Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
Issued by NWS San Francisco Bay Area, CA
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048 FXUS66 KMTR 021117 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 417 AM PDT Thu May 2 2024 ...New AVIATION... .SYNOPSIS... Issued at 307 AM PDT Thu May 2 2024 A ridge of high pressure will keep daytime temperatures mild to warm across the region throughout late week. Breezy onshore winds will keep temperatures cooler near the coast. Wet, unsettled conditions returning Friday night into Saturday, much cooler inland Saturday. Unseasonably cool daytime highs continuing into early next week then gradually warming by the middle of the week. && .SHORT TERM... (Today and tonight) Issued at 349 AM PDT Thu May 2 2024 Dry air, a continental influence is remaining locked in over the forecast area. The northerly 5.9 mb ACV-SFO and 2.6 mb UKI-STS pressure gradients are resulting in dry northerly wind flow, over the coastal waters gale warnings continue. Seeing some increases in water vapor and stratus/fog development over the coastal waters per recent satellite imagery while drier air/clear sky is still prevailing closer to the coastline. A trough moving across northernmost CA/OR will ease the ACV-SFO pressure gradient a little today and tonight, the UKI-STS gradient not really easing until tonight. Lower to mid level ridging continues through tonight. A lower level temperature inversion within 500-800 feet of the surface is seen on the Bodega Bay and Fort Ord profilers. Early May insolation tapping the lower level inversion will bring daytime temperatures back up a few degrees above early May normals inland. It`ll remain cooler along the coast today. Highs 60s coastside, 70s to lower 80s inland. && .LONG TERM... (Friday through Wednesday) Issued at 349 AM PDT Thu May 2 2024 Seeing good global and mesoscale model agreement, one long wave trough is now stationary along the West Coast, part of an unsteady northern hemispheric long wave trough pattern. A low pressure system from the Aleutian Islands will move through the long wave trough and bring rain to our forecast area Friday night and Saturday. Rain developing first over the North Bay Friday night, rain quickly spreading southeastward across much of the rest of the forecast area Saturday. Expect noticeably cooler temperatures especially inland Saturday with daytime highs in the upper 50s to mid 60s, warmest southern interior; daytime temperatures 5F to 15F below early May normals. The low is still expected to brush by and tap higher levels of water vapor extending far north of Hawaii, while retaining a strong mid-latitude influence e.g. it`s an appreciably cold core system up through the 700 mb level by comparison on Oakland upper air climatology, the pool of cold air a little more compact by the 500 mb level. Unlikely there`ll be layer instability extending above 700 mb, forecast 700-500 mb lapse rates are low and much more stable. Recent precipitable water values on the GFS maintain between 1.00" and 1.10" Saturday, not far from the max moving average on Oakland upper air sounding climatology in early May. Seeing some recent increases in model forecast rainfall amounts. For example over 0.50" to 1" rain totals North Bay, near 0.50" low elevations and up to 0.75" to 1" East Bay hills/mountains and the Santa Cruz Mountains, 0.10" to 0.20" interior north Central Coast to around 0.50" Big Sur Coast. The Bay Area and northernmost north Central Coast may receive over half if not nearly May normal precipitation from this system if current QPF verifies. As mentioned expect wet and cooler weather Saturday, gusty northwest winds over the coast temporarily subsiding with the passage of a surface cold front/trough. Chilly to cold overnight low temperatures for the time of year (40s coastside and bayside / 30s inland) are forecast late Saturday night to Sunday morning and Sunday night to Monday morning. San Francisco and Oakland downtown possibly including a few other locations may be nearing record lows Sunday and Monday mornings. Stay tuned to updates, right now Sun-Mon mornings look to be the chilliest. Forecast temperature guidance could edge a little lower between now and late weekend. Otherwise dry weather returns Sunday. The surface pressure pattern favors gusty northwest winds redeveloping over the coastal waters late in the weekend and continuing early next week. Daytime highs gradually warming by the middle of next week. && .AVIATION... (12Z TAFS) Issued at 417 AM PDT Thu May 2 2024 Generally VFR through the afternoon, with breezy northwest winds building through the day, gusting to 20-25 knots this afternoon and evening. Marginal LLWS concerns in the North Bay this evening, but shear magnitudes are too small to include in the TAFs. Expect stratus to fill towards and at the immediate coastline through the evening ans into Friday morning, as a trough approaches the region. Vicinity of SFO... VFR through the TAF period. West-northwest winds building through the day with gusts to 30 knots. A low confidence (20-30% probability) that wind gusts exceed 35 knots at the terminal. Model output shows some stratus streaming through the Golden Gate and San Bruno Gap this evening, but confidence is low, with OAK and SJC having slightly higher probabilities for MVFR-IFR ceilings, noting that "slightly higher" in this case only goes up to 10-20%. SFO Bridge Approach... Similar to SFO. Monterey Bay Terminals... VFR through the afternoon, with westerly winds building through the day, gusting to 25 knots. IFR-LIFR stratus builds at the coast and across the Monterey Bay region this evening, continuing through Friday morning. && .MARINE... (Tonight through next Tuesday) Issued at 226 AM PDT Thu May 2 2024 Strong winds continue through Friday, with gale force gusts of 40 to 45 knots possible. Strong winds will result in hazardous seas and steep wind waves with significant wave heights reaching 12 to 16 feet in the outer waters. Conditions gradually improve over the weekend and into next week as winds begin to ease. Rain chances begin early Saturday as a trough descends over the region. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory from 3 PM Friday to 3 AM PDT Saturday for Mry Bay-SF Bay N of Bay Bridge. Small Craft Advisory from 9 AM this morning to 3 AM PDT Friday for Mry Bay. Gale Warning until 9 PM PDT this evening for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm. Small Craft Advisory until 9 AM PDT this morning for Pigeon Pt to Pt Pinos 0-10 nm. Gale Warning from 9 AM this morning to 3 AM PDT Friday for Pigeon Pt to Pt Pinos 0-10 nm. Gale Warning until 3 AM PDT Friday for Pigeon Pt to Pt Pinos 10- 60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm. && $$ SHORT TERM...Canepa LONG TERM....Canepa AVIATION...DialH MARINE...DialH Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea