Marine Weather and Tide Forecast for Walnut Creek, CA

SHORT TERM
(Today and tonight)
Issued at 1231 AM PDT Mon Apr 21 2025

With weak zonal flow aloft, the weather is pretty benign today.
The Ft. Ord profiler is measuring the marine layer at 1,500 feet tonight. As a result, the coastal stratus deck extends into the San Francisco Bay and through the majority of the Salinas Valley.
These clouds will mix out by noon before what should be an beautiful afternoon. High temperatures are expected to approach 80 degrees in the warmer inland areas such as Santa Rosa, Livermore, and San Jose. That's about 5-10 degrees above normal, but no where near record territory. Despite the clouds mixing out, coastal areas will remain in the cooler marine layer air, with more seasonal temperatures generally in the 60s.

LONG TERM
(Tuesday through Sunday)
Issued at 1231 AM PDT Mon Apr 21 2025

Tuesday will start with less clouds than Monday as the marine layer compresses to around 500 feet. Otherwise the warmer temperatures will continue Tuesday afternoon, although an evening breeze will bring more of a chill as the sun goes down. In the upper levels, a moderate trough will move through far northern California late Tuesday - Wednesday. At the same time, the warm thickness tongue across California will smooth out causing surface temperatures to drop fairly significantly Wednesday. With more upper level moisture resulting in high cloud cover, additional cooling is expected Thursday, by which point temperatures will be roughly roughly 5-10 degrees lower than normal. A deeper trough approaches the coast on Friday. There is still some uncertainty regarding the timing and strength of this system, but the overall trend has been drier over the last couple days of model data. There's still a slight to moderate chance of very light rain Fri- Sat, but the chance for more significant rain >0.1" is currently only around 20% according to the NBM. Whether it rains or not, this system will likely bring some stronger onshore winds, with gusts up to 20 or 30 mph at times. The influence of this trough will likely extend into early next week before ridging returns.

AVIATION
(06Z TAFS)
Issued at 927 PM PDT Sun Apr 20 2025

Stratus and fog /MVFR-IFR/ continues along the coast from Point Sur to the vicinity of Point Reyes per satellite imagery. Drier air flow continues to advect southward over the northern coastal waters. Recent HRRR output has followed this pattern fairly closely, showing additional clearing taking place through the evening to the south of Point Reyes. Surface winds are forecast to become weakly cyclonic over the inner waters tonight and Monday morning, the wind field and radiational cooling aloft becoming a focus for regrowth of stratus and fog. Onshore winds will locally bring stratus and fog /MVFR-IFR/ inland. The marine layer depth has compressed to around 1200 feet per recent profiler data and spot checking coastal temperatures. A thinner marine layer will help speed up stratus and fog mix out times Monday morning.

Vicinity of SFO...VFR, then MVFR stratus ceiling forecast 09z early Monday, mixing out to VFR 17z Monday. West-northwest decreasing to a light west wind then shifting to light northeast wind Monday morning. West-northwest wind resuming Monday afternoon with gusts near 20 knots until early evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Satellite imagery shows stratus /MVFR-IFR/ filled in across the Monterey Bay. The marine layer depth at the Fort Ord profiler has recently varied between 1200 and 1400 feet.
HRRR output shows stratus and fog filling into the Salinas Valley tonight and Monday morning. Stratus and fog /MVFR-IFR/ mix out by around noon Monday. Onshore winds mainly continuing during the period between 5 and 15 knots.

MARINE
(Tonight through next Saturday)
Issued at 853 PM PDT Sun Apr 20 2025

Breezy to gusty north to northwest winds are building in the northern waters along with building north swell. Winds look to increase and spread across the outer waters into the work week.
The gusty occasionally gale force northerly winds in the afternoon look to become more widespread into the mid week.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory until 3 AM PDT early this morning for Pt Arena to Pt Reyes 0-10 nm.

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