT ROUND OF RED FLAGS. NORTHERLY GRADIENT IS AROUND 8 MB WITH
7 MB OFFSHORE FROM THE DESERTS. FIRST SHOT OF WINDS JUST NOW
STARTING TO SHOW UP WITH NORTHEAST GUSTS TO 25 MPH FROM NAPA HILLS
DOWN TO DIABLO. EVENT IS PERHAPS SLIGHTLY DELAYED BUT WINDS WILL
PICK-UP AND BECOME MORE WIDESPREAD THROUGH MIDDAY. HUMIDITY VALUES
GENERALLY 20-40% IN THE HILLS BUT WILL RAPIDLY DRY THROUGH THE
DAY. WOULD CATEGORIZE EVENT AS MODERATE IN STRENGTH BUT DRYNESS OF
FUELS IS CONCERNING. ERC CHARTS UPDATED AS OF OCT 20TH SHOW THE
NORTH BAY REGION AT RECORD DRY LEVELS FOR THIS DATE. RULE OF THUMB
IS IF YOU THROW A WEATHER EVENT (I.E WIND PLUS LOW HUMIDITY) ON
TOP OF RECORD DRY FUELS THE CHANCE FOR LARGE FIRES GOES UP
DRAMATICALLY. ANY BURSTS OF WIND WILL BE OF CONCERN. [AVIA]

The surge of stratus along the San Mateo coast is throwing a big curve ball but will see how it behaves once the northeast winds hit the Santa Cruz Mountains later this morning and then surface along Hwy 1. Usual round of morning conf calls will occur and all warnings will be reassessed at that time. ∨

THE SURGE OF STRATUS ALONG THE SAN MATEO COAST IS THROWING A BIG
CURVE BALL BUT WILL SEE HOW IT BEHAVES ONCE THE NORTHEAST WINDS
HIT THE SANTA CRUZ MTNS LATER THIS MORNING AND THEN SURFACE ALONG
HWY 1. USUAL ROUND OF MORNING CONF CALLS WILL OCCUR AND ALL
WARNINGS WILL BE REASSESSED AT THAT TIME. [AVI2]

Drying trend continues in earnest this afternoon and evening. Second shot of northeast winds tonight, mainly for the North and East Bay hills. The upper low west of Big Sur will likely keep humidity high for coastal San Mateo and possibly much of the southwest facing slopes of the Santa Cruz Mountains. ∨

DRYING TREND CONTINUES IN EARNEST THIS AFTERNOON AND EVENING.
SECOND SHOT OF NORTHEAST WINDS TONIGHT, MAINLY FOR THE NORTH AND
EAST BAY HILLS. THE UPPER LOW WEST OF BIG SUR WILL LIKELY KEEP
HUMIDITY HIGH FOR COASTAL SAN MATEO AND POSSIBLY MUCH OF THE
SOUTHWEST FACING SLOPES OF THE SANTA CRUZ MTNS. [AVI2]

Dolan/coleman fire will benefit from much higher humidity, light winds and a general cooling trend. ∨

DOLAN/COLEMAN FIRE WILL BENEFIT FROM MUCH HIGHER HUMIDITY, LIGHT
WINDS AND A GENERAL COOLING TREND. [AVI2]

Onshore winds return all regions through the day Friday with increasing humidity. Deep stratus push looking likely Friday night into Saturday to temporarily moisten the 1 and 10 hour fuel beds. ∨

ONSHORE WINDS RETURN ALL REGIONS THROUGH THE DAY FRIDAY WITH
INCREASING HUMIDITY. DEEP STRATUS PUSH LOOKING LIKELY FRIDAY NIGHT
INTO SATURDAY TO TEMPORARILY MOISTEN THE 1 AND 10 HOUR FUEL BEDS. [AVI2]

Will be watching the Sunday night into Monday wind event potential over the coming days. The setup for this event could be completely different and worse case scenario could bring strong and damaging winds to atypical locations as cold advection pattern would allow strong winds aloft to mix down. High confidence that very dry airmass will be in place. Temps will be cooler but that won't matter much given the record dry fuels beds. How the wind event sets up will be watched closely, often these type of troughs occur after we've received some type of season slowing rain event. ∨

WILL BE WATCHING THE SUNDAY NIGHT INTO MONDAY WIND EVENT POTENTIAL
OVER THE COMING DAYS. THE SETUP FOR THIS EVENT COULD BE COMPLETELY
DIFFERENT AND WORSE CASE SCENARIO COULD BRING STRONG AND DAMAGING
WINDS TO ATYPICAL LOCATIONS AS COLD ADVECTION PATTERN WOULD ALLOW
STRONG WINDS ALOFT TO MIX DOWN. HIGH CONFIDENCE THAT VERY DRY
AIRMASS WILL BE IN PLACE. TEMPS WILL BE COOLER BUT THAT WONT
MATTER MUCH GIVEN THE RECORD DRY FUELS BEDS. HOW THE WIND EVENT
SETS UP WILL BE WATCHED CLOSELY, OFTEN THESE TYPE OF TROUGHS OCCUR
AFTER WE`VE RECEIVED SOME TYPE OF SEASON SLOWING RAIN EVENT. [AVI2]

