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Area Forecast Discussion FXUS66 KMTR [Monterey CA] 180649 AFDMTR ∨ FXUS66 KMTR 180649 AFDMTR [HEAD] National Weather Service San Francisco California 11:49pm PDT Mon Aug 17 2026 ∨ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO CA 1149 PM PDT MON AUG 17 2026 [HEAD] New short term, long term. ∨ ...NEW SHORT TERM, LONG TERM... [DISC] Key Messages… updated at 4:28pm PDT Monday August 17 2026 ∨ .KEY MESSAGES... UPDATED AT 428 PM PDT MON AUG 17 2026 [DISC] - slight warming trend continues through Wednesday ∨ - SLIGHT WARMING TREND CONTINUES THROUGH WEDNESDAY [DISC] - marine layer remains compressed through mid week ∨ - MARINE LAYER REMAINS COMPRESSED THROUGH MID WEEK [DISC] - light winds continue to be mitigating factor for timber fire ∨ - LIGHT WINDS CONTINUE TO BE MITIGATING FACTOR FOR TIMBER FIRE [DISC] Short term. Issued at 11:45pm PDT Monday August 17 2026 (today and tonight) ∨ .SHORT TERM... ISSUED AT 1145 PM PDT MON AUG 17 2026 (TODAY AND TONIGHT) [DISC] Mid/upper level clouds continue to stream from southwest to northeast across our area with mild temperatures expected once again overnight into early Tuesday morning. The mild start to the day will help bump temperatures at least a few degrees (away from the marine layer) higher from Monday's values as the influence from upper level ridging over the Four Corners [intersection of UT, CO, NM & AZ] nudges west. H85 [height of the 850 mb level (nominally 5,000 ft)] temperatures will be around 23–24°C by peak heating which is in the 90th percentile for this time of year. With that, the warmest temperatures will be at higher elevations, especially the East Bay hills and Santa Lucias, including higher portions of the timber fire. Fortunately, light winds continue to be a mitigating factor to more rapid spreading of the fire. ∨ MID/UPPER LEVEL CLOUDS CONTINUE TO STREAM FROM SOUTHWEST TO NORTHEAST ACROSS OUR AREA WITH MILD TEMPERATURES EXPECTED ONCE AGAIN OVERNIGHT INTO EARLY TUESDAY MORNING. THE MILD START TO THE DAY WILL HELP BUMP TEMPERATURES AT LEAST A FEW DEGREES (AWAY FROM THE MARINE LAYER) HIGHER FROM MONDAYS VALUES AS THE INFLUENCE FROM UPPER LEVEL RIDGING OVER THE FOUR CORNERS NUDGES WEST. H85 TEMPERATURES WILL BE AROUND 23-24C BY PEAK HEATING WHICH IS IN THE 90TH PERCENTILE FOR THIS TIME OF YEAR. WITH THAT, THE WARMEST TEMPERATURES WILL BE AT HIGHER ELEVATIONS, ESPECIALLY THE EAST BAY HILLS AND SANTA LUCIAS, INCLUDING HIGHER PORTIONS OF THE TIMBER FIRE. FORTUNATELY, LIGHT WINDS CONTINUE TO BE A MITIGATING FACTOR TO MORE RAPID SPREADING OF THE FIRE. [DISC] Long term. Issued at 11:45pm PDT Monday August 17 2026 (Wednesday through Monday) ∨ .LONG TERM... ISSUED AT 1145 PM PDT MON AUG 17 2026 (WEDNESDAY THROUGH MONDAY) [DISC] Warmer temperatures persist Wednesday under the influence of the aforementioned ridging aloft, however the troughing over the Eastern Pacific pushes back east and slightly north by Thursday with a sharpening trough axis well offshore. The cool down for Thursday through the remainder of the extended forecast will be subtle and gradual. There are at least two tropical waves that will pass well