, Issued at 1201 AM PST Thu Nov 13 2025 (Today and tonight)
A deep upper level trough and strong surface cold front are approaching the coast and will bring substantial rain and wind through the first half of the day. The system is currently stacked back, meaning the surface low is east of the upper level low. This configuration implies both divergence aloft and a strong temperature gradient. The divergence aloft is causing the surface pressure to drop very quickly. In fact, the low is in the middle of explosive cyclogenesis (aka a Bomb Cyclone). This was defined originally by Tor Bergeron in the 1950s as a drop of 24 mb over 24 hours and refined by Sanders and Gyakum in 1980 to adjust this standard for different latitudes. Using the adjustment for 40N, the requirement drops to about 18 mb over 24 hours. The Ocean Prediction Center analyzed this low as 1002 mb at 18Z, and most guidance is hovering around 980 mb by 12Z this morning. That would be a drop of 22 mb over 18 hours, easily meeting the criteria for a bomb cyclone.
As the surface low deepens and the front gets closer over the next 12 hours, the pressure gradient will cause the winds to increase to a strong to southerly breeze that will pump a ribbon of humid (1.5" PW) air to the Bay Area and Central Coast. The strongest winds will be along the coast and in the higher elevations where gusts will routinely reach 60 mph between 3 AM and 8 AM. So far the strongest gust recorded has been 63 mph gust at Cobb Ridge located at 3,225 ft in the Mayacamas of northern Sonoma County. Winds will very gradually decrease through the afternoon and evening.
We have already seen a few showers and thunderstorms, but the main show is still a few hours away. The total accumulation so far has been a few hundredths south of the Golden Gate, with up to 1/2" in the coastal North Bay Mountains. The main rain band is just now moving into KMUX radar coverage and will bring steady rain to the Bay Area commute this morning. The IVT is expected to spike around 750-1000 kg/m/s and remain above 250 for around 36 hours. According to the CW3E AR Scale, this qualifies as a strong atmospheric river. Although the sharp spike may be inflating that definition, the heavy rain will not last more than a few hours and we are not expecting widespread river flooding. Be advised, however, that there will be some roadway flooding as the heavier rain moves through. Even without standing water, the combination of the morning rush hour, wet roads, reduced visibility and strong winds will make for dangerous conditions on the roads this morning.
The thunderstorm threat is increasing. While the models did not predict much activity before midnight, mother nature had other plans. Several lightning strikes were observed across the Central Coast and East Bay around 8-10 PM. These storms have moved into the Central Valley and continue to produce some lightning. Mainly in deference to these earlier storms, we have increased the chance of thunderstorms embedded in the main rain band to around 20-30%. If more thunderstorms form they will most likely be non- severe with heavy rain and lightning strikes as the primary hazard. That being said, the hodographs are nicely curved with ample low level shear and, while the environment seems to be CAPE limited with cool surface temps and still high 500 mb temps, we can't rule out a water spout or a brief tornado.
..issued at 1201 AM PST Thu Nov 13 2025 (Friday through Wednesday)
While the main show is today, unsettled weather will continue through the majority of the forecast period. The low discussed above will gradually become vertically stacked by Friday while getting cut-off from the jet stream. This will cause the system to transition from purely baroclinic to partially barotropic as it parks somewhere near the Channel Islands through Saturday. All the while the continued southerly flow will support periods of lighter rain showers, particularly along the Central Coast. The system will catch the next bus out of town on Sunday as the jet stream dips back down and kicks the system quickly to the NE. The trough axis will slide over the coast on Monday bringing a period of more moderate and widespread rain, followed by strong northerly winds and colder temperatures. Tuesday looks dry and cool before a third trough approaches the coast late Wednesday and may bring even more rain to the Bay Area and Central Coast. The uncertainty really balloons past Tuesday tough, so don't give up all hope for nicer weather next week.
(12z TAFS) Issued at 345 AM PST Thu Nov 13 2025
A strong cold front will move eastward across the Bay Area and north Central Coast through morning and afternoon. Strong southerly winds leading up to cold frontal passage will result in areas of low level wind shear (llws) mainly nearest the coast, however a few smaller areas of llws may extend inland as well. Heavy rain and a slight chance of thunderstorms will accompany the cold front. VFR-MVFR except IFR in heavy rain along and ahead of the cold front today. Post cold frontal winds will gradually subside as will llws in the wake of the front. Low clouds /MVFR-IFR/, less to much less wind tonight and Friday morning.
Vicinity of SFO, Strong southeasterly wind 25 to 35 kt through 18z this morning, easing somewhat after 18z today. Moderate to heavy rain today with MVFR ceiling. By late afternoon the cold front will have moved east of the terminal, winds continue ease through evening long after the cold front moved by the terminal. Generally VFR-MVFR tonight and Friday morning.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, Low level wind shear (llws) KMRY TAF for up to 60 knots of south-southeast wind just above the terminal for the morning hours. As the cold front presses in from the west during the morning, llws may extend beyond KMRY Airport. Otherwise well mixed winds are likely surface to aloft e.g. in the Salinas Valley. Once the downsloping (drying) southeasterly offshore winds yield to strong frontal convergence, upward vertical motion, cooler post frontal air bumping into plenty of latent heat release from a heavy water vapor plume from the subtropics, heavier rain will develop resulting in IFR conditions. Cold frontal passage will be west to east, timing approx late morning if not early to mid afternoon. Rain diminishes to showers after the front moves through, with lingering showers and diminishing winds much later today. MVFR with light southeast winds tonight and Friday morning.
(today through Tuesday) Issued at 313 AM PST Thu Nov 13 2025
Widespread hazardous marine conditions continue this morning, conditions gradually diminishing from north to south later in the morning and afternoon. Gales to storm force winds, heavy rain and a slight chance of thunderstorms will accompany a strong cold front as it moves eastward. Winds will then continue to steadily decrease tonight. Moderate to rough seas will build to become rough for the inner waters and very rough for the outer waters today through Friday. Seas abate to become moderate by Saturday.
Issued at 124 AM PST Thu Nov 13 2025
A Beach Hazards Statement is in effect from this afternoon through Friday evening. Long period westerly swell will result in an increased risk for sneaker waves and rip currents. Breaking waves of 13 to 18 feet with the highest waves up to 23 feet in favored locations are expected. Sneaker waves can unexpectedly run significantly farther up the beach than normal, including over rocks and jetties. Rip currents are typically more frequent and stronger in the vicinity of jetties, inlets, and piers.
Ca, High Wind Warning until 10 AM PST this morning for CAZ006-502- 505-509.
Beach Hazards Statement from 3 PM PST this afternoon through Friday evening for CAZ006-505-509-529-530.
Wind Advisory until 10 AM PST this morning for CAZ503-504-506.
Wind Advisory until 4 PM PST this afternoon for CAZ508-510- 512>518-528>530.
PZ, Gale Warning until 3 PM PST this afternoon for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm-SF Bay N of Bay Bridge.
Storm Warning until 9 AM PST this morning for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm.
