textproduct: San Francisco Bay Area

This forecast discussion was created in the public domain by the National Weather Service. It can be found in its original form here.

SYNOPSIS

Issued at 1234 PM PST Sun Nov 3 2024

Elevated fire weather concerns persist through the week. Offshore flow continues through Monday morning, with some onshore flow developing late Monday into Tuesday before another round of offshore flow arrives late Tuesday through Thursday.

SHORT TERM

(This evening through Monday) Issued at 1234 PM PST Sun Nov 3 2024

Satellite imagery shows clear skies across the region, with only a few clouds hanging on in the higher elevations. Highs today range from the mid 60s to the lower 70s in the inland valleys to the upper 50s to the lower 60s along the Pacific coast, with some temperatures in the low to mid 50s along the ridgetops.

Main focus of the forecast is on the developing northerly to northeasterly winds across the region, especially in the higher elevations. An inside slider continues to move through the Great Basin into the Desert Southwest, with the interaction between the low pressure and ridging over the Eastern Pacific combining to create a strong pressure gradient over the state. Gusty winds have already developed with the strongest gust so far being a 56 mph gust at the Mount Saint Helena West PGE station. Breezy and gusty offshore flow continues overnight into Monday morning with the gusts reaching 30 to 50 mph across the higher elevations, and through gaps and passes. Fire weather concerns in the short term remain relatively muted due to recent rainfall, although the offshore winds will help cure the fuels for a second system later this week.

The offshore winds will abate through Monday morning with some onshore flow developing that afternoon as the inside slider moves off to the east. Low temperatures range from the mid 40s to the mid 50s across most of the region, with the Sonoma County valleys seeing lows in the lower 40s and the southern reaches of Monterey County dipping down into the mid 30s. Monday's highs will be warmer than today's with temperatures in the mid to upper 70s in the inland valleys and the low to mid 60s along the coast.

In addition to all of the above, a Beach Hazards Statement will go into effect at 3 PM today through Monday evening, for the Pacific coastline except northern Monterey Bay, due to an incoming long period swell that will increase the risk of sneaker waves and rip currents. Breaking waves of 10 to 14 feet are expected, leading to long beach run-ups and large shore breaks on steep beaches. For those headed to the coasts, remain out of the water to avoid hazardous conditions, keep pets on a leash and away from the water, and never turn your back to the ocean!

LONG TERM

(Monday night through next Saturday) Issued at 1234 PM PST Sun Nov 3 2024

Mild onshore flow continues through the early part of Tuesday, as another trough develops up in the northern Rockies. Through the day, that trough descends into the Great Basin, where it develops into a cutoff low and brings us another round of offshore winds beginning Tuesday evening into Thursday. Even three days out, there's still some uncertainty as to how strong the event will be, but the models are coming into alignment on a moderate to strong offshore flow event that will bring elevated fire weather concerns to the region. Expect gusts in the higher elevations and gaps and passes to be somewhat stronger than those seen tonight into Monday morning, with isolated spots reaching 50-60 mph gusts Wednesday evening.

Towards the end of the week, there's some uncertainty about how quickly the offshore flow will pass, depending on how quickly the inside slider moves off to the south. A more progressive system will cause offshore flow to diminish rather quickly, while a slower moving system keeps offshore flow in place through Friday. Model output is hinting at the chance for rain for this upcoming weekend and beyond, but there is too much variance in the ensemble solutions to pin down any details at this time.

AVIATION

(00Z TAFS) Issued at 353 PM PST Sun Nov 3 2024

Satellite shows mostly clear skies with a few high clouds over a couple of the terminals. Observations show that some haze has developed over KHAF, creating MVFR conditions but that should clear within a hour or so. Therefore, expect VFR to prevail through the TAF period for all terminals. N/NW winds remain pretty breezy and gusty but will diminish to light to moderate overnight creating opportunity for LLWS to develop near the North Bay and East Bay terminals from 04-05Z and lasting until 11-12Z. Late Monday morning, winds will return to breezy and gusty.

Vicinity of SFO...High confidence VFR will prevail through the TAF period. NW winds remain gusty and strong but will diminish to light to moderate tonight. NW wind rebuild by Monday afternoon with possible gusty winds up to 20-22 kts.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR will prevail through the TAF period. W/NW winds will diminish from breezy and gusty to light and variable overnight. Moderate to relatively breezy NW winds return Monday afternoon.

MARINE

(Tonight through next Friday) Issued at 353 PM PST Sun Nov 3 2024

The strong Eastern Pacific subtropical high pressure system will continue to strengthen and move closer to the coast through tonight. The gradient between this system and a low pressure trough over California will support strong NNW winds with gale force gusts across the majority of the exposed marine zones. Buoys are reporting significant wave heights of 10 feet. Long period NW swell will arrive tonight, building combined seas to 15 feet.

FIRE WEATHER

Issued at 1234 PM PST Sun Nov 3 2024

The first of two pushes of offshore flow is upon us, with gusty north to northeast winds expected to continue through Monday morning. Although recent rainfall will help alleviate fire weather concerns in the short term, the dry winds will help cure the fuels in advance of a second offshore wind event beginning Tuesday evening. The models are converging on a moderate to strong offshore flow event during the midweek, but there's still considerable uncertainty on how severe the fire weather concerns will be. A lot of the fire weather concerns that will develop from this second system will depend on how dry the fuels become after this first push tonight. In addition, the relative humidity forecasts from Tuesday through Thursday may still need to be nudged downward to account for some lost evapotranspiration potential from tonight's drying winds. There was some discussion about issuing a Fire Weather Watch for the midweek event, but our colleagues in Eureka and Sacramento agreed that with so much uncertainty in how the fuels would react to the conditions tonight, it was best to hold off on issuing anything until Monday.

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MTR WATCHES/WARNINGS/ADVISORIES

CA...Beach Hazards Statement through Monday evening for CAZ006-505- 509-530.

PZ...Small Craft Advisory until 3 AM PST Monday for Mry Bay-SF Bay N of Bay Bridge.

Small Craft Advisory until 3 PM PST Monday for Pt Arena to Pt Reyes 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

Gale Warning until 9 PM PST this evening for Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm.

Gale Warning until 3 AM PST Monday for Pt Arena to Pt Reyes 10- 60 NM.


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