Marine Weather and Tide Forecast for Union City, CA

SHORT TERM
(Today and tonight)
Issued at 1206 AM PDT Mon Apr 28 2025

A 500 mb positively tilted trough extends across Southern California anchored by a low pressure center over the Rockies.
The lower pressure and residual moisture has allowed cloud cover to linger longer through the night than expected. In the last hour or so, the stars are finally starting to come out for much of the Bay Area as drier air moves in. The chance for widespread dense fog has decreased due to the lingering clouds keeping surface cooling in check. Despite this, there is still a decent chance for areas of fog during the Monday commute for areas currently under clear skies. If fog does form, it will mix out by late morning as the drying trend continues through the day. Mostly clear skies are expected this afternoon, which will be a nice change after a dreary weekend. At the same time, warmer air will filter in as a high pressure ridge moves in from the Eastern Pacific. Maximum temperatures should climb to the low to mid 70s for inland areas. Coastal areas will stay in the low 60s with some morning clouds as a 1000-foot marine layer starts to organize.

LONG TERM
(Tuesday through Sunday)
Issued at 1206 AM PDT Mon Apr 28 2025

The overall pattern is dynamic as the current trough exits Monday, a ridge builds Tue-Wed, a short wave trough moves through Thursday before a more substantial trough moves through Saturday.
This will cause the SFO-WMC gradient to swing from +7 mb to around -5 mb mid-week, and back positive by the weekend.

In the medium term the ridge will continue to build, and 850 mb temperatures are expected to climb from 3.7C on the Sunday 00Z sounding to roughly 13-15C by mid-week. That's a pretty drastic change, warming from around the 20th percentile to the 80th percentile for this time of year based on the sounding climatology. This will cause inland temperatures to climb into the upper 70s Tue-Wed, with mid 60s in the coastal marine layer. A short wave trough will move through Thursday, though the impacts will be limited mostly to increased cloud cover. Friday looks like a transition day as ridging briefly rebuilds before a more substantial long wave trough moves through Saturday. This system will bring overcast skies, cooler temperatures, and some light rain, but the biggest impact will likely be strong winds. The trough will support a fast moving cold front that will move through late Friday or early Saturday. As high pressure builds behind this front, the gradient will support strong NW winds. The NBM shows roughly an 80% chance of wind gusts exceeding 30 mph on Saturday for the majority of the area, with about a 40% chance of exceeding 40 mph along the coast and in higher terrain. The trend has been increasing, mainly driven by the ECMWF ensemble, which is quite a bit stronger and more confident than GEFS at this time.

AVIATION
(18Z TAFS)
Issued at 1039 AM PDT Mon Apr 28 2025

Generally VFR through the remainder of the day. Satellite shows stratus lingering at HAF but clearing is expected to occur by early this afternoon. The marine layer looks to compress tonight which will confine stratus to Bay Shoreline and coastal areas. Confidence is low that stratus will reach SJC/LVK but GFS and NAM guidance do indicate some potential for that to occur.
Moderate onshore winds are expected during the day with light, variable to at times offshore winds expected overnight. CIGs look to start clearing around 17-19Z tomorrow with most sites looking to clear just after the end of this TAF period.

Vicinity of SFO...VFR becoming MVFR overnight. Moderate confidence that MVFR CIGs will reach SFO overnight with most guidance in consensus that low clouds will extend into the SF Bay. The caveat is how much the marine layer is able to compress, if it compresses more than currently forecast that could limit the amount of cloud cover able to reach SFO. Moderate west to northwest winds continue during the day today and tomorrow with weaker onshore flow expected overnight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...CIGs have decreased across the Monterey Bay region with VFR to prevail through this afternoon. Low confidence on return timing of CIGs this evening. Kept similar to previous TAF with an earlier return around 03-04Z tonight for MRY.
LAMP, NAM, and GFS guidance suggests stratus could return much later overnight around 09Z. Decided to continue the 03-04Z time frame knowing the marine layer will compress tonight and HRRR shows CIGs reaching MRY earlier in the evening. Moderate west to northwest winds persist during the day before lighter, variable to at times offshore winds develop overnight.

MARINE
(Today through Saturday)
Issued at 1039 AM PDT Mon Apr 28 2025

Fresh to strong north to northwest winds strengthen over the coastal waters through the early work week as high pressure builds. Near gale force to isolated gale force gusts are possible over the far outer coastal waters. Moderate seas are expected over the outer waters as wave heights build to 8 to 11 feet. Winds diminish midweek as high pressure weakens as a shortwave trough moves through. Another, deeper, upper level trough and surface cold front will move across the coastal waters and bays late Friday.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this evening for Pt Arena to Pt Reyes 0-10 nm-Pt Pinos to Pt Piedras Blancas 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.