Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
Issued by NWS San Francisco Bay Area, CA
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835 FXUS66 KMTR 130249 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 749 PM PDT Fri Jul 12 2024 ...New UPDATE... .SYNOPSIS... Issued at 240 PM PDT Fri Jul 12 2024 One more day of excessive heat for inland areas before a cool-down over the weekend and near normal temperatures return next week. && .UPDATE... Issued at 743 PM PDT Fri Jul 12 2024 The Excessive Heat Warnings have expired and been replaced by Heat Advisories valid until 9PM Saturday. One more day of warm temps for these areas where the compounding impacts of the last several days may still cause issue, though the severity of heat is undoubtedly less. The Heat Advisories that were in effect before this change have been expired, and no further hazards will be issue for these areas. As of tonight, still looking at the low threat of dry lightning through this weekend, and the first signs of the elevated moisture that would cause this are evident on satellite moving in from the south. More details in the Fire Weather section. Behringer && .SHORT TERM... (This evening through Saturday) Issued at 240 PM PDT Fri Jul 12 2024 Several of the warmer inland areas are well on their way to triple digit heat this afternoon. Coastal areas are remaining in the upper 60s thanks to a 1,000 ft deep marine layer. As the ridge finally moves east on Saturday, significant relief is in store, and most guidance is trending a few degrees cooler over the last several model runs. For example the 10/12Z, 11/12Z, and 12/12Z ECMWF runs have predicted high temperatures at San Jose of 93, 91, and 89, respectively. Overall the Inland temperatures on Saturday will be roughly 10 degrees cooler than the last couple days, which will essentially end this 11-12 day heat wave. While the ridge weakening is good news for heat impacts, the new pattern may support some elevated convection and there is a slight chance for dry lightning this weekend. More details are in the fire weather section. && .LONG TERM... (Saturday night through next Thursday) Issued at 240 PM PDT Fri Jul 12 2024 A mid level low supported by an upper-level trough will linger off the coast through Monday before gradually pushing onshore Tuesday. This system will help regulate temperatures as cooler, more humid air moves in. The lower pressure will also allow the marine layer to gradually expand in depth and extend farther inland. We will enjoy a return to seasonal temperatures for the majority of the week. By next weekend, things get more uncertain. While most guidance agrees the 4-corners high will be a semi-permanent feature, ensemble clusters show a wide spread in the existence, timing and depth of an approaching trough around days 7-9. Until the guidance starts to merge on a common solution, don`t trust anything you hear about the weather next weekend. There may be another warm-up, but 7+ day forecasts aren`t the most reliable thing, and the uncertainty is even higher than normal. && .AVIATION... (18Z TAFS) Issued at 1102 AM PDT Fri Jul 12 2024 VFR prevails through the afternoon today with breezy W/NW winds. Marine stratus will make a return in the evening tonight to bring IFR/LIFR CIGs to North Bay and Monterey Bay terminals. There does remain some lack of confidence as to whether stratus will form a CIG over North Bay terminals, or predominantly remain FEW-SCT low clouds. At this moment, confidence for CIG formation over North Bay terminals is low-moderate. High confidence in LIFR CIGs developing at Monterey Bay terminals tonight. Vicinity of SFO...VFR through the TAF period. Winds NW and moderate this afternoon, but ease slightly into the late night. Stratus will likely impact KOAK but is not expected to bring CIGs to KSFO. Winds at KSFO turn more W/SW into the daytime Saturday as a low approaches the region. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...VFR through the late afternoon today, though stratus will begin to make an onshore push shortly after the 00Z hour. CIGs are expected to develop by 03/04Z with LIFR conditions lasting through the night. Towards the early morning of Saturday, visibilities at Monterey are likely to reduce significantly as mist and fog develops. && .AVIATION... (18Z TAFS) Issued at 1102 AM PDT Fri Jul 12 2024 VFR prevails through the afternoon today with breezy W/NW winds. Marine stratus will make a return in the evening tonight to bring IFR/LIFR CIGs to North Bay and Monterey Bay terminals. There does remain some lack of confidence as to whether stratus will form a CIG over North Bay terminals, or predominantly remain FEW-SCT low clouds. At this moment, confidence for CIG formation over North Bay terminals is low-moderate. High confidence in LIFR CIGs developing at Monterey Bay terminals tonight. Vicinity of SFO...VFR through the TAF period. Winds NW and moderate this afternoon, but ease slightly into the late night. Stratus will likely impact KOAK but is not expected to bring CIGs to KSFO. Winds at KSFO turn more W/SW into the daytime Saturday as a low approaches the region. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...VFR through the late afternoon today, though stratus will begin to make an onshore push shortly after the 00Z hour. CIGs are expected to develop by 03/04Z with LIFR conditions lasting through the night. Towards the early morning of Saturday, visibilities at Monterey are likely to reduce significantly as mist and fog develops. && .MARINE... (Tonight through next Wednesday) Issued at 436 PM PDT Fri Jul 12 2024 Winds out of the north continue to be fresh through much of Saturday for the northern outer waters. Winds begin to ease to become gentle to moderate starting Sunday, though turn to become more southerly as low pressure enters the region. Gentle winds then last through the majority of next week. Significant wave heights between 10 to 12 ft continue over the outer coastal waters with peak wave heights between 10 to 13 ft expected over the far northern outer coastal waters. && .FIRE WEATHER... Issued at 240 PM PDT Fri Jul 12 2024 Taking advantage of a weaker ridge, a mid-level low off the coast will pump moisture up from the south this weekend. This elevated moisture will lead to precipitable water values exceeding 1", which is the 90th percentile for this time of year. Combined with steep lapse rates, we expect this moisture to produce some elevated convection, however, there is only a 5-10% chance of thunderstorm development. Despite the low probability, there could be high impacts as any lightning that does develop won`t have much rain reach the surface, and we are come off a prolonged heat wave which dried fuels to record levels. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory until 8 PM PDT this evening for CAZ502-503-506-508- 512-516-528. Excessive Heat Warning until 8 PM PDT this evening for CAZ504- 510-513>515-517-518. Heat Advisory until 9 PM PDT Saturday for CAZ504-510-513>515-517- 518. PZ...Small Craft Advisory until 9 AM PDT Saturday for Pt Arena to Pt Reyes 10-60 NM. && $$ SHORT TERM...Flynn LONG TERM....Flynn AVIATION...SO MARINE...AC Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea