UPDATE
Issued at 908 AM PDT Sat Apr 26 2025

Light rain continues across southern Monterey County and San Benito County with a few wrap around showers located to the north over the Bay Area. Over the last 12 hours, up to 0.04" of rain has fallen over the Central Coast. Across the majority of the Bay Area, rainfall has been light (generally a few hundredths of an inch). The exception to this is in northeast Contra Costa County where localized wrap around showers produced up to 1/4" of rain within the last two hours. No reports of lightning so far but guidance continues to indicate up to a 15% chance of thunderstorms across the Central Coast through this afternoon.

SHORT TERM
(Today and tonight)
Issued at 1240 AM PDT Sat Apr 26 2025

An upper level low off the coast is moving toward Point Conception early this morning. This cold-core low is dropping the 500 mb temperature as low as -27C, which is in the bottom 5% for this time of year. With cold air aloft, the atmosphere will be unstable (relatively warm air near the surface will be buoyant and accelerate upward). This effect is most pronounced when the maximum surface heating in the afternoon lines up with the coldest air aloft. In this case, the timing doesn't line up. The coldest air is moving in early this morning, well before the maximum surface heating this afternoon. Nonetheless we are still expecting isolated showers to continue through the day, and there is still a slight chance for thunderstorms, mainly over the Central Coast.
There are 2 windows that are more favorable for stronger convection. The first is in the pre-dawn hours this morning over the coastal waters (which are 5-7 degrees F warmer than the land at the moment). The second is over southern Monterey County this afternoon between 11 AM and 3 PM due to enhanced surface heating.
For what it's worth, the higher resolution models are more aggressive than the global models (HRRR brings the surface CAPE above 200 J/kg to areas south of San Jose). The latest satellite imagery suggest overcast skies are moving in across the interior Central Coast and will likely stick around for most of the day.
This will reduce the surface temperature, limit the instability and decrease thunderstorm chances.

LONG TERM
(Sunday through Friday)
Issued at 1240 AM PDT Sat Apr 26 2025

As the bowling ball of cold air aloft moves further inland, it will eventually be picked up by a positively tilted trough early in the work week. This will cause a pretty stark change in the weather pattern as moist, cool onshore flow this weekend flips to warm, dry, offshore wind by Monday. Sunday will serve as a transition day with light showers lingering in the morning and skies clearing through the afternoon. Fortunately the offshore winds look pretty weak and diurnal wind shift will still dominate along the coast. The SFO- WMC gradient is only expected to drop somewhere between neutral and -6 mb. This is the type of pattern that brings fantastic weather to the Bay Area this time of year.
Inland highs will be in the mid 70s with coastal areas reaching the mid 60s. The weather will remain pretty consistent through the week as the positively tilted trough fades into a pure ridge by Thursday. Ensemble clusters suggest this ridge will break down next weekend, although the exact pattern is still uncertain. Some solutions bring another cut-off low through, while other have more straight-forward troughing. Either way, this looks like our next chance for rain. Both GEFS and ECMWF ensemble means show a modest amount around 1/10-1/4", but there are a few outliers among the members of both ensembles that suggest up to 1" is a possible scenario.

AVIATION
(18Z TAFS)
Issued at 1106 AM PDT Sat Apr 26 2025

Convective clouds starting to rapidly develop over higher terrain with upper low nearby. Most terminals are forecast to remain mainly dry but tafs will show vicinity showers. Most cigs should remain mvfr outside of heavier downpours. Cant rule out isolated lightning chances but best chances remain away from terminals over higher terrain and out towards the Central Valley. Best chance of showers will be afternoon hours, roughly 21-00z and then a final shot 02-06z as final shortwave rotates down the coast from North Bay to Central coast with most likely terminals to see showers being Half Moon Bay and Monterey under post frontal favorable NW wind flow pattern. Skies to quickly trend VFR after sunrise Sunday with drying trend building in behind upper trof.

Vicinity of SFO...WNW winds mainly under 15 kt with cigs mainly MVFR. Nearby showers this afternoon and into this evening. Drying trend returns by 12z Sunday.

SFO Bridge Approach...Similar to SFO with showers passing over the Bay possibly impacting visuals of the runways at times this afternoon and evening.

Monterey Bay Terminals...Building cumulus over the higher terrain around MRY and SNS with prevailing NW winds this afternoon and evening. Nearby showers this afternoon then better chances for light rain and lowering cigs for KMRY between 02-07z as final disturbances pushes through. Drying trend with VFR skies developing 13-17z Sunday.

MARINE
(Today through Thursday)
Issued at 421 AM PDT Sat Apr 26 2025

Showers will continue today due to a low pressure system moving southeastward over the coastal waters. Tonight and Sunday the low will move eastward with a few lingering showers possible over the coastal waters and bays. Breezy northwest winds will develop across the northern outer waters from later today to Sunday. High pressure will bring dry weather next week.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory from 9 PM this evening to 9 AM PDT Sunday for Pt Arena to Pt Reyes 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

Small Craft Advisory from 3 PM this afternoon to 9 PM PDT Sunday for Pt Arena to Pt Reyes 10-60 NM.

Small Craft Advisory from 9 PM this evening to 9 PM PDT Sunday for Pigeon Pt to Pt Pinos 10-60 NM.