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Area Forecast Discussion

FXUS66 KMTR [Monterey CA] 191701 AFDMTR ∨

FXUS66 KMTR 191701
AFDMTR [HEAD]

National Weather Service San Francisco Bay Area 9:01am PST Tue Nov 19 2019 ∨

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
901 AM PST TUE NOV 19 2019 [HEAD]

Synopsis. A region-wide cooling will occur on Tuesday as a frontal boundary sweeps through the region. Gusty and dry offshore winds will develop over the North and East Bay hills/mountains from late Tuesday night through early Thursday that will consequently result in critical fire weather conditions. Dry conditions, along with seasonable temperatures, are forecast from Thursday through next weekend. ∨

.SYNOPSIS...A REGION-WIDE COOLING WILL OCCUR ON TUESDAY AS A
FRONTAL BOUNDARY SWEEPS THROUGH THE REGION. GUSTY AND DRY OFFSHORE
WINDS WILL DEVELOP OVER THE NORTH AND EAST BAY HILLS/MOUNTAINS
FROM LATE TUESDAY NIGHT THROUGH EARLY THURSDAY THAT WILL
CONSEQUENTLY RESULT IN CRITICAL FIRE WEATHER CONDITIONS. DRY
CONDITIONS, ALONG WITH SEASONABLE TEMPERATURES, ARE FORECAST FROM
THURSDAY THROUGH NEXT WEEKEND. [DISC]

Discussion. As of 08:54am PST Tuesday… a frontal boundary continues to push across the region this morning resulting in an increase in northerly winds. Breezy to locally gusty winds, especially near the coast, and cold air advection will limit daytime warming with temperatures only reaching into the 60s for much of the region today. Rain chances persist over the Central Coast later in the day as a secondary boundary associated with a short-wave disturbance slides down the coastline. In wake of this, offshore winds will develop and begin to increase over the North and East Bay. With this said, the ongoing forecast remains on track this morning with no updates necessary at this time. For full details, please see the previous forecast discussion below as well as the fire weather section with regards to the increased fire weather concerns. ∨

.DISCUSSION...AS OF 08:54 AM PST TUESDAY...A FRONTAL BOUNDARY
CONTINUES TO PUSH ACROSS THE REGION THIS MORNING RESULTING IN AN
INCREASE IN NORTHERLY WINDS. BREEZY TO LOCALLY GUSTY WINDS,
ESPECIALLY NEAR THE COAST, AND COLD AIR ADVECTION WILL LIMIT
DAYTIME WARMING WITH TEMPERATURES ONLY REACHING INTO THE 60S FOR
MUCH OF THE REGION TODAY. RAIN CHANCES PERSIST OVER THE CENTRAL
COAST LATER IN THE DAY AS A SECONDARY BOUNDARY ASSOCIATED WITH A
SHORT-WAVE DISTURBANCE SLIDES DOWN THE COASTLINE. IN WAKE OF THIS,
OFFSHORE WINDS WILL DEVELOP AND BEGIN TO INCREASE OVER THE NORTH
AND EAST BAY. WITH THIS SAID, THE ONGOING FORECAST REMAINS ON
TRACK THIS MORNING WITH NO UPDATES NECESSARY AT THIS TIME. FOR
FULL DETAILS, PLEASE SEE THE PREVIOUS FORECAST DISCUSSION BELOW AS
WELL AS THE FIRE WEATHER SECTION WITH REGARDS TO THE INCREASED
FIRE WEATHER CONCERNS. [DISC]

Previous discussion… as of 3:25am PST Tuesday. Moisture has increased across the region overnight and a cool down is on the way as the weather pattern begins to shift. The longwave pattern aloft shows an amplified pattern with a ridge nosing into the Gulf of Alaska and a trough (with upper low) moving into the Pacific Northwest. The eastward movement of the trough/upper low is being helped by a decent jet Max [point or area of relative maximum wind speeds within a jet stream] diving southward and ultimately rounding the base of the trough. Additionally, as the jet Max [point or area of relative maximum wind speeds within a jet stream] moves south it will help to push a Vort Max [Vorticity Maximum, the highest value of positive vorticity (point location) within a region of positive vorticity] into Southern California with PVA [Positive Vorticity Advection] over the region today into Wednesday. At the surface, a cold front currently bisecting the Bay Area will continue to progress southward early today. The passing front will bring gusty winds over the coastal waters and cooler temperatures. ∨

.PREV DISCUSSION...AS OF 3:25 AM PST TUESDAY...MOISTURE HAS
INCREASED ACROSS THE REGION OVERNIGHT AND A COOL DOWN IS ON THE
WAY AS THE WEATHER PATTERN BEGINS TO SHIFT. THE LONGWAVE PATTERN
ALOFT SHOWS AN AMPLIFIED PATTERN WITH A RIDGE NOSING INTO THE GULF
OF ALASKA AND A TROUGH (WITH UPPER LOW) MOVING INTO THE PACNW.
THE EASTWARD MOVEMENT OF THE TROUGH/UPPER LOW IS BEING HELPED BY A
DECENT JET MAX DIVING SOUTHWARD AND ULTIMATELY ROUNDING THE BASE
OF THE TROUGH. ADDITIONALLY, AS THE JET MAX MOVES SOUTH IT WILL
HELP TO PUSH A VORT MAX INTO SOCAL WITH PVA OVER THE REGION TODAY
INTO WEDNESDAY. AT THE SURFACE, A COLD FRONT CURRENTLY BISECTING
THE BAY AREA WILL CONTINUE TO PROGRESS SOUTHWARD EARLY TODAY. THE
PASSING FRONT WILL BRING GUSTY WINDS OVER THE COASTAL WATERS AND
COOLER TEMPERATURES. [DISC]

Forecasted high temperatures are still on track to see a 10–15° drop from Monday to Tuesday. Highs will generally be in the 60s and possibly the 50s over the highest peaks. The aforementioned Vort Max [Vorticity Maximum, the highest value of positive vorticity (point location) within a region of positive vorticity] and associated PVA [Positive Vorticity Advection] will move southward and become a cut off upper low over Southern California Tuesday night into Wednesday. As this area of enhanced lift slides south enough moisture and lift will be present for a chance of pop up showers over the coastal waters and the Big Sur coast. For several runs now, high-resolution WRF [Weather Research and Forecasting model] and HRRR develop showers over the coastal waters/mountains of Big Sur after 4pm Tuesday through early Wednesday. Current forecast will carry scattered showers with some rainfall possible, but chances are still in the 20–30% range. ∨

FORECASTED HIGH TEMPERATURES ARE STILL ON TRACK TO SEE A 10-15
DEGREE DROP FROM MONDAY TO TUESDAY. HIGHS WILL GENERALLY BE IN THE
60S AND POSSIBLY THE 50S OVER THE HIGHEST PEAKS. THE
AFOREMENTIONED VORT MAX AND ASSOCIATED PVA WILL MOVE SOUTHWARD AND
BECOME A CUT OFF UPPER LOW OVER SOCAL TUESDAY NIGHT INTO
WEDNESDAY. AS THIS AREA OF ENHANCED LIFT SLIDES SOUTH ENOUGH
MOISTURE AND LIFT WILL BE PRESENT FOR A CHANCE OF POP UP SHOWERS
OVER THE COASTAL WATERS AND THE BIG SUR COAST. FOR SEVERAL RUNS
NOW, HI-RES WRF AND HRRR DEVELOP SHOWERS OVER THE COASTAL
WATERS/MOUNTAINS OF BIG SUR AFTER 4 PM TUESDAY THROUGH EARLY
WEDNESDAY. CURRENT FORECAST WILL CARRY SCATTERED SHOWERS WITH SOME
RAINFALL POSSIBLE, BUT CHANCES ARE STILL IN THE 20-30% RANGE. [DISC]

Of greater concerns is what happens on the backside of the departing upper low to the south. North to northeast winds will develop over the higher terrain of the N and East Bay Tuesday evening, peak early Wednesday and remain breezy to gusty into Thursday. At their peak, winds will be in the 35–45 mph range with top gusts close to 60 mph. The gusty offshore winds will help to set the stage for fire weather concerns. See fire section below for more details. ∨

OF GREATER CONCERNS IS WHAT HAPPENS ON THE BACKSIDE OF THE
DEPARTING UPPER LOW TO THE SOUTH. NORTH TO NORTHEAST WINDS WILL
DEVELOP OVER THE HIGHER TERRAIN OF THE N AND E BAY TUESDAY
EVENING, PEAK EARLY WEDNESDAY AND REMAIN BREEZY TO GUSTY INTO
THURSDAY. AT THEIR PEAK, WINDS WILL BE IN THE 35-45 MPH RANGE
WITH TOP GUSTS CLOSE TO 60 MPH. THE GUSTY OFFSHORE WINDS WILL HELP
TO SET THE STAGE FOR FIRE WEATHER CONCERNS. SEE FIRE SECTION BELOW
FOR MORE DETAILS. [DISC]

Winds ease on Thursday, but conditions will still remain dry. The 00Z [4pm PST] WRF [Weather Research and Forecasting model] model continues to show a southerly surge creeping up the Big Sur coast on Thursday as the ridge weakens and offshore gradient relaxes. Will have to watch how this scenario evolves, but an increase in clouds/fog along with cooler temperatures could occur. Otherwise, dry weather continues into the weekend with a slight warm up. ∨

WINDS EASE ON THURSDAY, BUT CONDITIONS WILL STILL REMAIN DRY. THE
00Z WRF MODEL CONTINUES TO SHOW A SOUTHERLY SURGE CREEPING UP THE
BIG SUR COAST ON THURSDAY AS THE RIDGE WEAKENS AND OFFSHORE
GRADIENT RELAXES. WILL HAVE TO WATCH HOW THIS SCENARIO EVOLVES,
BUT AN INCREASE IN CLOUDS/FOG ALONG WITH COOLER TEMPERATURES COULD
OCCUR. OTHERWISE, DRY WEATHER CONTINUES INTO THE WEEKEND WITH
A SLIGHT WARM UP. [DISC]

Farther down the road the medium range guidance is once again showing another offshore flow event Earl next week. So what about rain? Details vary, but solutions still show possible precipitation around Thanksgiving. ∨

FARTHER DOWN THE ROAD THE MEDIUM RANGE GUIDANCE IS ONCE AGAIN
SHOWING ANOTHER OFFSHORE FLOW EVENT EARL NEXT WEEK. SO WHAT ABOUT
RAIN? DETAILS VARY, BUT SOLUTIONS STILL SHOW POSSIBLE PRECIP
AROUND THANKSGIVING. [DISC]

Aviation. As of 04:00am PST Tuesday… for 12Z [4am PST] TAFs [Terminal Aerodrome Forecasts]. A cold front is pushing through the Central Coast bringing strong northwest winds and a thick cloud deck. Ceilings have lowered to MVFR [Marginal Visual Flight Rules]/IFR [Instrument Flight Rules] conditions and are expected to remain that way through most of the morning with mid to high level clouds lingering through the day. Patchy coastal fog is possible as the marine layer is slowly deepening to 1000 feet. There is still a chance of local drizzle possible, but confidence is low and therefore left out of the TAFs [Terminal Aerodrome Forecasts]. ∨

