Onshore flow will prevail into next week with fluctuations in the strength of onshore flow and marine layer depth. Night and morning coastal low clouds and fog will extend inland into portions of the valleys, then not as far inland by Sunday and Monday. There will be warming on Wednesday, then slow cooling spreading inland for Thursday and Friday. There will be a warming trend for Saturday into early next week as high pressure over the eastern Pacific expands across California.
For extreme southwestern California including Orange, San Diego, western Riverside and southwestern San Bernardino counties,
Onshore flow will prevail into next week with fluctuations in the strength of the onshore flow and with the depth of the marine layer. A weak low pressure system will move across southern California tonight and early Wednesday followed by high pressure aloft on Wednesday. Night and morning coastal low clouds and fog will extend inland into much of the valleys into Wednesday. High temperatures today will be within a degree or two of those on Monday for most areas. Wednesday will be warmer than today by a few degrees to 4 to 8 degrees for the mountains, inland valleys, and high desert.
A trough of low pressure moving inland to the north will strengthen the onshore flow for Thursday into Friday spreading slow cooling inland. There will be slow warming for Saturday with greater warming for Sunday or Monday with some model differences in the timing and strength of high pressure over the eastern Pacific expanding across California.
As with 24 hours ago, the model clusters that are slowest with the warming are driven primarily with ensemble members of the GFS. The current forecast is close to the deterministic NBM with steady, slow warming for Saturday through Monday for the mountains and deserts. There is greater spread in the high temperature guidance for the coast and valleys for Sunday into early next week with the deterministic NBM having slower warming for Saturday and Sunday and greater warming for Monday. With the warming, high temperatures on Monday would be around 5 degrees above average for coastal areas and 5 to 10 degrees above average farther inland.
170930z, Coast/valleys, Low clouds with bases around 1500 feet MSL and tops to 2200 feet will continue to spread into southern and western parts of the Inland Empire this morning. Local vis along inland higher terrain 3-5SM. Scatter out 16-18Z. Low clouds look to redevelop along and near coastal areas between 00-03Z this evening, with bases between 1500-2000 feet MSL moving inland overnight in similar coverage.
Mountains/Deserts, Mostly clear with unrestricted vis today and tonight. West winds with sfc gusts 25-35 kt over mountain ridges, desert slopes, and below passes this afternoon and evening. Moderate up/downdrafts possible over/east of the mountains.
No hazardous marine conditions are expected today through Saturday.
Ca, NONE. PZ, NONE.