1st Week Of Fall Will Be 'Roller Coaster Ride' Of Weather In Pass

RIVERSIDE COUNTY, CA — Summer is officially over, and the first week of autumn will feature "roller coaster" weather patterns throughout the Inland Empire, as well as the rest of Southern California, according to the National Weather Service.

"Welcome to fall," the agency said on Monday. "The weather for the first week of the season is very complex and messy, with a lot of chaotic moving parts."

In its Sunday forecast analysis, the NWS said that everything from dry offshore winds to rain showers are possible over the next six days in the region.

"This week's weather will be somewhat of a roller coaster ride, starting out warm and dry, then transitioning to a Santa Ana (wind) pattern ... before turning much cooler," according to an NWS statement.

Forecasters said that summer conditions will persist into Wednesday, with high temperatures in the Riverside metropolitan area generally in the mid- 90s and clear skies, while the Coachella Valley's highs will top out in the low 100s.

A trough of low pressure currently sliding toward northern Mexico will veer northeast into Arizona by Tuesday, packing turbulent conditions.

"In SoCal, the greatest impacts from this system will likely be the gusty offshore winds in the mountains and inland valleys (Tuesday)," the NWS said. "Downslope flow will bring warming to the inland valleys and elevated fire weather concerns."

Isolated thunderstorms in the desert and mountain areas are possible as the trough over Arizona lurches to the east, meteorologists said.

Another trough will begin sprawling across Southern California on Thursday, dominating regional weather into the weekend, according to the NWS.

"Stronger onshore pressure gradients will bring cooler weather and a deeper marine layer Friday and Saturday, perhaps deep enough for scattered light rain showers," the agency said.

A chance of rain is in the forecast for the Riverside metropolitan area and Coachella Valley Thursday night through Saturday night.

By the weekend, a significant drop in the outside temperature is expected.

"Over the weekend a very deep and unseasonable trough of low pressure amplifies along the West
Coast, bringing much cooler weather with temps 10-20 degrees below average," the NWS said. "That`s assuming the trough develops the way models depict today... Stay tuned to forecast updates and don't be surprised if the forecast changes from day to day with all the chaos going on."

Here in Banning, the National Weather Service forecast (as of Monday morning) is as follows for the coming days:

Monday
Sunny, with a high near 86. West wind 5 to 15 mph, with gusts as high as 20 mph.

Monday Night
Mostly clear, with a low around 64. Southwest wind 5 to 10 mph becoming southeast after midnight. Winds could gust as high as 20 mph.

Tuesday
Sunny, with a high near 92. East wind around 15 mph, with gusts as high as 30 mph.

Tuesday Night
Mostly clear, with a low around 68. East wind 5 to 10 mph.

Wednesday
Mostly sunny, with a high near 88. Southeast wind 5 to 10 mph becoming southwest in the afternoon. Winds could gust as high as 20 mph.

Wednesday Night
A slight chance of showers after 11pm. Mostly cloudy, with a low around 64. Chance of precipitation is 20%.

Thursday
A slight chance of showers. Partly sunny, with a high near 80. Chance of precipitation is 20%.

Thursday Night
A slight chance of showers. Partly cloudy, with a low around 60.

Friday
A slight chance of showers. Mostly sunny, with a high near 77.

Friday Night
A slight chance of showers. Mostly cloudy, with a low around 58.

Saturday
A slight chance of showers. Mostly sunny, with a high near 74.

Saturday Night
A slight chance of showers. Partly cloudy, with a low around 54.

Sunday
Mostly sunny, with a high near 72.

— City News Service contributed to this report