What Causes a Polar Vortex? Extreme Winter Storms to Hit Central, Northwestern States

Extreme winter weather is predicted to expand into multiple states this weekend as a "polar vortex" causes snow, ice and freezing rain.

Arctic high pressure pushing south from Canada will result in "frigid temperatures" to the U.S. midsection from Friday to early next week, in some cases more than 40 degrees below average temperatures, according to the National Weather Service (NWS).

The NWS's prediction center has forecast potential for snow and ice across Washington and Oregon between Thursday and Saturday, with a wintery storm spell moving into the region causing "widespread snowfall" in both Portland and Seattle.

Predictions suggest that weather pattern will bring multiple rounds of freezing rain and ice build up from northern Texas into the mid-Mississippi, Ohio and Tennessee Valleys on Thursday night. Additional storms are taking shape from Arkansas to Kentucky.

A polar vortex is an area of low pressure and cold air that surrounds both of Earth's poles. The vortex at the North Pole expands in winter, sending cold air south.

As the NSW explains in a fact-sheet on its website about the phenomenon: "It always exists near the poles but weakens in summer and strengthens in winter.

"The term 'vortex' refers to the counterclockwise flow of air that helps keep the colder air near the Poles. Many times during winter... the polar vortex will expand, sending cold air southward with the jet stream. In short, there is no cause to be alarmed when you hear about the polar vortex, but you should be prepared for colder temperatures."

A series of winter storms moving into the Pacific NW will result in widespread snowfall accumulations across the higher terrain and lowlands. While uncertainty remains, it is becoming more likely that moderate/heavy snow will impact both Seattle and Portland by late Friday. pic.twitter.com/DzkKukaZwG

— NWS Weather Prediction Center (@NWSWPC) February 11, 2021

A winter storm will continue to bring multiple rounds of freezing rain resulting in significant ice accumulations from northern Texas into the mid-Mississippi, Ohio & Tennessee Valleys through Thursday night. Very dangerous driving conditions are possible. pic.twitter.com/Drbu3qlcxm

— NWS Weather Prediction Center (@NWSWPC) February 10, 2021

The latest forecasting from the NWS, published Thursday, was clear: anyone in the path of the storms should brace for severe cold weather over the coming days.

The prediction center said that freezing winter storms will cause widespread snowfall in Washington and Oregon through this weekend, with bitter arctic air pushing across the central U.S. and continuing to expand further south through the weekend.

It said: "A very cold and active weather pattern is set to continue across the country to end the first full week of February, with a plethora of winter weather hazards."

The center said in its Thursday forecast a continuing ice storm will impact regions from central Texas to the Ohio Valley, noting the "amount of ice will likely lead to hazardous travel conditions, power outages, and scattered tree damage" around the region.

Wintery weather is a possibility across the Pacific Northwest, with low pressure forecast to enter into southern Oregon from Thursday evening. By Friday, the NWS said that cold temperatures could reach as far east as the Lower Mississippi Valley.

It added: "Temperatures will also make a nosedive across the Northwest, where several daily low records could fall. Wind chill advisories and wind chill warnings remain in effect and stretch from much of the Northern Plains to Midwest.

"Wind combined with subzero temperatures could make it feel as cold as -50 degrees in some northern spots. This bitter cold can be dangerous and lead to frostbite in less than 10 minutes. Be sure to plan ahead and dress appropriately if spending time outdoors."

New York City snow storm
A man digs out of the snow in Brooklyn snow in on February 02, 2021 in New York City. Extreme wintery weather is predicted to expand into multiple states this weekend as a “polar vortex” causes snow, ice and freezing rain. Spencer Platt/Getty