to our south, the first on Thursday followed by a more organized wave with tropical development possible by the end of the weekend into the beginning of next week. We'll be keeping an eye on any midlevel moisture advection north from either of the two waves. ∨ WARMER TEMPERATURES PERSIST WEDNESDAY UNDER THE INFLUENCE OF THE AFOREMENTIONED RIDGING ALOFT, HOWEVER THE TROUGHING OVER THE EPAC PUSHES BACK EAST AND SLIGHTLY NORTH BY THURSDAY WITH A SHARPENING TROUGH AXIS WELL OFFSHORE. THE COOL DOWN FOR THURSDAY THROUGH THE REMAINDER OF THE EXTENDED FORECAST WILL BE SUBTLE AND GRADUAL. THERE ARE AT LEAST TWO TROPICAL WAVES THAT WILL PASS WELL TO OUR SOUTH, THE FIRST ON THURSDAY FOLLOWED BY A MORE ORGANIZED WAVE WITH TROPICAL DEVELOPMENT POSSIBLE BY THE END OF THE WEEKEND INTO THE BEGINNING OF NEXT WEEK. WE`LL BE KEEPING AN EYE ON ANY MIDLEVEL MOISTURE ADVECTION NORTH FROM EITHER OF THE TWO WAVES. [DISC] Aviation. (06Z [11pm PDT] TAFs [Terminal Aerodrome Forecasts]) issued at 9:59pm PDT Monday August 17 2026 ∨ .AVIATION... (06Z TAFS) ISSUED AT 959 PM PDT MON AUG 17 2026 [AVIA] IFR [Instrument Flight Rules]-LIFR [Low Instrument Flight Rules] stratus is expanding inland with high clouds making it difficult to gauge the extent of the stratus deck in several areas across the North Bay and SF Bay regions, while a moderate northwest breeze persists for a couple more hours. Stratus will generally impact most of the terminals through the overnight period with low confidence of impacts at Livermore. May need to monitor observations to see if the high clouds result in impaired stratus development at STS [Santa Rosa CA]. Stratus will mix out back to the coastal regions on Tuesday morning, with gentle to moderate onshore breezes developing in the afternoon and evening. Tuesday night, expect lower ceilings and less inland stratus development near and beyond the end of the TAF [Terminal Aerodrome Forecast] period as the marine layer continues to compress. ∨ IFR-LIFR STRATUS IS EXPANDING INLAND WITH HIGH CLOUDS MAKING IT DIFFICULT TO GAUGE THE EXTENT OF THE STRATUS DECK IN SEVERAL AREAS ACROSS THE NORTH BAY AND SF BAY REGIONS, WHILE A MODERATE NORTHWEST BREEZE PERSISTS FOR A COUPLE MORE HOURS. STRATUS WILL GENERALLY IMPACT MOST OF THE TERMINALS THROUGH THE OVERNIGHT PERIOD WITH LOW CONFIDENCE OF IMPACTS AT LVK. MAY NEED TO MONITOR OBSERVATIONS TO SEE IF THE HIGH CLOUDS RESULT IN IMPAIRED STRATUS DEVELOPMENT AT STS. STRATUS WILL MIX OUT BACK TO THE COASTAL REGIONS ON TUESDAY MORNING, WITH GENTLE TO MODERATE ONSHORE BREEZES DEVELOPING IN THE AFTERNOON AND EVENING. TUESDAY NIGHT, EXPECT LOWER CEILINGS AND LESS INLAND STRATUS DEVELOPMENT NEAR AND BEYOND THE END OF THE TAF PERIOD AS THE MARINE LAYER CONTINUES TO COMPRESS. [AVI2] Vicinity of SFO [San Francisco CA]… IFR [Instrument Flight Rules] stratus continues through the night with lingering moderate winds diminishing in the next couple of hours. The stratus deck will mix out on Tuesday morning with breezy northwest winds resuming in the afternoon. Tuesday night, the terminal area sits at the edge of where high resolution model output paints the stratus deck, making the forecast for stratus impacts