September 10, 2017/pm
Summary: A cut off low remains off the southern California coast this afternoon. The far eastern edge of the low is moving some cloud cover over mainly the southern and western portions of the valley. Doppler radar continues to pick up scattered showers, generally just west of the Channel Islands and moving northwestward.
This is going to be a difficult puppy to forecast, but most of the models this afternoon are indicating a slow movement northward which should drag up a batch of monsoon moisture Monday through Tuesday. Just how close the low moves to the coast will large determine the risk of precipitation.
There’s a chance of scattered showers and isolated thunderstorms from mainly Monday afternoon through Tuesday. By Wednesday, the system will have moved right over the valley for a slight chance of showers. By Wednesday night it will have moved to the east of the Sierra Nevada, ending the rain threat.
On Wednesday, considerably cooler weather will arrive as the surface flow becomes on shore, sending a deep marine layer inland and cooling temperatures back into the mid to upper 80s. this will hold through at least Friday.
Over the weekend, upper level high pressure will slowly build for a warming trend with at least mid 90s reappearing by Sunday. No big heat wave shows up as a lingering trough of low pressure will remain over the Pacific Northwest and possibly northern California.
Forecast: Partly cloudy tonight. Variable cloudiness at times Monday through Tuesday night with a chance of scattered light showers and isolated thunderstorms. A slight chance of showers Wednesday, mainly north of Kern County. Clearing Wednesday night. Becoming mostly clear Thursday through Sunday.
Temperatures: Overnight lows will cool into the upper 60s to the mid 70s in Kern County. Highs Monday will warm into the upper 90s to the lower 100s. Lows Monday night will cool into the upper 60s to the mid 70s. Highs Tuesday will generally run in the mid 90s.
Next update: September 11