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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
Plaincast — the National Weather Service forecast, decoded into plain English
What is an Area Forecast Discussion?
Area Forecast Discussions are the real forecasts, written 3 to 4 times daily by NWS meteorologists reading the models and interpreting what they mean for your area. They offer far deeper insight than any weather app, but they're written in dense meteorological shorthand. Plaincast uses Anthropic's Claude to summarize them into plain English, side by side with the annotated original.
Plaincast decodes the National Weather Service's Area Forecast Discussion — the real forecast, written 3 to 4 times a day by the meteorologist on shift — into plain English. The discussion is where a forecaster explains their reasoning: which models disagree, what they are watching, and how confident they are. Below is the current edition for San Francisco, with its shorthand expanded. The full experience — an AI plain-English summary beside the annotated original — loads with JavaScript, and every one of the 68 forecast offices has its own edition.
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.
This is the plain-text edition, decoded without AI so it loads anywhere. Read the whole San Francisco discussion at /o/MTR/, see what changed since the last one, or open The National Desk for where the weather is today.