Severe Thunderstorm Watch issued for Lawrence County until 11 p.m.

The Polar Vortex is on the move; Below zero temperatures spilling in to the United States

Cold air is arriving in central Indiana this evening.  A cold front is passing through the state as of 7pm.  Winds are increasing along and behind the front.  Within the last two hours winds have gusted as high as 46 mph in Muncie.

Winds will remain higher than normal this evening through late Wednesday night with sustained winds 12-25 mph and winds gusting to 30 mph at times.  This is one of the reasons wind chill values will be so low Wednesday morning.

Cold air is spilling in to the northern United States this evening.  The temperature has already dropped to below zero at International Falls, Minnesota.

Observed temperatures in North America Monday afternoon.

The brunt of the cold air is on the move through central Canada, west of Hudson Bay.  Temperatures are -20° to -35° as of 5 p.m. Monday.  (That is air temperature, not wind chill!)

Also keep in mind this air is very dry.  Dew point temperatures, the measure of the moisture in the air, is -30° to -40°.  While the air will not be that dry when it reaches Indiana, you will definitely notice the static shock factor being much higher Wednesday and Thursday.   You'll likely want to keep hand lotion and chap stick with you for the middle of the week.

Latest check of snow and ice cover over North America shows the ground north/northwest of the Midwest is covered by snow all the way up to the Arctic Ocean.  We check the snow/ice cover to see if there is bare ground that could moderate the temperature of the air as it flows down to the Midwest.  That does not look to be the case at this time.

Snow and ice cover analysis for the Northern Hemisphere as of Monday, January 28.

HOW COLD WILL IT GET

Forecast low temperatures Wednesday morning.

My current forecast calls for -9° for a low temperature Wednesday morning.  A couple things could have a big impact on that temperature.

  1. That temperature assumes we have a small amount of snow on the ground from Monday evening's weather system passing through the state.
  2. What will cloud cover be like Wednesday morning.  Currently, data suggests passing clouds late Tuesday in to Wednesday morning.
  3. Winds are forecast to be sustained at 15-25 mph.  That should keep the temperature from completely bottoming out Wednesday morning.  Some of the computer models project a low temperature around -13°.  If winds lighten, we could certainly drop lower than -9°, but I'm taking in to account some wind through the overnight.  Keep in mind, if we do keep winds 15-25 mph wind chill values will be brutal Wednesday morning.  Right now I think we could be talking about -35° to -15° wind chill values late Tuesday in to Wednesday morning.

Some of these same questions can be asked for how warm we get Wednesday afternoon.  At this point we are splitting hairs.  Know this, it is going to be COLD Wednesday.  It will be a good day to stay inside.

I'm sticking with a high temperature slightly above 0° in Indianapolis for the afternoon.  Mainly because I do not think there will be much snow on the ground at the airport and we will see some sunshine.  I think that gets us up to 2°.

Go north of Indianapolis and temperatures will not make it out from below zero throughout the day Wednesday.  A high temperature of -5° or -6° looks possible for areas near Kokomo and Peru.

Forecast high temperatures Wednesday afternoon.

One concern this evening through Thursday morning is the previously mentioned wind.  Combine that with cold air and we start talking very cold wind chill values.

Computer model projection of wind chill values Tuesday.

Wind chill values will go below zero starting late Monday night and continue through throughout the day Tuesday.

As the true arctic - and even polar - air arrives late Tuesday night, you will see a dramatic decrease in wind chill values.

Computer model projection of wind chill values Wednesday.

Computer models project wind chill values could be -30° to -45° at sunrise Wednesday.  At that level of cold frostbite can happen to bare skin in as little as 10-13 minutes.

Notice through the course of the day wind chill values remain below -10°, and in some cases below -20°.  That works out to the potential for frostbite happening to bare skin in 20-25 minutes.  That's during the day!  This is why I've been strongly suggesting to find something to do inside for the day.

Once we get passed Thursday afternoon temperatures should begin to rise.  They will rise late Thursday and throughout the day Friday.  Long range data suggests temperatures back in to the 50°s before the weekend is over.  That's right, a 63° temperature swing Thursday morning through Sunday afternoon.  Know what that means?  Potholes will begin appearing all around central Indiana.

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