A Big Change Is Coming To The Pacific Northwest

Tom Moore
Published: May 18,2016

Dip in the jet stream will bring changes to the Pacific Northwest.

The Pacific Northwest has been extremely warm and dry for the past several months with only a few cool and wet spells — but that's all about to change. A potent weather system will slide into the region from the Pacific by Thursday resulting in much cooler and wetter conditions.

2016: Warm And Dry Through Mid May

Temperatures have generally been above average since the beginning of the year.
April was a particularly warm month with much of the region experiencing temperatures near record levels and some areas recorded their all-time warmest April according to the National Center For Environmental Information. Frequent ridges of high pressure aloft blocked Pacific moisture and kept temperatures well above average.

Warm and dry conditions have extended into May.
For example, Seattle has recorded above-average temperatures on 14 of the first 16 days of the month. Only 0.13 inches of rain has fallen. Average rainfall through the first 16 days of May is 1.01 inches.
Medford, Oregon, has recorded above-average temperatures for the first 16 days of May. Only 0.17 inches of rain has fallen during that time. Average rainfall through the first 16 days of May is 0.70 inches.

Changing Pattern - Cool And Wet

By Thursday, a southward dip in the jet stream will slide into the Pacific Northwest.  Moisture will be flowing in from the Pacific from late Wednesday through much of the upcoming weekend. With daytime heating, the moist air rises into cold air aloft allowing clouds and showers to form readily.
Rainfall totals of one half to one inch can be expected (mainly west of the Cascades of Washington and Oregon) through Sunday. Totals up to two inches are possible in the higher elevations. Similar amounts are in the forecast for higher elevations of of northern Idaho, western Montana and northwest Wyoming.
With temperatures falling quickly, snow levels will fall. Look for wet snow around the passes of Washington (around 4,000 feet) and in northern Oregon (around 4,500 feet). Snow levels in Idaho and western Montana will be generally above 6,500 feet by Thursday night. Snowfall accumulations will generally be on the light side.
Starting on Thursday, high temperatures will fall below, or in some cases significantly below average across the Northwest. On Thursday, cities like Seattle and Portland could remain in the 50s for most, if not all of the day. Although slowly moderating, temperatures will likely remain below average across much of the Northwest into the weekend.
(FORECAST:  Seattle | Portland | Medford | Spokane | Boise)

Northwest Temperatures Compared To Average

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