.AVIATION...AS OF 04:00 AM PST TUESDAY...FOR 12Z TAFS. A COLD
FRONT IS PUSHING THROUGH THE CENTRAL COAST BRINGING STRONG
NORTHWEST WINDS AND A THICK CLOUD DECK. CIGS HAVE LOWERED TO
MVFR/IFR CONDITIONS AND ARE EXPECTED TO REMAIN THAT WAY THROUGH
MOST OF THE MORNING WITH MID TO HIGH LEVEL CLOUDS LINGERING
THROUGH THE DAY. PATCHY COASTAL FOG IS POSSIBLE AS THE MARINE
LAYER IS SLOWLY DEEPENING TO 1000 FEET. THERE IS STILL A CHANCE OF
LOCAL DRIZZLE POSSIBLE, BUT CONFIDENCE IS LOW AND THEREFORE LEFT
OUT OF THE TAFS. [AVIA]

As the front passes, northwest winds strengthen in the afternoon producing locally strong gusts in addition to a brief period of low-level wind shear. Unidirectional northwest winds will remain through the TAF [Terminal Aerodrome Forecast] period with more inland terminals seeing a reduction in winds Tuesday night into Wednesday morning, where coastal terminals can expect the stronger winds into the morning. Low clouds are expected to mix out by the late afternoon, but high clouds should remain through the evening. ∨

AS THE FRONT PASSES, NORTHWEST WINDS STRENGTHEN IN THE AFTERNOON
PRODUCING LOCALLY STRONG GUSTS IN ADDITION TO A BRIEF PERIOD OF
LLWS. UNIDIRECTIONAL NORTHWEST WINDS WILL REMAIN THROUGH THE TAF
PERIOD WITH MORE INLAND TERMINALS SEEING A REDUCTION IN WINDS
TUESDAY NIGHT INTO WEDNESDAY MORNING, WHERE COASTAL TERMINALS CAN
EXPECT THE STRONGER WINDS INTO THE MORNING. LOW CLOUDS ARE
EXPECTED TO MIX OUT BY THE LATE AFTERNOON, BUT HIGH CLOUDS SHOULD
REMAIN THROUGH THE EVENING. [AVI2]

Vicinity of KSFO [San Francisco CA]… northwest winds remain breezy and producing strong isolated gusts. The western coast of the SF Peninsula has low visibility/ceilings, while near the airport currently sees no impacts to visibility, though ceilings are low. The low clouds will mix out by the early afternoon, but the main story will be the confidence in the northwest wind strengthening and producing strong gusts. Observations will be monitored closely to whether an Airport Weather Warning for winds is needed. There is also a chance for the potential for low-level wind shear tomorrow evening as the surface winds slowly reduce, while high elevation winds remain strong. ∨

VICINITY OF KSFO...NORTHWEST WINDS REMAIN BREEZY AND PRODUCING
STRONG ISOLATED GUSTS. THE WESTERN COAST OF THE SF PENINSULA HAS
LOW VIS/CIGS, WHILE NEAR THE AIRPORT CURRENTLY SEES NO IMPACTS TO
VIS, THOUGH CIGS ARE LOW. THE LOW CLOUDS WILL MIX OUT BY THE EARLY
AFTERNOON, BUT THE MAIN STORY WILL BE THE CONFIDENCE IN THE
NORTHWEST WIND STRENGTHENING AND PRODUCING STRONG GUSTS.
OBSERVATIONS WILL BE MONITORED CLOSELY TO WHETHER AN AIRPORT
WEATHER WARNING FOR WINDS IS NEEDED. THERE IS ALSO A CHANCE FOR
THE POTENTIAL FOR LLWS TOMORROW EVENING AS THE SURFACE WINDS
SLOWLY REDUCE, WHILE HIGH ELEVATION WINDS REMAIN STRONG. [AVI2]

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

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

Monterey Bay terminals… low clouds and ceilings remain over the peninsula with a chance of reduced visibility through the morning hours. Clouds will mix out by late morning/early afternoon. Northwest winds will strengthen Tuesday especially in the afternoon to evening producing strong gusts. As the winds subside Tuesday evening, there is lower confidence regarding the cloud cover near the terminals. Few models are showing minimal chances of drizzle possible while others remain dry with mid level clouds lingering around the Bay. ∨

MONTEREY BAY TERMINALS...LOW CLOUDS AND CIGS REMAIN OVER THE
PENINSULA WITH A CHANCE OF REDUCED VIS THROUGH THE MORNING HOURS.
CLOUDS WILL MIX OUT BY LATE MORNING/EARLY AFTERNOON. NORTHWEST
WINDS WILL STRENGTHEN TUESDAY ESPECIALLY IN THE AFTERNOON TO
EVENING PRODUCING STRONG GUSTS. AS THE WINDS SUBSIDE TUESDAY
EVENING, THERE IS LOWER CONFIDENCE REGARDING THE CLOUD COVER NEAR
THE TERMINALS. FEW MODELS ARE SHOWING MINIMAL CHANCES OF DRIZZLE
POSSIBLE WHILE OTHERS REMAIN DRY WITH MID LEVEL CLOUDS LINGERING
AROUND THE BAY. [AVI2]

Fire weather. As of 3:25am PST Tuesday… no major update on the night shift. Red Flag Warning still remains in effect for the North and East Bay hills/mountains from 4am PST Wednesday through 7am PST Thursday. As mentioned above, N to NE winds will begin to ramp up Tuesday evening. Relative humidity will initially be on the high side, but once the offshore flow kicks in relative humidity will lower by early Wednesday. North to northeast winds of 20–30 mph with gusts of 35–45 mph will be likely over the higher terrain of the North and East Bay, especially on Wednesday night. The usual wind-prone sites (Mt St Helena and Mt Diablo) may possibly experience gusts in excess of 60 mph. While dry conditions will linger into late week, wind speeds will diminish during the day Thursday. ∨

