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Unsettled this weekend; strong high pressure builds next week

By Nic Loyd

WSU Meteorologist

Published on December 1, 2017 3:35PM

One final frontal passage will cause the recent unsettled weather pattern to persist into this weekend. Therefore, widespread light rain (and isolated wet snow), mountain snow, and breezes can be expected. However, the main meteorological storyline should be the major pattern change that is set to occur early next week. For the first time in a long while, a strong ridge of high pressure looks to develop across the region. As a result, rather calm, stable and precipitation-free conditions are likely to develop, and may linger for the foreseeable future.

As you may recall, such a pattern in the summer would lead to a sunny heat wave. However, as we enter December, this upper level dome of warm air is expected to initiate the development of temperature inversions, stagnant atmospheric conditions, and potentially poor air quality in some places. Thus, despite the rapidly warming air mass next week, somewhat chilly weather is forecast for the lowlands, at least for a while.

Temperatures could be a tough call, and will likely be highly dependent upon the details surrounding the ultimate coverage and persistence of the fog/freezing fog and low clouds. Areas that remain clear are anticipated to observe larger diurnal temperature fluctuations, while locations that become mired in low clouds may see small day to night changes. Generally, the progression of these types of high pressure events is such that regions of night/morning fog eventually give way to a more widespread low cloud deck east of the Cascades, and another for interior western Washington.

It will be important to watch for slick morning roads later next week due to the potential for freezing fog and freezing drizzle in the lowlands. For the higher elevations, and especially the exposed slopes in the Coast Range, Olympics and Cascade west slopes, very mild and pleasant weather is possible by the end of the period.

Here are the key upcoming weather intervals:

• Unsettled this weekend

• Clearer, drier, and calmer early next week

• Increasing stagnation and low clouds later next week

• Temperatures generally slightly above normal. Highs in the 40s on Monday, and then warmer, especially at the coast, later in the week.

• Cooling in the lowlands early next week, and then warming in the mountains and at the coast later in the period.

• Rain likely on Saturday in the west, with a chance of rain (or possibly isolated wet snowfall) in the east.

• A chance of lingering showers on Sunday.

• Mostly dry next week.

• Breezy at times this weekend, and generally light thereafter.


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