Warm and dry today. Temperatures will fluctuate a few degrees each day through Wednesday, remaining around 5 to 10 degrees above normal. Patchy fog is possible this morning along the coast, followed by more widespread night and morning low clouds the remainder of the week. Much cooler with increasing chances of precipitation and gusty onshore winds Thursday through Saturday.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
, Aviation/marine discussion updated,
Surface dew points have increased into the mid 50s along parts of the coast this morning, but so far no fog development is evident on satellite imagery. Surface pressure gradients are very weakly offshore, around -0.2 mb SAN-DAG, and trending onshore, which may allow for patchy fog to form along the coast later this morning. Otherwise scattered high clouds to our southwest will begin to spread into the region later this afternoon. With the return of onshore flow, some cooling will occur west of the mountains today with minor warming in the deserts. High temperatures will be around 10 degrees above normal across much of the area - in the 80s in the valleys and high desert and 90s in the low desert.
The upper level ridge will continue to shift east and break down on Monday with a weak short wave trough moving across So Cal. This is followed by weak transitory ridging on Tuesday, which weakens on Wednesday. Minor daily fluctuations in temperatures will occur with highs around 5-10 degrees above normal. More persistent onshore flow will allow the marine layer to become more established, with more widespread low clouds and fog across the coastal areas and western valleys each night and morning, potentially extending into the far west and southern parts of the Inland Empire by Wednesday morning.
There is still a lot of uncertainty in the timing of the upper trough later in the week, though ensemble consensus has trended slower with its arrival. Around 26% of the ensemble space, comprised mostly of the GEFS, is faster with the eastward progression of the upper low, bringing in light precipitation as early as Thursday. By Friday, all ensemble members have the low in a position that would bring us precipitation, though again the GEFS with its faster track would put the bulk of the precipitation on Friday, while the slower EC and Canadian ensembles are focused more around late Friday into Saturday. There remains considerable spread in precipitation amounts as well. Nbm mean accumulations for the 48 hr period from 5 AM Friday through 5 AM Sunday has around 0.25-0.50 inch for the mountains westward with local amounts near 0.75 inch on the coastal slopes, around 0.10-0.20 inch for the high desert, and less than 0.10 inch in the low desert. Nbm snow level ranges from around 7000-8000 ft Friday and Saturday. In addition to precipitation, gusty southwest to west winds and much cooler conditions are expected late in the week with high temperatures around 5 to 10 degrees below normal by Saturday.
051800z, Generally VFR with increasing clouds AOA 15k ft today. There is higher confidence in more widespread low clouds 800-1200 ft MSL spreading inland tonight after 08Z later this evening, vis restrictions 2-5 SM over higher valley terrain. These low clouds will begin to scatter out tomorrow from 16-18Z Monday. Clouds AOA 15k ft will also decrease tomorrow.
No hazardous marine conditions expected through Thursday. Winds and seas may increase late week due to an incoming weather system. Low confidence in details at this point.
Ca, None. PZ, None.
