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Forecast

September 30, 2018/pm update

September 30, 2018

Summary:  I’m watching on satellite imagery this afternoon two large areas of cloud cover.  The first batch is off the central and northern California coast with a finger of  mid and high level clouds extending into north/central California.  To our south, the edge of the remnants from tropical storm Rosa is about 150 miles south of Kern County.  Doppler radar out of San Diego and Yuma is depicting showers and thunderstorms as far north as the California/Mexico border with showers and thunderstorms spreading into southwest Arizona.  It will be a wet 36 hours over southeast California as the deepest and richest tropical moisture will surge into that region with the heaviest precipitation expected to be over western Arizona.

 

In the meantime, we have been watching with great interest a low pressure system racing southeastward towards the central coast.  It’s scheduled to arrive Tuesday.  This is going to be a very interesting weather event if the elements come into play as the majority of models suggest.  By midday Tuesday, that low should be just off the central coast while the remnants of Rosa move into the Great Basin.  Models this afternoon are continuing to show the trend of significant instability stretching from the Kings and Tulare County lines northward and Los Angeles County to the south.  The mixing of at least some tropical moisture with some somewhat cooler air moving in aloft may result in the development of an area of significant precipitation over the south valley beginning Tuesday and lasting through Wednesday morning.

 

The chance for measurable rain will diminish some Wednesday afternoon and night but some models are showing at least a small chance of showers into Thursday morning.  As far as amounts of precipitation are concerned, the wettest solutions are showing between .25 and .50 with others showing less than .25.  The only way this scenario will not play itself out would be if the low just off shore settles in a few hundred miles further west.  In any case, this system will rapidly weaken as it moves into southern California Thursday.

 

Over the weekend, a broad trough of low pressure will cover the western states with a west/northwest flow over California.  This will maintain at least marginally below average temperatures through next weekend and well into the following week with dry conditions prevailing.

 

Forecast: Becoming partly cloudy tonight.  Increasing cloudiness Monday.  Mostly cloudy Monday night through Wednesday with a chance of showers late Monday night then numerous showers later Tuesday through Wednesday morning with a slight chance of thunderstorms.  Showers tapering off Wednesday afternoon with a chance of showers Wednesday night and a slight chance of showers Thursday.  Mostly clear to occasionally partly cloudy Thursday night through Sunday.

 

Short Term:  Overnight lows will range in the mid 50s to the lower 60s.  Highs Monday will warm into the upper 80s. lows Monday night will only cool into the mid 60s to the lower 70s with highs Tuesday in the upper 70s to the lower 80s.                                                      

 

Next report:  October 1/am