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 PWAT'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 precip throughout the week, high resolution guidance such as the RREF, HRRR 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 PWAT's rebound as the ECMWF 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).
Confidence is low at this point, though both the ECMWF and GFS show a weakening of the Four Corners ridge, and thus potentially less hot temperatures, starting next Sunday.
Take breaks in the shade, hydrate and seek A/C when possible!
231700z, Coast, Low clouds and locally dense fog linger along the immediate coast in San Diego County. Moderate confidence in cigs and vis at the immediate coast clearing 20Z Sun-00Z Mon. Moderate confidence in cigs impacting coastal SD between 10-15Z Mon with bases 200-800ft MSL. Lowered vis 1-3 SM expected with vis less than 1 SM near higher coastal terrain. Low clouds and vis restrictions may linger along the immediate coast after 15Z Mon.
Otherwise, VFR conditions through the TAF period with FEW-SCT clouds AOA 20,000ft MSL after 20Z.
No hazardous marine conditions are expected through Friday.
A 4-5 foot southerly swell (from 170 degrees) at 13-15 seconds will move into the area Wednesday and Thursday, leading to elevated surf for the south facing beaches of northern San Diego County and Orange County. Breaking waves of 4 to 6 feet expected, sets up to 8 feet possible at beaches that face due south. Surf gradually subsides on Friday.
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.
