Snow showers and snow squalls are likely to develop across the Northeast on Thursday. Lake effect snow will persist downwind of the Great Lakes. An arctic blast will bring frigid temperatures, gusty winds and dangerous wind chills to the Northern Plains before expanding to the South and East. A major winter storm will begin impacting the Southern Plains and Lower Mississippi Valley Friday. Read More >
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919 FXUS66 KMTR 220546 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 946 PM PST Wed Jan 21 2026 ...New AVIATION, MARINE... .KEY MESSAGES... Updated at 116 PM PST Wed Jan 21 2026 - Morning fog across North Bay and East Bay Valleys - Sprinkles or very light rain tonight into Thursday morning across the Central Coast and portions of the Bay Area - Increased offshore wind potential across higher terrain of the North Bay late Friday into Saturday && .UPDATE... Issued at 745 PM PST Wed Jan 21 2026 The 00Z weather balloon found dry air in the low levels beneath a quite deep moist layer. The current cloud deck extends from roughly 13,000 ft to 33,000 ft. The radar is showing some good returns over the water, but the upper level low is basically just spinning in place after being abandoned by the jet stream. There is still a slight chance for some of this light rain to reach the coast and push inland through the night, but it will be battling the dry air below 700 mb. && .SHORT TERM... Issued at 116 PM PST Wed Jan 21 2026 (This afternoon through Thursday) Generally quiet with largely mild conditions this afternoon across the Bay Area and Central Coast. Fog continues to slowly erode at this hour, with predominantly mid/upper level clouds continuing to overspread the area. Our upper low continues churn and WV/RAP mesoanalysis trends indicates that it continues to make it slow trek to the south and east. This is in line with current thinking. Radar imagery this afternoon has shown a couple of brief attempts at a loosely organized bands of what is largely virga/fall streaks. While the trends haven`t been encouraging, satellite imagery indicates still some mid-level cumuliform clouds/instability that may swing to the NE and give us another shot as sprinkles or very light rain after 4pm this evening and continuing through the pre-dawn hours on Thursday and this seems in alignment with latest short term guidance. As noted this morning, PoPs of 20-40% are advertised which remains along the higher end of the near/short term hi-resolution model guidance. Rain amounts at this time are anticipated to average around a few hundredths of an inch with the higher end scenario (10% chance of occuring) advertising a larger QPF footprint (light rain as far as the North Bay) and up to a tenth of an inch across the higher terrain of Central Coast. As the main upper low continues to pivot eastward, subtle 700mb WAA may lift northward through the Central Valley and into the North Bay. While some orographic ascent cannot be ruled out along the eastern slopes of higher terrain, the dry low levels should translate to a low probability for measurable precipitation here, even though radar may look rather ominous. Otherwise, fog, albeit limited due to the cloud cover, may continue overnight and into early Thursday morning. However, additional low level mixing thanks to the elevated wind field make keep the footprint smaller than previous nights. && .LONG TERM... Issued at 116 PM PST Wed Jan 21 2026 (Thursday night through next Tuesday) Thursday evening will feature a subtle PV anomaly will ripple through the Great Basin and help sweep the initial upper low eastward. In its` wake, mid/upper level ridging is forecast. This will promote surface pressure rises across the Great Basin and tighten local MSLP gradients across the region. More importantly, the 925mb flow will increase with even coarser guidance advertising 30-40 knots out of the north through the Sacramento Valley. The synoptic scale background/pattern recognition in tandem with the Extreme Forecast Index (EFI) would suggest an opportunity to alter messaging to advertise a noticeable uptick in winds, largely across the higher terrain of the North Bay and East Bay Hills. 2km PG&E WRF cross sections also indicate the potential for mountain wave type activity near and downwind of Mt. Saint Helena which could help enhance wind gusts. Given the highly localized nature of these phenomenon, have opted for targeted edits across the Mayacamas and higher terrain of the East Bay such that wind gusts reflect a blend of some of the higher end NBM percentiles. While fuel moistures have dried some, ERC values remain safely below critical fire weather thresholds. That said, please always be mindful that winter fuels could still promote some fire growth/smoke production. Overall, the themes in the extended forecast have not changed much. Ridging is anticipated to resume this weekend and largely dominate the weather pattern across the region through the early to middle part of next week. Thereafter, about one-quarter of the multi-model ensemble advertises more vigorous troughing across the Pacific NW. This would dampen out the ridge such that mid/upper level flow becomes more southwesterly, potentially opening the door for a disturbance or two. While the official forecast paints broad PoPs across most areas (minus the far interior Central Coast), there still remains some model variability with some NWP "clusters" indicating little to no chance for precipitation. We`ll continue to delve deeper into the model guidance with time. && .AVIATION... (06Z TAFS) Issued at 925 PM PST Wed Jan 21 2026 MVFR/IFR cigs and visibility are possible in the North Bay early Thursday morning with chances increasing after sunrise, then mixing out by late morning early afternoon. VFR is expected to prevail through the forecast period for terminals in the Bay Area and Monterey Bay. Vicinity of SFO...VFR is expected to prevail through the forecast period, with a slight chance of MVFR cigs from low stratus development around sunrise Thursday morning. Steadier onshore flow returns late in the TAF period, that could result in MVFR cigs just beyond the forecast period. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Weak offshore flow tonight into early Thursday will keep terminals in VFR with a slight chance in MVFR cig development after sunrise Thursday morning, before mixing out by late morning if low stratus develops. VFR for the remainder of the forecast otherwise. && .MARINE... (Tonight through next Tuesday) Issued at 925 PM PST Wed Jan 21 2026 Moderate seas with gentle to moderate breezes will continue through Thursday morning when winds will begin to increase with fresh northerly breezes and building seas into Friday. Near gale force winds from Friday morning through late Friday night over the northern outer waters will result in hazardous conditions for small craft. Seas will begin to gradually ease Saturday afternoon and remain light to moderate into the beginning of next week. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory from 3 PM Thursday to 3 AM PST Saturday for Pt Arena to Pt Reyes 10-60 NM. && $$ SHORT TERM...Bain LONG TERM....Bain AVIATION...JM MARINE...JM Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, X, and YouTube at: www.facebook.com/nwsbayarea x.com/nwsbayarea www.youtube.com/nwsbayarea |
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