, Issued at 158 PM PDT Mon Sep 15 2025 (This evening through Tuesday)
The Bay Area and Central Coast warm up is upon us. The compressed/shallow marine layer that brought coastal fog/clouds quickly vanished by mid morning. Weak low level offshore developed as noted on visible satellite showing clouds eroding over land and "rolling" westward over the waters. Latest 24 hour trends show a solid 5-10 degrees warmer than Sunday afternoon as max temps soar into the 90s across the interior. Temperatures are a tad cooler at the coast, but still above normal with max temps in the 70s and 80s. Parts of San Francisco may even have a shot at hitting 90 degrees today.
So what's it look like the rest of the short term? More of the same as high pressure overhead and a mild airmass both contribute to above normal temperatures. Latest hi-res models do suggest another narrow strip of low level moisture along the immediate coastline Monday night. Therefore, Tuesday will start off with pockets of clouds and fog, which will quickly vanish by mid morning. Expecting active thermal belts tonight as well. Even with the narrow strip of moisture higher terrain will remain dry and mild with lows in the 60s and lower 70s. The temperature dial gets turned up on Tuesday as 850mb temps jump 2 celsius. Current forecast is leaning toward the warmer end of model guidance with more widespread 90s across the interior. Latest prob guidance gives a 30-50% chc of the hottest interior locations breaking 100 degrees. Thermal belts will be active again Tuesday night into Wednesday with not a lot of relief.
..issued at 158 PM PDT Mon Sep 15 2025 (Tuesday night through next Sunday)
Tuesday night into Wednesday is the time period where the forecast begins to get really interesting. Wednesday will likely be the hottest day of the bunch as 850mb temperates peak. If we're going to break 100 across the interior Wednesday will be the day to do it with probs now up to 50-70%. Still "cooler" toward the coast, but highs well above normal and in the 70s to near 90 degrees. HeatRisk values Monday through Wednesday to increase and become more widespread Moderate. Even a few pockets of Major HeatRisk on Wednesday, but given the item of year will not issue any heat related products. That being said, if you have outdoor plans on Wednesday take heat safety precautions with hydration and plan accordingly. Wednesday temperatures could be exacerbated by increasing tropical moisture making it muggy and "feel" warmer. This is where the forecast gets interesting.
Late Tuesday night and Wednesday focus quickly turns southward as left over tropical moisture from Mario begins advecting northward. The longwave pattern shows the ridge that brought heat begin to shift eastward as a robust trough approaches from the west. Much farther south is the left over pieces of Mario. The moisture/left over circulation are in a bit of squeeze between the departing ridge and approaching trough. As such, the transport/steering flow is right into Central CA. 12Z model suite vary on details, but still paint a similar picture. PWATs rapidly increase off the SoCal and Central Coast Wednesday (150-200% PON). There is a little bit of instability over the coastal waters as well. As the day progresses more moisture and instability increase across the coastal waters and Central Coast. Chances for showers and thunderstorms will increase by Wednesday afternoon and Wednesday night over the Central Coast before spreading through the rest of the Bay Area Thursday. Point soundings show a classic inverted v profile indicating dry lightning potentially at the onset before transitioning to wetter storms Thursday. Pretty impressive PWAT values being kicked around for Thursday with values exceeding 1.5 inches. Highest confidence continues to be on the amount of moisture. Lacking confidence will be extent of lift and instability. Those two are more nuanced with subtle indicators in the way of 1.5PVU anomalies/weak shortwave trough and lower end lapse rates. MUCAPE is pretty solid, as the CAMS are getting more in focus, but need more than just MUCAPE. Convective threat eases by late Thursday with lingering showers Friday and into early Saturday. Simply put, this has the potential to be a higher impact event with initial dry lightning changing to wetter storms, especially for the Central Coast. Lastly, wet vs dry. As mentioned, initially dry,but hard to ignore the PWAT. As such, QPF has increase substantially over the Central Coast with vales above Big Sur reaching over 0.5". Amounts quickly taper to less than 0.10" to the north.
(18z TAFS) Issued at 1034 AM PDT Mon Sep 15 2025
VFR conditions have returned to all TAF sites this morning and are likely to remain that way through much of the afternoon and evening. However, coastal sites such as KHAF remain sub-IFR but are forecast to scattered out by around 19Z. The marine layer will remain shallow, generally less than 500 feet in depth with moderate to high confidence for fog/low ceilings to impact coastal areas such as KMRY, KSNS, and KHAF this evening and continuing into Tuesday morning. For the Bay Area terminals, looking for the potential for a few hours early Tuesday morning for IFR conditions, moderate confidence. Any low ceilings or visibilities will clear by around 15Z-17Z Tuesday and will return to VFR.
Vicinity of SFO, VFR. Onshore winds are forecast to increase this afternoon before becoming light/variable early Tuesday morning. Moderate confidence for IFR ceilings to develop over the terminal between 12Z-16Z Tuesday before VFR conditions return and onshore winds increase.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, VFR. Onshore winds are forecast to increase this afternoon before easing after sunset. There is moderate to high confidence for IFR ceilings/visibilities to return this evening and lower to LIFR late in the night and into Tuesday morning.
(today through Saturday) Issued at 1034 AM PDT Mon Sep 15 2025
Winds continue to diminish across the waters through today while fair weather persists. Moderate seas continue, especially offshore, and will subside through midweek before building again late week. Tropical remnant moisture is anticipated to enter the region by midweek. Isolated showers and thunderstorms are possible beginning late Wednesday through Thursday.
Ca, None. PZ, Small Craft Advisory until 3 PM PDT this afternoon for Pt Arena to Pt Reyes 10-60 NM.
