Minor to major HeatRisk continues for much of the region through today before cooler weather returns for Tuesday and beyond. Thunderstorm chances continue each afternoon and evening in the mountains and deserts through Wednesday, with best chances and highest rain rates Monday and Tuesday. Patchy coastal low clouds and fog this morning followed by a deepening marine layer after Monday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
This morning, Outflow from a collapsed MCS (Mesoscale Convective System) over western AZ is moving westward across Riverside County and producing isolated, weak tstms. These storms will likely collapse before reaching western Riverside or San Bernardino Counties but there is a small chance that they could reach the Coachella Valley intact by 3 am. If any storms reach western Riverside County, they will likely be quite weak. Although locally gusty winds could still be produced. The marine layer remains quite shallow and low clouds are slow to develop. Low cloud development could be further disrupted as the outflow from the MCS over AZ moves west of the mtns, although the outflow will be much weakened as it moves westward.
The high pressure over the southwest will continue to dominate our weather through Tuesday even as it weakens in response to a series of shortwave troughs moving inland to the north. The position of the high will allow the monsoonal flow to continue bringing deep- layer moisture into SoCal from the southeast. This will continue to support the potential for afternoon/evening showers and tstms, mainly in the mtns and deserts. Daytime high temperatures will gradually lower through the week but remain above normal through Monday. Today, we will still have minor HeatRisk in the inland valleys and mtns, and major HeatRisk in the deserts. By Tuesday, daytime high temperatures will be near or a few degrees below normal. The marine layer will gradually deepen as the high aloft weakens.
For Wed through next weekend (according to model consensus), a trough of low pressure deepens along the coast. This will bring more pronounced cooling, with daytime high temperatures as much as 10 degrees below normal in some inland areas by Thursday. The below-normal temperatures will continue into next weekend. The trough will also bring dry, southwest flow aloft, reducing the potential for pm showers/tstms by Wed and essentially eliminating it for Thursday through next weekend. In addition, the marine layer will deepen and low clouds and fog could spread inland to the coastal slopes during the nights and mornings.
090530z. Coast, Very patchy low clouds based 900-1300 ft MSL have started to develop over coastal areas late this evening. Clouds will slowly expand in coverage Sunday morning with cigs most likely for coastal TAF sites between 11-15Z Sunday. Any cigs should scatter out Sunday by 16Z.
Valleys/Mountains/Deserts, SCT-BKN cumulus expected over mtns 19Z Sun-03Z Mon with 20-35% chance of TSRA in the mtns. High clouds may drift into the valleys and deserts with bases AOA 10000 ft MSL Sun afternoon and evening.
No hazardous marine conditions are expected through Thursday.
Astronomical high tides are expected to exceed 7 ft Monday through Wednesday between 8-9:30 PM PDT. Surf is not expected to play a large role in elevating the tides further, with a surf forecast of only 2-3 ft. Regardless, tides exceeding 7 ft can result in minor tidal overflow into low-lying areas along the beach, including beach parking lots.
Ca, Heat Advisory until 8 PM PDT this evening 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 this evening for Apple and Lucerne Valleys-Coachella Valley-San Diego County Deserts- San Gorgonio Pass near Banning.
PZ, None.
