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.
Revised in 8 passages since the 10:27 AM discussion. See every revision.
Monsoonal moisture will decrease this weekend, with a slight chance of showers and thunderstorms for the mountains and lower deserts returning for Monday afternoon. Above average high and low temperatures will continue through next week. Widespread moderate to locally major HeatRisk for the coast, valleys, and mountains except near the beaches and for the higher elevations in the mountains, with major to extreme HeatRisk for the lower deserts.
FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE. SAN DIEGO. WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES.
This morning's marine layer was very shallow - around 500 ft deep with areas of fog between I-5 and I-15. Otherwise, yet another day of summer sunshine is in store for the region with a few cirrus clouds passing by. Low clouds are expected to redevelop later this evening, bringing patchy dense fog to coastal areas and western valleys overnight tonight. The marine layer will compress even more throughout next week, yielding overnight fog mainly to coastal areas and perhaps down to the beaches.
While southwesterly flow aloft is not the most ideal setup for monsoonal moisture, thunderstorm chances return for early this week. Pulses of higher precipitable water's above 1.3 inches are forecast to move over our mountains early Monday through Tuesday afternoon. While some long range models continue to show no precipitation throughout the week, high resolution guidance such as the RREF, the high-res rapid-refresh model and HiRes-FV3 show scattered thunderstorms Monday afternoon, yielding around a 20-35% chance for a shower/t-storm for a given area over the mountains and adjacent desert slopes. Chances drop to 10-20% Tuesday afternoon and drop further thereafter, though chances may increase again for late week if precipitable water's rebound as the the European model is forecasting.
Temperatures are still on track to increase Monday through Wednesday, yielding temperatures generally 8 to 12 degrees above average - backing off slightly from yesterday's forecast. Nevertheless, Major HeatRisk is on track to expand all the way to coastal areas by late week as highs inland range from 95-107 degrees F with nighttime low only dropping to the mid-70s (above the very thin inversion a few-hundred feet above sea level). The low deserts are consistently expected to see highs of 110-115F Tuesday through Friday along with Major/Extreme HeatRisk.
While highs in coastal areas mid-late week will mainly remain below 90 degrees F, overnight temperatures will struggle to drop below the lower 70s, which will especially affect those without access to air conditioning.
The Heat Advisory remains in effect for inland areas through 10 AM Tuesday, followed by an Extreme Heat Watch through Friday 8 PM for the whole region (except for the lower deserts which are already in an Extreme Heat Warning through Friday evening).
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