.FIRE WEATHER....AS OF 3:25 AM PST TUESDAY...NO MAJOR UPDATE ON
THE NIGHT SHIFT. RED FLAG WARNING STILL REMAINS IN EFFECT FOR THE
NORTH AND EAST BAY HILLS/MOUNTAINS FROM 4 AM PST WEDNESDAY
THROUGH 7 AM PST THURSDAY. AS MENTIONED ABOVE, N TO NE WINDS WILL
BEGIN TO RAMP UP TUESDAY EVENING. RELATIVE HUMIDITY WILL INITIALLY
BE ON THE HIGH SIDE, BUT ONCE THE OFFSHORE FLOW KICKS IN RELATIVE
HUMIDITY WILL LOWER BY EARLY WEDNESDAY. NORTH TO NORTHEAST WINDS
OF 20 TO 30 MPH WITH GUSTS OF 35 TO 45 MPH WILL BE LIKELY OVER THE
HIGHER TERRAIN OF THE NORTH AND EAST BAY, ESPECIALLY ON WEDNESDAY
NIGHT. THE USUAL WIND-PRONE SITES (MT ST HELENA AND MT DIABLO)
MAY POSSIBLY EXPERIENCE GUSTS IN EXCESS OF 60 MPH. WHILE DRY
CONDITIONS WILL LINGER INTO LATE WEEK, WIND SPEEDS WILL DIMINISH
DURING THE DAY THURSDAY. [AVIA]

Fire weather concerns will return early next week as medium range models suggest another round of offshore flow impacting the region and potentially more widespread. Stay tuned - fire season is definitely not over yet. ∨

FIRE WEATHER CONCERNS WILL RETURN EARLY NEXT WEEK AS MEDIUM RANGE
MODELS SUGGEST ANOTHER ROUND OF OFFSHORE FLOW IMPACTING THE
REGION AND POTENTIALLY MORE WIDESPREAD. STAY TUNED - FIRE SEASON
IS DEFINITELY NOT OVER YET. [AVIA]

Marine. As of 08:54am PST Tuesday… the cold front continues to move southward over the coastal waters this morning. Northwest winds are forecast to increase today with gale force winds developing over the northern outer waters Tuesday evening and into Wednesday. Northwest swell builds and as the northwest winds increase, wind generated waves will also be generated creating large and hazardous seas Tuesday night into Wednesday. Winds and waves will subside Thursday. ∨

.MARINE...AS OF 08:54 AM PST TUESDAY...THE COLD FRONT CONTINUES
TO MOVE SOUTHWARD OVER THE COASTAL WATERS THIS MORNING. NORTHWEST
WINDS ARE FORECAST TO INCREASE TODAY WITH GALE FORCE WINDS
DEVELOPING OVER THE NORTHERN OUTER WATERS TUESDAY EVENING AND INTO
WEDNESDAY. NORTHWEST SWELL BUILDS AND AS THE NORTHWEST WINDS
INCREASE, WIND GENERATED WAVES WILL ALSO BE GENERATED CREATING
LARGE AND HAZARDOUS SEAS TUESDAY NIGHT INTO WEDNESDAY. WINDS AND
WAVES WILL SUBSIDE THURSDAY. [AVIA]

MTR Watches/Warnings/Advisories

Today: Small Craft Advisory…Pigeon Pt [Pescadero CA] to Pt Pinos [Monterey CA] 0–10 nm [11 miles] Small Craft Advisory…Pt Pinos [Monterey CA] to Pt Piedras Blancas [San Simeon CA] 0–10 nm [11 miles] Small Craft Advisory…Pt Arena [Mendocino CA] to Pigeon Pt [Pescadero CA] 10–60 nm [69 miles] until 2pm GLW…Pt Arena [Mendocino CA] to Pigeon Pt [Pescadero CA] 10–60 nm [69 miles] from 2pm Small Craft Advisory…Monterey Bay Small Craft Advisory…Pigeon Pt [Pescadero CA] to Pt Piedras Blancas [San Simeon 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…Pt Reyes [San Francisco CA] to Pigeon Pt [Pescadero CA] 0–10 nm [11 miles] Small Craft Advisory…SF Bay from 2pm ∨

.MTR WATCHES/WARNINGS/ADVISORIES...
.TDAY...SCA...PIGEON PT TO PT PINOS 0-10 NM
SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
SCA...PT ARENA TO PIGEON PT 10-60 NM UNTIL 2 PM
GLW...PT ARENA TO PIGEON PT 10-60 NM FROM 2 PM
SCA...MRY BAY
SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM
SCA...PT ARENA TO PT REYES 0-10 NM
SCA...PT REYES TO PIGEON PT 0-10 NM
SCA...SF BAY FROM 2 PM [WARN]

Public Forecast: Rgass/MM; Aviation: DK; Marine: DRP; Fire Weather: MM ∨

PUBLIC FORECAST: RGASS/MM
AVIATION: DK
MARINE: DRP
FIRE WEATHER: MM [CRED]

