SHORT TERM
(This evening through Monday)
Issued at 112 PM PDT Sun Sep 15 2024

The weather pattern today is dominated by a cold front working through the Bay Area and into the Central Coast. The cold front has brought noticeable cooler temperatures across the board, with highs reaching the low to mid 70s in the inland valleys, the upper 70s to low 80s in the North Bay valleys and southern Monterey County, the mid to upper 60s in the Bayshore, and the upper 50s to mid 60s along the Pacific coast. Monday is set to be even cooler inland, with even the North Bay valleys and southern Monterey County seeing temperatures in the low to mid 70s.

Northwest winds should continue to build through the day, with the strongest gusts tonight into early Monday morning before winds diminish later in the morning through the afternoon. The strongest gusts will be through the gaps, passes, and favorably oriented (northwest-southeast) valleys and coastal regions (e.g. the Salinas Valley, the San Bruno Gap, the Sonoma Coast, and the Santa Cruz County coast west of Capitola). These areas will see gusts up to 35- 40 mph, occasionally 45-50 mph. The rest of the region should see gusts of 25-35 mph.

Chances of drizzle and light rain arrive late tonight into Monday afternoon, but accumulations are expected to be pretty light. The higher elevations are expected to see a tenth to a quarter of an inch of rain, with some isolated areas seeing nearly half an inch.
The forecast for the lower elevations continues to be even lighter, with a tenth of an inch being the absolute maximum and the North Bay and southern Monterey County largely missing out.

Low clouds continue to linger across the San Francisco Bay Area and the southern Monterey Bay. Some clearing is possible through the afternoon, but the cooler temperatures could keep stratus around at the immediate coast and some of the higher elevations. Tonight, the strong winds and rain make for a pretty low confidence forecast for stratus coverage, with the best forecast suggesting more mid-level cloud cover across the region.

LONG TERM
(Monday night through next Saturday)
Issued at 112 PM PDT Sun Sep 15 2024

Temperatures cooler than seasonal averages continue through the next few days, and another upper level low arrives late Tuesday into Wednesday. This low isn't as strong as the one that's coming through today, so the winds won't be as gusty, and rainfall totals will be similar to those from the system today and Monday. Of note, the National Blend is trying to slip a very low chance (10-15% probability) for thunderstorms for the Wednesday system, and a cursory look at the K-Index suggests that, with values up to 32 across the region, the potential for isolated thunderstorms exists. Not very confident at this stage for anything to happen, but definitely something to keep an eye on for the next couple of days as the forecast is refined.

After the upper level low moves out, the pattern shifts to a slight ridge with temperatures close to or slightly above seasonal averages by the weekend, and the CPC outlooks suggest that the seasonal to warm temperatures continue into the last weekend of September.

AVIATION
(00Z TAFS)
Issued at 502 PM PDT Sun Sep 15 2024

It's MVFR-VFR with increasing areas of strong and gusty west- northwest winds. Surface winds are generally coupled to winds aloft this afternoon during maximum diurnal mixing. Expect turbulent conditions however due to vertical mixing of winds non-convective low level wind shear (llws) should remain minimal; for now llws not advertised in the 00 TAFs, will amend if this changes based on pilot reports (pireps), etc. Cold air advection with the incoming low pressure system to our north will periodically result in a few areas of some downsloping and lee- side warming over the Bay Area terrain.
With the low center passing over the Bay Area tonight and Monday morning a few showers will develop as well.

Vicinity of SFO...Gusty west wind continuing this evening, gusts recently have approached 40 knots. VFR-MVFR during the period. A few showers developing tonight and Monday morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Gusty west to northwest winds 15 to 30 knots continuing this evening. VFR-MVFR during the period. A few showers developing tonight and Monday morning.

MARINE
(Tonight through next Friday)
Issued at 438 PM PDT Sun Sep 15 2024

Back to back early season cold fronts will move through the coastal waters today and Wednesday resulting in widespread strong northwesterly breezes with near gale force gusts. In addition, there is also up to a 10% chance for thunderstorms which could produce lightning, locally heavy rainfall, and locally stronger winds. Seas will remain rough outside of protected waters through the forecast period.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Monday for Mry Bay-SF Bay N of Bay Bridge.

Gale Warning until 3 AM PDT Monday for Pt Arena to Pt Reyes 0-10 nm.

Gale Warning until 9 PM PDT this evening for Pt Pinos to Pt Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

Small Craft Advisory until 9 AM PDT Monday for Pigeon Pt to Pt Pinos 0-10 nm.

Gale Warning until 3 PM PDT Monday for Pt Arena to Pt Reyes 10- 60 NM.

Small Craft Advisory until 9 PM PDT Monday for Pigeon Pt to Pt Pinos 10-60 NM.