September 30, 2018
Summary: The low which resulted in much cooler temperatures yesterday has weakened and moved northward into Oregon. In the meantime, a low is racing southeastward over the eastern Pacific and will be approaching the central coast late Monday night and Tuesday. There are significant differences on models this morning as compared to 24 hours ago, or even last night. Most of the data this morning indicates the low will skirt the central coast and only very slowly move south/southeastward at midweek.
We also have to deal with Hurricane Rosa which is beginning to make its northeasterly turn to begin its track towards the northern Baja coast. Rosa will weaken a great deal from this point on but will still have a tropical storm status when it moves over northern Baja Monday. By Tuesday, the center of circulation will be over western Arizona as a tropical depression. This brings some interesting possible solutions to our weather Tuesday and Wednesday. The low off the central coast, according to some models, could form a demarcation line over southcentral California, essentially from the Antelope Valley on the south to Kern County on the north. Basically what that means is the low will be bumping up against a tropical air mass which by then will be infiltrating Nevada and southern California. This will raise the stakes, if it occurs at all, over Kern County. With all these model differences taking place over the past 24 hours, I’m quite sure these differences will continue right up until the event. For now, it appears Kern County could receive the heaviest amount of precipitation with lighter amounts further north.
There is also another possibility here. The low off the central coast could park farther off shore which would greatly reduce rainfall amounts with even a slight chance of no precipitation at all, but as of this juncture that appears unlikely.
Rainfall amounts over Kern County, and possibly southern Kings and Tulare County, could range between .25 and .50, and generally less than .25 in Fresno and Madera Counties. There will be a small chance of showers after midnight Monday night with showers becoming likely Tuesday through Wednesday with a slight chance of thunderstorms. The chance of showers should begin to diminish Wednesday night with dry weather Thursday through Friday.
Behind all this will linger a trough of low pressure over the interior west with a massive high over the eastern Pacific Ocean. There will be a weak low skirting into the Great Basin Saturday which will give a minimal chance of showers to the Sierra Nevada, but no precipitation is expected on the valley floor.
The following week also looks dry, but with a weak trough lingering over the west for fairly seasonal temperatures.
Forecast: Mostly clear today with occasional clouds. Partly cloudy tonight. Increasing cloudiness Monday. Mostly cloudy Monday night through Wednesday night with a chance of showers after midnight Monday night. Rain becoming likely Tuesday through Wednesday, especially in the south valley, with a slight chance of thunderstorms. Partly cloudy Thursday. Mostly clear Thursday night through Sunday.
Short Term: Highs today will warm into the low to mid 80s. Lows tonight will cool into the low to mid 50s north of Kern County and the lower 60s in Kern County. Highs Monday will warm into the mid to upper 80s, cooling into the upper 50s to the mid 60s Monday night with highs in the mid 70s to near 80 Tuesday.
Winds: Winds will be light today then will be out of the west to northwest at 10 to 20 MPH with stronger gusts Monday through Tuesday.
Next report: Sunday afternoon/September 30