Issued at 753 PM PDT Sun Oct 18 2026
The cooler weather has arrived! Across the Bay Area and Central Coast, temperatures dropped 10-20 degrees within the last 24 hours with some spots experiencing up to a 30 degree drop. Accompanied with the lower temperatures is an increase in humidity. The marine layer has reformed with a current depth around 1500-2000 feet. Moderate, gusty onshore winds will help push stratus further inland tonight. So, enjoy the stratus while you can because it won't last long! Tomorrow, temperatures are expected to drop another 10-20 degrees with gusts around 20 mph. Breezier locations may experience gusts up to 30-35 mph which gradually diminish Monday evening.
, Issued at 145 PM PDT Sun Oct 18 2026 (This evening through Monday night)
24 hour trends are cooler across much of the forecast area, due to cool air advection from the surface up through the lower levels of the atmosphere. Daytime highs today will peak close to October 18th normal highs. A pattern shift to long wave troughing is developing and the trough will usher in below to much below mid-late October normal temperatures during the upcoming week. Wet weather will accompany the trough by mid-week.
..issued at 145 PM PDT Sun Oct 18 2026 (Tuesday through next Saturday)
The northern hemisphere long wave trough pattern contracted somewhat after late September 2026 (interestingly e.g. after the persistent far downstream Nor'Easter). Just what storms do, the north-south meridional temperature/energy exchanges temporarily reduced the meridional temperature gradient resulting in some contraction that increased the chances we'd have long wave ridging (and warm/hot spells) which we had at times in October. Warm/hot spells are most frequent here in Sep-Oct after a long dry summer, still relatively high Sun angle and especially when coupled to (dry, downsloping) offshore winds.
As mentioned a pattern shift to long wave troughing is taking place, not so much because of an expansion in long wave troughs rather the result of a now progressive zonal pattern entering the entire western CONUS. Strong polar jet stream winds on the back side of the trough will drive the trough south-southeastward from the Gulf of Alaska temporarily cutting off a 500 mb low ~ a few hundred miles to our west-southwest from late Monday night to Wednesday night. During this time the subtropical jet stream will merge with the polar jet stream near the base of the newly forming 500 mb cut-off low. The cold core low will dig deep passing over higher sea surface temperatures in contrast to the cold core low, steepening temperature lapse rates and instability and water vapor availability will cause showers and thunderstorms to form. The greatest instability will be over the coastal and offshore waters while the low approaches land during mid-week it'll encounter marginal diurnal surface instability and much less if any land surface based instability at night. Precipitable water is forecast to reach near the 90th percentile during the mid week timeframe; cold air within the low will help result in measurable rain and any thunderstorm development will be "wet" rain producers (vs "dry" thunderstorms). As of current time, the southern half of the forecast area stands the best chance of highest measurable rain with lesser amounts to the north.
Forecast rainfall amounts for Tuesday night through Thursday: 0.10" to 0.25" in the North Bay, 0.20" to 0.50" across the rest of the Bay Area and 0.33" to 1" across Monterey and San Benito counties. Southerly breezes will prevail, but the low will be wrapping cold air around from the south as well and daytime highs are forecast to remain below normal during the period. Far inland highs will struggle to reach 70F in rain cooled air Wednesday and Thursday.
For late in the week dry weather will return along with an increase in daytime highs reaching back to the 70s inland Friday and Saturday with 60s closest to the coastline.
(06z TAFS) Issued at 1001 PM PDT Sun Oct 18 2026
MVFR stratus is building into the valleys of the greater SF Bay Area and patches around Monterey Bay with further expansion expected overnight. Clearing times Monday morning and afternoon will be rather late owing to an incoming trough that will lower temperatures and expand the marine layer. Gentle to moderate onshore winds will persist through Monday evening, when winds diminish and turn southerly. Low confidence in the stratus extent and ceilings beginning on Monday night owing to potential mixing out of the lower layers as the trough approaches. Any rain chances from the incoming trough come later on Tuesday, after the TAF period ends.
Vicinity of SFO, MVFR ceilings persist through Monday morning. Moderate northwest winds will continue through Monday evening with strong gusts expected in the afternoon and evening hours with a more southerly component as the winds diminish Monday evening. Low confidence for stratus returning to the terminal Monday night.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, MVFR ceilings at the terminals will clear late Monday morning or early afternoon. Gentle to moderate northwest winds prevail through Monday evening, with light southerly flow developing Monday night.
(tonight through next Saturday) Issued at 1001 PM PDT Sun Oct 18 2026
Moderate to fresh northwesterly breezes will prevail through Monday, with hazardous conditions for small craft lingering at the inner coastal waters south of Pigeon Point through Monday morning. Winds will diminish and back to a gentle southerly breeze Tuesday and Wednesday before returning to moderate to fresh northerly breezes Thursday. Rough seas across the outer waters will subside to become moderate Monday, rebuilding to become rough Tuesday. Light rain showers are expected Tuesday through Thursday.
Ca, None. PZ, Small Craft Advisory until 3 AM PDT Monday for Pigeon Pt to Pt Pinos 0-10 nm.
Small Craft Advisory until 9 AM PDT Monday for Pt Pinos to Pt Piedras Blancas 0-10 nm.
