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FXUS66 KMTR [Monterey CA] 221850 AFDMTR 

FXUS66 KMTR 221850
AFDMTR [HEAD]

National Weather Service San Francisco Bay Area 11:50am PDT Sat Sep 22 2018 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
1150 AM PDT SAT SEP 22 2018 [HEAD]

Synopsis. Marine layer stays in place along the coast the rest of Saturday into Sunday morning as another upper trough approaches and keeps temperatures on the cool side of normal. As that features moves inland high pressure builds Sunday night through most of next week. This will bring a noted warming trend with fire weather concerns for the North Bay hills early in the week. Temperatures may cool again by about Friday as an upper trough moves inland. 

.SYNOPSIS...MARINE LAYER STAYS IN PLACE ALONG THE COAST THE REST
OF SATURDAY INTO SUNDAY MORNING AS ANOTHER UPPER TROUGH APPROACHES
AND KEEPS TEMPERATURES ON THE COOL SIDE OF NORMAL. AS THAT
FEATURES MOVES INLAND HIGH PRESSURE BUILDS SUNDAY NIGHT THROUGH
MOST OF NEXT WEEK. THIS WILL BRING A NOTED WARMING TREND WITH FIRE
WEATHER CONCERNS FOR THE NORTH BAY HILLS EARLY IN THE WEEK.
TEMPERATURES MAY COOL AGAIN BY ABOUT FRIDAY AS AN UPPER TROUGH
MOVES INLAND. [DISC]

Discussion. As of 11:50am PDT Saturday… Fire Weather Watch was issued earlier this morning for the North Bay mountains to be in effect from 11pm Sunday through Tuesday. In the short term the marine layer remains around 1400 feet along the coast with lunch time trends showing most inland areas running about 10° cooler than yesterday while smaller cooling trends are noted at the coast. Look for mostly sunny and pleasant weather inland this afternoon as the sun works its magic with afternoon readings back into the 70s to near 80. 

.DISCUSSION...AS OF 11:50 AM PDT SATURDAY...FIRE WEATHER WATCH
WAS ISSUED EARLIER THIS MORNING FOR THE NORTH BAY MOUNTAINS TO BE
IN EFFECT FROM 11 PM SUNDAY THROUGH TUESDAY. IN THE SHORT TERM THE
MARINE LAYER REMAINS AROUND 1400 FEET ALONG THE COAST WITH LUNCH
TIME TRENDS SHOWING MOST INLAND AREAS RUNNING ABOUT 10 DEGREES
COOLER THAN YESTERDAY WHILE SMALLER COOLING TRENDS ARE NOTED AT
THE COAST. LOOK FOR MOSTLY SUNNY AND PLEASANT WEATHER INLAND THIS
AFTERNOON AS THE SUN WORKS ITS MAGIC WITH AFTERNOON READINGS BACK
INTO THE 70S TO NEAR 80. [DISC]

Incoming upper trough over Oregon will keep the marine layer in place overnight and allow it to potentially deepen some as it spreads into the bays overnight. Slightly deeper marine layer should mean less fog Sunday morning but perhaps more drizzle along the coastal slopes. Skies may be slightly slower to clear on Sunday with a deeper marine layer but still expect mostly sunny and seasonable temps for the second half of the weekend with most inland areas back into the 70s. 

INCOMING UPPER TROUGH OVER OREGON WILL KEEP THE MARINE LAYER IN
PLACE OVERNIGHT AND ALLOW IT TO POTENTIALLY DEEPEN SOME AS IT
SPREADS INTO THE BAYS OVERNIGHT. SLIGHTLY DEEPER MARINE LAYER
SHOULD MEAN LESS FOG SUNDAY MORNING BUT PERHAPS MORE DRIZZLE
ALONG THE COASTAL SLOPES. SKIES MAY BE SLIGHTLY SLOWER TO CLEAR
ON SUNDAY WITH A DEEPER MARINE LAYER BUT STILL EXPECT MOSTLY SUNNY
AND SEASONABLE TEMPS FOR THE SECOND HALF OF THE WEEKEND WITH MOST
INLAND AREAS BACK INTO THE 70S. [DISC]

Main forecast item of impact will be developing north winds after sunset Sunday night. Looks like initial shot of winds will reach northern Napa County before midnight. Impacts will be fire weather related and for now the Fire Weather Watch has been hoisted. As north winds continue into early Monday morning over Napa County the humidity values will decrease. Wind speeds look only moderate over the hills with sustained 10–20 mph and gusts in the 35 mph range. So it's a marginal event but warranted given the dry state of fuels, time of year and duration of the event. Winds will ease on Monday but humidity will continue to lower as temperatures warm into the 80s and 90s under a classic fall offshore wind pattern. Latest NAM [North American Meso (formerly Eta) model] solutions show a second burst of winds late Monday night into Tuesday morning with humidity values showing no recovery and likely hovering around 15% for much of Monday night/early Tuesday morning. Winds will ease on Tuesday but the watch remains in place through the daytime burn period as hot temps and low humidity will continue. 

