A storm system is expected to bring strong winds, widespread heavy rainfall, and flooding concerns to the Hawaiian Islands through the weekend. Strong to severe thunderstorms are forecast from the Southern Plains to the Mid-Missouri Valley this afternoon and evening. Large hail and strong winds are the primary threats. Read More >
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728 FXUS66 KMTR 091840 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 1140 AM PDT Thu Apr 9 2026 ...New SHORT TERM, LONG TERM, 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... (18Z TAFS) Issued at 1134 AM PDT Thu Apr 9 2026 Quiet weather as we await our next chance for rain. Satellite shows a mix of low, mid, and high level clouds with the lower clouds gradually eroding. Conditions vary from IFR to MVFR right now, and should become MVFR to VFR for most sites over the next couple of hours. Cumulus clouds may build up and may lead to some VCSH around areas of the North Bay. By later this evening and into the overnight hours, the first round of rain showers will move through starting in the north and gradually spreading south. MVFR to IFR conditions are expected with this, and should improve to MVFR to VFR after the front moves through. There`s also 15-20% of thunderstorms with this system. Should we get enough moisture, instability, and lift tomorrow afternoon, we could see some vicinity thunderstorms around the north bay terminals. Vicinity of SFO...Clearing skies around SFO, with VFR conditions expected for several hours. Lingering low level clouds around the site are expected but shouldn`t return to MVFR status in until 01- 03Z. Onshore flow is expected to bump up to around 10-15kt this afternoon, before decreasing shortly after sunset. Rain showers arrive after 6Z and will be intermittent through the morning hours. CAMs show precip chances dwindling after that, with perhaps a few showers skirting by during the afternoon. As noted above, there is a chance for isolated thunderstorms, but confidence was too low to add any mention of VCTS or PROB30 Thunder. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Stratus hugs the Monterey Bay this morning, which has left the TAF sites with MVFR and IFR cigs. Satellite shows it slowly clearing and models didn`t catch on to this very well. Timing of VFR cigs may need to be adjusted if the clouds take longer to dissipate. Low cigs and vis return tonight, with the chance for rain arriving late tonight and into tomorrow morning. && .MARINE... (Today through Tuesday) Issued at 1134 AM PDT Thu Apr 9 2026 Unsettled weather is expected through the weekend, including increasing winds, building seas, and thunderstorms. Thunderstorms will be capable of producing gusty and erratic winds, 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. Fresh north winds last through midweek. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ SHORT TERM...Flynn LONG TERM....Flynn AVIATION...KR MARINE...KR 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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