, Issued at 343 AM PST Mon Dec 15 2025 (Today and tonight)
Today will start off foggy once again for bayshore, coastal, and valley locations. Low visibility could make driving conditions hazardous. If driving, slow down, use your low-beam headlights, and leave plenty of distance ahead of you. If commuting, allow extra drive time to reach your destination safely.
A change is on the way though! In fact it can be seen in the form of high clouds streaming in from the west. These high clouds are associated with a storm force low off the coast of the Oregon/Washington border that is headed to British Columbia. The accompanying cold front will lose steam as it approaches the area, all but becoming stationary. While rainfall is possible as early as tonight, it will more than likely have to wait until tomorrow. This is when some form of upper-level support (longwave trough) skirts the region. The aforementioned feature will act to sweep through what is left of the first cold front by bringing a gale force low and its attendant cold front along with it. Rainfall will be light and beneficial, generally remaining confined north of the Golden Gate with the Central Coast remaining dry outside of maybe some coastal/higher terrain drizzle. Probably of more interest is that this pattern change will finally put at least a temporary end to the gloomy days as the atmosphere becomes too turbulent to support radiation fog.
..issued at 343 AM PST Mon Dec 15 2025 (Tuesday through Sunday)
Some lingering rain showers are possible Wednesday and Thursday, but generally speaking it will be dry. The next system arrives Friday as a surface low pressure system enters into Northern California. The attendant cold front will become a stationary front Saturday into Sunday. This will be the thing to watch as stationary fronts offer an area of convergence and are a conveyor belt of moisture. Still, as of now, everything this week seems beneficial, especially coming off of a notable dry spell for November/December. When all is said and done, the official rainfall total forecast for the week (Monday through Sunday) has 2.50"-4.00" for the higher terrain of the North Bay, 1.25"-2.50" for North Bay Interior Valleys, 0.50"-1.25" for the East Bay, South Bay, San Francisco Peninsula, and Central Coast, and 0.50" or less for the Interior Central Coast.
The Climate Prediction Center continues to highlight a moderate risk for precipitation Monday, December 22nd through Friday, December 26th, moderate risk for high winds Monday, December 22nd through Sunday, December 28th, and a high risk for precipitation for the North Bay Monday, December 22nd through Thursday, December 25th. All of the rainfall that we receive this preceding week will undoubtedly play a role in potential impacts next week.
(12z TAFS) Issued at 441 AM PST Mon Dec 15 2025
Fog and dense fog coverage continues to increase. Conditions are near ideal for fog development as well as the transport of fog on light offshore winds. The Central Valley's tule fog and low stratus ceilings continue to extend westward across the low lying areas of the Bay Area. Fog and dense fog are also developing over the north Central Coast. Lower to mid level stability is strengthening with 500 mb ridging, this will reinforce the stable cap over the fog, dense fog and low stratus ceilings. Cirrus clouds are also inbound from the west which may slow diurnal warming and mixing today, which is already feeble because of the low December Sun angle. The 12z TAFs are pessimistic and lean heavily near persistence; extent of LIFR-IFR on the surface observations at this hour is greatly elevated, increasing the probability of aviation travel issues through morning and much of the day. On the public and marine side, dense fog advisories are in effect until 11 am today for essentially all low lying areas including across the bays. With WMC-SFO 4.0 mb and SAC-SFO 1.5 mb offshore pressure gradients, this pattern of cold air channeling into the Bay Area remains strongly anchored in. Clearing will be slow going today, fog and low stratus return tonight and Tuesday morning.
Vicinity of SFO, A cold channel of air, including low stratus and fog /LIFR-IFR/ formation continues to extend from the Central Valley into the Bay Area, including cold continental air reaching the immediate coastline e.g. KHAF this morning. In the SFO approach zone to SJC surface visibilities are low, visibility down to 1/2 to 1/4 mile in fog and ceilings ~ 200 feet. Improvement in conditions will take time, the 12z TAF advertises MVFR-VFR by 22z today. IFR returns 04z tonight with IFR continuing to Tuesday morning. With cold air, fog and low stratus wobbling around the Bay during the morning, this may result in sharply decreasing runway visual ranges at any time.
SFO Bridge Approach, Conditions are poor visibility and low stratus ceiling this morning. In the SFO approach zone to SJC surface visibilities are low, visibility down to 1/2 to 1/4 mile in fog and ceilings ~ 200 feet. Cold air conducive to fog, dense fog and low stratus is an extension from the Central Valley, all remaining well entrenched to the South Bay and Santa Clara Valley. Improvement in conditions will take time, the best probability of MVFR-VFR will be in the mid to late afternoon. IFR returns tonight and Tuesday morning.
Monterey Bay Terminals, Low stratus ceiling, fog and dense fog continue to form under favorable long December night-time cooling hours. Cold air drainage winds may help somewhat earlier mix out times here on the north Central Coast this morning, however recent satellite imagery and surface observations show a fair amount of LIFR-IFR. 12z TAFs for KMRY and KSNS indicate VFR returning by late morning, a low to moderate confidence forecast. The highest probability of VFR is during the afternoon, then stratus and fog /IFR/ returns tonight and Tuesday morning.
(today through Saturday) Issued at 343 AM PST Mon Dec 15 2025
Southerly flow will prevail north of Pigeon Point ahead of an approaching frontal system. Conditions are ideal for dense fog across the bays and clearing may be slow today from the San Francisco Bay to the West Delta. Mainly light winds will prevail across the coastal waters except northwesterly winds becoming gusty across the southern coastal waters today to Tuesday. Winds will become gusty with increasing rain chances over the northern waters mid-week. Light seas will gradually build becoming moderate to rough by mid week.
Ca, Dense Fog Advisory until 11 AM PST this morning for CAZ506-508- 510-513-516-528>530.
PZ, Dense Fog Advisory until 11 AM PST this morning for Mry Bay-SF Bay N of Bay Bridge.
Small Craft Advisory from 3 PM this afternoon to 3 PM PST Tuesday for Pt Pinos to Pt Piedras Blancas 0-10 nm.
