Arctic wind to be followed by Sunday snow

As if brutally cold arctic winds weren’t enough, forecasters this morning said this weekend’s expected freeze will be followed by potentially heavy snows Sunday and Monday. The so-called “polar vortex” that has gotten so much attention across the U.S. this winter will be sending its calling card across the region starting tonight. Lows are expected to drop to 15 degrees with northeast wind gusts to 33 mph. The combined wind chill on exposed skin will feel like minus 4 in Spokane. Similar cold will be felt in surrounding locales. Friday night’s low will also be Saturday’s high in Spokane as arctic air floods over the region through mountain gaps in British Columbia. Winds will be strongest in the Purcell Trench between Sandpoint and Rathdrum as well as in Coeur d’Alene and the Rathdrum Prairie. Spokane could see gusts as high as 33 mph on Saturday and 28 mph Saturday night. Wind chills could reach minus 11 on Saturday night with a low of 7 in Spokane. The upper-level low pressure area pushing arctic air southwestward out of Canada will bump up against a Pacific low carrying precipitation as early as Saturday night. The combined force of the two opposing lows could produce significant snow for the region through the morning commute on Monday. National Weather Service forecasters are calling for amounts in the 4 to 10 inch range for Sunday and Monday. With wind gusts continuing on Sunday, there is a chance for drifting snow. Temperatures moderate starting Monday and go above freezing on Tuesday with any precipitation falling as rain starting on Tuesday. The “polar vortex,” also known as the Hudson Bay vortex, is a wintertime shift in wind circulation and air pressure over extreme northern regions. The upper-level jet stream of winds normally circle the North Pole around a deep low pressure area. Occasionally the center of the low shifts southward toward Hudson Bay, creating a sub-polar vortex that pushes deep arctic air southward from the arctic into the U.S. That feature has repeated itself several times this winter. Locally, it is responsible for the region’s coldest and sometimes even its snowiest winter weather because of its potential to combine cold air with Pacific moisture. That is what may occur Sunday and Monday. The cold at times will penetrate into western Washington and Oregon and northern California.