Turning Colder!

Monday, November 23, 2015
1:19 pm

Well, I got pretty busy this past week and the weekend after putting off all my work to deal with that windstorm. It wasn’t quite as big as I thought it was going to be, but it was still pretty windy around the area with 45-70 mph gusts throughout all of Washington and some unexpected 50 mph gusts near Portland.

If you really wanted high winds, you had to head to the mountains. Mission Ridge hit 137 mph and had gusts above 100 many times during the day. In fact, they had a 14-consecutive-hour stretch of 90+ mph gusts! White Pass hit 115, and for an 8-hour period, 7 of those hours featured gusts between 113 and 119 mph. One hour was relatively calm with a peak gust of 99 mph. More of the same was found at Crystal Mountain and Rattlesnake Ridge. Credit to Scott Sistek for neatly organizing some of these top wind speeds.

Valid 04:00 pm PST, Mon 23 Nov 2015 – 12hr Fcst
UW Atmospheric Sciences

This week, we are much calmer, drier, and cooler, with a massive ridge of high pressure over the Northeast Pacific and a large trough over our region. Embedded in this larger trough is a system that is making its way into our area as we speak.

Credit: WeatherOn

Unlike our relentless atmospheric rivers last week that brought feet of rain to the southwestern slopes of the Olympics and caused major flooding on rivers flowing off the Olympics and Central Cascades, this storm is relatively quick moving and cool, with snow levels hovering around 1,500-2,000 feet. There will be a few inches of snow in the passes, but nothing out of the ordinary for this time of the year, and we certainly won’t see any river flooding!

After this cold front sweeps through tonight, cold air originating from southern British Columbia will rush through the Fraser River Valley into Western Washington. This commonly happens when we have a large ridge in the Eastern Pacific and a large trough over our region. However, the ridge in the Pacific is not nearly amplified enough, the trough over our area is not deep enough, and it is still relatively early in the season, so the air entering our region won’t be as cool as it has been with some of these events in the past. Right now, we are looking at highs in the low 40s for Seattle tomorrow with cooler temperatures further north and warmer temperatures off the coast.

Valid 10:00 pm PST, Tue 24 Nov 2015 – 42hr Fcst
Credit: UW Atmospheric Sciences

The reason this “Fraser River outflow” exists in the first place is because these arctic air masses are often associated with high pressure. Cold air is denser than warm air, meaning that for a given column of the atmosphere, the column with cold air will have more mass and thus exert a higher pressure on the surface below. Accordingly, high pressure often resides over the interior of British Columbia when we have these outbreaks. Wind generally flows from high to low pressure, and it accelerates at the end of gaps, meaning that places like Western Whatcom County, Lummi Island, and the San Juan Islands near Rosario Strait can get pretty blustery when we have these setups. In fact, a wind advisory is in effect for the North Interior Tuesday and Tuesday night for winds of 20-35 mph with gusts to 50 mph, and gale warnings are in effect for the Strait of Juan de Fuca and waters around the San Juan Islands.

The combination of cold air and strong winds brings the threat of low wind-chills to the North Interior. There have been far worse arctic outbreaks, with 80 mph gusts and low temperatures below 0 degrees, but still, things will feel very cold, with windchill factors in the teens and 20s for much of Tuesday and Tuesday night. Bundle up!

Credit: National Weather Service

Tuesday night fill feature clear skies, decreasing winds, and our coldest temperatures of the year, with low temperatures in the low 30s for Seattle and in the 20s in more outlying areas. The dark asphalt in Seattle and other cities around Western Washington absorbs heat during the day and radiates it off to space at night, helping keep these cities a few degrees warmer at night than other places throughout Western Washington. Wednesday and Wednesday night will continue to be cold and clear, and temperatures will finally start to moderate for Turkey Day and the weekend (but we will still remain pretty chilly).

But what about the snow?

There was some hoopla late last week and over the weekend about a possible snow event happening Monday night into Tuesday. Right now, it doesn’t look like that will happen. By the time the really cold air originating from the Fraser River Valley gets here, we will have dried out substantially, and even if we did have some precipitation in the area, it would likely be in the form of rain or a rain-snow mix, as temperatures are just not cool enough to support snow accumulation, especially in the Seattle metropolitan area. Sorry kids. The places that have the best chance of seeing some snow are the typically rainshadowed communities on the northeastern tip of the Olympic Peninsula, because now that our flow is coming from the northeast instead of the southwest, they are on the windward side of the Olympics! Still, accumulations will be negligible below 500-1000 feet.

Valid 04:00 pm PST, Tue 24 Nov 2015 – 36hr Fcst
Credit: UW Atmospheric Sciences

It’s a boring week for weather, and a nice change of pace! I’ve been able to practice saxophone, rake some leaves, and even sleep a little!

Thanks for reading,
Charlie

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