MAIN FORECAST ITEM OF IMPACT WILL BE DEVELOPING NORTH WINDS AFTER
SUNSET SUNDAY NIGHT. LOOKS LIKE INITIAL SHOT OF WINDS WILL REACH
NORTHERN NAPA COUNTY BEFORE MIDNIGHT. IMPACTS WILL BE FIRE WEATHER
RELATED AND FOR NOW THE FIRE WEATHER WATCH HAS BEEN HOISTED. AS
NORTH WINDS CONTINUE INTO EARLY MONDAY MORNING OVER NAPA COUNTY
THE HUMIDITY VALUES WILL DECREASE. WIND SPEEDS LOOK ONLY MODERATE
OVER THE HILLS WITH SUSTAINED 10-20 MPH AND GUSTS IN THE 35 MPH
RANGE. SO ITS A MARGINAL EVENT BUT WARRANTED GIVEN THE DRY STATE
OF FUELS, TIME OF YEAR AND DURATION OF THE EVENT. WINDS WILL EASE
ON MONDAY BUT HUMIDITY WILL CONTINUE TO LOWER AS TEMPERATURES
WARM INTO THE 80S AND 90S UNDER A CLASSIC FALL OFFSHORE WIND
PATTERN. LATEST NAM SOLUTIONS SHOW A SECOND BURST OF WINDS LATE
MONDAY NIGHT INTO TUESDAY MORNING WITH HUMIDITY VALUES SHOWING NO
RECOVERY AND LIKELY HOVERING AROUND 15% FOR MUCH OF MONDAY
NIGHT/EARLY TUESDAY MORNING. WINDS WILL EASE ON TUESDAY BUT THE
WATCH REMAINS IN PLACE THROUGH THE DAYTIME BURN PERIOD AS HOT
TEMPS AND LOW HUMIDITY WILL CONTINUE. [DISC]

Public forecast will show seasonably warm/hot temps Tuesday and Wednesday with thermal trough along the coast and light offshore flow. Coastal highs in the 70s with lots of 80s and lower 90s inland. The pattern may break down late Thursday or Friday as an upper trough approaches the coast. 

PUBLIC FORECAST WILL SHOW SEASONABLY WARM/HOT TEMPS TUESDAY AND
WEDS WITH THERMAL TROUGH ALONG THE COAST AND LIGHT OFFSHORE FLOW.
COASTAL HIGHS IN THE 70S WITH LOTS OF 80S AND LOWER 90S INLAND.
THE PATTERN MAY BREAK DOWN LATE THURSDAY OR FRIDAY AS AN UPPER
TROUGH APPROACHES THE COAST. [DISC]

Aviation. As of 11:10am PDT Saturday… marine intrusion that brought widespread VLIFR [Very Low Instrument Flight Rules]-IFR [Instrument Flight Rules] ceilings throughout the region has retreated away from all terminals late this afternoon. Widespread stratus remains parked along the coast and in the South Bay which may impact some approaches, but generally seeing VFR [Visual Flight Rules] everywhere as of 11am. Expect to see some passing high clouds arrive from the north through the day. Breezy onshore winds will develop near the coast and through coastal gaps through the mid afternoon through early evening. Early return is a definite possibility for many terminals tonight if the layer does not fully mix out by the early afternoon. Will monitor and update TAFs [Terminal Aerodrome Forecasts] accordingly. 

.AVIATION...AS OF 11:10 AM PDT SATURDAY... MARINE INTRUSION THAT
BROUGHT WIDESPREAD VLIFR-IFR CIGS THROUGHOUT THE REGION HAS
RETREATED AWAY FROM ALL TERMINALS LATE THIS AFTERNOON. WIDESPREAD
STRATUS REMAINS PARKED ALONG THE COAST AND IN THE SOUTH BAY WHICH
MAY IMPACT SOME APPROACHES, BUT GENERALLY SEEING VFR EVERYWHERE AS
OF 11AM. EXPECT TO SEE SOME PASSING HIGH CLOUDS ARRIVE FROM THE
NORTH THROUGH THE DAY. BREEZY ONSHORE WINDS WILL DEVELOP NEAR THE
COAST AND THROUGH COASTAL GAPS THROUGH THE MID AFTERNOON THROUGH
EARLY EVENING. EARLY RETURN IS A DEFINITE POSSIBILITY FOR MANY
TERMINALS TONIGHT IF THE LAYER DOES NOT FULLY MIX OUT BY THE EARLY
AFTERNOON.  WILL MONITOR AND UPDATE TAFS ACCORDINGLY. [AVIA]

