For millions of Americans across a large swath of the country, the holiday week is beginning with made even more miserable by heavy snow expected Tuesday and Wednesday in several central and northwestern states.
A developing ‘bomb cyclone’ has prompted alerts from Washington state to Maryland that cover over 50 million people, according to the National Weather Service, and that number is expected to grow over the coming days.
A ‘bomb cyclone’ is a term used by meteorologists to describe a rapidly strengthening storm. Specifically, it means a drop of 24 millibars (a term used to measure atmospheric pressure), in 24 hours. These storms frequently occur with winter nor’easters, but in this case, the bomb cyclone is expected to occur in the Plains. That’s because of the extreme temperature difference between the warm and moist air in advance of the storm and the extreme Arctic air mass moving in from Canada.
This weather phenomenon is expected to be the pressure equivalent of a category 2 hurricane as it reaches the Great Lakes, with the weather service now calling the strength of the low a “once-in-a-generation” event.
More than 40 million people are under wind chill alerts across much of the central and northwestern US, including in places by a separate storm system last week. Parts of Alabama and Tennessee are also under a wind chill watch as the “feel like” temperatures are expected to plummet below zero.
On Tuesday, the sprawling weather system is delivering dangerously cold temperatures and snow to Montana, North Dakota, South Dakota and most of Minnesota, where high temperatures will remain below zero, at the NWS.
The air feels so cold, frostbite on exposed skin can occur in under 10 minutes in most of the impacted areas, and some isolated locations in under five minutes, forecasters warn.
“In addition to the brutally cold temperatures, dangerous wind chill values of 35 to 55 degrees below zero are possible into the end of the week across these areas,” the Monday.
Wind chill advisories are in place for Sioux, South Dakota, and Fargo, North Dakota, Tuesday, when the dangers of frostbite are settling in. Wind chill, which indicates what the wind feels like, will be as low as 40 degrees below zero, and in Wyoming on Wednesday night could hit a staggering 70 degrees below zero.
“Starting tonight, the worst of the arctic air mass will reach our area, bringing dangerous temperatures and wind chills. Slippery roads will continue with additional accumulating snow expected Tuesday afternoon through Wednesday morning,” the , said Monday evening.
Drastic temperature drops are coming. In Denver, for example, the temperature will be 50 degrees at noon on Wednesday but is expected to drop to 12 below by daybreak on Thursday. Similarly, New Yorkers will enjoy 60-degree weather on Friday in Manhattan and then see a temperature of 24 degrees as a high on Christmas Eve.
Snowfall has already begun in Seattle, which is under a winter storm warning Tuesday. The storm will move east into portions of Idaho Tuesday morning and then spread out across northern and central Montana later in the afternoon.
Overall, most of the US is expected to see abnormally cold temperatures this week. In fact, more than 80% of the country, excluding Hawaii and Alaska, are forecast to see below-freezing temperatures.
In Montana, Helena and Missoula are under winter storm warnings beginning Tuesday, and Billings is under a wind chill advisory through noon Friday.
The storm is also expected to intensify as it approaches the Midwest, where the greatest impacts are forecast. Snow will begin in the region Wednesday and last through much of the Christmas weekend.
In parts of central Minnesota, several inches of fluffy snow are expected Wednesday, followed by high winds, creating the potential for blizzard conditions. A blizzard is defined as having winds of at least 35 mph along with falling or blowing snow which reduces visibility to a quarter-mile or less, for at least three hours.
“By Thursday, wind gusts of 40-50 mph appear likely. With the fluffy snow in place, blizzard conditions are highly likely area wide, even in areas that typically aren’t favored for whiteout conditions.