and development time low to moderate confidence. ∨ VICINITY OF SFO... IFR STRATUS CONTINUES THROUGH THE NIGHT WITH LINGERING MODERATE WINDS DIMINISHING IN THE NEXT COUPLE OF HOURS. THE STRATUS DECK WILL MIX OUT ON TUESDAY MORNING WITH BREEZY NORTHWEST WINDS RESUMING IN THE AFTERNOON. TUESDAY NIGHT, THE TERMINAL AREA SITS AT THE EDGE OF WHERE HIGH RESOLUTION MODEL OUTPUT PAINTS THE STRATUS DECK, MAKING THE FORECAST FOR STRATUS IMPACTS AND DEVELOPMENT TIME LOW TO MODERATE CONFIDENCE. [AVI2] SFO [San Francisco CA] bridge approach… lower confidence for stratus impacts on Tuesday night compared to the terminal area. Otherwise similar to SFO [San Francisco CA]. ∨ SFO BRIDGE APPROACH... LOWER CONFIDENCE FOR STRATUS IMPACTS ON TUESDAY NIGHT COMPARED TO THE TERMINAL AREA. OTHERWISE SIMILAR TO SFO. [AVI2] Monterey Bay terminals… IFR [Instrument Flight Rules] stratus has developed across the region with a decrease to LIFR [Low Instrument Flight Rules] ceilings expected through the night. The stratus will mix out through Tuesday morning, with some uncertainty on clearing times. Moderate confidence that MRY [Monterey CA] will scatter out sometime Tuesday afternoon. Light winds will persist through Tuesday morning before gentle to moderate northwest winds resume in the afternoon and evening. Opted for a persistence forecast for IFR [Instrument Flight Rules]-LIFR [Low Instrument Flight Rules] stratus returning to the terminals early Tuesday evening. ∨ MONTEREY BAY TERMINALS... IFR STRATUS HAS DEVELOPED ACROSS THE REGION WITH A DECREASE TO LIFR CEILINGS EXPECTED THROUGH THE NIGHT. THE STRATUS WILL MIX OUT THROUGH TUESDAY MORNING, WITH SOME UNCERTAINTY ON CLEARING TIMES. MODERATE CONFIDENCE THAT MRY WILL SCATTER OUT SOMETIME TUESDAY AFTERNOON. LIGHT WINDS WILL PERSIST THROUGH TUESDAY MORNING BEFORE GENTLE TO MODERATE NORTHWEST WINDS RESUME IN THE AFTERNOON AND EVENING. OPTED FOR A PERSISTENCE FORECAST FOR IFR-LIFR STRATUS RETURNING TO THE TERMINALS EARLY TUESDAY EVENING. [AVI2] Marine. (tonight through next Sunday) issued at 9:14pm PDT Monday August 17 2026 ∨ .MARINE... (TONIGHT THROUGH NEXT SUNDAY) ISSUED AT 914 PM PDT MON AUG 17 2026 [AVIA] A fresh to strong northwest breeze will develop tonight and persist through the end of the forecast period. Locally stronger winds are possible in the coastal jet regions north of Point Reyes [San Francisco CA] and along the Big Sur coast. Seas build to 7–9 feet by Tuesday and Wednesday before subsiding later in the week. ∨ A FRESH TO STRONG NORTHWEST BREEZE WILL DEVELOP TONIGHT AND PERSIST THROUGH THE END OF THE FORECAST PERIOD. LOCALLY STRONGER WINDS ARE POSSIBLE IN THE COASTAL JET REGIONS NORTH OF POINT REYES AND ALONG THE BIG SUR COAST. SEAS BUILD TO 7 TO 9 FEET BY TUESDAY AND WEDNESDAY BEFORE SUBSIDING LATER IN THE WEEK. [AVI2] Fire weather. Issued at 2:00pm PDT Monday August 17 2026 ∨ .FIRE WEATHER... ISSUED AT 200 PM PDT MON AUG 17 2026 [AVIA] The marine layer will gradually compress over the next 24–36 hours, as high pressure builds over the region. As a result, nocturnal drying will be possible through at least mid-week for the higher elevations, with more widespread fair to moderate recoveries developing over the higher elevations, especially in and around the timber fire. ∨ THE MARINE LAYER WILL GRADUALLY COMPRESS OVER THE NEXT 24 TO 36 HOURS, AS HIGH PRESSURE BUILDS OVER THE REGION. AS A RESULT, NOCTURNAL DRYING WILL BE POSSIBLE THROUGH AT LEAST MID-WEEK FOR THE HIGHER ELEVATIONS, WITH MORE WIDESPREAD FAIR TO MODERATE RECOVERIES DEVELOPING OVER THE HIGHER ELEVATIONS, ESPECIALLY IN AND AROUND THE TIMBER FIRE. [AVI2] MTR Watches/Warnings/Advisories
