Marine Weather and Tide Forecast for Castro Valley, CA

SHORT TERM
(Today and tonight)
Issued at 1203 AM PDT Wed Apr 30 2025

The threat for fog returns later this morning. The marine layer is currently around 1,000 feet according to area profilers. With some light dry offshore wind in the North Bay, the best chance for fog is along the San Francisco Peninsula coast and Monterey Bay region, including Big Sur and the Salinas Valley. A few upper level clouds and some wind could limit radiation fog, but even so, the typical foothill locations will almost certainly be dealing with reduced visibility in the marine layer cloud deck. Slightly elevated coastal areas such as Corallitos and Hurricane Point have the best chance.

A weak short wave trough is moving from north to south across California today. This system will bring slightly colder air to the upper levels while the surface temperature remains warm. With relatively high moisture (PW around 0.8") and conditionally unstable lapse rates, there is a chance for some isolated convection today. In fact the HRRR, NAM, and ECMWF deterministic model soundings for Santa Rosa all agree that the MUCAPE will exceed 1,000 J/kg this afternoon. On the other hand, some weak offshore winds will keep the low-level moisture suppressed and there will be a bit of convective inhibition below the LCL. Most likely if this convection is realized, it will only create some puffy cumulus clouds. There is very little support in the guidance for thunderstorms, or even rain, but there is still a non-zero chance based on the instability and relatively high integrated moisture.

LONG TERM
(Thursday through Tuesday)
Issued at 1203 AM PDT Wed Apr 30 2025

By Thursday the weak disturbance and associated instability will move into southern California. This will allow the ridge to rebuild over northern and central California, bringing us another day of warm inland temperatures and cool marine layer conditions along the coast. Temperatures will start to fall a bit on Friday as a much more robust trough approaches the coast. This system will support a fast moving cold front at the surface late Friday or early Saturday, and could bring some pre-frontal rain. The models have almost universally backed off on the rain chances, but we still have PoPs around 15%. While we expect overcast skies and much cooler temperatures, the biggest story with this system is wind. The trough will spawn a cut-off low that moves into Southern California by Saturday. The gradient between the low and higher pressure over the Eastern Pacific will support 50-70 mph winds at 500 mb. As the atmosphere becomes well mixed Saturday afternoon, some of this momentum will transfer down to the surface where NW winds of 15-30 mph, and gusts as high as 50 mph are expected. The strongest winds will be along the coast and in higher terrain.

By Sunday the low will start to move inland towards the desert Southwest. We will still be dealing with lingering strong winds, but it should be an improvement over Saturday. Early next week a ridge will start to rebuild, decreasing the wind speed and causing the temperatures will gradually recover. By mid-week we should be back to the nice seasonal weather we've had this week.

AVIATION
(12Z TAFS)
Issued at 406 AM PDT Wed Apr 30 2025

Currently a mixed bag of VFR-IFR at the terminals. The marine layer depth is at 1,600 feet and is expected to deepen as a shortwave trough traverses the region from north to south. As a result, ceilings and visibilities will be relatively higher in addition to being able to mix out relatively quicker. VFR is expected by this afternoon with clouds sticking to the coast.
Winds will be diurnal through the TAF period.

Vicinity of SFO...Currently VFR with westerly flow. It's going to be another nail biter this morning with IFR/MVFR stratus to the north of OAK and SFO within the San Francisco Bay. The time period of possibility for stratus to make a run at the terminal is between now and 17Z.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently IFR with westerly flow at MRY and IFR with northerly flow at SNS. Both terminals will begin to gradually improve by mid-to-late morning, but low clouds are expected to hug the coast throughout the day. Diurnal winds will prevail through the TAF period with a return to IFR conditions towards the end of the TAF period.

MARINE
(Today through Monday)
Issued at 406 AM PDT Wed Apr 30 2025

Strong northwesterly breezes with near-gale force gusts will continue over the outer waters through Thursday morning along with rough seas. Strong northwesterly breezes return Friday afternoon, strengthening to become gale-force by Saturday. Rough seas return to the outer waters by Saturday.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory until 9 AM PDT this morning for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm.

Small Craft Advisory until 3 PM PDT Thursday for Pt Arena to Pt Reyes 10-60 NM.