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Near to slightly below normal temperatures persist in the marine layer this week

Warm and dry conditions continue above 1000 feet

Short Term

Not too much change in the forecast today as the Bay Area and Central Coast remain in between an upper level trough to the north and a ridge over the Desert Southwest. Ridging remains more dominant through this evening before the center of the ridge shifts eastward early Monday and troughing becomes more dominant over the region. High temperatures are forecast to peak in the upper 80s to low 90s across the interior with far interior Monterey County reaching the low 100s. Coastal areas are benefiting from a shallow (~1000 foot) marine layer that brought patchy stratus and drizzle to the coast and the SF Bay shoreline. This will keep temperatures cooler in coastal areas with highs peaking in the 60s to low 70s.

Heading into Monday, the center of the upper level ridge will shift eastward with troughing becoming the dominant feature over us. The return of troughing will help the marine layer to (slightly) deepen and bring it from approximately 1000 ft to 1200-1500 ft. A slightly deeper marine layer will allow for a greater inland intrusion of stratus, but, stratus is not likely to be as widespread as it was last week. Temperatures are expected to drop by around 5 degrees for most interior locations. This will see a return of highs in the low to mid 80s while the higher elevations above the marine layer will stay comparatively warmer in the upper 80s to low 90s. Coastal areas will remain in the 60s to low 70s with additional periods of coastal drizzle likely during the early morning hours. The one questionable part of the forecast is if any thunderstorms will be able to develop across the North Bay Interior Mountains (particularly Napa County) early Monday morning. The Euro suggests that there will be sufficient moisture, instability, and lift as a weak shortwave trough moves in to California for orographically driven thunderstorms to develop there early Monday morning. the blend-of-models forecast guidance gives around a 5% chance of thunderstorms developing. Any precipitation that falls would likely be virga/evaporate before reaching the surface given model Skew-T soundings showing a large dry layer between the mid and lower levels of the atmosphere. Confidence remains low overall in storm development, however, as other models (the American global model, the regional model, the high-res rapid-refresh model, RRFS) do not support storms developing tomorrow morning with the Euro being an outlier.

Long Term

Troughing prevails through Tuesday with high temperatures remaining in the 60s to 70s along the coast, 80s across the interior, upper 80s to low 90s across the higher elevations, and upper 90s to low 100s across the interior Central Coast. Stratus is expected along the coast and portions of the SF Bay shoreline but continues to be limited in extent. The center of the upper level ridge shifts back westwards Wednesday to Thursday with high temperatures warming by around 5 degrees across the interior (largely returning temperatures to the upper 80s to 90s). Friday into the weekend, temperatures cool by a few degrees as ridging weakens and troughing deepens/strengthens over the Pacific. Troughing looks to continue into next week with a deep upper level low moving into the Pacific Northwest and Northern California. It will be worth keeping an eye on this incoming trough and the arrival of any potential tropical moisture towards the end of the forecast period. The latest NHC guidance shows three active areas of tropical interest offshore of Mexico with recently named TS Iselle in the vicnity as well. Guidance is starting to indicate some tropical moisture from these systems may be brought north as the trough arrives but it is unclear how far north this tropical moisture will go. Some models keep it more over Southern California while others bring it up into Monterey/San Benito counties. Models are already showing an increase in southerly swell associated with the uptick in tropical activity across the Eastern Pacific this weekend into early next week.