Issued at 1005 AM PDT Wed May 27 2026
Rain showers persisted overnight into early this morning with the the Santa Cruz Mountains and Santa Lucia Range picking up the greatest totals. Areas of the Santa Cruz Mountains picked up generally less than 0.05" while the Santa Lucia Range saw upwards of 0.25" at White Rock Ridge. This activity continues to diminish late this morning, but we are expecting convection to fire up in the East Bay Hills, Eastern Santa Clara Hills, the Santa Cruz Mountains and the Central Coast (County of Monterey/San Benito) this afternoon. This is as the atmosphere becomes more unstable with CAPE values between 100-400 J/kg. However, probabilities for thunderstorms remain less than 10% through the afternoon and early evening. Additional rain showers are forecast to increase in coverage (especially across the Central Coast) late this evening and into Thursday morning. Please see more in the previous forecast discussion below.
RGass
, Issued at 1151 PM PDT Tue May 26 2026 (Today and tonight)
The center of the upper level disturbance responsible for the cool and unsettled weather yesterday and today will remain mostly stationary throughout the day. However it will weaken slightly over the course of the day with subtle H50 height increases from early this morning into this evening. The unusually cool air aloft, once again looking at H50 level, will be below the tenth percentile at around -21C to -22C, with H85 temps right around the tenth percentile at 5C to 6C. The cooler than normal temperatures aloft are transferring to the surface with low lying interior locations running 5F-10F degrees below normal for this time of year, and much cooler than normal at higher elevations, especially the highest peaks of Big Sur around 25F-30F degrees below normal.
As the upper low rotates overhead today, portions of the Bay Area, East Bay and South Bay will see periods of sunshine helping to produce marginal surface instability from around 100-300 J/Kg of CAPE this afternoon. Vertical wind profiles don't favor organized convection, with little to no 0-6km wind shear. Like yesterday in Napa County and Contra Costa County the best chances for rainfall amounts above 0.10" will be areas of terrain enhancement. The hills of eastern Contra Costa County and eastern Santa Clara County have approximately 20%-50% chance of exceeding 0.10" by late this afternoon. NBM thunderstorm chances are less than 10% area wide.
A portion of the upper level low will begin to retrograde back toward the coast tonight into early Thursday morning, increasing rain chances off shore that eventually begin to move onshore along the coast late tonight and farther inland through Thursday morning. Rain totals along the coast late tonight into early Thursday morning will be light, primarily less than a 0.10" from Santa Cruz south down the Big Sur coastline.
..issued at 1151 PM PDT Tue May 26 2026 (Thursday through Tuesday)
Thursday will continue the unsettled pattern with a shift south across primarily the South Bay and Central Coast as the upper low begins to shift inland to the southeast during the day Thursday. The clouds and cooler temperatures will linger during the day Thursday with only light rainfall amounts where rain does occur, with less than a 0.10" expected.
Progressive upper ridging behind the exiting low to the east on Friday gives way to zonal flow aloft on Saturday as temperatures begin to rebound back closer to normal by Sunday into the beginning of next week. While we do gradually warm up through the remainder of the extended forecast beginning Friday, a signal for troughing in the syntopic pattern continues beyond the current extended forecast that should help maintain more seasonal temperatures.
(18z TAFS) Issued at 1122 AM PDT Wed May 27 2026
The cold core 500 mb low continues to straddle the CA/NV border. A spoke of 700 mb to 500 mb troughing/instability extending outward from the low center continues to move southward over the southern half of our forecast area at the moment. It's cold for late May at the mandatory pressure levels 925 mb through 500 mb on this morning's 12z Oakland upper air sounding: < 10th percentile for late May. With solar input and surface heating today, expect a few more showers along with isolated lightning in the unstable air. KMUX shows a recent isolated thunderstorm over northeastern Santa Clara county, drifting to the southwest. Will continue to closely monitor KMUX radar and satellite through today.
The aforementioned 500 mb low and high precipitable water it has entrained (near 90th percentile) bring the potential for more wet weather tonight and Thursday. Will closely monitor radar and satellite imagery.
Vicinity of SFO, VFR. East to northeast wind 5 knots shifts to westerly and increases to 15 to 22 knots in the afternoon with gusts diminishing below 20 knots beginning 03z this evening. Wind shifts to southeasterly 5 knots Thursday morning then to westerly 12 knots Thursday afternoon.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, Lingering MVFR ceilings are expected to scatter out by the afternoon, if they have not already. Onshore moderate breezes (~10-14kt) will persist through the afternoon with the Salinas valley experiencing gusts up to 20kts. MVFR ceilings will return this evening (00-02Z). Light rain showers begin to approach the Monterey Bay coastline late Wednesday night with winds slightly diminishing. Medium confidence in the timing of the rain showers as they may arrive an hour earlier or later, though they are expected to stick around for the remainder of the TAF period. Winds begin to shift SE early Thursday morning. There is low confidence at this time that visibility will be impacted, however I wouldn't be surprised if the rain showers cause a slight reduction to visibility (minimum 5SM).
(today through Monday) Issued at 1005 AM PDT Wed May 27 2026
Northwesterly winds continue to diminish through today and overnight into widespread gentle to moderate breezes over the outer and inner waters. Wind gusts also become more moderate, with the outer northern waters experiencing locally strong gusts through Thursday morning. Rough seas with heights of 11-16 ft continue to abate through today and become more moderate (5-9 ft) by Friday morning. Another round of strong to near-gale force winds are expected to develop over the weekend with building rough seas again.
Ca, None. PZ, Small Craft Advisory until 3 PM PDT Thursday for Pt Arena to Pt Reyes 10-60 NM.
Small Craft Advisory until 9 AM PDT Thursday for Pigeon Pt to Pt Pinos 10-60 NM.
