An anomalously early heat wave will continue to intensify and expand across the West and Southwest as the week progresses. Numerous daily and potentially monthly record highs are expected to be broken. Critical fire weather conditions will continue over the next couple of days across portions of the High Plains as gusty winds and dry conditions persist. Read More >
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560 FXUS66 KMTR 180900 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 200 AM PDT Wed Mar 18 2026 ...New SHORT TERM, LONG TERM... .KEY MESSAGES... Updated at 149 PM PDT Tue Mar 17 2026 - Early season, long duration heat wave bringing record-breaking temperatures and Moderate HeatRisk continues through at least Friday - Elevated potential for grass fires through the week due to warm and dry conditions with periods of moderate offshore winds - Gradual cooling trend begins this weekend && .SHORT TERM... Issued at 121 AM PDT Wed Mar 18 2026 (Today and tonight) Yesterday broke numerous daily max temperature records, and even a few monthly records. Most notably, 93 degrees at Redwood City broke the monthly record of 90 degrees set just the day prior. The earliest 93 degree day on record is April 9th. Temperatures are cooling nicely overnight in the North Bay and interior valleys, but higher elevations and even some coastal areas are still in the mid 60s. Downtown San Francisco was still 70 degrees at midnight. The ridge axis has moved east of us, and will be centered over the SE California desert today, before moving into Arizona tomorrow. While the distance to the center of the ridge is increasing, the strength of the high pressure is also increasing. This combination will keep our 500 mb heights and 850 mb temperatures fairly consistent at around 5910 m and 20 C. Both higher than we`ve recorded in March outside of the last couple days. As such, today will be very similar to yesterday for inland areas, though there will be slightly more marine influence along the immediate coast. The current satellite shows a bank of low stratus off the coast of Pt. Reyes moving south. These clouds will probably not make landfall, but they are a sign that boundary layer averaged winds have shifted from offshore yesterday to onshore this morning. Offshore winds still dominate above the very shallow boundary layer, however. The compression from the high pressure will keep this more humid air confined to the coast while the rest of the area gets another dry, hot afternoon. && .LONG TERM... Issued at 121 AM PDT Wed Mar 18 2026 (Thursday through Tuesday) Rinse and repeat through Friday. Expect record breaking heat each afternoon as the ridge of high pressure stalls over the desert SW. Confidence is increasing that the heat wave will start to break on Saturday. Our latest forecast has temperatures dropping around 10 degrees on Saturday, and another 5 on Sunday. That would bring us back into the 70s for most inland areas and 60s along the coast to start next week. By the way, that`s still 5-15 degrees above normal for this time of year. As the ridge breaks down there is good chance for stronger winds this weekend, which will bring some additional relief to the hot temperatures, but also brings some enhanced fire weather conditions for fine dead fuels. The next chance for any rain is around the end of the month or early April, but the ensemble members diverge spectacularly by that point, and it`s just as likely that another dry heatwave moves in. && .AVIATION... (06Z TAFS) Issued at 1232 AM PDT Wed Mar 18 2026 It`s essentially VFR across all of the forecast area however satellite imagery shows an area of near surface cooler air and stratus/fog moving southward of Point Arena and not far from coastal Sonoma County. The marine layer depth is compressed to approx 500 feet under strong high pressure aloft. Point Arena buoy showed the air/sea surface temps were 49F/52F after the passage of stratus/fog, after 04z. Pockets of cool coastal air and night-time radiative cooling through daybreak will help additional patches of stratus/fog to form and may bring LIFR-IFR at KHAF beginning early this morning. Meanwhile radiative cooling will set up cool air drainage winds most likely (like previous mornings) over the Salinas Valley, Monterey Peninsula, Carmel to Carmel Valley. Cool air drainage winds is a land breeze which will likely prevent stratus/fog from reaching the north Central Coast. Anyhow, will monitor satellite and observations and amend TAFs if needed. Elsewhere over the Bay Area the current synoptic/meso scale pattern favors VFR. Vicinity of SFO...VFR. Light and variable wind becoming northwest 5 to 10 knots in the afternoon. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...VFR. Radiative cooling to space may help form a patch or two of stratus/fog. Otherwise surface observations are showing the return of cool air drainage winds. Land breezes will continue through morning helping to keep VFR going at the terminals; will amend of course if stratus/fog /LIFR-IFR/ gain a better foothold. During the day moderate to higher confidence VFR due to residual drainage winds (like the last couple days tapping warm air parcels aloft and bringing these parcels to sea level much warmer and drier). Southeast winds 5 to 10 knots possibly up to 15 knots in the Salinas Valley diminishing and shifting over to sea breezes 10 to 12 knots in the afternoon. && .MARINE... (Tonight through next Sunday) Issued at 449 PM PDT Tue Mar 17 2026 Moderate NW breezes will prevail offshore, with gentle breezes within 10NM. Seas are moderate from a combination of wind waves and a low southerly swell. Similar conditions will persist through Thursday before winds increase to a strong NNW breeze with rough seas from Friday through Sunday. && .CLIMATE... Issued at 113 AM PDT Tue Mar 17 2026 The following are the record high temperatures at the long term sites for March 17th, 18th, 19th, and 20th. Location Mar 17 Mar 18 Mar 19 Mar 20 Santa Rosa 87 in 1996 84 in 2010 83 in 2004 84 in 2004 San Rafael 84 in 1972 80 in 1996 81 in 1964 82 in 1960 Kentfield 87 in 1914 89 in 1914 83 in 1996 82 in 2001 Napa 92 in 1914 87 in 1914 86 in 1914 86 in 2004 Richmond 83 in 2004 78 in 1996 80 in 1996 81 in 2004 Livermore 87 in 1972 86 in 2004 82 in 2015 87 in 1915 San Francisco 85 in 1914 86 in 1914 80 in 2010 78 in 2004 SFO Airport 82 in 2004 77 in 2004 78 in 2010 78 in 2004 Redwood City 85 in 2004 84 in 2004 81 in 2010 82 in 2004 Half Moon Bay 83 in 2004 75 in 1978 79 in 2010 75 in 2010 Oakland Museum 85 in 2004 81 in 2004 81 in 1984 78 in 2001 San Jose 88 in 1914 87 in 1914 82 in 1988 78 in 2004 Salinas Airport 87 in 2004 84 in 1960 87 in 1997 80 in 1934 The following are the record high temperatures at the long term sites for the entire month of March. Location Santa Rosa 91 on March 16, 2004 San Rafael 88 on March 25, 1952 Kentfield 91 on March 28, 1923 Napa 92 on March 17, 1914 Richmond 87 on March 31, 2021 Livermore 90 on March 25 and 26, 2025 San Francisco 87 on March 11, 2005 SFO Airport 85 on March 25, 1952 Redwood City 90 on March 16, 2026 Half Moon Bay 83 on March 31, 2000 and March 17, 2004 Oakland Museum 88 on March 11, 2005 San Jose 89 on March 14, 2015 Salinas Airport 92 on March 14, 2015 && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory until 8 PM PDT Friday for CAZ006-502>506-508>510- 512>518-528>530. PZ...None. && $$ SHORT TERM...Flynn LONG TERM....Flynn AVIATION...Canepa 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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