.MTR WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...SMALL CRAFT ADVISORY FROM 3 AM TUESDAY TO 3 AM PDT WEDNESDAY FOR PT ARENA TO PT REYES 10-60 NM. [WARN]
SHORT TERM...JM LONG TERM....JM AVIATION...DIALH MARINE...DIALH [WRN2] VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO [LINK] Follow us on Facebook, x, and YouTube at: www.facebook.com/nwsbayarea x.com/nwsbayarea www.youtube.com/nwsbayarea ∨ FOLLOW US ON FACEBOOK, X, AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSBAYAREA X.COM/NWSBAYAREA WWW.YOUTUBE.COM/NWSBAYAREA [DISC] |
Point Forecast Half Moon Bay CA 18 Aug 03:15am PDT Today Patchy fog before 8am. Otherwise, cloudy, then gradually becoming mostly sunny, with a high near 67°. Calm wind becoming west 5 to 8 mph in the morning. Tonight Patchy fog after 4am. Otherwise, mostly cloudy, with a low around 54°. West wind around 5 mph becoming calm in the evening. Wednesday Patchy fog before 8am. Otherwise, cloudy through mid morning, then becoming mostly sunny, with a high near 64°. Calm wind becoming west 5 to 8 mph in the afternoon. Wednesday Night Mostly cloudy, with a low around 54°. West wind 3 to 8 mph. Thursday Mostly cloudy, with a high near 63°. Light west wind becoming WNW 5 to 9 mph in the morning. Thursday Night Cloudy, with a low around 54°. Friday Mostly cloudy, with a high near 61°. Friday Night Mostly cloudy, with a low around 53°. Saturday Mostly cloudy, with a high near 62°. Saturday Night Mostly cloudy, with a low around 53°. Sunday Mostly cloudy, with a high near 62°. Sunday Night Mostly cloudy, with a low around 53°. Monday Mostly cloudy, with a high near 61°. Today Patchy fog before 8am. Otherwise, cloudy, then gradually becoming mostly sunny, with a high near 67. Calm wind becoming west 5 to 8 mph in the morning. Tonight Patchy fog after 4am. Otherwise, mostly cloudy, with a low around 54. West wind around 5 mph becoming calm in the evening. Wednesday Patchy fog before 8am. Otherwise, cloudy through mid morning, then becoming mostly sunny, with a high near 64. Calm wind becoming west 5 to 8 mph in the afternoon. Wednesday Night Mostly cloudy, with a low around 54. West wind 3 to 8 mph. Thursday Mostly cloudy, with a high near 63. Light west wind becoming west northwest 5 to 9 mph in the morning. Thursday Night Cloudy, with a low around 54. Friday Mostly cloudy, with a high near 61. Friday Night Mostly cloudy, with a low around 53. Saturday Mostly cloudy, with a high near 62. Saturday Night Mostly cloudy, with a low around 53. Sunday Mostly cloudy, with a high near 62. Sunday Night Mostly cloudy, with a low around 53. Monday Mostly cloudy, with a high near 61. |
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