Marine. As of 8:28am PDT Thursday… gale force winds in the northern outer waters and squared seas, 11 feet at 11 seconds, elsewhere will bring hazardous conditions to mariners today. Winds will ease through Friday and over the weekend as the high over the eastern Pacific weakens and as high pressure strengthens again over the Great Basin. Mixed seas will persist with a moderate northwest swell and longer period southerly swell. ∨

.MARINE...AS OF 8:28 AM PDT THURSDAY...GALE FORCE WINDS IN THE
NORTHERN OUTER WATERS AND SQUARED SEAS, 11 FEET AT 11 SECONDS,
ELSEWHERE WILL BRING HAZARDOUS CONDITIONS TO MARINERS TODAY. WINDS
WILL EASE THROUGH FRIDAY AND OVER THE WEEKEND AS THE HIGH OVER
THE EASTERN PACIFIC WEAKENS AND AS HIGH PRESSURE STRENGTHENS AGAIN
OVER THE GREAT BASIN. MIXED SEAS WILL PERSIST WITH A MODERATE
NORTHWEST SWELL AND LONGER PERIOD SOUTHERLY SWELL. [AVIA]

MTR Watches/Warnings/Advisories

Today: Red Flag Warning…GLW…Pt Arena [Mendocino CA] to Pigeon Pt [Pescadero CA] 10–60 nm [69 miles] Small Craft Advisory…Pt Arena [Mendocino CA] to Pt Reyes [San Francisco CA] 0–10 nm [11 miles] Small Craft Advisory…Pigeon Pt [Pescadero CA] to Pt Piedras Blancas [San Simeon CA] 10–60 nm [69 miles] ∨

.MTR WATCHES/WARNINGS/ADVISORIES...
.TDAY...RED FLAG WARNING...GLW...PT ARENA TO PIGEON PT 10-60 NM
SCA...PT ARENA TO PT REYES 0-10 NM SCA...PIGEON PT TO PT PIEDRAS
BLANCAS 10-60 NM [WARN]

Public Forecast: Rgass/RWW; Aviation: Lorber; Marine: DRP; Fire Weather: RWW ∨

PUBLIC FORECAST: RGASS/RWW
AVIATION: LORBER
MARINE: DRP
FIRE WEATHER: RWW [CRED]

VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO [LINK]

Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea ∨

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

Weather NWS glossary About NWS point forecasts Hourly Weather Graph Long-range forecast Radar Satellite Max Temps Graphical Forecast	Area Forecast Discussion FXUS66 KMTR [Monterey CA] 221805 AFDMTR ∨ FXUS66 KMTR 221805 AFDMTR [HEAD] National Weather Service San Francisco Bay Area 11:05am PDT Thu Oct 22 2020 ∨ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 1105 AM PDT THU OCT 22 2020 [HEAD] Synopsis. Moderate offshore wind event is developing and offshore winds will spread over the Bay Area Hills today ushering in a much drier airmass while temperatures remain seasonably warm. A second burst of moderate offshore winds in the hills tonight while low clouds and fog will return to the coast. Winds turn onshore Friday leading to a noted cooling trend into Saturday. A dry cold front over Nevada on Sunday will keep temperatures near normal and allow for another round of strong winds Sunday night into Monday as a very dry airmass settles over the state. Warming trend starts next week with sunny and warm afternoons but some of the coldest nights so far this fall as interior valleys cool into the 30s at night. ∨ .SYNOPSIS...MODERATE OFFSHORE WIND EVENT IS DEVELOPING AND OFFSHORE WINDS WILL SPREAD OVER THE BAY AREA HILLS TODAY USHERING IN A MUCH DRIER AIRMASS WHILE TEMPERATURES REMAIN SEASONABLY WARM. A SECOND BURST OF MODERATE OFFSHORE WINDS IN THE HILLS TONIGHT WHILE LOW CLOUDS AND FOG WILL RETURN TO THE COAST. WINDS TURN ONSHORE FRIDAY LEADING TO A NOTED COOLING TREND INTO SATURDAY. A DRY COLD FRONT OVER NEVADA ON SUNDAY WILL KEEP TEMPERATURES NEAR NORMAL AND ALLOW FOR ANOTHER ROUND OF STRONG WINDS SUNDAY NIGHT INTO MONDAY AS A VERY DRY AIRMASS SETTLES OVER THE STATE. WARMING TREND STARTS NEXT WEEK WITH SUNNY AND WARM AFTERNOONS BUT SOME OF THE COLDEST NIGHTS SO FAR THIS FALL AS INTERIOR VALLEYS COOL INTO THE 30S AT NIGHT. [DISC] Discussion. As of 09:10am PDT Thursday… the ongoing forecast for today remains on track as we are seeing an increase in northeasterly winds across the northern portion of the Santa Cruz Mountains. Additionally, wind gusts of 30–45 mph and humidity values in the 15–25% range persist over the Diablo Range with slightly weaker winds in the North Bay mountains. Thus, will continue with the ongoing Red Flag Warnings in place. Meanwhile, a much deeper marine layer along the Central Coast resulted in widespread stratus along the coast from Point Reyes [San Francisco CA] southward and well inland into the Salinas Valley. That said, no changes are anticipated this morning. Please see the previous forecast discussions below and be on the lookout for updates by this afternoon as we Hone in on the details related to our next offshore wind event from Sunday into early next week. ∨ .DISCUSSION...AS OF 09:10 AM PDT THURSDAY...THE ONGOING FORECAST FOR TODAY REMAINS ON TRACK AS WE ARE SEEING AN INCREASE IN NORTHEASTERLY WINDS ACROSS THE NORTHERN PORTION OF THE SANTA CRUZ MOUNTAINS. ADDITIONALLY, WIND GUSTS OF 30 TO 45 MPH AND HUMIDITY VALUES IN THE 15-25% RANGE PERSIST OVER THE DIABLO RANGE WITH SLIGHTLY WEAKER WINDS IN THE NORTH BAY MOUNTAINS. THUS, WILL CONTINUE WITH THE ONGOING RED FLAG WARNINGS IN PLACE. MEANWHILE, A MUCH DEEPER MARINE LAYER ALONG THE CENTRAL COAST RESULTED IN WIDESPREAD STRATUS ALONG THE COAST FROM POINT REYES SOUTHWARD AND WELL INLAND INTO THE SALINAS VALLEY. THAT SAID, NO CHANGES ARE ANTICIPATED THIS MORNING. PLEASE SEE THE PREVIOUS FORECAST DISCUSSIONS BELOW AND BE ON THE LOOKOUT FOR UPDATES BY THIS AFTERNOON AS WE HONE IN ON THE DETAILS RELATED TO OUR NEXT OFFSHORE WIND EVENT FROM SUNDAY INTO EARLY NEXT WEEK. [DISC] Previous discussion… as of 3:35am PDT Thursday. No changes to ongoing red flags. Forecast is complicated and full of nuance. Offshore wind event is perhaps delayed slightly but north winds are making their way down the state at this time. The Knoxville Creek RAWS [Remote Automated Weather Station] is often our first signal that winds are approaching and the last observations shows north winds gusting to 21 mph. Latest mesoscale [medium-scale (km to 10s of km)] models bring burst of northeast winds over the North and East Bay hills starting soon through mid-morning. Current pattern is supported by a strong 8 mb northerly gradient down the coast while the SFO [San Francisco CA]-Winnemucca [NW Nevada] is strengthening to 6.5 as the main upper trough is digging into the northern Rockies. In general the trend for this event appears to be showing a weakening trend in terms of winds compared to what was forecast a few days ago. Nonetheless will keep all current Red Flag headlines in place for now. Latest fuels analysis continues to show many regions of the Bay Area at historically dry fuels for this date. History is not on our side as we are close the Anniversary date of last years kincade fire and the Oakland Hills firestorm of 1991. Other complicating factor is a shallow southerly surge that has moved up the Central Coast and pushing a sliver of fog up towards Half Moon Bay. This shallow layer will bring cooling to the Monterey Bay region with higher humidity. Will be interesting to watch that finger of fog this morning as the offshore winds hit the Santa Cruz Mountains around sunrise and then drop down towards the ocean. Latest NAM [North American Meso (formerly Eta) model] model shows the offshore winds Winning out and eroding the coastal fog layer. However its possible the winds ride over the top and the surge continues northwards towards Ocean Beach and the Golden Gate Bridge, best estimate at this time is it won't make it much past pillar point this morning. ∨ .PREV DISCUSSION...AS OF 3:35 AM PDT THURSDAY...NO CHANGES TO ONGOING RED FLAGS. FORECAST IS COMPLICATED AND FULL OF NUANCE. OFFSHORE WIND EVENT IS PERHAPS DELAYED SLIGHTLY BUT NORTH WINDS ARE MAKING THEIR WAY DOWN THE STATE AT THIS TIME. THE KNOXVILLE CREEK RAWS IS OFTEN OUR FIRST SIGNAL THAT WINDS ARE APPROACHING AND THE LAST OBS SHOWS NORTH WINDS GUSTING TO 21 MPH. LATEST MESOSCALE MODELS BRING BURST OF NORTHEAST WINDS OVER THE NORTH AND EAST BAY HILLS STARTING SOON THROUGH MID-MORNING. CURRENT PATTERN IS SUPPORTED BY A STRONG 8 MB NORTHERLY GRADIENT DOWN THE COAST WHILE THE SFO-WMC IS STRENGTHENING TO 6.5 AS THE MAIN UPPER TROUGH IS DIGGING INTO THE NORTHERN ROCKIES. IN GENERAL THE TREND FOR THIS EVENT APPEARS TO BE SHOWING A WEAKENING TREND IN TERMS OF WINDS COMPARED TO WHAT WAS FORECAST A FEW DAYS AGO. NONETHELESS WILL KEEP ALL CURRENT RED FLAG HEADLINES IN PLACE FOR NOW. LATEST FUELS ANALYSIS CONTINUES TO SHOW MANY REGIONS OF THE BAY AREA AT HISTORICALLY DRY FUELS FOR THIS DATE. HISTORY IS NOT ON OUR SIDE AS WE ARE CLOSE THE ANNIVERSARY DATE OF LAST YEARS KINCADE FIRE AND THE OAKLAND HILLS FIRESTORM OF 1991. OTHER COMPLICATING FACTOR IS A SHALLOW SOUTHERLY SURGE THAT HAS MOVED UP THE CENTRAL COAST AND PUSHING A SLIVER OF FOG UP TOWARDS HALF MOON BAY. THIS SHALLOW LAYER WILL BRING COOLING TO THE MONTEREY BAY REGION WITH HIGHER HUMIDITY. WILL BE INTERESTING TO WATCH THAT FINGER OF FOG THIS MORNING AS THE OFFSHORE WINDS HIT THE SANTA CRUZ MOUNTAINS AROUND SUNRISE AND THEN DROP DOWN TOWARDS THE OCEAN. LATEST NAM MODEL SHOWS THE OFFSHORE WINDS WINNING OUT AND ERODING THE COASTAL FOG LAYER. HOWEVER ITS POSSIBLE THE WINDS RIDE OVER THE TOP AND THE SURGE CONTINUES NORTHWARDS TOWARDS OCEAN BEACH AND THE GOLDEN GATE BRIDGE, BEST ESTIMATE AT THIS TIME IS IT WONT MAKE IT MUCH PAST PILLAR POINT THIS MORNING. [DISC] The offshore winds will keep temperatures warm with lots of 80s across the region. The northeast winds will dry the boundary layer through the day with humidity values lowering for all locations away from the coast, keeping the fire danger high, even in many of the valleys where winds will be light. ∨ THE OFFSHORE WINDS WILL KEEP TEMPERATURES WARM WITH LOTS OF 80S ACROSS THE REGION. THE NORTHEAST WINDS WILL DRY THE BOUNDARY LAYER THROUGH THE DAY WITH HUMIDITY VALUES LOWERING FOR ALL LOCATIONS AWAY FROM THE COAST, KEEPING THE FIRE DANGER HIGH, EVEN IN MANY OF THE VALLEYS WHERE WINDS WILL BE LIGHT. [DISC] Offshore flow to stay in place tonight for the Bay Area while the Central Coast will be cooler and cloudier as a weak low west of Big Sur will impact the weather for locations south of Santa Cruz. ∨ OFFSHORE FLOW TO STAY IN PLACE TONIGHT FOR THE BAY AREA WHILE THE CENTRAL COAST WILL BE COOLER AND CLOUDIER AS A WEAK LOW WEST OF BIG SUR WILL IMPACT THE WEATHER FOR LOCATIONS SOUTH OF SANTA CRUZ. [DISC] Red Flag Warnings set to expire at 8am Friday and all indications show a return of onshore winds through the day with rapid increases of humidity near the coast and bay as well as the Santa Cruz Mountains while humidity relief will be slower for the North and East Bay hills. ∨ RED FLAG WARNINGS SET TO EXPIRE AT 8 AM FRIDAY AND ALL INDICATIONS SHOW A RETURN OF ONSHORE WINDS THROUGH THE DAY WITH RAPID INCREASES OF HUMIDITY NEAR THE COAST AND BAY AS WELL AS THE SANTA CRUZ MOUNTAINS WHILE HUMIDITY RELIEF WILL BE SLOWER FOR THE NORTH AND EAST BAY HILLS. [DISC] Saturday morning could start out with extensive marine stratus covering much of the Bay Area as the low west of Big Sur will keep onshore winds in place with plenty of low level moisture. The combination of clouds, onshore breezes and cooler temps aloft will bring noted cooling for Saturday with highs generally upper 60s and lower 70s regionwide. ∨ SATURDAY MORNING COULD START OUT WITH EXTENSIVE MARINE STRATUS COVERING MUCH OF THE BAY AREA AS THE LOW WEST OF BIG SUR WILL KEEP ONSHORE WINDS IN PLACE WITH PLENTY OF LOW LEVEL MOISTURE. THE COMBINATION OF CLOUDS, ONSHORE BREEZES AND COOLER TEMPS ALOFT WILL BRING NOTED COOLING FOR SATURDAY WITH HIGHS GENERALLY UPPER 60S AND LOWER 70S REGIONWIDE. [DISC] Another potent shortwave drops into the northern Rockies on Sunday. This will set the stage for another potentially strong offshore wind event. This set-up looks different. The air over the Great Basin will be very cold as a back door cold front drops down the Sierra. North to northeast winds will sweep over the region as early as Sunday afternoon but especially Sunday night into Monday. Strong cold advection will bring a favorable stability profile to allow strong winds aloft to mix down into the valleys so it may not just be wind in the usual North and East Bay hills. Will need to consider Fire Weather Watches as well as potential for High Wind Watches. Still far enough out to keep significant model differences in play with the ECMWF [European Center for Medium-Range Weather Forecasts model] generally farther west and winder. However, no models bring any precipitation to the Bay Area while portions of the Sierra could see some showers. ∨ ANOTHER POTENT SHORTWAVE DROPS INTO THE NORTHERN ROCKIES ON SUNDAY. THIS WILL SET THE STAGE FOR ANOTHER POTENTIALLY STRONG OFFSHORE WIND EVENT. THIS SET-UP LOOKS DIFFERENT. THE AIR OVER THE GREAT BASIN WILL BE VERY COLD AS A BACK DOOR COLD FRONT DROPS DOWN THE SIERRA. NORTH TO NORTHEAST WINDS WILL SWEEP OVER THE REGION AS EARLY AS SUNDAY AFTERNOON BUT ESPECIALLY SUNDAY NIGHT INTO MONDAY. STRONG COLD ADVECTION WILL BRING A FAVORABLE STABILITY PROFILE TO ALLOW STRONG WINDS ALOFT TO MIX DOWN INTO THE VALLEYS SO IT MAY NOT JUST BE WIND IN THE USUAL NORTH AND EAST BAY HILLS. WILL NEED TO CONSIDER FIRE WX WATCHES AS WELL AS POTENTIAL FOR HIGH WIND WATCHES. STILL FAR ENOUGH OUT TO KEEP SIGNIFICANT MODEL DIFFERENCES IN PLAY WITH THE ECMWF GENERALLY FARTHER WEST AND WINDER. HOWEVER, NO MODELS BRING ANY PRECIP TO THE BAY AREA WHILE PORTIONS OF THE SIERRA COULD SEE SOME SHOWERS. [DISC] After the winds ease on Monday, lingering northeast flow will allow temps to warm quickly back into the 70s and lower 80s given the very dry airmass. However some of the coldest night so far this fall are likely with 30s for the valleys of the North Bay and Central Coast likely Tuesday–Thursday of next week as the thermometer gets long with mild days and cool nights. Tranquil high pressure looks to be in the cards all of next week through Halloween with no precipitation forecast. ∨ AFTER THE WINDS EASE ON MONDAY, LINGERING