Vicinity of KSFO [San Francisco CA]VFR [Visual Flight Rules] with some impacts to approach through the next hour or two due to lingering low clouds near SMB. Breezy afternoon winds. IFR [Instrument Flight Rules] clouds will attempt to return overnight through tomorrow morning. 

VICINITY OF KSFO...VFR WITH SOME IMPACTS TO APPROACH THROUGH THE
NEXT HOUR OR TWO DUE TO LINGERING LOW CLOUDS NEAR SMB. BREEZY
AFTERNOON WINDS. IFR CLOUDS WILL ATTEMPT TO RETURN OVERNIGHT
THROUGH TOMORROW MORNING. [AVI2]

SFO [San Francisco CA] bridge approach… same as terminal. 

SFO BRIDGE APPROACH...SAME AS TERMINAL. [AVI2]

Monterey Bay terminals… VFR [Visual Flight Rules] through day with chance of early return in the 02–04Z [7–9pm PDT] Sun timeframe. Light to breezy onshore winds by the afternoon, weakening overnight. LIFR [Low Instrument Flight Rules] to IFR [Instrument Flight Rules] ceilings with patchy dense fog possible again tomorrow morning. 

MONTEREY BAY TERMINALS...VFR THROUGH DAY WITH CHANCE OF EARLY
RETURN IN THE 02-04Z SUN TIMEFRAME. LIGHT TO BREEZY ONSHORE WINDS
BY THE AFTERNOON, WEAKENING OVERNIGHT. LIFR TO IFR CIGS WITH
PATCHY DENSE FOG POSSIBLE AGAIN TOMORROW MORNING. [AVI2]

Fire weather. As of 10:49am PDT Saturday… Fire Weather Watch has been issued for the North Bay mountains from 11pm Sunday night through Tuesday afternoon. North winds reach Napa County late Sunday then drive humidity lower during the pre-dawn hours of Monday. Event looks moderate but confidence is pretty high on pattern developing. Fuels remain critically dry. Winds probably not strong enough to bring major wind damage but any new starts will likely move with any wind, lowering humidity and dry fuels. Biggest threat area looks to be Napa County hills, northeast Sonoma County and around Mt Tam. Winds will ease during the day Monday as temperatures warm up into the upper 80s and 90s inland. 

.FIRE WEATHER...AS OF 10:49 AM PDT SATURDAY...FIRE WEATHER WATCH
HAS BEEN ISSUED FOR THE NORTH BAY MOUNTAINS FROM 11 PM SUNDAY
NIGHT THROUGH TUESDAY AFTERNOON. NORTH WINDS REACH NAPA COUNTY
LATE SUNDAY THEN DRIVE HUMIDITY LOWER DURING THE PRE-DAWN HOURS OF
MONDAY. EVENT LOOKS MODERATE BUT CONFIDENCE IS PRETTY HIGH ON
PATTERN DEVELOPING. FUELS REMAIN CRITICALLY DRY. WINDS PROBABLY
NOT STRONG ENOUGH TO BRING MAJOR WIND DAMAGE BUT ANY NEW STARTS
WILL LIKELY MOVE WITH ANY WIND, LOWERING HUMIDITY AND DRY FUELS.
BIGGEST THREAT AREA LOOKS TO BE NAPA COUNTY HILLS, NORTHEAST
SONOMA COUNTY AND AROUND MT TAM. WINDS WILL EASE DURING THE DAY
MONDAY AS TEMPERATURES WARM UP INTO THE UPPER 80S AND 90S INLAND. [AVIA]

A second shot of dry northeast winds is now shown in the NAM [North American Meso (formerly Eta) model] solutions at 925 mb. Thus expect more winds Monday night into early Tuesday with even drier humidity (well under 30% overnight). Continued warm/hot day inland on Tuesday with winds easing. Pattern remains warm and dry for much of next week. 

