A warming trend continues for much of the week, with temperatures reaching 10-20 degrees above normal by Wednesday when elevated Santa Ana winds return. A pattern shift late in the week brings a return of cooler weather and a chance of light precipitation into next weekend.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
This evening, Sfc pressure gradients remain offshore but are trending weaker and winds across the region are mostly less than 10-15 mph. No locations south of LA County are reporting low clouds or fog at this time but satellite imagery shows areas of low clouds and fog over the coastal waters. Short-range, high- resolution models indicate a 40-60 percent chance for low clouds and fog over the coastal areas, with the potential for visibility less than 1 mile at times through about 9 am Sunday.
From previous discussion, Warm weather and light winds will prevail through tomorrow as weak upper level ridging moves in. Temperatures will slowly rise through Monday/Tuesday with zonal flow aloft, providing afternoon highs in the 70s along the coasts, 80s for the valleys and inland areas, 60s and 70s for the mountains, and 80s to 90s for the deserts.
A closed low over the PacNW will transition to an open trough and move into the Four Corners on Wednesday, with gusty offshore winds developing across much of the region. Despite the weak to moderate easterly flow, elevated fire weather conditions may exist on Wednesday as relative humidity drops to single digits everywhere east of the valleys. This dry, warm flow will also cause temperatures to reach almost 20 degrees above normal, reaching the 90s for some desert areas. While temperatures peak Wednesday, highs remain unseasonably warm into Thursday as the trough slowly propagates southward through Arizona. Given these unseasonably high temperatures, those outside may be caught off guard by the heat. Make sure to practice proper heat safety, remaining hydrated and taking frequent breaks in the shade, and avoid outdoor work during the hottest hours of the day.
The pattern changes substantially on Friday as the prevailing hot and dry weather comes to an end. While there remains substantial disagreement among the models later this week, some runs continue to indicate a chance for some precipitation as an upper level low moves into Southern California on Friday, followed closely by a secondary trough set to come across late weekend. The signal remains fairly weak for precipitation with this first low, chances slightly better with the second, but there is still good agreement on the substantially cooler weather expected to accompany this pattern shift. Highs may fall noticeably Friday compared to Thursday, closer to near normal, with the cooler weather prevailing through the weekend.
230500z, Coast, Areas of low clouds/fog, locally dense, will gradually develop within 5-10 miles of the coast 07Z-12Z Sun with BKN/OVC bases 200-500 ft MSL with tops to 600 ft MSL. Areas of VIS 0- 2 will occur, and there is a 50% chance of VIS below 1 mile at SAN, 60% chance at CRQ and 50% chance at SNA. Most areas will clear 14Z- 17Z Sun, except for low BKN stratus lingering at the coast through 19Z Sun. Mostly VFR conditions will prevail Sun afternoon, but low clouds/fog, possibly dense, could return Sun night but with low confidence on timing/location.
Valleys/Mountains/Deserts, Mostly clear skies with unrestricted VIS will prevail through Sun evening.
Areas of dense fog will occur over the coastal waters overnight and Sunday morning with visibility below 1 NM at times, locally below 1/4 NM. There is a 60% chance of fog with visibility below 1 NM returning Sunday night and Monday morning. Otherwise, no hazardous marine conditions are expected through Thursday.
Ca, None. PZ, None.