NORTHEAST FLOW WILL ALLOW TEMPS TO WARM QUICKLY BACK INTO THE 70S AND LOWER 80S GIVEN THE VERY DRY AIRMASS. HOWEVER SOME OF THE COLDEST NIGHT SO FAR THIS FALL ARE LIKELY WITH 30S FOR THE VALLEYS OF THE NORTH BAY AND CENTRAL COAST LIKELY TUE-THURSDAY OF NEXT WEEK AS THE THERMOMETER GETS LONG WITH MILD DAYS AND COOL NIGHTS. TRANQUIL HIGH PRESSURE LOOKS TO BE IN THE CARDS ALL OF NEXT WEEK THROUGH HALLOWEEN WITH NO PRECIP FORECAST. [DISC] Aviation. As of 11:05am PDT Thursday… for the 18Z [11am PDT] TAFs [Terminal Aerodrome Forecasts]. Mostly VFR [Visual Flight Rules] conditions except for lingering stratus at coastal terminals around Monterey Bay and into the Salinas Valley. Southerly surge has pushed stratus up the coast to Sonoma County and is continuing northward. No inland penetration expected around SF Bay Area today. VFR [Visual Flight Rules] continuing through the day, except around Monterey Bay which looks to hold onto IFR [Instrument Flight Rules]/MVFR [Marginal Visual Flight Rules] skies through early afternoon, and possibly throughout the day. Winds light and variable, except for some gusty northerly winds in the East Bay affecting KLVK [Livermore CA]. Winds shoud be predominantly onshore and moderate this afternoon, with breezier conditions through coastal gaps. Overnight, strong northerly winds aloft expected in North Bay. Low-level wind shear included in KAPC [Napa CA] TAF [Terminal Aerodrome Forecast] from 04Z [9pm PDT] at 2000 ft/25 kt [29 mph]. Will continue to monitor for updates. ∨ .AVIATION...AS OF 11:05 AM PDT THURSDAY...FOR THE 18Z TAFS. MOSTLY VFR CONDITIONS EXCEPT FOR LINGERING STRATUS AT COASTAL TERMINALS AROUND MONTEREY BAY AND INTO THE SALINAS VALLEY. SOUTHERLY SURGE HAS PUSHED STRATUS UP THE COAST TO SONOMA COUNTY AND IS CONTINUING NORTHWARD. NO INLAND PENETRATION EXPECTED AROUND SF BAY AREA TODAY. VFR CONTINUING THROUGH THE DAY, EXCEPT AROUND MONTEREY BAY WHICH LOOKS TO HOLD ONTO IFR/MVFR SKIES THROUGH EARLY AFTERNOON, AND POSSIBLY THROUGHOUT THE DAY. WINDS LIGHT AND VARIABLE, EXCEPT FOR SOME GUSTY NORTHERLY WINDS IN THE EAST BAY AFFECTING KLVK. WINDS SHOUD BE PREDOMINANTLY ONSHORE AND MODERATE THIS AFTERNOON, WITH BREEZIER CONDITIONS THROUGH COASTAL GAPS. OVERNIGHT, STRONG NORTHERLY WINDS ALOFT EXPECTED IN NORTH BAY. LLWS INCLUDED IN KAPC TAF FROM 04Z AT 2000FT/25KT. WILL CONTINUE TO MONITOR FOR UPDATES. [AVIA] Vicinity of KSFO [San Francisco CA]… VFR [Visual Flight Rules] throughout the TAF [Terminal Aerodrome Forecast] period. Light to calm wind becoming northwest 10–15 knots [12–17 mph] in the afternoon and evening. ∨ VICINITY OF KSFO...VFR THROUGHOUT THE TAF PERIOD. LIGHT TO CALM WIND BECOMING NORTHWEST 10-15 KNOTS IN THE AFTERNOON AND EVENING. [AVI2] SFO [San Francisco CA] bridge approach… similar to KSFO [San Francisco CA]. ∨ SFO BRIDGE APPROACH...SIMILAR TO KSFO. [AVI2] Monterey Bay terminals… IFR [Instrument Flight Rules]/MVFR [Marginal Visual Flight Rules] with stratus lingering. Lifting to VFR [Visual Flight Rules] at KSNS [Salinas CA] by around 19Z [12pm PDT]. Clouds may linger throughout the day at KMRY [Monterey CA]. Light and variable winds becoming west to northwest near 10 knots [12 mph] in the afternoon. Return of stratus overnight with possible patchy fog in coastal areas. IFR [Instrument Flight Rules]/LIFR [Low Instrument Flight Rules] overnight into mid-morning. ∨ MONTEREY BAY TERMINALS...IFR/MVFR WITH STRATUS LINGERING. LIFTING TO VFR AT KSNS BY AROUND 19Z. CLOUDS MAY LINGER THROUGHOUT THE DAY AT KMRY. LIGHT AND VARIABLE WINDS BECOMING WEST TO NORTHWEST NEAR 10 KNOTS IN THE AFTERNOON. RETURN OF STRATUS OVERNIGHT WITH POSSIBLE PATCHY FOG IN COASTAL AREAS. IFR/LIFR OVERNIGHT INTO MID-MORNING. [AVI2] Fire weather. As of 4:03am PDT Thursday… no changes to current round of red flags. Northerly gradient is around 8 mb with 7 mb offshore from the deserts. First shot of winds just now starting to show up with northeast gusts to 25 mph from Napa Hills down to Diablo. Event is perhaps slightly delayed but winds will pick-up and become more widespread through midday. Humidity values generally 20–40% in the hills but will rapidly dry through the day. Would categorize event as moderate in strength but dryness of fuels is concerning. ERC [Energy Release Component] charts updated as of October 20th show the North Bay region at record dry levels for this date. Rule of thumb is if you throw a weather event (ie wind plus low humidity) on top of record dry fuels the chance for large fires goes up dramatically. Any bursts of wind will be of concern. ∨ .FIRE WEATHER...AS OF 4:03 AM PDT THURSDAY...NO CHANGES TO CURRENT ROUND OF RED FLAGS. NORTHERLY GRADIENT IS AROUND 8 MB WITH 7 MB OFFSHORE FROM THE DESERTS. FIRST SHOT OF WINDS JUST NOW STARTING TO SHOW UP WITH NORTHEAST GUSTS TO 25 MPH FROM NAPA HILLS DOWN TO DIABLO. EVENT IS PERHAPS SLIGHTLY DELAYED BUT WINDS WILL PICK-UP AND BECOME MORE WIDESPREAD THROUGH MIDDAY. HUMIDITY VALUES GENERALLY 20-40% IN THE HILLS BUT WILL RAPIDLY DRY THROUGH THE DAY. WOULD CATEGORIZE EVENT AS MODERATE IN STRENGTH BUT DRYNESS OF FUELS IS CONCERNING. ERC CHARTS UPDATED AS OF OCT 20TH SHOW THE NORTH BAY REGION AT RECORD DRY LEVELS FOR THIS DATE. RULE OF THUMB IS IF YOU THROW A WEATHER EVENT (I.E WIND PLUS LOW HUMIDITY) ON TOP OF RECORD DRY FUELS THE CHANCE FOR LARGE FIRES GOES UP DRAMATICALLY. ANY BURSTS OF WIND WILL BE OF CONCERN. [AVIA] The surge of stratus along the San Mateo coast is throwing a big curve ball but will see how it behaves once the northeast winds hit the Santa Cruz Mountains later this morning and then surface along Hwy 1. Usual round of morning conf calls will occur and all warnings will be reassessed at that time. ∨ THE SURGE OF STRATUS ALONG THE SAN MATEO COAST IS THROWING A BIG CURVE BALL BUT WILL SEE HOW IT BEHAVES ONCE THE NORTHEAST WINDS HIT THE SANTA CRUZ MTNS LATER THIS MORNING AND THEN SURFACE ALONG HWY 1. USUAL ROUND OF MORNING CONF CALLS WILL OCCUR AND ALL WARNINGS WILL BE REASSESSED AT THAT TIME. [AVI2] Drying trend continues in earnest this afternoon and evening. Second shot of northeast winds tonight, mainly for the North and East Bay hills. The upper low west of Big Sur will likely keep humidity high for coastal San Mateo and possibly much of the southwest facing slopes of the Santa Cruz Mountains. ∨ DRYING TREND CONTINUES IN EARNEST THIS AFTERNOON AND EVENING. SECOND SHOT OF NORTHEAST WINDS TONIGHT, MAINLY FOR THE NORTH AND EAST BAY HILLS. THE UPPER LOW WEST OF BIG SUR WILL LIKELY KEEP HUMIDITY HIGH FOR COASTAL SAN MATEO AND POSSIBLY MUCH OF THE SOUTHWEST FACING SLOPES OF THE SANTA CRUZ MTNS. [AVI2] Dolan/coleman fire will benefit from much higher humidity, light winds and a general cooling trend. ∨ DOLAN/COLEMAN FIRE WILL BENEFIT FROM MUCH HIGHER HUMIDITY, LIGHT WINDS AND A GENERAL COOLING TREND. [AVI2] Onshore winds return all regions through the day Friday with increasing humidity. Deep stratus push looking likely Friday night into Saturday to temporarily moisten the 1 and 10 hour fuel beds. ∨ ONSHORE WINDS RETURN ALL REGIONS THROUGH THE DAY FRIDAY WITH INCREASING HUMIDITY. DEEP STRATUS PUSH LOOKING LIKELY FRIDAY NIGHT INTO SATURDAY TO TEMPORARILY MOISTEN THE 1 AND 10 HOUR FUEL BEDS. [AVI2] Will be watching the Sunday night into Monday wind event potential over the coming days. The setup for this event could be completely different and worse case scenario could bring strong and damaging winds to atypical locations as cold advection pattern would allow strong winds aloft to mix down. High confidence that very dry airmass will be in place. Temps will be cooler but that won't matter much given the record dry fuels beds. How the wind event sets up will be watched closely, often these type of troughs occur after we've received some type of season slowing rain event. ∨ WILL BE WATCHING THE SUNDAY NIGHT INTO MONDAY WIND EVENT POTENTIAL OVER THE COMING DAYS. THE SETUP FOR THIS EVENT COULD BE COMPLETELY DIFFERENT AND WORSE CASE SCENARIO COULD BRING STRONG AND DAMAGING WINDS TO ATYPICAL LOCATIONS AS COLD ADVECTION PATTERN WOULD ALLOW STRONG WINDS ALOFT TO MIX DOWN. HIGH CONFIDENCE THAT VERY DRY AIRMASS WILL BE IN PLACE. TEMPS WILL BE COOLER BUT THAT WONT MATTER MUCH GIVEN THE RECORD DRY FUELS BEDS. HOW THE WIND EVENT SETS UP WILL BE WATCHED CLOSELY, OFTEN THESE TYPE OF TROUGHS OCCUR AFTER WE`VE RECEIVED SOME TYPE OF SEASON SLOWING RAIN EVENT. [AVI2] Marine. As of 8:28am PDT Thursday… gale force winds in the northern outer waters and squared seas, 11 feet at 11 seconds, elsewhere will bring hazardous conditions to mariners today. Winds will ease through Friday and over the weekend as the high over the eastern Pacific weakens and as high pressure strengthens again over the Great Basin. Mixed seas will persist with a moderate northwest swell and longer period southerly swell. ∨ .MARINE...AS OF 8:28 AM PDT THURSDAY...GALE FORCE WINDS IN THE NORTHERN OUTER WATERS AND SQUARED SEAS, 11 FEET AT 11 SECONDS, ELSEWHERE WILL BRING HAZARDOUS CONDITIONS TO MARINERS TODAY. WINDS WILL EASE THROUGH FRIDAY AND OVER THE WEEKEND AS THE HIGH OVER THE EASTERN PACIFIC WEAKENS AND AS HIGH PRESSURE STRENGTHENS AGAIN OVER THE GREAT BASIN. MIXED SEAS WILL PERSIST WITH A MODERATE NORTHWEST SWELL AND LONGER PERIOD SOUTHERLY SWELL. [AVIA] MTR Watches/Warnings/Advisories Today: Red Flag Warning…GLW…Pt Arena [Mendocino CA] to Pigeon Pt [Pescadero CA] 10–60 nm [69 miles] Small Craft Advisory…Pt Arena [Mendocino CA] to Pt Reyes [San Francisco CA] 0–10 nm [11 miles] Small Craft Advisory…Pigeon Pt [Pescadero CA] to Pt Piedras Blancas [San Simeon CA] 10–60 nm [69 miles] ∨ .MTR WATCHES/WARNINGS/ADVISORIES... .TDAY...RED FLAG WARNING...GLW...PT ARENA TO PIGEON PT 10-60 NM SCA...PT ARENA TO PT REYES 0-10 NM SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM [WARN] Public Forecast: Rgass/RWW; Aviation: Lorber; Marine: DRP; Fire Weather: RWW ∨ PUBLIC FORECAST: RGASS/RWW AVIATION: LORBER MARINE: DRP FIRE WEATHER: RWW [CRED] VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO [LINK] Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea ∨ FOLLOW US ON FACEBOOK, TWITTER, AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSBAYAREA WWW.TWITTER.COM/NWSBAYAREA WWW.YOUTUBE.COM/NWSBAYAREA [DISC]	Point Forecast Half Moon Bay CA 22 Oct 12:55pm PDT This Afternoon Sunny, with a high near 75°. ENE wind 8 to 13 mph becoming light and variable. Tonight Partly cloudy, with a low around 50°. Calm wind becoming ENE around 5 mph. Friday Mostly sunny, with a high near 68°. Calm wind becoming SW around 6 mph in the afternoon. Friday Night Mostly cloudy, with a low around 52°. SW wind 5 to 7 mph. Saturday Partly sunny, with a high near 65°. SW wind 8 to 14 mph, with gusts as high as 18 mph. Saturday Night Mostly cloudy, with a low around 51°. Sunday Partly sunny, with a high near 65°. Sunday Night Mostly clear, with a low around 48°. Monday Sunny, with a high near 68°. Breezy. Monday Night Mostly clear, with a low around 50°. Tuesday Sunny, with a high near 69°. Tuesday Night Mostly clear, with a low around 49°. Wednesday Sunny, with a high near 70°. This Afternoon Sunny, with a high near 75. East northeast wind 8 to 13 mph becoming light and variable. Tonight Partly cloudy, with a low around 50. Calm wind becoming east northeast around 5 mph. Friday Mostly sunny, with a high near 68. Calm wind becoming southwest around 6 mph in the afternoon. Friday Night Mostly cloudy, with a low around 52. Southwest wind 5 to 7 mph. Saturday Partly sunny, with a high near 65. Southwest wind 8 to 14 mph, with gusts as high as 18 mph. Saturday Night Mostly cloudy, with a low around 51. Sunday Partly sunny, with a high near 65. Sunday Night Mostly clear, with a low around 48. Monday Sunny, with a high near 68. Breezy. Monday Night Mostly clear, with a low around 50. Tuesday Sunny, with a high near 69. Tuesday Night Mostly clear, with a low around 49. Wednesday Sunny, with a high near 70.
This page is generated dynamically from the National Weather Service's NWS point forecast and Area Forecast Discussion, reformatted for readability. NWS glossary; about point forecasts. For more information, visit the Lobitos Weather Project home page. Comments and corrections are welcome: