Strengthening high pressure to the east will bring a warming trend through Wednesday with moderate HeatRisk for Tuesday and Wednesday for the deserts, mountain elevations below 500 feet, and portions of the Inland Empire. High temperatures will warm to 5 to 10 degrees above average for inland areas. This will be followed by a cooling trend through next weekend with high temperatures for next Sunday as much as 8 to 12 degrees below average for the valleys and coastal slopes of the mountains.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Current satellite imagery and 500mb analysis reveal the subtropical ridge centered across northern Mexico has strengthened some compared to yesterday. This favors the efficient marine layer clearing we've seen this morning and also a slight uptick in afternoon temperatures. This ridge is still progged to strengthen further, become more broad, and nudge northward through midweek, centering over El Paso by tomorrow. The placement of this ridge also establishes southeasterly flow aloft, allowing for an influx of mid level moisture into the area. The ridge and the moisture will likely serve to limit the vertical depth and inland extent of the marine layer through midweek. The main consequence will be the notable warming trend, that takes afternoon temperatures 5-10 degrees above normal by Wednesday. More importantly, the moisture will inhibit overnight cooling, leading to mild nights, with low temperatures running 5-10 degrees above normal as well and limiting overnight relief from he warm daytime temperatures. This brings areas of moderate HeatRisk into the inland valleys on Wednesday, with locally major HeatRisk for the deserts.
With the mid level moisture in place, some shower chances are in the forecast for Tuesday/Wednesday, but look to be fairly inconsequential. A shortwave rounding the western edge of the ridge on Tuesday passes west of our area, but could still provide enough synoptic support to generate elevated showers across the area. Any showers not over the mountains will likely be unable to overcome dry sub-cloud air and fall as virga, with little to no measurable precipitation in the mountains (where PoPs are 15-20%). More surface based showers will be possible in the mountains on Wednesday, but with the mid level moisture layer remaining fairly thin, shower/storm duration would likely be quite short as well. Still, a strike or two of lighting can't be ruled out.
Ensembles continue to push a longwave trough into the Pacific Northwest for Thursday into Friday, which should help weaken the ridge and nudge it south/east as well as kick out the mid level moisture. This results in a cooling trend into the weekend with the marine layer deepening again. Temperatures return to near average for Thurs/Fri with the potential for afternoon highs 10 degrees or more below normal for the weekend. While there is some disagreement in the exact timing/depth of this trough in the ensemble spread, it appears strong enough to bring some elevated onshore wind gusts to the region this weekend, primarily in the mountains and deserts where gusts 30-50 mph (and locally higher) are possible.
221800z, Coast/Valleys, Cigs expected to return 03-06Z Tuesday. Bases are expected to be 700-1200 ft MSL with KCRQ the most likely location for cigs under 1000 ft MSL. KSAN and KSNA have a 50% chance of cigs under 1000 ft MSL. Low clouds are expected to reach into the portions of the valleys, with only 40 percent chance of cigs at KONT. Areas of vis reductions down to 3-5 SM possible near higher coastal terrain and in the valleys on the edge of the cloud deck. Low clouds and vis reductions will clear 15-17Z Tue.
Mountains/Deserts, VFR conditions expected into Tue with periods of high clouds AOA 15000 ft MSL after 19Z Tue.
No hazardous marine conditions are expected through Saturday.
Another uptick in surf expected Tuesday through Thursday with the arrival of a 3 ft 15 to 18 second period south swell from 190 to 210 degrees. Surf of 4 to 6 ft expected. Strong rip currents expected through the week.
Ca, None. PZ, None.
