Marine Weather and Tide Forecast for Diablo, CA

SHORT TERM
(Today and tonight)
Issued at 203 AM PDT Tue May 20 2025

Heights will ever so slightly fall today as a subtle upper-level shortwave trough skirts the region, but temperatures will still remain seasonably warm. High pressure over the Eastern Pacific Ocean and low pressure over the Desert Southwest will support a tight surface pressure gradient that will be conducive for northwesterly flow that will be locally strong over the waters, along the coastline, and through northwest/southeast oriented valleys such as the Salinas and Santa Clara. The return of onshore flow has allowed for cooler and moister conditions and subsequently the reformation of the marine layer, albeit an interesting looking one as offshore/downslope flow in the higher terrain of the North Bay and Santa Cruz Mountains is resulting in compressional warming that's effectively wiping out the marine layer in those spots. Elevated fire weather conditions will be prevalent, primarily across the brush and grasses of the interior, through Thursday as dry and gusty conditions continue.

LONG TERM
(Wednesday through Monday)
Issued at 203 AM PDT Tue May 20 2025

A low amplitude upper-level shortwave ridge will nudge into the region Wednesday, bringing the warmest conditions of the week with temperatures of 10 degrees above normal. Global ensemble clusters are all in agreement of heights falling through Friday due to an upper-level shortwave trough, which will translate to temperatures returning to seasonal normals by Friday as the brief, gradual cooling trend brings temperatures down by 5 degrees each day. Agreement in global ensemble clusters continues with heights rebuilding Saturday as an upper-level shortwave ridge builds into the West, kicking off another brief, gradual warming trend.
Oakland Museum (OAMC1) and San Francisco Downtown (SFOC1) will put their daily minimum temperature records in jeopardy this week.
Oakland Museum (OAMC1): Wednesday (5/21), Saturday (5/24), Sunday (5/25), and Monday (5/26), previous records of 49, 49, 49, and 50 degrees respectively set in 1986, 2011, 1980, and 2008 respectively, the official forecast is 51, 51, 51, and 53 degrees respectively. San Francisco Downtown (SFOC1) on Friday (5/23) and Sunday (5/25), previous records of 47 degrees set in 2010 and 1953 respectively, the official forecast is 50 degrees.

AVIATION
(06Z TAFS)
Issued at 835 PM PDT Mon May 19 2025

It's VFR over land except patches of stratus and fog /LIFR-IFR/ are developing along the immediate coastline. Late afternoon and early evening satellite imagery showed standing waves within the stratus and fog.

The ACV-SFO pressure gradient is 7.2 mb, the UKI-STS pressure gradient is strong at 2.6 mb, the onshore gradient SFO-SAC is 2.7 mb. Pressure gradients initiate atmospheric motion; the overall pressure pattern in recent days has favored gusty northwest winds over the coastal waters and gusty west winds across the San Francisco Bay, this is common during spring and even early summer seasons. The marine layer varies in depth from several hundred feet to locally up over 1500 feet e.g. Fort Ord profiler.

A general convergence of higher dewpoint air (water vapor) in contact with chilly sea surface temps 50F-55F trapped beneath the lower level temperature inversion ahead of overnight cooling both due to temperature advection and radiative cooling to space favor additional stratus and fog /LIFR-IFR/.

Vicinity of SFO...Strong west wind continuing through the evening, with gusts 35-40 knots up through midnight. Increasing convergence of stratus and fog on the ocean side of the peninsula will likely advect on westerly wind reaching SFO late tonight and early Tuesday morning, a dry surface based cold front will move southward along the coast temporarily moving the stratus inland to the terminal before drier post frontal air moves in for early return to VFR Tuesday. West wind increasing to 20 to 30 knots with possibly higher gusts Tuesday afternoon and evening. Current HRRR output shows VFR for Tuesday night.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...It's currently VFR, however expect an increasing probability of stratus with patchy fog /LIFR-IFR/ with onshore winds 10 to 20 knots during the evening. Expect LIFR-IFR in stratus, fog including possibly a few patches of late night and/or morning drizzle tonight and Tuesday morning. Conditions improving to VFR by late Tuesday morning and early afternoon.
Onshore winds 10 to 20 knots Tuesday afternoon and early evening.

MARINE
(Tonight through next Sunday)
Issued at 810 PM PDT Mon May 19 2025

Surface high pressure will result in widespread strong northerly gale force gusts over the inner and outer waters through Tuesday.
Hazardous seas will persist Wednesday through Friday with strong northwesterly winds occasionally near gale force gusts.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory until 3 AM PDT early this morning for SF Bay N of Bay Bridge.

Small Craft Advisory until 9 PM PDT this evening for Mry Bay.

Gale Warning until 9 PM PDT this evening for Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.

Gale Warning until 3 AM PDT Wednesday for Pt Arena to Pt Reyes 10-60 NM.