Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
Issued by NWS San Francisco Bay Area, CA
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671 FXUS66 KMTR 240639 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 1139 PM PDT Mon Sep 23 2024 ...New AVIATION... .SYNOPSIS... Issued at 110 PM PDT Mon Sep 23 2024 Heat Advisory in effect for the interior East Bay, South Bay, and Santa Cruz Mountains as hot temperatures peak today. Slight cooling tomorrow with temperatures returning to near the seasonal average on Wednesday, slightly warming by Friday. && .UPDATE... Issued at 909 PM PDT Mon Sep 23 2024 The marine layer is struggling to exist tonight, as such low-level cloud cover is making an exit down the central coast. This will lead to a fairly clear night with only some passing high-level clouds. Expect some warm temperatures in the higher elevations tonight, with a focus on the East Bay, leading to another hot day for Tuesday. Because of the lack of relief from the heat, the East Bay will continue to be under a Heat Advisory through tomorrow evening with a cooler night to follow. && .SHORT TERM... (This evening through Tuesday) Issued at 110 PM PDT Mon Sep 23 2024 Today`s warm to hot weather comes courtesy of a delicate dance in the upper levels of the atmosphere, with a ridge sliding into the Pacific Northwest creating warm conditions up and down the West Coast, enhanced by a subtle low pressure system retrograding westward off Point Conception, both features combining to create easterly flow in the upper levels, as visible earlier this morning with the cirrus clouds streaming into the state from Nevada. High temperatures today rise into the mid 90s to near 100 in the inland valleys, into the mid 80s to lower 90s along the Bayshore, and in the mid 60s to the lower 70s along the Pacific coast. Low temperatures tonight are generally in the upper 50s to the mid 60s in the valleys, with some cooler temperatures at the immediate coast where the remnants of the marine layer will lie, and up to the low to mid 70s in the higher elevations. Some cooling is expected in the coastal regions tomorrow, with high temperatures in places like downtown San Francisco, the Santa Cruz county coast, and the Salinas area dropping around 5 degrees. Across the inland areas, little cooling is expected. A Heat Advisory is now in effect for the interior East bay, the South Bay, and the Santa Cruz Mountains today, due to the widespread risk for heat related illnesses for sensitive populations (children, the elderly, pregnant women, those with certain medical conditions), and the possibility for heat-related impacts for everyone without adequate hydration and/or cooling. In the South Bay and the Santa Cruz Mountains, the Heat Advisory will expire at 8 PM today, while the Advisory continues through Tuesday night in the interior East Bay as lingering heat sustains the risk for heat-related illnesses. Here`s a reminder about heat safety: * Stay hydrated and drink plenty of fluids. * Wear lightweight, light-colored clothing. * Reduce time spent outdoors or stay in the shade. * Never leave people or pets unattended in vehicles. * Use sunscreen if going to the coast or the pool. Winds will generally be lightly onshore in the afternoon and evening, and calm to nearly calm overnight and into the morning. Although some weak onshore flow is possible at the higher elevations tonight, low wind speeds and some overnight recovery keep the fire weather concerns low. && .LONG TERM... (Tuesday night through next Sunday) Issued at 110 PM PDT Mon Sep 23 2024 The upper level ridge moves off to the east late Tuesday into Wednesday, allowing the weak upper level low to merge into a stronger upper level trough that sets up into the Eastern Pacific. Temperatures across the region will cool rather dramatically, close to or slightly below seasonal averages for this time of year. Later on in the week, a zonal pattern towards our north and a series of weak upper level troughs towards our south and southwest will keep our region somewhat warm heading into the upcoming weekend, although not as hot as the temperatures seen today. CPC outlooks keep a lean towards temperatures above, and precipitations below, seasonal averages through the first week of October. && .AVIATION... (06Z TAFS) Issued at 1139 PM PDT Mon Sep 23 2024 The marine layer remains compressed and varied in depth from 400 to 600 feet along the north Central Coast to sea level along the San Mateo county coastline northward to the coastal North Bay. A coastally trapped southerly wind reversal recently developed with the SMX-SFO pressure gradient varied between 1 mb and 2 mb. Satellite imagery shows coastal stratus and fog /VLIFR-IFR/ advancing northward and advancing into the northern Salinas Valley. In general forecast models are under-forecasting the SMX-SFO gradient at the present time and indicate the SMX-SFO strengthening Tuesday. A coupling to the mid- upper level low to our southwest may help speed up the southerly wind reversal pattern overnight through Tuesday. Vicinity of SFO...VFR. Light and variable wind becoming northwest 10 to 14 knots Tuesday afternoon and evening. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Coastal stratus and fog /VLIFR-IFR/ are advancing into the northern Salinas Valley while it`s VFR in the vicinity of KMRY. A coastally trapped southerly wind reversal is developing, however the light northwest wind (transporting stratus and fog) to KSNS may be briefly offset by a light southeast wind overnight. In general since meso-scale models are currently under- forecasting the SMX-SFO (and SNS-SJC gradient) and forecast a strengthening in that respect Tuesday, expect a general increase in coverage of stratus and fog /VLIFR-IFR/ moving inland overnight and Tuesday morning. Diurnal mixing Tuesday will help lift conditions to MVFR-VFR with an early return of stratus ceilings first to KSNS then KMRY, typically the timing for southerly wind reversals. && .MARINE... (Tonight through next Sunday) Issued at 909 PM PDT Mon Sep 23 2024 Gentle to moderate northwesterly breezes will continue through Wednesday. Northwesterly breezes increase and seas rebuild to become rough in the outer waters by Thursday. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory until 8 PM PDT Tuesday for CAZ510-515. PZ...None. && $$ SHORT TERM...DialH LONG TERM....DialH AVIATION...Canepa MARINE...Sarment 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