Edouard will continue to bring gusty winds, heavy rainfall, and a flash flood threat over parts of eastern Texas. Severe thunderstorms and heavy rain are possible across portions of the eastern Great Lakes to the Mid-Atlantic today. Severe storms are also expected across the northern Rockies. Dangerous heat persists over the central and eastern states through Friday night. Read More >
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047 FXUS66 KMTR 021201 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 501 AM PDT Wed Sep 2 2026 ...New AVIATION, MARINE... .KEY MESSAGES... Updated at 1015 PM PDT Tue Sep 1 2026 - Cooler weather continues this week - Rain likely Wednesday and Thursday morning for the North Bay && .SHORT TERM... Issued at 1015 PM PDT Tue Sep 1 2026 (Tonight through Thursday) Now that meteorological Summer (June - August) is over, the marine layer won`t be as persistent. We`ve been through "May Grey", "June Gloom", "No Sky July", and "Fogust", but there isn`t a cute name for September. That`s for a good reason. The combination of early season cold fronts and offshore wind events tend to disrupt the marine layer periodically in the fall. At the current moment, the marine layer has gotten too deep for its own good. It was measured at 5,200 feet on the 00Z sounding. That`s about as deep as we ever see it before it mixes out. Since the balloon launch, the depth has only grown due to unstable surface layer mixing from below, and a 500 mb trough encouraging expansion above. The air mass is cold for this time of year. The 00Z weather balloon measured the 850 mb (~5,000 ft) temperature at 42F. That makes the top 10 coldest 850 temps we`ve seen in the first week of September. The normal today is 66F. 42F is the normal for late February. Despite this, if you`re in a coastal city it may actually feel warm since the marine layer is taking a little vacation. Inland areas are really feeling the difference though, with temperatures 10-15 F cooler than normal. September is typically the warmest month for many of our cities, so below normal is a good thing for most. The approaching trough is supporting a cold front located about 200 miles west of the OR/CA border. There is some very light pre- frontal rain reaching the ground in the North Bay tonight, but we`ve only seen a few scattered hundredths so far. This rain will pick-up through the morning. The best window for Santa Rosa is 5-10 AM. The total accumulation should be between a few hundredths and a tenth of an inch this morning. The pre-frontal rain band will dry out quite a bit as it moves south, with much lower rain chances south of the Golden Gate. Temperatures today will be very similar to yesterday (60s and 70s), although there will be more cloud cover across the Bay Area, so it may feel a little cooler despite the 850 temps rebounding a bit. The actual cold front arrives to the North Bay Thursday morning, bringing a more significant round of rain. The latest forecast has increased the qpf to a respectable 0.25-0.5" across Sonoma and Marin County. That`s real rain. The normal for the entire month is 0.15" at Santa Rosa. Like Wednesday, the rain chances drop off significantly south of the Golden Gate, but we do expect a few hundredths across the coastal areas of the cwa gradually moving south through the day Thursday. Temperatures will continue to stay well below normal through the day. && .LONG TERM... Issued at 1015 PM PDT Tue Sep 1 2026 (Thursday night through next Tuesday) After the front moves through Thursday night the marine layer will gradually start to reorganize on Friday, but it will take some time. The 500 mb trough will spawn a cut-off low that will linger somewhere over the Pacific Northwest. Meanwhile high pressure over the SW US will start to build towards California. The gradient between these two features will keep persistent W-SW flow at 500 mb well into next week. As the low starts to weaken, the high will exert more influence, allowing the temperatures to gradually rise through the weekend and into early next week. The exact location of the cut-off low is the wildcard in the forecast. Without the steering influence of the jet stream, it`s very tricky to pin down where this thing will meander. If it happens to take a dive south to California, it could open the door for tropical moisture associated with Tropical Storm Marie to reach Southern California. Direct impacts from this tropical cyclone are looking much less likely now. The storm speed has slowed and it will most likely continue to march NW into the open ocean. The associated moisture may still reach southern California, but even in that scenario, it`s unlikely any significant rain makes it further north than the Central Coast. && .AVIATION... (12Z TAFS) Issued at 427 AM PDT Wed Sep 2 2026 Low level clouds remain patchy this morning with high level clouds filtering in across the region. The main short term adjustment in the 12Z TAFs was to remove MVFR ceilings from most airports. Confidence that low level clouds will develop is decreasing given the incoming showers and high clouds disrupting stratus formation along the coast. The marine layer also remains mixed out given the deep incoming trough to the West Coast. Showers are starting to move in on radar with STS reporting light rain this morning. Highest confidence in light rain reaching STS/APC but cannot rule out a stray shower making it to SFO/OAK/HAF this morning. Shower chances decrease by late this morning before more widespread shower chances return tonight. The SFO-WMC gradient peaks around +10 mb this afternoon which supports another day of breezy onshore winds during the afternoon/evening across the region. For the longer term, main adjustments were to push back the arrival of lower clouds tonight and tweak the timing of more widespread showers arriving. Guidance is leaning towards low clouds coming in closer to 09-12Z tonight with the weak cold front arriving in that same timeframe. Rain chances increase earlier across the North Bay before increasing across the rest of the region closer to 12Z/shortly after the end of this TAF period. Vicinity of SFO...Patchy MVFR CIGs are possible this morning but confidence is decreasing that they will develop. Cloud cover has been coming in higher (bases around 5000 ft) and is expected to remain elevated through this evening. Showers are expected to remain north of SFO this morning but cannot rule out a stray shower bringing a trace of rain to SFO this morning. Ceilings lower overnight tonight and the potential for light rain increases as a weak cold front approaches the region. MVFR CIGs could return as early as 12Z but have pushed it back to 15Z to better align with LAMP and HRRR guidance. Rain potential increases around 15Z as showers progress north to south tonight. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...High clouds starting to drift in over the Monterey Bay Region. The marine layer remains mixed out this morning which is resulting in much less widespread stratus this morning. The marine layer is forecast to remain mixed out through Thursday as a deep upper level trough moves into the West Coast and brings rain potential. Showers are expected to stay north of MRY/SNS this morning but shower chances increase slightly tonight into tomorrow. MVFR-IFR CIGs are expected to arrive between 03-06Z with slightly higher confidence in an arrival closer to 06Z ahead of an incoming weak cold front. && .MARINE... (Today through Monday) Issued at 427 AM PDT Wed Sep 2 2026 Light northwesterly breezes with occasional moderate gusts persist through the week with slight to moderate wind driven seas. Winds increase, becoming more moderate, late this week with diurnal, fresh gusts expected in the vicinity of the Monterey Bay. Long period southerly swell associated with tropical cyclone activity arrives Friday into the weekend. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ SHORT TERM...Flynn LONG TERM....Flynn AVIATION...Kennedy MARINE...Kennedy 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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