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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] 191701 AFDMTR ∨ FXUS66 KMTR 191701 AFDMTR [HEAD] National Weather Service San Francisco Bay Area 9:01am PST Tue Nov 19 2019 ∨ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 901 AM PST TUE NOV 19 2019 [HEAD] Synopsis. A region-wide cooling will occur on Tuesday as a frontal boundary sweeps through the region. Gusty and dry offshore winds will develop over the North and East Bay hills/mountains from late Tuesday night through early Thursday that will consequently result in critical fire weather conditions. Dry conditions, along with seasonable temperatures, are forecast from Thursday through next weekend. ∨ .SYNOPSIS...A REGION-WIDE COOLING WILL OCCUR ON TUESDAY AS A FRONTAL BOUNDARY SWEEPS THROUGH THE REGION. GUSTY AND DRY OFFSHORE WINDS WILL DEVELOP OVER THE NORTH AND EAST BAY HILLS/MOUNTAINS FROM LATE TUESDAY NIGHT THROUGH EARLY THURSDAY THAT WILL CONSEQUENTLY RESULT IN CRITICAL FIRE WEATHER CONDITIONS. DRY CONDITIONS, ALONG WITH SEASONABLE TEMPERATURES, ARE FORECAST FROM THURSDAY THROUGH NEXT WEEKEND. [DISC] Discussion. As of 08:54am PST Tuesday… a frontal boundary continues to push across the region this morning resulting in an increase in northerly winds. Breezy to locally gusty winds, especially near the coast, and cold air advection will limit daytime warming with temperatures only reaching into the 60s for much of the region today. Rain chances persist over the Central Coast later in the day as a secondary boundary associated with a short-wave disturbance slides down the coastline. In wake of this, offshore winds will develop and begin to increase over the North and East Bay. With this said, the ongoing forecast remains on track this morning with no updates necessary at this time. For full details, please see the previous forecast discussion below as well as the fire weather section with regards to the increased fire weather concerns. ∨ .DISCUSSION...AS OF 08:54 AM PST TUESDAY...A FRONTAL BOUNDARY CONTINUES TO PUSH ACROSS THE REGION THIS MORNING RESULTING IN AN INCREASE IN NORTHERLY WINDS. BREEZY TO LOCALLY GUSTY WINDS, ESPECIALLY NEAR THE COAST, AND COLD AIR ADVECTION WILL LIMIT DAYTIME WARMING WITH TEMPERATURES ONLY REACHING INTO THE 60S FOR MUCH OF THE REGION TODAY. RAIN CHANCES PERSIST OVER THE CENTRAL COAST LATER IN THE DAY AS A SECONDARY BOUNDARY ASSOCIATED WITH A SHORT-WAVE DISTURBANCE SLIDES DOWN THE COASTLINE. IN WAKE OF THIS, OFFSHORE WINDS WILL DEVELOP AND BEGIN TO INCREASE OVER THE NORTH AND EAST BAY. WITH THIS SAID, THE ONGOING FORECAST REMAINS ON TRACK THIS MORNING WITH NO UPDATES NECESSARY AT THIS TIME. FOR FULL DETAILS, PLEASE SEE THE PREVIOUS FORECAST DISCUSSION BELOW AS WELL AS THE FIRE WEATHER SECTION WITH REGARDS TO THE INCREASED FIRE WEATHER CONCERNS. [DISC] Previous discussion… as of 3:25am PST Tuesday. Moisture has increased across the region overnight and a cool down is on the way as the weather pattern begins to shift. The longwave pattern aloft shows an amplified pattern with a ridge nosing into the Gulf of Alaska and a trough (with upper low) moving into the Pacific Northwest. The eastward movement of the trough/upper low is being helped by a decent jet Max [point or area of relative maximum wind speeds within a jet stream] diving southward and ultimately rounding the base of the trough. Additionally, as the jet Max [point or area of relative maximum wind speeds within a jet stream] moves south it will help to push a Vort Max [Vorticity Maximum, the highest value of positive vorticity (point location) within a region of positive vorticity] into Southern California with PVA [Positive Vorticity Advection] over the region today into Wednesday. At the surface, a cold front currently bisecting the Bay Area will continue to progress southward early today. The passing front will bring gusty winds over the coastal waters and cooler temperatures. ∨ .PREV DISCUSSION...AS OF 3:25 AM PST TUESDAY...MOISTURE HAS INCREASED ACROSS THE REGION OVERNIGHT AND A COOL DOWN IS ON THE WAY AS THE WEATHER PATTERN BEGINS TO SHIFT. THE LONGWAVE PATTERN ALOFT SHOWS AN AMPLIFIED PATTERN WITH A RIDGE NOSING INTO THE GULF OF ALASKA AND A TROUGH (WITH UPPER LOW) MOVING INTO THE PACNW. THE EASTWARD MOVEMENT OF THE TROUGH/UPPER LOW IS BEING HELPED BY A DECENT JET MAX DIVING SOUTHWARD AND ULTIMATELY ROUNDING THE BASE OF THE TROUGH. ADDITIONALLY, AS THE JET MAX MOVES SOUTH IT WILL HELP TO PUSH A VORT MAX INTO SOCAL WITH PVA OVER THE REGION TODAY INTO WEDNESDAY. AT THE SURFACE, A COLD FRONT CURRENTLY BISECTING THE BAY AREA WILL CONTINUE TO PROGRESS SOUTHWARD EARLY TODAY. THE PASSING FRONT WILL BRING GUSTY WINDS OVER THE COASTAL WATERS AND COOLER TEMPERATURES. [DISC] Forecasted high temperatures are still on track to see a 10–15° drop from Monday to Tuesday. Highs will generally be in the 60s and