Halloween forecast updates: How much rain will there be this week?

Cool, wet fall weather is expected to haunt Western Washington this week. A pair of Pacific weather systems will generate this autumn weather with the higher terrain of the mountains receiving their first more noteworthy snow of the season.

The first weather system is an area of lower pressure aloft associated with a cool, unstable air producing scattered showers and some sun breaks Monday. Temperatures are only expected to rise into the 50s alongside the risk of a late-day thunderstorm. This system will continue heading further inland for decreasing showers and sunbreaks Tuesday.

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The next weather system will sweep a frontal system onshore Wednesday for a resumption of rain. Right behind it is another lower pressure system aloft bringing additional showers late Wednesday into Thursday.

The big question for trick or treaters is whether those showers will taper off by Thursday evening. A few haunting showers cannot be ruled out, yet most of the ghosts and goblins roaming neighborhoods will likely avoid getting wet. Temperatures, though, will be cool during the evening hours, mainly in the 45-50 degree range.

Any lingering showers on Friday should end with more sun breaks. Highs for much of the week will be in the upper 40s to mid-50s. October is the month when average high temperatures tumble the most in a year, moving from the mid-60s at the start of the month, dropping to the mid-50s by Halloween.

This week, the mountains will likely receive their first meaningful snowfall of the season. Snow levels are expected to hover between 3,500 and 4,500 feet through the week. Each passing weather system will dump moisture. For the passes of 4,000 feet or higher, an accumulation of two to four inches is quite possible, while higher elevations like the volcanoes could get eight inches or more through the week.

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Stevens, White, Chinook and Cayuse Passes will likely have some snow on the roads at times. Motorists moving across Snoqualmie Pass at about 3000 feet may experience wet snowflakes splatting windshields on occasion. Just in time, effective Friday, Nov. 1, studded tires can be used.

For those looking ahead to the coming weekend, right now it does not look too soggy with just a few showers and breaks in the cloud cover at times. The Seattle Seahawks host the Los Angeles Rams on Sunday and the game may be a dry, but cool one.

Also, recall that on early Sunday morning, clocks ‘fall back’ one hour as time shifts from Pacific Daylight Time to Pacific Standard Time.

May your week and your Halloween be a safe and fun one.

Ted Buehner is the KIRO Newsradio meteorologist. You can read more of Ted’s stories here and follow him on X