Arctic Express Coming to the Northwest
If you live in western Washington, you might want to check that your heating system still works.
If you live in eastern Washington on the slopes of the Cascades, you might want to make sure you have a snow shovel.
If you live in western Montana, you might want to get your chains ready and stock up on food.
An unusually early and intense Arctic express will hit the region this weekend. And our days of Blob warmth will be over for a while.
Let me start by showing you a stunning image from the NOAA/NWS Climate Prediction Center (CPC)–their 6-10 day forecast for temperature. Specifically, it gives the probabilities of below normal (blue) and above normal (red) temperatures.
Wow— my colleagues in NOAA are quite sure that below-normal temperature will reign along the entire West Coast as well as the northern Plains States.
The action starts late Friday.
A huge upper level ridge develops in the Pacific, resulting in northerly flow over the western U.S., with a strong trough of low pressure/heights moving into the Pacific Northwest (see upper level– 500 hPa map for 5 PM Friday below). This pattern will not only bring Arctic air south over the Northwest but will isolate the Northwest from the warming impacts of the Blob (the region of warm water over the northeast Pacific). As a result, western Washington will experience much colder minimum temperatures than observed during the past few months.
Now the details. Here is a forecast map for 8 AM Saturday, showing sea level pressure (solid lines), lower atmosphere temperatures (color shading) and surface winds. There is an intense pressure change (gradient) near the international border, with cold temperatures behind—this is commonly called the Arctic Front. Low pressure, associated with the upper level trough, is centered over SE Washington.
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