possibly the 50s over the highest peaks. The aforementioned Vort Max [Vorticity Maximum, the highest value of positive vorticity (point location) within a region of positive vorticity] and associated PVA [Positive Vorticity Advection] will move southward and become a cut off upper low over Southern California Tuesday night into Wednesday. As this area of enhanced lift slides south enough moisture and lift will be present for a chance of pop up showers over the coastal waters and the Big Sur coast. For several runs now, high-resolution WRF [Weather Research and Forecasting model] and HRRR develop showers over the coastal waters/mountains of Big Sur after 4pm Tuesday through early Wednesday. Current forecast will carry scattered showers with some rainfall possible, but chances are still in the 20–30% range. ∨ FORECASTED HIGH TEMPERATURES ARE STILL ON TRACK TO SEE A 10-15 DEGREE DROP FROM MONDAY TO TUESDAY. HIGHS WILL GENERALLY BE IN THE 60S AND POSSIBLY THE 50S OVER THE HIGHEST PEAKS. THE AFOREMENTIONED VORT MAX AND ASSOCIATED PVA WILL MOVE SOUTHWARD AND BECOME A CUT OFF UPPER LOW OVER SOCAL TUESDAY NIGHT INTO WEDNESDAY. AS THIS AREA OF ENHANCED LIFT SLIDES SOUTH ENOUGH MOISTURE AND LIFT WILL BE PRESENT FOR A CHANCE OF POP UP SHOWERS OVER THE COASTAL WATERS AND THE BIG SUR COAST. FOR SEVERAL RUNS NOW, HI-RES WRF AND HRRR DEVELOP SHOWERS OVER THE COASTAL WATERS/MOUNTAINS OF BIG SUR AFTER 4 PM TUESDAY THROUGH EARLY WEDNESDAY. CURRENT FORECAST WILL CARRY SCATTERED SHOWERS WITH SOME RAINFALL POSSIBLE, BUT CHANCES ARE STILL IN THE 20-30% RANGE. [DISC] Of greater concerns is what happens on the backside of the departing upper low to the south. North to northeast winds will develop over the higher terrain of the N and East Bay Tuesday evening, peak early Wednesday and remain breezy to gusty into Thursday. At their peak, winds will be in the 35–45 mph range with top gusts close to 60 mph. The gusty offshore winds will help to set the stage for fire weather concerns. See fire section below for more details. ∨ OF GREATER CONCERNS IS WHAT HAPPENS ON THE BACKSIDE OF THE DEPARTING UPPER LOW TO THE SOUTH. NORTH TO NORTHEAST WINDS WILL DEVELOP OVER THE HIGHER TERRAIN OF THE N AND E BAY TUESDAY EVENING, PEAK EARLY WEDNESDAY AND REMAIN BREEZY TO GUSTY INTO THURSDAY. AT THEIR PEAK, WINDS WILL BE IN THE 35-45 MPH RANGE WITH TOP GUSTS CLOSE TO 60 MPH. THE GUSTY OFFSHORE WINDS WILL HELP TO SET THE STAGE FOR FIRE WEATHER CONCERNS. SEE FIRE SECTION BELOW FOR MORE DETAILS. [DISC] Winds ease on Thursday, but conditions will still remain dry. The 00Z [4pm PST] WRF [Weather Research and Forecasting model] model continues to show a southerly surge creeping up the Big Sur coast on Thursday as the ridge weakens and offshore gradient relaxes. Will have to watch how this scenario evolves, but an increase in clouds/fog along with cooler temperatures could occur. Otherwise, dry weather continues into the weekend with a slight warm up. ∨ WINDS EASE ON THURSDAY, BUT CONDITIONS WILL STILL REMAIN DRY. THE 00Z WRF MODEL CONTINUES TO SHOW A SOUTHERLY SURGE CREEPING UP THE BIG SUR COAST ON THURSDAY AS THE RIDGE WEAKENS AND OFFSHORE GRADIENT RELAXES. WILL HAVE TO WATCH HOW THIS SCENARIO EVOLVES, BUT AN INCREASE IN CLOUDS/FOG ALONG WITH COOLER TEMPERATURES COULD OCCUR. OTHERWISE, DRY WEATHER CONTINUES INTO THE WEEKEND WITH A SLIGHT WARM UP. [DISC] Farther down the road the medium range guidance is once again showing another offshore flow event Earl next week. So what about rain? Details vary, but solutions still show possible precipitation around Thanksgiving. ∨ FARTHER DOWN THE ROAD THE MEDIUM RANGE GUIDANCE IS ONCE AGAIN SHOWING ANOTHER OFFSHORE FLOW EVENT EARL NEXT WEEK. SO WHAT ABOUT RAIN? DETAILS VARY, BUT SOLUTIONS STILL SHOW POSSIBLE PRECIP AROUND THANKSGIVING. [DISC] Aviation. As of 04:00am PST Tuesday… for 12Z [4am PST] TAFs [Terminal Aerodrome Forecasts]. A cold front is pushing through the Central Coast bringing strong northwest winds and a thick cloud deck. Ceilings have lowered to MVFR [Marginal Visual Flight Rules]/IFR [Instrument Flight Rules] conditions and are expected to remain that way through most of the morning with mid to high level clouds lingering through the day. Patchy coastal fog is possible as the marine layer is slowly deepening to 1000 feet. There is still a chance of local drizzle possible, but confidence is low and therefore left out of the TAFs [Terminal Aerodrome Forecasts]. ∨ .AVIATION...AS OF 04:00 AM PST TUESDAY...FOR 12Z TAFS. A COLD FRONT IS PUSHING THROUGH THE CENTRAL COAST BRINGING STRONG NORTHWEST WINDS AND A THICK CLOUD DECK. CIGS HAVE LOWERED TO MVFR/IFR CONDITIONS AND ARE EXPECTED TO REMAIN THAT WAY THROUGH MOST OF THE MORNING WITH MID TO HIGH LEVEL CLOUDS LINGERING THROUGH THE DAY. PATCHY COASTAL FOG IS POSSIBLE AS THE MARINE LAYER IS SLOWLY DEEPENING TO 1000 FEET. THERE IS STILL A CHANCE OF LOCAL DRIZZLE