Brace yourself: Western Washington’s coldest weather of the season coming up

The coldest weather of the season is on tap starting this holiday weekend and extending into next week in Western Washington.

Strong high pressure aloft has been steering Pacific weather systems away from the region in recent days and is expected to continue to do so well into next week. This weather pattern has led to no significant rainfall since the 10th of the month.

The Seattle-Tacoma International (Sea-Tac) Airport has had only 1.01 inches of rain this month, the third driest January on record if little or no rainfall occurs by the end of the month. The driest January on record at Sea-Tac was back in 1985 with only 0.58 inches of precipitation.

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The strong upper-level high pressure also created a strong temperature inversion — much warmer temperatures aloft than near the surface, leading to high temperatures struggling to reach the lower 40s. The average high temperature in mid-January is in the mid and upper 40s.

For much of the Puget Sound region and southwest interior, the temperature inversion has left the morning clouds and fog intact throughout the day. Other parts of Western Washington though have had plenty of sunshine including the mountains.

More sunshine on the horizon

A very weak passing weather system to the north through Friday will help break up this temperature inversion and its associated clouds and fog heading into the weekend. Expect more sunshine, yet quite cool temperatures. With the clearing skies, nighttime temperatures will dip into the 20s to lower 30s, while highs will labor to reach 40 degrees.

The recent drier weather has put a pause on building the mountain snowpack. The Northwest Avalanche Center released its latest snowpack report on January 15, revealing a range of 69% of normal at Hurricane Ridge to 129% at White Pass. Most other Cascade reports including Stevens Pass and Snoqualmie Pass were in the 70 to 90% of average for mid-January.

For those planning to play in the mountain snow or drive across the Cascade passes this holiday weekend, expect lots of sunshine with freezing levels only between 1,000 and 2,000 feet. Have those sunglasses handy.

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Possibility of snow?

For those wondering if this cold weather will lead to the possibility of lowland snow, one key element that is missing is moisture. Yes, it is cold enough for snow. Looking at longer-range weather charts, the next source of moisture coming in from the Pacific Ocean is anticipated to be late next week. Yet, these longer-range charts have considerable uncertainty. So for those who would like a snow day, there is hope. And for those who despise snow, there is also hope.

At some point, this period of cold dry weather will break down. It is not uncommon that during the transition back to warmer weather, lowland snow can fall in Western Washington.

At this moment, prepare for colder than average temperatures and dry weather this holiday weekend that is expected to hold into next week. After that, stay tuned to learn when and how the transition to milder conditions will unfold.

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