Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
Issued by NWS San Francisco Bay Area, CA
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016 FXUS66 KMTR 220616 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 1111 PM PDT Sat Sep 21 2024 ...New AVIATION... .SYNOPSIS... Issued at 124 PM PDT Sat Sep 21 2024 Gradual warming continues through the rest of the weekend with temperatures near or slightly below seasonal averages. Even warmer temperatures expected Monday and Tuesday with moderate HeatRisk possible inland. && .UPDATE... Issued at 844 PM PDT Sat Sep 21 2024 Another calm night ahead with some low clouds moving inland with a touch of fog and even some drizzle added in for that extra Bay Area flavor in the forecast. Not much to update in the near term tonight. There is still a lot of interesting model shenanigans going on in the second half of next week, which just means there is a fair amount of uncertainty on how cool the cooling trend will be. Regardless, temperatures still look to peak on Monday, with slight cooling on Tuesday. -Murdock && .SHORT TERM... (This evening through Sunday) Issued at 124 PM PDT Sat Sep 21 2024 Warmer temperatures are starting to make their way into the interior regions, with temperatures generally running 5 to 10 or occasionally 15 degrees above those at the same time yesterday. The stratus deck has pared back to the immediate coast, as the marine layer has gradually compressed with observations from the Fort Ord profiler showing a marine layer depth around 1500 feet today compared to nearly 2000-2200 feet this time yesterday. Overnight stratus is expected to develop into the coastal valleys although the interior East Bay and the Morgan Hill-Hollister corridor are expected to remain clear. Today`s temperatures should be warmer than yesterday`s, although the extensive stratus coverage this morning led me to bump down the high temperature forecast in the interior valleys by a few degrees. The current forecast shows high temperatures today ranging from the 80s across the inland valleys, to the 70s and low 80s near the Bayshore, and the low to mid 60s along the Pacific coast. Even warmer temperatures are forecast on Sunday, although some uncertainty continues into this period. A shortwave trough begins to develop off the coast of California through the day, interrupting the expanding upper level high over this part of the region and moderating the warming trend. As of time of writing, the inland valleys are expected to reach into the low to mid 90s on Sunday, with temperatures in the Bayshore up to the mid 70s to mid 80s and the Pacific coast rising to the mid to upper 60s. Low temperatures remain in the 50s across the lower elevations, up to the mid 60s along the thermal belts. && .LONG TERM... (Sunday night through next Friday) Issued at 124 PM PDT Sat Sep 21 2024 The upper level disturbance builds ever so slightly into the beginning of the upcoming work week, migrating further offshore through the next couple days with a potential window for the development of a closed low, before the pulse is absorbed into the polar jet mid week. The interaction between this upper level disturbance and the upper level ridge pushing into the northwestern United States will dominate our weather pattern for the next several days. In particular, the positioning of the low off the California coast will result in light offshore flow during the overnight and morning hours, although onshore flow should dominate the afternoon and evening hours. Temperatures are expected to peak on Monday and Tuesday, when moderate HeatRisk is possible in the interior regions. Highs in the inland valleys are expected to rise into the mid to upper 90s on those days. Of note, the extent of heat-related impacts is correlated to how cold it gets overnight, with significant uncertainty across the thermal belts, but also near San Francisco Bay. For example, the reasonable range of low temperatures near San Francisco International Airport is around 15 degrees. From the midweek onward, persistent upper level troughing should moderate temperatures to near the seasonal average through the end of the week. && .AVIATION... (06Z TAFS) Issued at 1111 PM PDT Sat Sep 21 2024 The marine layer depth currently varies from 900 feet to 1700 feet per Bodega Bay, Fort Ord and Point Sur profilers. Coastal stratus and fog /LIFR-IFR/ are redeveloping and will move inland tonight and Sunday morning. Northerly and southerly pressure gradients (and corresponding wind directions) juxtaposed over the coastal waters within a stationary surface trough have eased since earlier in the day; gradients were under-forecast by the meso-scale models and with plenty of stratus/fog to our southeast along the CA coast the SMX-SFO pressure gradient may continue Sunday. Currently the 2.7 mb SFO-SAC pressure gradient (onshore wind) is the predominating gradient across the forecast area. Precipitable water on the Saturday evening Oakland upper air sounding was a little above mid September normal, however there still should be decent radiative cooling tonight to daybreak Sunday helping with stratus and fog development (favorable due to lengthening night time hours). Stratus and fog /VLIFR-IFR/ mixes out back to the coastline and bays late Sunday morning and afternoon. Elsewhere MVFR-VFR conditions Sunday. Vicinity of SFO...VFR except IFR ceiling is forecast 09z 18z Sunday. Onshore wind 5 to 15 knots. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...LIFR-IFR in stratus and fog tonight and Sunday morning, conditions improving to MVFR-VFR by late Sunday morning and early afternoon. Light and variable winds tonight and Sunday morning becoming onshore 5 to 15 knots by late morning and afternoon. && .MARINE... (Tonight through next Friday) Issued at 844 PM PDT Sat Sep 21 2024 The pressure gradient between subtropical high pressure over the Eastern Pacific Ocean and low pressure over the West Coast will support strong northwesterly breezes and rough seas in the outer waters through Monday. Northwesterly breezes decrease and seas abate beginning Tuesday. Seas rebuild to become rough in the outer waters towards the end of the forecast period. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory until 3 AM PDT Monday for Pt Arena to Pt Reyes 10-60 NM. && $$ 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