Swell Matrix

Area Forecast Discussion

National Weather Service San Francisco CA

426 am PDT Sun apr 5 2026

Short Term

, Issued at 1238 AM PDT Sun Apr 5 2026 (Today and tonight)

Temperatures warmed well for the afternoon and early evening in spite of the overcast high clouds leading to a few daily high temperature records tying: Salinas and Half Moon Bay.

These warmer conditions are the result of a building ridge pattern, which will also call for warmer overnight temperatures and reduced humidities. Expect lows to fall to the upper 40s in the far interior, while the rest of the region sees the mid to lower 50s.

The slightly warmer start and reduced humidity coupled with the building ridge will allow for Sunday to see the hottest temperatures in the forecast. Winds will be light or still in most places as temperatures climb 10 to 15 degrees above average for most areas. A few isolated interior and high elevations look to see highs 20 degrees above average. The immediate coast will peak in the upper 60s to mid 70s, while most of the inland areas see the 80s. There will be some hotter spots in the Santa Cruz Mountains and interior Monterey Co that could break into the 90s.

The pattern changes quickly that night as the ridge pushes east and a weak short-wave trough opens over California. This will allow for a fair increase in onshore flow and reduce pressure enough to reform the marine layer. These factors will cause chances for fog and low stratus to return to the coast and interior valleys by Monday morning.

Long Term

..issued at 1238 AM PDT Sun Apr 5 2026 (Monday through Saturday)

Expect notably cooler conditions for Monday from the increased onshore flow, better humidity retention, and that reformed marine layer. Highs, will still be above average but only by a few degrees. Expect widespread highs in the 70s, with the immediate coast in the 60s and the far interior seeing the low 80s.

Tuesday and Wednesday continue the cooling trend as cloud cover increases ahead of a building trough and low pressure approach from the west.

This low will bring rain chances back to for forecast, but has been slowing it's time of arrival over the last few forecast updates. Initial warm-sector drizzle looks to hit the coast by mid to late Wednesday morning, while actual measurable rain will be holding off until late that night and into Thursday morning. The slowing of this system also calls for rain chances lasting longer than previous forecasts. Chances for widespread light rain and drizzle last through Friday with lingering, spottier chances lasting into Saturday afternoon.

Despite the prolonged rain chances, rainfall amounts still look fairly light. Most of the lower elevations of the Bay Area will only see a few hundredths, then up to a tenth for higher elevations in the Bay Area and lower terrain around the Monterey Bay, while higher elevations in the Santa Cruz Mountains and Big Sur Coast look to pass that quarter inch mark. Isolated peaks in the Santa Lucias could pass the half inch mark.

Confidence in the spread of rainfall amounts is still shaky, particularly Friday and Saturday. Models seem to be struggling on the track of the low and the momentum loss. While widespread chances for light rain and drizzle come with good confidence, there is still good potential for these rainfall totals to see some shifting. If the low takes a different track or stalls over the area it could lead to fairly notable changes in where the focus of the rainfall will be. That being said, overall rainfall across the models still looks fairly light. Even if the low stalls over the Central Coast, rainfall may only increase by a few tenths on the highest peaks on Big Sur.

Aviation

(12z TAFS) Issued at 420 AM PDT Sun Apr 5 2026

Lingering offshore flow (much less than 24 hrs ago) and a dry BL has led to another morning of VFR conditions with a few high clouds overhead. Expect VFR through early tonight. Looking farther west over the ocean ad stratus deck is inching east. Latest timing brings a compressed marine layer back to the coast this evening and nosing inland late tonight. Impacts initially to HAF and MRY 00-04Z and after 09Z low clouds infiltrate SF Bay.

Vicinity of SFO, VFR through late tonight. CIGS around 1k feet return for the Monday AM rush.

SFO Bridge Approach, Similar to SFO.

Monterey Bay Terminals, VFR. Low cigs return after 00Z and then remain tonight.

Marine

(today through Friday) Issued at 420 AM PDT Sun Apr 5 2026

High pressure to the north will maintain light to moderate breezes over the coastal waters through early next week. Locally stronger winds will develop near the Big Sur Coast by midweek. Unsettled weather returns the middle of next thanks to a low pressure system over the Pacific. The low pressure will bring fresh to strong gusts across the northern waters, and moderate seas.

Watches, Warnings, Advisories

Ca, None. PZ, None.

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