Extremely dangerous cold and wind chill into Thursday

Tuesday morning weather headlines:

• It's cold out there and it's going to get a lot colder

• Gusty winds will increase the frostbite hazard substantially

• Plan clothing, activities and travel carefully through Thursday

• Saturday will feel like spring

The big picture

The arctic air mass headed our way is huge and will affect large portions of Canada and then the U.S. from the Northern Plains and Great Lakes to the Ohio Valley and the Northeast.

Wind chill is a measure of the combined cooling effects of the air temperature and the speed of the air across a surface. Faster speeds remove heat more quickly from both people and objects. It is determined experimentally.

Wind chill speeds cooling but will not cause an object to become colder than the actual air temperature. So yes, your vehicle is affected by wind chill in that it will cause it to cool more quickly after it is shut down, but it will not become colder than the actual temperature.

Wind chill warnings for very dangerous conditions have been posted from North Dakota south to Missouri and east to Pennsylvania and West Virginia over the next few days.

Wind chill warnings are issued in Minnesota when the wind chill is forecast to be minus 35 or lower. Warmer parts of the country need not be so frigid for warnings to be issued.

Severity

We in Minnesota get used to and even enjoy the cold weather that kills mosquitoes and freezes the lakes so we can drive on them. But what we have coming now is the kind of arctic blast that can easily cost people parts of ears, noses, fingers and toes.

Game plan for Tuesday

The cold air has arrived. Now, frigid northwest winds are sweeping southeastward across the state.

Winds in open areas will gust to more than 30 mph Tuesday. Temperatures might recover slightly in the morning, but persistent northwesterly blasts will cause falling temperatures Tuesday afternoon.

I expect Twin Cities temperatures to fall to around 15 below by late afternoon. Wind chills around the state will be in the  minus 30s and minus 40s all day while the northwest corner will be in the  minus 50s.

Meanwhile, a winter weather advisory will be in effect for western and south central Minnesota where the wind will reduce visibility due to blowing snow, mainly  Tuesday afternoon.

Looking ahead

As mentioned, the arctic outbreak will last through Thursday. Here is how the wind chills should play out for some Minnesota cities including the Twin Cities (darker blue):

Lowest wind chills expected Wednesday morning

The combination of frigid air and some wind should push wind chills down to a range of about  minus 45 to minus 65 by Wednesday morning.

Actual low temperatures on thermometers are forecast to be between 25 and 40 below zero. The Twin Cities likely will have a low somewhere around 28 below. Outside the urban heat island, low temperatures might sink to around 30 below all the way to the Iowa border.

Winds will be lighter on Wednesday but temperatures will remain nasty all day. Look for highs mostly in the teens below zero and even 20s below for afternoon highs in northwestern Minnesota around Hallock and Bemidji.

Another frigid morning on Thursday

Low temperatures on Thursday are likely to be mostly in the range from 25 below to 40 below again, but with light wind. The Twin Cities could easily flirt with the record low for Jan. 31 -- 27 below.

Afternoon highs might "warm" slightly to the negative singles. Hurray.

Think spring

Milder temperatures on Friday will precede a spring-like warmup on Saturday. Temperatures in the 30s will feel like 80 degrees after this week. Rock County in the southwest corner might even touch 40 Saturday afternoon.