A SECOND SHOT OF DRY NORTHEAST WINDS IS NOW SHOWN IN THE NAM
SOLUTIONS AT 925 MB. THUS EXPECT MORE WINDS MONDAY NIGHT INTO
EARLY TUESDAY WITH EVEN DRIER HUMIDITY (WELL UNDER 30% OVERNIGHT).
CONTINUED WARM/HOT DAY INLAND ON TUESDAY WITH WINDS EASING.
PATTERN REMAINS WARM AND DRY FOR MUCH OF NEXT WEEK. [AVI2]

Marine. As of 9:00am PDT Saturday… the wind flow shifts today, becoming prevailing northwesterly across the entire waters. The strongest winds are expected to be in the outer waters north of Point Reyes [San Francisco CA] this morning before spreading southward through the weekend. Seas mixed today. Predominately a lower period, light to moderate height northwest swell with a very weak southerly swell mixed in. 

.MARINE...AS OF 9:00 AM PDT SATURDAY...THE WIND FLOW SHIFTS
TODAY, BECOMING PREVAILING NORTHWESTERLY ACROSS THE ENTIRE WATERS.
THE STRONGEST WINDS ARE EXPECTED TO BE IN THE OUTER WATERS NORTH
OF POINT REYES THIS MORNING BEFORE SPREADING SOUTHWARD THROUGH THE
WEEKEND. SEAS MIXED TODAY. PREDOMINATELY A LOWER PERIOD, LIGHT TO
MODERATE HEIGHT NORTHWEST  SWELL WITH A VERY WEAK SOUTHERLY SWELL
MIXED IN. [AVIA]

MTR Watches/Warnings/Advisories

.MTR WATCHES/WARNINGS/ADVISORIES...
.TNGT...SCA...PT ARENA TO PIGEON PT 10-60 NM
SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM FROM 3 AM
SCA...PT REYES TO PIGEON PT 0-10 NM
SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM
SCA...PT ARENA TO PT REYES 0-10 NM
SCA...SF BAY UNTIL 11 PM [WARN]

Public Forecast: RWW; Aviation: DRP; Marine: DRP; Fire Weather: RWW 

PUBLIC FORECAST: RWW
AVIATION: DRP
MARINE: DRP
FIRE WEATHER: RWW [CRED]
VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO [LINK]

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Point Forecast

Half Moon Bay Airport

22 Sep 2:15pm PDT

This Afternoon Mostly sunny, with a high near 62°. NW wind around 11 mph.
Tonight Patchy fog after 11pm. Otherwise, increasing clouds, with a low around 52°. NW wind 6 to 11 mph becoming light WNW after midnight.
Sunday Patchy fog before 11am. Otherwise, cloudy, then gradually becoming mostly sunny, with a high near 61°. Light WNW wind becoming NW 9 to 14 mph in the morning.
Sunday Night Patchy fog after 11pm. Otherwise, mostly cloudy, then gradually becoming clear, with a low around 51°. NW wind 9 to 14 mph becoming light and variable in the evening.
Monday Sunny, with a high near 69°. SSW wind around 6 mph.
Monday Night Mostly clear, with a low around 53°.
Tuesday Sunny, with a high near 73°.
Tuesday Night Mostly clear, with a low around 54°.
Wednesday Sunny, with a high near 73°.
Wednesday Night Patchy fog after 11pm. Otherwise, mostly cloudy, with a low around 54°.
Thursday Patchy fog. Otherwise, mostly sunny, with a high near 69°.
Thursday Night Patchy fog. Otherwise, mostly cloudy, with a low around 54°.
Friday Patchy fog. Otherwise, mostly sunny, with a high near 66°.
This Afternoon
Mostly sunny, with a high near 62. Northwest wind around 11 mph.
Tonight
Patchy fog after 11pm. Otherwise, increasing clouds, with a low around 52. Northwest wind 6 to 11 mph becoming light west northwest after midnight.
Sunday
Patchy fog before 11am. Otherwise, cloudy, then gradually becoming mostly sunny, with a high near 61. Light west northwest wind becoming northwest 9 to 14 mph in the morning.
Sunday Night
Patchy fog after 11pm. Otherwise, mostly cloudy, then gradually becoming clear, with a low around 51. Northwest wind 9 to 14 mph becoming light and variable in the evening.
Monday
Sunny, with a high near 69. South southwest wind around 6 mph.
Monday Night
Mostly clear, with a low around 53.
Tuesday
Sunny, with a high near 73.
Tuesday Night
Mostly clear, with a low around 54.
Wednesday
Sunny, with a high near 73.
Wednesday Night
Patchy fog after 11pm. Otherwise, mostly cloudy, with a low around 54.
Thursday
Patchy fog. Otherwise, mostly sunny, with a high near 69.
Thursday Night
Patchy fog. Otherwise, mostly cloudy, with a low around 54.
Friday
Patchy fog. Otherwise, mostly sunny, with a high near 66.

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: