A storm system near the Hawaiian Islands is expected to bring periods of heavy rainfall, strong winds, and isolated strong to severe thunderstorms through Friday. Several rounds of severe thunderstorms are forecast to impact parts of the Great Plains into the Midwest this weekend into next week. Moderate to heavy rainfall and high elevation snow is expected this weekend over California and Oregon. Read More >
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237 FXUS66 KMTR 100503 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 1003 PM PDT Thu Apr 9 2026 ...New AVIATION, MARINE... .KEY MESSAGES... Updated at 1134 AM PDT Thu Apr 9 2026 - Widespread rain showers and thunderstorms this weekend && .SHORT TERM... Issued at 1134 AM PDT Thu Apr 9 2026 (This afternoon through Friday) The sky is chaotic over the Bay Area, filled with marine layer stratus, mid level cumulus, and high level cirrus all stacked on top of each other with sunbreaks in between. The cut-off low is now 450 miles due west of the Monterey Peninsula and has picked up some speed, now moving at about 15 mph to the West. This system will continue at a similar speed and direction for the next 24 hours, before it starts to feel the effects of the jet stream, opens up into a wave and moves inland to Northern California. While the sun will come out at times this afternoon, conditions will be cooler than the last couple days, and noticeably more humid. Dew points are in the mid 50s, with 100% relative humidity observed across the majority of cwa in this morning. This humid air is thanks to SW winds ahead of the cut-off low pumping tropical moisture into California. The PW has remained over 0.9" for the last 3 balloon launches going back to Wednesday morning. Shower and thunderstorm chances will start later today, but mainly confined to the North Bay. More widespread rain is expected by Friday morning. The low pressure system will make landfall somewhere along the coast in far northern California, bringing a pseudo-cold front to the Bay Area. High resolution models are starting simulate this first band of rain and the consensus is for an organized, but somewhat weak initial push of showers moving through from around 2 AM to 9 AM Friday before showers become more isolated through the day. Despite the isolated nature of the showers, there is still a 20% chance for thunderstorms in the afternoon, though most of the activity is expected in the Central Valley and across the Sierra. All told we expect less than 1/4 inch on Friday. && .LONG TERM... Issued at 1134 AM PDT Thu Apr 9 2026 (Friday night through next Wednesday) If the rain on Friday leaves you unimpressed, wait until the weekend is over before putting your rain boots back in the attic. A reinforcing short wave trough will move quickly down from the Gulf of Alaska, colliding and merging with the pre-existing cut- off low and associated moisture. This convergence is expected in the afternoon or early evening, which is when the peak of the storm activity will arrive to the Bay Area and Central Coast. This frontal passage will also serve as a lifting mechanism for convection, which is arriving at a good time of day to capitalize on the maximum surface based instability generated from afternoon insolation. The combination of low-level moisture left over from the tropical air mass advection, instability from relatively warm surface temperatures quickly cooling with height (850 mb temperatures near freezing), and a lifting mechanism from the cold front, are all favorable for thunderstorms to develop Saturday afternoon/evening. The addition of wind shear delivered from the jet stream allows these storms to separate updrafts and downdrafts, prolonging their lifespan. If we get enough low-level shear we could even see some rotating thunderstorms, and we can`t rule out a weak waterspout or even brief tornado. Anglers should take special note of the expected weather and have a plan to reach safe harbor quickly when the weather turns. Even without thunderstorms, the marine conditions will deteriorate through the day Saturday. If thunderstorms develop, the associated wind gusts are capable of capsizing small vessels. Fishing leads to more lightning deaths in the U.S. than any other activity. When thunder roars, head indoors! One change to the forecast is that Sunday now looks more active. It should still be a transition day as high pressure starts to rebuild, but the rain may not scatter out until the afternoon, rather than the morning. Adding it all up, we are expecting anywhere from 1-2" across the majority of the Bay Area and Central Coast. That number has continued to trend up. The floor of the probabilistic forecast is pretty high. There is a 90% chance that SFO gets at least 1" of rain according to the ECMWF ensemble. Typically the "dry" scenario is much lower for our rainy forecasts, but it seems unlikely that this particular storm will be a dud. Monday still looks dry for now. As the storm breaks, we`ll be left with cold temperatures. Lows will be in the 40s for most, and upper 30s in the coldest pockets. A gradual warming trend is expected through mid-week, stabilizing near normal with much drier conditions expected. && .AVIATION... (06Z TAFS) Issued at 1003 PM PDT Thu Apr 9 2026 MVFR-IFR stratus is developing at the coast and moving inland through the next few hours, and will be reinforced overnight by the first band of showers expected to arrive sometime Friday morning. As the showers pass, ceilings should lift to become generally VFR-MVFR, along with isolated to scattered thunderstorms across the region, with the best chances focused on the North Bay and East Bay on Friday afternoon and evening. Have decided to go ahead and put VCTS in for the STS, APC, and LVK TAFs for the 18-00Z time period, but note that this is a lower confidence forecast. Chances for thunderstorms decrease on Friday evening, but scattered showers remain possible through the end of the TAF period, with another band of widespread rainfall expected after the end of the TAF period on Saturday afternoon through Sunday. Onshore wind flow will continue to diminish tonight, with light winds overnight before moderate southwest winds prevail through much of Friday. Gustier winds are expected where thunderstorms do develop. Vicinity of SFO... VFR conditions continue through the next couple of hours. MVFR conditions will set up overnight as a band of showers passes through the terminal area through Friday morning, with VFR conditions with mid-level clouds returning once the showers pass. Friday afternoon should see a moderate southwesterly flow develop through the evening. There is around a 25-35% chance of thunderstorms at the terminal Friday afternoon and evening, but confidence is too low to put VCTS or PROB30 in the TAF at this time. Chances for showers continue through the end of the TAF period. SFO Bridge Approach... Similar to SFO. Monterey Bay Terminals... MVFR stratus is developing around the terminals with a "sucker hole" at present around MRY, with a band of showers expected to pass through the region through the course of Friday morning. VFR conditions return as the showers pass with breezy southwest winds developing Friday afternoon. There is a 20- 35% probability of thunderstorm development at the terminals Friday afternoon and evening, but confidence is too low to put VCTS or PROB30 in the TAF at this time. Chances for showers continue through the end of the TAF period, with a low confidence forecast that winds at the terminals will abate overnight with potential development of MVFR stratus. && .MARINE... (Tonight through next Wednesday) Issued at 1003 PM PDT Thu Apr 9 2026 Unsettled weather is expected Friday through the weekend, including increasing winds, building seas, and a few rounds of thunderstorms. Thunderstorms will be capable of producing frequent lightning, gusty and erratic winds, localized heavy rain, small hail, and waterspouts. Gentle to moderate south to southwest winds will become fresh to strong by Saturday, with occasional near gale force gusts. Winds become westerly late Saturday and northerly by late Sunday as the low pressure system passes near the northern waters. Fresh north winds last through midweek. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Gale Watch from Saturday morning through late Saturday night for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm. && $$ SHORT TERM...Flynn LONG TERM....Flynn AVIATION...DialH MARINE...DialH 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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