Near seasonal temperatures through the first half of the upcoming week with an increase in both high and low temperatures for the middle to end of next week. Chances for afternoon showers and thunderstorms will decrease and remain confined to the higher mountain peaks for much of this week, with the potential for more widespread shower and thunderstorm activity for the latter half of next week. The marine layer will remain mostly confined to the coast, reaching into portions of the valleys at times.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Highs today are forecast to be a few degrees warmer than yesterday across the area which will bring conditions near to slightly above average for this time of year. The broad ridge of high pressure over the western United States has kept the door for moisture open, indicated by the 1.65 inches of precipitable water on the 12Z KNKX sounding. There remains chances for showers and thunderstorms over area mountains this afternoon, but the lack of atmospheric forcing may be a limiting factor. High resolution model guidance is showing a few light showers developing over the San Bernardino mountains, but chances of rainfall rates exceeding 0.50" per hour is less than 10 percent. Shower/thunderstorm chances will decrease into early next week as upper level ridging shifts east, which will limit the atmospheric moisture influx.
For the middle of next week, the ridge is forecast to shift south over Texas and strengthen. There remains some uncertainty in the ensembles on the position of the high and how far west the ridge axis will extend. 20 percent of ensemble guidance has the ridge of high pressure extending far enough west to allow for a moisture increase. This would be the most favorable pattern for afternoon showers and thunderstorms.
The position of the ridge will also influence how warm it will get. Current forecast follows the NBM and has an increase in highs and lows for the middle to end of the week. The current forecast supports an increase in moderate HeatRisk west of the mountains and areas of major HeatRisk in the deserts, mainly due to elevated low temperatures. Limited overnight cooling will exacerbate impacts from the heat, especially for vulnerable populations and those without air conditioning.
181800z. Coast/Valleys, This morning's low clouds have cleared out to sea, with VFR conditions prevailing through the afternoon and FEW-SCT mid level clouds near 15-20kft MSL. Low marine clouds are expected to fill back in and push ashore by 03z, bringing CIGs to San Diego County around 04-06z Sunday. These clouds should spread northward into Orange County and up to 15-20 miles inland by 10-12z. Cloud bases will likely be similar to this morning, around 1000- 1200ft MSL, with VIS reductions down to 2-5 SM locally for higher coastal terrain. Clearing back to the coasts expected by 16-17z Sunday.
.Mountains/Deserts, VFR conditions expected through the period with FEW-SCT mid-level clouds AOA 15,000ft MSL. SCT Cu based 10-12 kft MSL have developed over the mountain ridgetops this afternoon, with chances for ISO-SCT SHRA/TSRA, most likely after 21z through 01z Sunday. Any storms that develop may produce lightning, gusty winds, and vis reductions.
No hazardous marine conditions are expected through Wednesday.
High amplitude southerly swell (4-5 ft with a period of 12-13 seconds) will build Sunday, bringing elevated to high surf and strong rip and longshore currents for Sunday through at least Tuesday. Highest surf, up to 7-8 ft, will be along south and southwest-facing beaches. Further details can be found in the High Surf Advisory. Surf falls a bit Tuesday and into Wednesday before another southerly swell (4-5 ft with a period of ~14 seconds) brings another round of elevated to high surf for the end of the week and into the early weekend. The high risk for strong rip currents will remain from Sunday through next week.
Ca, High Surf Advisory from 5 PM Sunday to 11 PM PDT Tuesday for Orange County Coastal Areas-San Diego County Coastal Areas.
PZ, None.
