, Issued at 911 PM PDT Wed Mar 25 2026 (Tonight through Friday)
Generally quiescent conditions are forecast during the short term period, with the exception being across some of the higher terrain of the North Bay Interior Mountains as well as parts of the East Bay Hills tonight, but especially pre-dawn Friday morning.
A dry/cool frontal boundary continues to slide southward through portions of the North Bay this evening, with a pretty discernible northerly wind shift evident on observations upstream across Lake and Mendocino Counties. This frontal boundary will usher in some cooler air and as noted previously, min temperatures should be a touch cooler (at least across the North Bay), but sunrise Thursday compared to the past few days. Overall, not anticipating a potential for widespread frost/freeze conditions, though a few spots may dip down into the upper 30s across extreme northern Sonoma and Napa Counties.
925mb flow does increase some on Thursday morning, in the immediate wake of the front, but the real potential for any type of mountain wave activity is greater on Friday morning. This will be due to building high pressure in the wake of the front through the day on Thursday. As the MSLP gradient tightens beneath a largely stable regime, flow will become trapped and forced around the complex terrain. Areas such as Mt. St. Helena and other peaks across the North Bay Mountains may see winds gust as great as 45 mph pre-dawn Friday morning. The SJSU/PG&E WRF as well as our in- house model highlight this potential well.
Otherwise, mid/upper level clouds will continue to invade from the southwest resulting in partly sunny skies. Despite largely filtered sunshine, high temperatures will remain 10 to 15 degrees above normal. This trend will continue through the weekend.
..issued at 911 PM PDT Wed Mar 25 2026 (Friday night through next Wednesday)
The weekend is anticipated to be quite pleasant. With the magnitude of offshore flow weakening slightly, this may allow for the afternoon sea-breeze to bring MaxTs down a few degrees compared to the previous days. Still highs are expected to remain 5 to 10 degrees above normal.
Our ridge pattern that has resulted in our well above normal heat will yield to more pronounced troughing as we venture into next week. There do remain some temporal and spatial differences in the placement of more vigorous shortwaves in the longwave trough and we'll continue to examine the latest guidance as it arrives for next week.
Some of the synoptic scale progs from the deterministic guidance advertise swift mid-level flow extending from the southwest with favored large scale ascent beneath the exit region of a 50 knot jet. This will equate to cooler conditions next week. At this time, Monday appears largely precipitation-free and this is a slight change from previous forecast cycles due to a slower evolution of the upper trough as it amplifies across the West Coast. Overall, NWP is in fair to good agreement with this feature. After a few days of troughing, a corridor of 180-200% of normal precipitable water air will stretch from the Central Pacific eastward toward California. Both GEFS and EPS renditions of the probability of Integrated Vapor Transport (a useful tool for quantifying moisture transport) above 250 kilogram/meter/second have gradually increased from less than 10% 72 hours ago to near 50% in the latest guidance. There are some spatial differences among model guidance with regard to the exact location of this plume of rich moisture and thereby the placement of the greatest rainfall and we'll continue to iron out these details through the weekend.
Current forecast rain amounts appear respectable for this time of year, with the greatest potential for at least 1" of rainfall across the North Bay from late Monday into Wednesday. Chances for at least 2" of rainfall (which would be the higher end rain amount) are around 10% across the Western Sonoma Hills, Santa Cruz Mountains, and the Diablo Range. As noted above, once we get closer, we'll be able to refine these rain amounts.
With actual upper level dynamics, surface/low level cyclogenesis appears that it'll give some of the higher terrain and Pacific Coast regions around a 40-70% chance for SW'ly wind gusts near/above 40 mph. Increased onshore flow and subsequent cloud cover will also equate to temperatures being 5 to 15 degrees below normal by the time we get into next week with daytime highs ranging between the mid 50s to mid 60s.
(12z TAFS) Issued at 524 AM PDT Thu Mar 26 2026
There's patchy coastal stratus /IFR-MVFR/ this morning, otherwise VFR is forecast. The northerly ACV-SFO pressure gradient is strong at 8.0 mb, UKI-STS is 2.0 mb and the SFO-SAC gradient is onshore 1.7 mb.
Later today, tonight and Friday morning the WMC-SFO gradient rapidly steepens to ~ 10 mb with a strong zonal i.e. west-east jet stream on the synoptic scale across the northern CONUS. Mentioning this for multiple reasons: 1) the pattern will be dry in our forecast area supporting VFR, 2) there'll be a temporary period of low level wind shear favoring the North Bay tonight and Friday morning, 3) the synoptic pattern has been very energetic as we have seen either side of the now deamplified, flatter yet still strong CONUS long wave ridge, 4) the WMC-SFO gradient rapidly weakens by Saturday, 5) rarely does the jet stream take a west-east route when the WMC-SFO steepens like this, instead it's often north-south while advancing eastward across the Pacific Northwest and 6) suspect the rapid motion of the surface high with origins at higher latitudes i.e. exiting the Bering Sea two-three days ago is related to the negative PDO i.e. corner of the Pacific where sea surface temps remain colder than normal (favoring more swiftly moving weather systems).
Vicinity of SFO, VFR. West to northwest wind shifting to light northeasterly this morning then northwest 10 knots in the afternoon and evening. Light wind shifting to northeasterly late tonight and Friday morning.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, VFR. Light and variable winds becoming onshore 10 to 15 knots today, winds decreasing to light easterly to southeasterly tonight and Friday morning.
(today through Tuesday) Issued at 421 AM PDT Thu Mar 26 2026
Northwesterly gales will persist through today mainly across the northern outer waters. Surface high pressure will build over the Great Basin today, tonight and Friday morning resulting in winds and seas easing across the coastal waters tonight, Friday. Onshore winds will then prevail through the weekend. A wet weather pattern develops next week.
Ca, None. PZ, Small Craft Advisory until 9 AM PDT this morning for Pigeon Pt to Pt Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm.
Small Craft Advisory until 9 PM PDT this evening for Pt Pinos to Pt Piedras Blancas 0-10 nm.
Gale Warning until 9 PM PDT this evening for Pt Arena to Pt Reyes 10-60 NM.
Gale Warning until 9 AM PDT this morning for Pigeon Pt to Pt Pinos 10-60 NM.
