Issued at 901 PM PDT Thu Jul 24 2025
KMUX radar shows an isolated and steadily weakening shower (echo tops now only 22 thousand feet) over northern Napa County. Haven't been able to find any measurable precipitation reports under this shower, it's likely virga (evaporating before reaching the ground) for the most part. More convection can be seen moving westward from the northern Sierra Nevada and across the Central Valley, in the northeastern quadrant of a weak and closed 500 mb low pressure center (582 decameters height) located over the north Central Coast. Weak upper level jet stream winds located at the base of the closed low are just barely nudging the low eastward. Low clouds are otherwise filling back in along the coast tonight. No forecast updates are planned for tonight. For additional info on the forecast please see details below.
, Issued at 102 PM PDT Thu Jul 24 2025 (This evening through Friday)
Temperatures will continue to be below average for this time of year as a cut-off low pressure remains off of the San Francisco Bay Area/Central Coast. Thus, expect little day-to-day change in forecast maximum and minimum temperatures. Low clouds have scattered out and/or dissipated across the region as of this writing. Low clouds, coastal drizzle and favored orographic lift locations across the region once again tonight into early Friday morning.
As the cut-off low moves inland over the San Francisco Bay Area on Friday, there will be enough MUCAPE (most unstable CAPE) and generally between 1.10-1.30" of PWATs across the far northern portions of the North Bay to produce a less than 5% chance of high based convection. The greatest timeframe will be early to mid- morning on Friday, yet confidence remains low enough not to include in the official forecast. Again, afternoon maximum temperatures will continue to be below average on Friday.
From previous forecaster: "A Coastal Flood Advisory (the last one of this sequence) is in effect from 9PM Thursday through 2AM Friday. Minor coastal flooding can be expected during high tide along the Bayshore of San Francisco Bay and San Pablo Bay. Localized nuisance flooding can be expected in coastal locations that are directly next to Richardson Bay such as Sausalito, Tam Valley, Manzanita, the Sausalito-Mill Valley Bike Path, and the Manzanita Park N Ride. Do not drive around barricades or through water of unknown depth."
..issued at 102 PM PDT Thu Jul 24 2025 (Friday night through next Wednesday)
As mentioned above, there is enough MUCAPE and PWATs are forecast to range from 1.10-1.30" across the northern portions of the North Bay to again result in less than 5% chance of high based convection Friday night into early Saturday morning.
By Sunday, the upper level cut-off low pressure will be absorbed in the mean flow aloft. As such, a slight warming trend is forecast for Sunday afternoon, but only by a few degrees across the interior while the coast holds steady. Global ensemble clusters then indicate that the ridge across much of the remainder of the United States will build westward and into the Intermountain West. This will result in a warming trend from Monday and throughout the remainder of the week. However, the coast will remain under the influence of the marine layer that is forecast to compress as the high pressure builds westward.
(00z TAFS) Issued at 555 PM PDT Thu Jul 24 2025
Cloud cover is beginning to build along the coast with MVFR CIGS affecting HAF. These CIGs will begin to fill around the bays move farther inland into the evening, filling over the Monterey Bay terminals, ST, and OAK by the early night. Winds look to reduce across the district into the evening, becoming light to moderate through the night and much of Friday morning. CIGS continue to spread deeper inland into the late night with Widespread CIGs expected. HAF,MRY, and STS look to fall to IFR-level CIGS overnight. Sites begin to clear in the late morning with most TAF sites going VFR in the afternoon. The exception will be HAF, which will go from IFR to MVFR CIGs, but will not clear through the TAF period. Expect modest wind increases into Friday with most areas peaking around 15 kt winds and the occasional stray gust. Winds reduce again that evening with CIGs quickly returning into the bays and becoming widespread again that night.
Vicinity of SFO, VFR lasts into the evening. Winds reduce slightly as MVFR CIGs cross over the SF Peninsula and fill over SFO in the late evening and early night. Cloud cover scatters in the early afternoon as west winds increase, but re-fills over the terminal again in the early evening on Friday.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, Winds look to reduce into the mid evening but stay moderate as MVFR CIGS build. Winds reduce further into the night and MRY falls to IFR CIGs, but snaps back to MVFR in the mid morning. The terminals clear in the early afternoon on Friday as winds increase, but MVFR CIGs build back into MRY again in the late afternoon.
(tonight through next Wednesday) Issued at 555 PM PDT Thu Jul 24 2025
Gentle winds will increase to a moderate NW breeze Friday. A fresh breeze will push through the San Francisco and Monterey Bays through Friday afternoon, generating occasional whitecaps. Otherwise low seas will prevail through the weekend. A deep marine layer will bring consistent low cloud cover and periods of drizzle.
Ca, Coastal Flood Advisory until 2 AM PDT Friday for CAZ006-506-508.
PZ, None.
