High temperatures will continue to warm for inland areas today, to around 20 degrees above average for portions of the inland valleys with locally gusty Santa Ana winds to 35 mph near the coastal slopes of the mountains through this morning. Cooling for the coast and valleys on Thursday and Friday will spread inland over the weekend as high pressure aloft weakens and weak onshore lower-level flow returns. A shallow marine layer will return for Thursday and Friday with night and morning coastal low clouds spreading locally into the western valleys over the weekend as the marine layer slowly deepens. High temperatures will be coolest on Sunday and Monday, but still 10 to 15 degrees above average for inland areas.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
.Morning Update,
Light offshore winds continue across coastal facing slopes and passes near 20-30 MPH, with other areas seeing calmer winds. These winds will continue to be persistent throughout much of the day. We continue to expect the warmest temperatures to occur by this afternoon with moderate to high confidence in seeing high temperatures reach 85 degrees or more across parts of the Inland Empire and San Diego County valleys. Highs look to reach near 80 degrees across the lower deserts as well as within a few miles of the coastline. Some places may break record daily highs today, including Chula Vista, Riverside, Ramona, Palomar Mtn, and Borrego Springs. The forecast remains on track to show a subtle cooling trend into the weekend with dry weather expected for at least the next week.
.Previous Discussion (315 AM Wednesday),
(today through Friday), High temperatures for inland areas will continue to warm today, to around 20 degrees above average for portions of the inland valleys and lower coastal mountain slopes, while coastal areas cool a few degrees. High temperatures for today will range from the lower to mid 70s near the coast to the 80s for the valleys with the lower to mid 80s for the lower deserts. Northeast winds along and below the coastal slopes of the mountains into this morning will locally gust to 35 mph.
Greater cooling of a few to around 5 degrees will spread into the coast and valleys on Thursday as weak onshore flow and a shallow marine layer returns. High temperatures on Friday will be a few degrees cooler for the coast and valleys with not much change for the deserts. High temperatures on Friday will range from the mid to upper 60s near the coast to the mid 70s to lower 80s for the valleys with the lower to mid 80s for the lower deserts.
Some patchy low clouds and locally dense fog could return near the coast Thursday night into Friday morning with a more likely return along with increasing coverage of low clouds and fog for Friday night into Saturday morning.
(Saturday through Tuesday), Slow cooling will continue to spread inland for Saturday and Sunday with not much change on Monday as weak onshore flow continues and the marine layer slowly deepens. Night and morning coastal low clouds will increase in coverage over the weekend and may locally extend inland into the far western valleys.
Even with the cooling, high temperatures for inland areas on Sunday and Monday will still be around 10 to 15 degrees above average for inland areas, ranging from the mid to upper 60s near the coast to the mid to upper 70s for the inland valleys with the lower deserts around 80.
For the middle and latter part of next week, the calibrated deterministic NBM continues to show slowly warming high temperatures, but with increasing spread in the high temperature guidance due to increasing spread in the strength of high pressure aloft along the West Coast. For Ontario, the spread between the 25th and 75th percentile of the high temperature guidance increases from as little as two degrees for today through Friday of this week, to 10 degrees for Thursday and Friday of next week.
101630z, Clear skies with continuing VFR conditions expected through the TAF period. Winds continue to be a bit breezy in the foothills and locally adjacent valleys with areas of northeast winds gusting 25-30 kts through 22Z. There is a small chance for some patchy fog along the immediate coast beginning around 05Z Thursday but confidence isn't high enough that conditions would fall below VFR to include in the TAFs at this time.
Patchy, intermittent fog development possible after midnight tonight which could reduce local visibility below 1 NM at times through Friday morning. Otherwise, no hazardous marine conditions are anticipated through Sunday.
Ca, None. PZ, None.
