Area Forecast Discussion

KEY MESSAGES

Updated at 1206 PM PDT Mon Sep 14 2026

- Cooling trend and below normal temperatures through mid-week; return to seasonal temperatures late week into weekend

UPDATE

Issued at 838 PM PDT Mon Sep 14 2026

Pleasant September day around the region under sunny skies and closer to seasonal averages for temps. There was a warming of 3 to 8 degrees when comparing high temps from Sunday to Monday. 60s and 70s near the coast with more widespread 80s across the interior. The offshore gradient noted below eased and winds are beginning to weaken too.

No update needed this evening, but will be watching the stratus development closely. Patchy stratus is hugging the coast near Monterey and Half Moon Bay. Forecast has more stratus developing overnight as the offshore gradient relaxes further and flow along with the coast over the waters.

SHORT TERM

Issued at 1206 PM PDT Mon Sep 14 2026 (This evening through Tuesday night)

Today will be the warmest day of the upcoming week with a slight cooling trend kicking off tomorrow. The upper level trough that brought us cooler weather last week has progressed eastward towards the Intermountain West. In its place, zonal flow has developed over Central California with slight troughing to redevelop Tuesday. The transition from more zonal flow to slight troughing will see temperatures cool 2-5 degrees across the region. This will bring interior temperatures down from the mid to upper 80s today to the low to mid 80s tomorrow. Coastal areas stay cooler with highs in the 60s to 70s.

Moderate offshore winds were observed along the ridgeline of the Vaca Range early this morning but have since been trending downwards. Mt. St. Helena (elevation of 4340 ft) reported a NNE gust of 40 mph at 2:40 AM which was the strongest wind gust observed from this event. The SFO-WMC gradient peaked at -6.10 around 7AM this morning and has since dropped to -4.90 as of 10AM. It is forecast to shift positive (onshore) by late this afternoon with light onshore winds returning everywhere. The return of onshore winds should help marine stratus to redevelop/move inland tonight. The only caveat to this is we currently have a dry airmass over us which could keep stratus development limited for one more night. Breezy onshore winds redevelop Tuesday afternoon and evening with gusts to around 20-30 mph most likely in the East Bay Valleys, Salinas Valley, higher elevations, and directly along the coast.

LONG TERM

Issued at 1206 PM PDT Mon Sep 14 2026 (Wednesday through next Sunday)

Troughing becomes more dominant by Wednesday as another upper level low pushes into the Oregon/California border. We are not anticipating any rain or thunderstorms for this system across our region but it will bring an unusually cold airmass across our region. High temperatures Wednesday and Thursday will be running 5-6 degrees below normal across the lower elevations and closer to 10-15 degrees below normal in the higher elevations and along the coast. This will keep interior temperatures securely in the 70s and coastal temperatures in the low to mid 60s. Favored hotspots across the interior Bay Area and Central Coast will reach the low 80s. The upper level low deepens and tries to become cut-off from the jet stream Thursday into Friday. Fortunately, it is a quick moving system and maintains a neutral tilt. If it took a more positive tilt and dug in more over NE California/Nevada then it would be more reminiscent of an inside slider which would raise offshore wind concerns. As it stands right now, this system will just bring a round of gusty onshore winds Wednesday into Thursday with gusts peaking between 20 to 30 mph. Locally higher gusts are possible at favored windy locations (Altamont Pass, higher elevations, etc.). The passage of the upper level trough will allow the marine layer to deepen and see a return of our nightly/early morning stratus along the coast and portions of the interior.

Troughing influence wanes Friday into the weekend as weak ridging builds in over California. This will see a gradual return to more seasonal temperatures in the low to mid 80s across the interior, 60s to 70s along the coast, and upper 80s to low 90s across favored hot spots in the Bay Area and interior Central Coast. Even though the ridge is weak, it will still compress the marine layer and most likely result in less stratus cover across the interior.

AVIATION

(06Z TAFS) Issued at 1007 PM PDT Mon Sep 14 2026

Gentle to moderate onshore breezes continue this evening, becoming light overnight. Above the surface, a weak offshore flow continues to keep stratus out of most terminals this TAF period but will gradually diminish by Tuesday morning. Wednesday night looks more promising for widespread stratus due to the absence of an offshore flow and the passage of an upper-level trough, which will allow the marine layer to deepen. That being said, VFR prevails this evening except at HAF where MVFR ceilings have already formed. Medium confidence for APC to develop borderline MVFR-IFR ceilings early Tuesday morning and scatter out by mid Tuesday morning. Diurnal onshore breezes increase Tuesday afternoon into the evening.

Vicinity of SFO...VFR with gentle onshore breezes through the night. Low confidence on the development of MVFR ceilings tonight, therefore the TAF advertises SCT decks. If ceilings become robust overnight, they will likely be short-lived and scatter out by late Tuesday morning. Wednesday has a higher chance of developing MVFR ceilings, likely after the current TAF cycle. Diurnal onshore breezes prevail through the TAF period.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Gentle onshore winds continue through the night and increase by Tuesday morning. High confidence for IFR ceilings to develop around midnight, filling in over MRY first followed by SNS. Stratus is expected to scatter out by late Tuesday morning resulting in a short period of VFR conditions. An earlier onset of MVFR stratus is expected tomorrow evening around sunset.

MARINE

(Tonight through next Sunday) Issued at 1007 PM PDT Mon Sep 14 2026

Northwesterly breezes will begin to diminish tonight with hazardous conditions for small craft lingering across the northern waters at least into Wednesday morning. Moderate to rough seas will prevail through Tuesday before subsiding to become slight to moderate Wednesday through Friday.

FIRE WEATHER

Issued at 436 AM PDT Mon Sep 14 2026

A few patches of coastal stratus have developed overnight. North to northeast breezes have developed in the higher terrain. Offshore winds will diminish by late morning or early afternoon and return to diurnally breezy onshore winds in the afternoon and evening. A surface to lower level trough of low pressure will develop along the north Central Coast Tuesday through Tuesday night. Surface to lower level troughing will expand to include the Bay Area Wednesday through Thursday. This will bring higher humidity with good recoveries from sea level to lower elevations to around 2500 feet, however above this elevation especially along the higher ridgetops thermal ridging and much lower humidity will persist during mid-week.

As such, areas above the marine layer often experience nocturnal drying that will likely continue through early this upcoming week.

MTR WATCHES / WARNINGS / ADVISORIES

CA...None. PZ...Small Craft Advisory until 3 AM PDT Wednesday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.

Small Craft Advisory until 3 AM PDT Tuesday for Pt Pinos to Pt Piedras Blancas 0-10 nm.

Small Craft Advisory until 9 AM PDT Tuesday for Pigeon Pt to Pt Pinos 10-60 NM.