textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 148 PM PDT Sun Jul 19 2026

- Near or slightly below normal temperatures and higher humidity through the first half of the upcoming week.

- The marine layer and mid to upper level cloud cover will continue to help keep temperatures cooler under building high pressure.

- Approximately 5% chance of elevated showers with isolated thunderstorms Tuesday afternoon through Wednesday evening.

SHORT TERM

Issued at 158 AM PDT Mon Jul 20 2026 (Today and tonight)

A 581 decameter geopotential height low remains located 500 miles west of San Francisco. The southern branch of the polar/subtropical jet stream is just forward of this low with jet stream winds to our southwest through northeast. These jet stream winds have helped quickly transport high and mid level clouds away from TS Elida in the last 24 hours or so. GOES-West Geostationary Lightning Mapper showed lightning approx 600 miles southwest of Point Conception earlier Sunday, but since Sunday evening it's been quiet. This lightning activity was closer to the northward moving and weakening center of TS Elida.

KMUX has occasionally shown widely scattered high based showers over our forecast area, but there have been no measurable rain or lightning reports so far. A band of light high based rain is developing over the coastal waters as well. We're in a little bit of unknown territory here with mainly minor energy transformations taking place, complexities that occur whenever tropical moisture travels northward and interacts with the mid-high latitude synoptic pattern. At the moment, the high based showers/band of light rain correspond to an area of weaker 500 mb positive vorticity that is forecast to continue moving northward of our forecast area along with the aforementioned upper level jet stream. So in a way, the combination of parameters and the steady diffusing of mid and high level clouds (water vapor) with minimal to no organization so far appear to be self limiting, leaning the pattern toward stability, keeping convective potential at a minimum.

Cloud cover will be a mix of stratus and mid and high level clouds today. The sun may break out over the southern interior today, possibly some sunny breaks farther north to the South Bay as well. Daytime highs today will be about the same it was on Sunday, varying from the mid to upper 60s along the coast to the 70s bayside to the 80s and 90s well inland. Tonight lows will cool to the 50s except in the 60s in the hills and mountains.

LONG TERM

Issued at 158 AM PDT Mon Jul 20 2026 (Tuesday through Sunday)

With generally decreasing 500 mb positive vorticity Monday this will help keep convective potential at a minimum with exception of the North Bay Monday afternoon to early evening when there may be a brief uptick in positive vorticity. However, even the 00z NAM output for this timeframe shows minimal convective potential along with convective inhibition. The HRRR, RRFS and GFS show essentially no convective potential.

For Tuesday, 500 mb positive vorticity is essentially non-existant including in the 00z NAM cross sections. Residual mid to high level clouds may still be around, but there'll likely won't be a lifting mechanism left to destabilize an atmospheric layer or air parcels. The westerlies, wind shear and drier air is destructive to tropical origin convective development, but there can be the exception to this when a steep east to west moisture gradient helps temporarily destabilize a lifted layer or air parcels. Given model trends and further dissipation of TS Elida, this is unlikely Tuesday when the tail end of the moisture gradient moves across the forecast area. Stay tuned to the latest updates.

Otherwise it'll be summertime dry weather, warm to hot inland and coolest at the coast and bays mid to late week. The high pressure system over the interior west will gradually shift southward then slowly move to the Four Corners by the weekend.

AVIATION

(06Z TAFS) Issued at 1000 PM PDT Sun Jul 19 2026

High clouds are obscuring low level stratus across the region but observations and cameras indicate it is starting to move inland. Pushed back the timing of stratus arrival for Bay Area sites slightly with the thinking being high clouds are slowing down the arrival of low level stratus. Confidence is mixed as to if stratus will reach SJC and LVK so have included a tempo for stratus at SJC but not at LVK. Stratus is forecast to start out MVFR but will compress to IFR overnight. LIFR conditions and fog are possible along the coastline. Conditions improve by late morning with the exception of the coast where some models indicate stratus could linger through the entire day. The marine layer compresses to around 1000 ft tonight (and again tomorrow night) so we can expect stratus to return late tomorrow evening for most sites. Diurnally breezy onshore winds continue.

Vicinity of SFO...High clouds are streaming into the Bay Area with cameras showing stratus approaching SFO. Highest confidence in stratus making it to SFO around 08Z but it may arrive as early as 06Z. Most likely MVFR CIGs but IFR CIGs may temporarily develop during the early morning hours. Clearing will take place by the late morning and remain VFR through the rest of the day. Models indicate some potential for stratus to return tomorrow night but confidence is mixed this far out given the compressing marine layer and high level clouds.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...LIFR conditions to persist through the late morning with some potential for reductions in visibility and fog overnight. Highest confidence in reduced visibilities to around 2-3SM but the LAMP model does show dense fog developing during the early morning hours. Clearing will take place by late morning with SNS around 17Z and MRY around 19/20Z before stratus returns early that evening. The MRY TAF is on the more optimistic side in terms of clearing with LAMP guidance keeping stratus over the site through the entirety of tomorrow.

MARINE

(Tonight through next Saturday) Issued at 1000 PM PDT Sun Jul 19 2026

Slight to moderate seas and a gentle to moderate northwesterly breeze will persist through the upcoming workweek. Long period southerly swell is forecast to increase due to tropical cyclone activity across the Eastern Pacific. Southerly swell heights are anticipated to remain in the slight category but mixed seas may result in hazardous boating conditions through the week. Additionally, there are non-zero chances for high based showers which could result in pockets of gusty outflow winds and subsequent steep seas now through mid-week.

FIRE WEATHER

Issued at 148 PM PDT Sun Jul 19 2026

Near to slightly cooler than normal temperatures will continue through the week with typical diurnal intrusion of the marine layer each night and retreat to the coast each morning as onshore flow persists. However, above 1500-2000ft we'll see relatively weak thermal belting the first half of the week with continued warm overnights and poor RH recovery at higher elevations.

Guidance is trending toward an increasing potential for elevated showers and isolated thunderstorms Tuesday afternoon through Wednesday evening. Chances are below 5% in the official forecast but may increase in subsequent updates tonight and Monday. The primary concern is dry lightning strikes across the North Bay, with lesser chances farther south into the Bay Area.

MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...None.