POSSIBLE, BUT CONFIDENCE IS LOW AND THEREFORE LEFT OUT OF THE TAFS. [AVIA] As the front passes, northwest winds strengthen in the afternoon producing locally strong gusts in addition to a brief period of low-level wind shear. Unidirectional northwest winds will remain through the TAF [Terminal Aerodrome Forecast] period with more inland terminals seeing a reduction in winds Tuesday night into Wednesday morning, where coastal terminals can expect the stronger winds into the morning. Low clouds are expected to mix out by the late afternoon, but high clouds should remain through the evening. ∨ AS THE FRONT PASSES, NORTHWEST WINDS STRENGTHEN IN THE AFTERNOON PRODUCING LOCALLY STRONG GUSTS IN ADDITION TO A BRIEF PERIOD OF LLWS. UNIDIRECTIONAL NORTHWEST WINDS WILL REMAIN THROUGH THE TAF PERIOD WITH MORE INLAND TERMINALS SEEING A REDUCTION IN WINDS TUESDAY NIGHT INTO WEDNESDAY MORNING, WHERE COASTAL TERMINALS CAN EXPECT THE STRONGER WINDS INTO THE MORNING. LOW CLOUDS ARE EXPECTED TO MIX OUT BY THE LATE AFTERNOON, BUT HIGH CLOUDS SHOULD REMAIN THROUGH THE EVENING. [AVI2] Vicinity of KSFO [San Francisco CA]… northwest winds remain breezy and producing strong isolated gusts. The western coast of the SF Peninsula has low visibility/ceilings, while near the airport currently sees no impacts to visibility, though ceilings are low. The low clouds will mix out by the early afternoon, but the main story will be the confidence in the northwest wind strengthening and producing strong gusts. Observations will be monitored closely to whether an Airport Weather Warning for winds is needed. There is also a chance for the potential for low-level wind shear tomorrow evening as the surface winds slowly reduce, while high elevation winds remain strong. ∨ VICINITY OF KSFO...NORTHWEST WINDS REMAIN BREEZY AND PRODUCING STRONG ISOLATED GUSTS. THE WESTERN COAST OF THE SF PENINSULA HAS LOW VIS/CIGS, WHILE NEAR THE AIRPORT CURRENTLY SEES NO IMPACTS TO VIS, THOUGH CIGS ARE LOW. THE LOW CLOUDS WILL MIX OUT BY THE EARLY AFTERNOON, BUT THE MAIN STORY WILL BE THE CONFIDENCE IN THE NORTHWEST WIND STRENGTHENING AND PRODUCING STRONG GUSTS. OBSERVATIONS WILL BE MONITORED CLOSELY TO WHETHER AN AIRPORT WEATHER WARNING FOR WINDS IS NEEDED. THERE IS ALSO A CHANCE FOR THE POTENTIAL FOR LLWS TOMORROW EVENING AS THE SURFACE WINDS SLOWLY REDUCE, WHILE HIGH ELEVATION WINDS REMAIN STRONG. [AVI2] SFO [San Francisco CA] bridge approach… similar to KSFO [San Francisco CA]. ∨ SFO BRIDGE APPROACH...SIMILAR TO KSFO. [AVI2] Monterey Bay terminals… low clouds and ceilings remain over the peninsula with a chance of reduced visibility through the morning hours. Clouds will mix out by late morning/early afternoon. Northwest winds will strengthen Tuesday especially in the afternoon to evening producing strong gusts. As the winds subside Tuesday evening, there is lower confidence regarding the cloud cover near the terminals. Few models are showing minimal chances of drizzle possible while others remain dry with mid level clouds lingering around the Bay. ∨ MONTEREY BAY TERMINALS...LOW CLOUDS AND CIGS REMAIN OVER THE PENINSULA WITH A CHANCE OF REDUCED VIS THROUGH THE MORNING HOURS. CLOUDS WILL MIX OUT BY LATE MORNING/EARLY AFTERNOON. NORTHWEST WINDS WILL STRENGTHEN TUESDAY ESPECIALLY IN THE AFTERNOON TO EVENING PRODUCING STRONG GUSTS. AS THE WINDS SUBSIDE TUESDAY EVENING, THERE IS LOWER CONFIDENCE REGARDING THE CLOUD COVER NEAR THE TERMINALS. FEW MODELS ARE SHOWING MINIMAL CHANCES OF DRIZZLE POSSIBLE WHILE OTHERS REMAIN DRY WITH MID LEVEL CLOUDS LINGERING AROUND THE BAY. [AVI2] Fire weather. As of 3:25am PST Tuesday… no major update on the night shift. Red Flag Warning still remains in effect for the North and East Bay hills/mountains from 4am PST Wednesday through 7am PST Thursday. As mentioned above, N to NE winds will begin to ramp up Tuesday evening. Relative humidity will initially be on the high side, but once the offshore flow kicks in relative humidity will lower by early Wednesday. North to northeast winds of 20–30 mph with gusts of 35–45 mph will be likely over the higher terrain of the North and East Bay, especially on Wednesday night. The usual wind-prone sites (Mt St Helena and Mt Diablo) may possibly experience gusts in excess of 60 mph. While dry conditions will linger into late week, wind speeds will diminish during the day Thursday. ∨ .FIRE WEATHER....AS OF 3:25 AM PST TUESDAY...NO MAJOR UPDATE ON THE NIGHT SHIFT. RED FLAG WARNING STILL REMAINS IN EFFECT FOR THE NORTH AND EAST BAY HILLS/MOUNTAINS FROM 4 AM PST WEDNESDAY THROUGH 7 AM PST THURSDAY. AS MENTIONED ABOVE, N TO NE WINDS WILL BEGIN TO RAMP UP TUESDAY EVENING. RELATIVE HUMIDITY WILL INITIALLY BE ON THE HIGH SIDE, BUT ONCE THE OFFSHORE FLOW KICKS IN RELATIVE HUMIDITY WILL LOWER BY EARLY WEDNESDAY. NORTH TO NORTHEAST WINDS OF 20 TO 30 MPH WITH GUSTS OF 35 TO 45 MPH WILL BE LIKELY OVER THE HIGHER TERRAIN OF THE NORTH AND EAST BAY, ESPECIALLY ON WEDNESDAY NIGHT. THE USUAL WIND-PRONE SITES (MT ST HELENA AND MT DIABLO) MAY POSSIBLY EXPERIENCE GUSTS IN EXCESS OF 60 MPH. WHILE DRY CONDITIONS WILL LINGER INTO LATE WEEK, WIND SPEEDS WILL DIMINISH DURING THE DAY THURSDAY. [AVIA] Fire weather concerns will return early next week as medium range models suggest another round of offshore flow impacting the region and potentially more widespread. Stay tuned - fire season is definitely not over yet. ∨ FIRE WEATHER CONCERNS WILL RETURN EARLY NEXT WEEK AS MEDIUM RANGE MODELS SUGGEST ANOTHER ROUND OF OFFSHORE FLOW IMPACTING THE REGION AND POTENTIALLY MORE WIDESPREAD. STAY TUNED - FIRE SEASON IS DEFINITELY NOT OVER YET. [AVIA] Marine. As of 08:54am PST Tuesday… the cold front continues to move southward over the coastal waters this morning. Northwest winds are forecast to increase today with gale force winds developing over the northern outer waters Tuesday evening and into Wednesday. Northwest swell builds and as the northwest winds increase, wind generated waves will also be generated creating large and hazardous seas Tuesday night into Wednesday. Winds and waves will subside Thursday. ∨ .MARINE...AS OF 08:54 AM PST TUESDAY...THE COLD FRONT CONTINUES TO MOVE SOUTHWARD OVER THE COASTAL WATERS THIS MORNING. NORTHWEST WINDS ARE FORECAST TO INCREASE TODAY WITH GALE FORCE WINDS DEVELOPING OVER THE NORTHERN OUTER WATERS TUESDAY EVENING AND INTO WEDNESDAY. NORTHWEST SWELL BUILDS AND AS THE NORTHWEST WINDS INCREASE, WIND GENERATED WAVES WILL ALSO BE GENERATED CREATING LARGE AND HAZARDOUS SEAS TUESDAY NIGHT INTO WEDNESDAY. WINDS AND WAVES WILL SUBSIDE THURSDAY. [AVIA] MTR Watches/Warnings/Advisories Today: Small Craft Advisory…Pigeon Pt [Pescadero CA] to Pt Pinos [Monterey CA] 0–10 nm [11 miles] Small Craft Advisory…Pt Pinos [Monterey CA] to Pt Piedras Blancas [San Simeon CA] 0–10 nm [11 miles] Small Craft Advisory…Pt Arena [Mendocino CA] to Pigeon Pt [Pescadero CA] 10–60 nm [69 miles] until 2pm GLW…Pt Arena [Mendocino CA] to Pigeon Pt [Pescadero CA] 10–60 nm [69 miles] from 2pm Small Craft Advisory…Monterey Bay Small Craft Advisory…Pigeon Pt [Pescadero CA] to Pt Piedras Blancas [San Simeon 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…Pt Reyes [San Francisco CA] to Pigeon Pt [Pescadero CA] 0–10 nm [11 miles] Small Craft Advisory…SF Bay from 2pm ∨ .MTR WATCHES/WARNINGS/ADVISORIES... .TDAY...SCA...PIGEON PT TO PT PINOS 0-10 NM SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM SCA...PT ARENA TO PIGEON PT 10-60 NM UNTIL 2 PM GLW...PT ARENA TO PIGEON PT 10-60 NM FROM 2 PM SCA...MRY BAY SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM SCA...PT ARENA TO PT REYES 0-10 NM SCA...PT REYES TO PIGEON PT 0-10 NM SCA...SF BAY FROM 2 PM [WARN] Public Forecast: Rgass/MM; Aviation: DK; Marine: DRP; Fire Weather: MM ∨ PUBLIC FORECAST: RGASS/MM AVIATION: DK MARINE: DRP FIRE WEATHER: MM [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 19 Nov 8:00am PST Today Partly sunny, with a temperature rising to near 61 by 11am, then falling to around 53 during the remainder of the day. WNW wind 11 to 18 mph, with gusts as high as 24 mph. Tonight Cloudy during the early evening, then gradual clearing, with a low around 48°. NNW wind around 9 mph. Wednesday Sunny, with a high near 64°. North wind 7 to 10 mph. Wednesday Night Clear, with a low around 46°. NE wind 7 to 13 mph. Thursday Sunny, with a high near 62°. NE wind 11 to 16 mph becoming light and variable in the afternoon. Winds could gust as high as 22 mph. Thursday Night Partly cloudy, with a low around 47°. Friday Mostly sunny, with a high near 62°. Friday Night Mostly clear, with a low around 46°. Saturday Sunny, with a high near 64°. Saturday Night Clear, with a low around 45°. Sunday Sunny, with a high near 63°. Sunday Night Mostly clear, with a low around 45°. Monday Mostly sunny, with a high near 63°. Today Partly sunny, with a temperature rising to near 61 by 11am, then falling to around 53 during the remainder of the day. West northwest wind 11 to 18 mph, with gusts as high as 24 mph. Tonight Cloudy during the early evening, then gradual clearing, with a low around 48. North northwest wind around 9 mph. Wednesday Sunny, with a high near 64. North wind 7 to 10 mph. Wednesday Night Clear, with a low around 46. Northeast wind 7 to 13 mph. Thursday Sunny, with a high near 62. Northeast wind 11 to 16 mph becoming light and variable in the afternoon. Winds could gust as high as 22 mph. Thursday Night Partly cloudy, with a low around 47. Friday Mostly sunny, with a high near 62. Friday Night Mostly clear, with a low around 46. Saturday Sunny, with a high near 64. Saturday Night Clear, with a low around 45. Sunday Sunny, with a high near 63. Sunday Night Mostly clear, with a low around 45. Monday Mostly sunny, with a high near 63.
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