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,
Another mostly clear day across the region. Over the San Bernardino Mountains, there is some cumulus development, though much less vertically developed than at this time yesterday. With southwesterly steering flow aloft and limited PWAT, chances for any showers this afternoon are around 10% over the southern San Diego County mountains and less elsewhere. The marine layer this morning was only around 500-1000 feet deep, yielding patchy fog west of the I-15 corridor down to the coastal mesas. This pattern should continue for at least the next few nights with the marine layer expanding a few hundred feet Sunday night then contracting again Monday night.
Thunderstorm chances look rather limited throughout the entire forecast period; Monday being the only day with more than zero confidence for perhaps a few showers/thunderstorms as PWAT's may briefly rise above 1.3 inches. Model spread in PWAT values diverge quite significantly through the rest of the week, so precip chances remain uncertain.
In terms of heat, the ridge of high pressure across the Four Corners Region is here to stay through the end of August. The ridge tightens ever so slightly Sunday, allowing temperatures to back off a few degrees inland and in the deserts for Monday afternoon before slowly expanding and intensifying again through the middle of the week. Highs increase 2 to 4 degrees into Tuesday, then another few degrees into Wednesday with a net increase of 5 to 10 degrees over these two days (4-8 above average Monday to 10-14 above average Wednesday). These very hot temperatures stick around until at least Friday with limited guidance showing any weakening of the ridge through the end of the 7-day forecast period. Heatrisk for the inland valleys increase from predominantly moderate through Tuesday to Major through Friday. For coastal areas and higher elevations, HeatRisk transitions from Minor through Monday to Moderate and locally Major (all the way to the beaches) for the remainder of the week. The combination of hot daytime temperatures with overnight temperatures struggling to drop below the lower 70s will especially affect those without access to air conditioning.
In raw numbers, Monday highs look like,
, 80s at the coast, 90s inland, 100-105F in the IE and around 110F in the lower deserts.
Wed/Thurs/Fri highs look like,
, upper 80s/low 90s at the coast, 95-105F inland, 105-110F in the IE and 114-117F in the lower deserts.
The Heat Advisory for inland areas through 10 AM Tuesday is then 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.
Take breaks in the shade, hydrate and seek A/C when possible!
221810z, Coast, Mostly clear by this afternoon through the evening hours. Low to moderate chance on cigs returning at the beaches after 04Z this evening. Confidence higher on cigs impacting coastal TAF sites between 10-15Z Sun with bases near 500-1000 ft MSL. Locally lower cigs near 200-400 ft MSL in higher terrain. Vis lowering near 2-4 sm for most areas, locally below 1 sm. Clouds clearing 14-16Z with moderate confidence on timing.
Otherwise, Mostly clear through the TAF period.
No hazardous marine conditions are expected through Tuesday. Increasing south swell mid to late next week starting Wednesday with waves up to 6 feet.
Ca, Extreme Heat Watch from Tuesday morning through Friday evening for Apple and Lucerne Valleys-Orange County Coastal Areas- Orange County Inland Areas-Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Coastal Areas-San Diego County Mountains-San Diego County Valleys- Santa Ana Mountains and Foothills.
Heat Advisory until 10 AM PDT Tuesday for Orange County Inland Areas-Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-San Diego County Mountains-San Diego County Valleys-Santa Ana Mountains and Foothills.
Extreme Heat Warning until 8 PM PDT Friday for Coachella Valley- San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
