Issued at 633 PM PDT Sat Aug 8 2026
A deeper marine layer than the forecast combined with strong onshore flow contributed to cooler than expected temperatures across the lower elevations today. The focus shifts to tomorrow's high temperatures and heat potential. The current forecast has significantly higher temperatures for tomorrow when compared to today's observed highs, particularly in the interior regions where the Heat Advisory remains in effect. The 00Z (5 PM PDT) OAK sounding showed a marine layer inversion at around 250 to 500 feet, which would limit the marine layer clouds to the immediate coast. It will be interesting to see how the marine layer evolves overnight, particularly as a wedge of drier air clears much of the stratus offshore the North Bay. Add to this the possibility for offshore flow down the northern Sacramento Valley and people across the interior might be in for some thermal whiplash tomorrow. The overnight shift will evaluate the forecast high temperatures and consider the need to issue a Heat Advisory for the North Bay interior valleys and the San Francisco Bayshore regions.
DialH
, Issued at 104 PM PDT Sat Aug 8 2026 (This evening through Sunday night)
The deeper marine layer, around 1600 feet in depth per the OAK Upper Air Sounding, early this morning has resulted in slightly cooler temperatures across the lower elevations. As high pressure over the Four Corners region continues to build westward across the Bay Area and Central Coast, temperatures aloft remain very warm to hot! As such, the Heat Advisory remains in effect for much of the interior through 10 PM PDT Sunday. This is as the marine layer is forecast to eventually compress to around 500 feet by Sunday morning under the building high pressure and 850mb temperatures are between 27-30C Sunday afternoon. Afternoon temperatures in the Heat Advisory are forecast to warm into the mid 90s and up to 105 deg F in the warmest interior locations where the most widespread moderate to isolated major HeatRisk are present. Overnight lows are also forecast to be warm and range from the mid 60s in the hills just above the marine influences to low 80s (especially in the higher elevations). Afternoon temperatures closer to the coast are forecast to be in the 60s to mid 70s largely due to the onshore winds and marine influences. Overnight lows near the coast are forecast to be in the 50s as stratus returns overnight. If the depth of the marine layer is higher than currently forecast, temperatures will be slower to warm Sunday afternoon.
Minor coastal flooding is also expected around the time of the highest high tide (evening/overnight) for bayshore locations along the San Francisco, San Pablo, and Monterey bays through Thursday morning. The Pacific Coast may need to be added Sunday through Tuesday to the advisory. We are waiting to see how high the observed levels are tonight (Saturday) before making that decision. Please see the CFW product we have out for additional details. Also, for more on the fire weather concerns this weekend, please see the Fire Weather Section of the AFD below.
During this weekend's heat event, remember:
* Stay hydrated and drink plenty of fluids. * Wear lightweight and light-colored clothing. * Reduce time spent outdoors or stay in the shade. * Never leave people or pets unattended in vehicles. * Use sunscreen if going to the coast or the pool.
..issued at 104 PM PDT Sat Aug 8 2026 (Monday through next Friday)
Ensemble clusters are in decent agreement that a mid/upper level shortwave trough will develop by Monday off of the West Coast. However, the high pressure aloft will persist over the Four Corners region and over the eastern Pacific. This will bring temperatures closer to near seasonal norms by Monday and through Wednesday, also lowering HeatRisk to the minor category across the interior.
By late in the week, temperatures cool to below normal as a mid/upper level through develops off of the Bay Area and Central Coast. As this low pressure approaches the coastline late in the week and monsoonal moisture advects northward around the high over the Four Corners, there is the potential for high-based convection. The main question is if there will be enough instability. While this is still far out in time and low confidence, any dry lightning would be problematic from a fire weather standpoint. Be sure to check back for additional details as we move closer to midweek.
(06z TAFS) Issued at 1001 PM PDT Sat Aug 8 2026
IFR-LIFR stratus is making its way inland as the marine layer remains close to 1500 feet deep, and expected to make its way into the coastal valleys through the night. Warmer air lurking offshore is evidenced in the clearing off the coast of the North Bay, but there's low confidence for its impacts to the coastal stratus as the immediate coast remains under the stratus deck. May need to monitor the evolution of the warmer air through the night. Low confidence that LVK gets a brief ceiling sometime early Sunday morning. Stratus will dissipate through Sunday morning, and breezy onshore flow will resume in the afternoon. The high resolution models do show some compression of the marine layer resulting in much less stratus development, but with similar forecast misses over the last couple of days, confidence is low.
Vicinity of SFO, VFR through the next couple of hours with moderate northwest winds. Moderate confidence of IFR ceilings developing after midnight with dissipation expected late Sunday morning. Breezy west winds develop Sunday afternoon and evening, with low confidence for stratus impacts Sunday night.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, IFR-LIFR stratus persists through the night with light to gentle winds. Stratus will dissipate through Sunday morning with breezy onshore winds resuming in the afternoon. Low to moderate confidence that stratus returns to the terminals Sunday evening a few hours before the end of the TAF period.
(tonight through next Friday) Issued at 1001 PM PDT Sat Aug 8 2026
Fresh to strong northwest winds persist into early next week. In response, moderate seas build to rough seas up to 12 feet by Sunday, lasting through the middle of next week. Northern coastal waters will be hazardous for small craft with occasional near gale force gusts possible through the weekend. The San Francisco Bay north of the Bay Bridge into the Delta continues to experience gusty onshore winds through Sunday night. Long period southerly swells at around 15 to 17 seconds are still present in the coastal waters.
Ca, Coastal Flood Advisory until 2 AM PDT Thursday for CAZ006-506- 508-529-530.
Heat Advisory until 10 PM PDT Sunday for CAZ503-504-510-512>518.
PZ, Small Craft Advisory from 9 AM to 9 PM PDT Sunday for Pt Arena to Pt Reyes 0-10 nm-SF Bay N of Bay Bridge.
Small Craft Advisory until 3 AM PDT Monday for Pt Arena to Pt Reyes 10-60 NM.
