High temperatures for inland areas of around 4 to 8 degrees above average through Friday will cool slightly to a few to around 5 degrees above average for early next week. Greater monsoonal moisture on Thursday and Friday and again around Monday of next week will bring a chance of afternoon showers and thunderstorms for the mountains and deserts. Night and morning low clouds will continue for the coastal waters into coastal areas.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, UPDATED AVIATION DISCUSSION for 06Z CYCLE,
This afternoon, clear skies are prevailing across the region. The ridge is at its maximum westward reach today, yielding the hottest temperatures for the inland valleys this week. Widespread 100F to 105F readings are anticipated across the Inland Empire with mid to upper 90s in the interior valleys.
Highs Thursday may back off a degree or two, then remain very steady through early next week, only fluctuating by a degree or two each day. Today through early next week, highs will hover around 109-113F in the lower deserts with persistent areas of Major HeatRisk as a result of overnight lows only falling to the mid/upper 80s, about 5- 8 degrees above average.
The center of the ridge retracts slightly eastward, spinning around the Four Corners region and opening the door for monsoonal moisture. Around a 15-25% chance for afternoon isolated showers and a t-storm Thursday and Friday over the mountains, with lesser chances over the weekend as the ridge axis moves south and PWAT's decrease. Chances for more scattered shower/t-storm activity increase again early next week as the GFS shows the ridge access rotating and potentially re- opening the door to more mid-level moisture.
Throughout the forecast period, the marine layer will be fairly shallow, between 1,000-2000 feet deep, as the influence of the ridge continues. Low clouds should develop and push up to 20 miles inland as they typically do in the evening, except for nights with greater high cloud coverage, which could delay the formation of low clouds.
for extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
This evening, the marine layer is about as deep as it was at this time yesterday but the low clouds seem slower to increase in coverage and advance inland. This may be due to a weaker inversion as a result of some cooling just above the inversion.
From previous discussion, Our weather continues to be controlled by the dominant upper ridge currently positioned over southern Arizona and the low/trough centered over the Gulf of Alaska. As a result, the marine layer mixed out efficiently today with sunny skies extending several miles out to sea this afternoon. High temperatures today coming in right around climatological normals to 5 degrees below normal - topping out in the 80s to low 90s for most with 100-110 degrees for the deserts. As we head through the weekend and into next week, this ridge doesn't budge much and stays relatively weak. Still, temperatures increase very gradually through Tuesday, with high temperatures by Tuesday afternoon only a couple of degrees warmer than today. The marine layer will continue to spread inland each night and retreat back to sea each day with depth varying between 700 and 1400ft.
By the middle part of next week, the center of the ridge slides a bit closer to New Mexico, but also broadens and strengthens considerably, bringing more substantial warming for Wednesday and Thursday. Thursday and Friday will likely be the hottest days of the next week, with widespread moderate HeatRisk stretching towards the coasts and high HeatRisk spreading out of the deserts locally to inland valleys. High temperatures reaching or exceeding 100 degrees for inland valleys Thurs/Fri with the deserts likely exceeding 115 degrees (~90% chance). Available moisture will likely be quite below normal for early August most of next week, but recover to closer to normal by the end of the week. Still, chances for any monsoonal thunderstorms by the end of next week stay low, about 10 percent or less.
AVIATION, 020300Z. Coasts/western Valleys, Low clouds based 700-1200 feet MSL are slowly moving inland, reaching its full inland extent by 07Z. Vis reduced 0-5SM over higher coastal terrain and western valleys. Scatter out Saturday 15-17Z. Vfr conditions Saturday afternoon. Low clouds redevelop at the coast around 04z Sun.
Inland Valleys/Mountains/Deserts, Mostly clear with VFR conditions through late Saturday.
MARINE, No hazardous marine conditions are expected through Wednesday.
SKYWARN, Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions.
200500z. Coast, Patchy low clouds with bases 800-1200 ft MSL are currently offshore but will slowly spread into coastal areas after 07Z with coverage remaining patchy. Low cloud coverage increases after 09Z, especially in San Diego County, with areas of clouds reaching 5-10 miles inland. Local VIS reduced to 3-5 miles on elevated coastal terrain 10Z-15Z. Expect clearing to the beaches around 15-16z.
Otherwise, mostly clear through Thursday morning. Slight chance (15- 20%) of SHRA/TSRA over the mtns from 20z Thu - 01z Fri. SCT clouds based around 10 kft expected regardless of storm development.
No hazardous marine conditions are expected through Sunday.
Ca, Heat Advisory until 8 PM PDT Thursday for San Bernardino and Riverside County Valleys-The Inland Empire.
Extreme Heat Warning until 8 PM PDT Friday for Coachella Valley- San Diego County Deserts-San Gorgonio Pass near Banning.
PZ, None.
