, Issued at 1201 AM PDT Mon Sep 21 2026 (Today and tonight)
The local weather pattern remains dominated by a cut-off low with a broad rotation centered to the west of Monterey and San Luis Obispo Counties. The satellite imagery reveals scattered to broken high clouds associated with the low pressure system, some low clouds developing across the inland valleys, and some convective activity south of the Monterey County coast that has been potent enough to show up on the radar returns. One of those cells even lit up LightningCast (long story short, a satellite based algorithm for lightning probability) with a 50% probability of lightning but fell apart before reaching the southern Monterey County shore. However, most of them haven't corresponded to any rainfall at the surface, as the 00Z (5 PM PDT) sounding from Oakland revealed that the lower layers remain very dry. But could we still see a high based thunderstorm through the night? It's unlikely, even if the HRRR continues to hold on to K-Index values up to 22C, which would correspond to isolated thunderstorms, and some lightning flash signals near the Santa Lucia range around 4 AM to 8 AM. CAPE values are still the limiting factor; the 00Z OAK sounding continued to show a conditionally unstable layer with lapse rates around 8.5 C/km, but this layer was still below the moist air. This is supported by the reflectivity values at -10 C and -20 C, which remain below the values that would be necessary to support the ice particles that would be necessary for thunderstorm development. We will continue to monitor the cells as they develop, because while the risk of lightning is very small, the chance that it would be accompanied by wetting rains (at least 0.1" of rain) are zero, thus posing an obvious concern for dry lightning-induced fire starts.
As the low moves onshore later this morning and passes through to our south, cool conditions will continue with highs ranging from the middle 70s to lower 80s in the inland valleys, the middle 60s to the middle 70s near the Bays, and the upper 50s to middle 60s along the Pacific coast. Typical diurnal onshore winds develop this afternoon and evening with gusts reaching 20 to 30 miles per hour through gaps and passes, and within the northern Salinas Valley.
..issued at 1201 AM PDT Mon Sep 21 2026 (Tuesday through Sunday)
The cut-off low will continue to move to the east and will be out of our area by Tuesday morning, degrading into a shortwave trough as it moves into the Great Basin. This will allow more zonal flow to develop over the region and start a warming trend through Wednesday and Thursday. The word "ridge" might be a little strong for what the models are expecting, but there is definitely a northward bump in the flow that develops by Wednesday. Temperatures on Wednesday and Thursday will range from the middle 80s to middle 90s in the inland valleys to the middle 70s to middle 80s near the Bays, and the middle 60s to lower 70s along the Pacific coast. There are some pockets of Moderate HeatRisk (moderate risk for heat-related illness among sensitive populations) possible on those two days in favored interior locations, but widespread heat impacts are not expected. As the previous forecaster noted, Heat Advisories in late September typically happen with offshore flows and longer duration events.
By Friday, another trough arrives from the eastern Pacific and reverses the warming trend, with temperatures closer to seasonal averages into the weekend. Longer-range outlooks show a slight lean towards temperatures warmer than seasonal averages and precipitation totals above seasonal averages for the last few days of September into the first few days of October.
(18z TAFS) Issued at 1113 AM PDT Mon Sep 21 2026
Starting the day off with widespread MVFR ceilings with IFR ceilings in the North Bay. Conditions gradually improve to VFR by the early afternoon at most sites with lower confidence for clearing at HAF and MRY. This clearing window will be short-lived as an early onset of MVFR to IFR stratus is expected to roll in around/after sunset. Overnight, there is a low chance (20%) for drizzle, mainly at HAF, MRY, SNS, APC, and OAK. Ceilings are expected to hang on through late Tuesday morning at the earliest. Moderate onshore winds increase to 10-15 kt through the afternoon and ease below 10 kt overnight as they shift south to southwest, depending on the local terrain.
Vicinity of SFO, MVFR ceilings persist with moderate confidence on a brief scattering period this afternoon. Southwest winds gradually become westerly and increase to moderate through the day before switching back to a light SW flow overnight. Borderline MVFR-IFR ceilings return early this evening between 5-8 PM PDT with medium to high confidence on the timing and heights. These conditions will persist through early Tuesday afternoon as those westerly winds increase. Current model guidance is hinting at a low, non-zero chance for drizzle at the terminals early Tuesday morning, but confidence is too low to include in the TAF.
SFO Bridge Approach, High chance for the bridge to clear before the terminal and is expected to develop ceilings shortly after SFO.
Monterey Bay Terminals, MVFR stratus hangs on through this afternoon. Low confidence on whether MRY will fully scatter out due to the persistent onshore flow and expansive stratus feed over the ocean. Overall, borderline MVFR-IFR ceilings develop at both terminals early this evening right before sunset and drop to IFR overnight through Tuesday morning. Medium confidence on exactly when IFR ceilings develop. After midnight, there is a 20-30% chance for drizzle to impact the terminals, though confidence is too low to include in the TAF.
(today through Saturday) Issued at 1113 AM PDT Mon Sep 21 2026
The gradient between high pressure over the Pacific and lower pressure over California is supporting a moderate to strong NW breeze across the coastal waters. Winds are strongest north of Pt. Reyes. The stronger winds will move south to impact the majority of exposed waters over the next 36 hours. These winds will build rough seas, with significant wave height peaking at 10-12 feet Tuesday night. Conditions will gradually improve Wednesday through Thursday.
Ca, None. PZ, Small Craft Advisory from 3 PM this afternoon to 9 PM PDT Tuesday for Pt Arena to Pt Reyes 0-10 nm.
Small Craft Advisory from 3 PM to 9 PM PDT Tuesday for Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm.
Small Craft Advisory until 9 PM PDT Tuesday for Pt Arena to Pt Reyes 10-60 NM.
