Average Temperatures

General Discussions: ASK John: Average Temperatures

By wisangler on Wednesday, December 19, 2007 - 02:59 pm: Edit Post

Hello John,

My question relates to how the average temperatures for a certain region are derived. I'm in East-Central Wisconsin and have been enjoying the below freezing temps and open snowmobile trails. Upon watching the weather on the news, the weatherman showed the "5-day outlook" with temperatures approaching the mid-30s (boooooo!) and quoted "temperatures returning to average levels for December". I gave a little thought to that and can't imagine mid 30s in the second half of December being the norm. Unless this weatherperson was only using the last couple years to derive at his "average temps".

Add this to the constant implications by the local weatherman that snow is bad and warm weather is a wonderful treat during winter. (double booooo!)

Thanks for the info, and keep up the great work on the site. It's refreshing to read the forecasts of someone who doesn't forecast snow as if it was Armageddon.

By John Dee on Wednesday, December 19, 2007 - 06:37 pm: Edit Post


Not sure where that weather man got his info from, but mid-30's at this time of the year would not be average for your locale.

The average high for Milwaukee for today is 32 and for Green Bay is 28. If you are somewhere in between them, then your average temp would be too.


By Chords on Wednesday, December 19, 2007 - 10:38 pm: Edit Post

The NWS National Records began in 1895. And many local records were kept starting around then also or after the turn of the century. My guess is that an average would span close to 100 years for most locations.

By Average Joe on Thursday, December 20, 2007 - 12:25 am: Edit Post

John, I found an article by Richard Koeneman, WGN Weather Center Meteorologist: Normal temperatures—how odd!

In his article from September 2007, he mentions:


a “normal” temperature is the 30-year average derived from the period 1971-2000

Would that be a "standard" for how local normals are obtained? If so, how often would they change which 30-year span of data is used?

By John Dee on Thursday, December 20, 2007 - 11:49 am: Edit Post


Some time ago they decided to compute averages using 30 years worth of data. I believe thier thinking was that climate changes (now it big business) and they wanted the averages to follow those swings.

I do not know how often they change the 30 year span used for computing the averages. I would guess around every 10 years.


By Average Joe on Thursday, December 20, 2007 - 12:59 pm: Edit Post

Thank you John. I noticed you have made several contributions to the WGN weather center. Twice now blowing snow. TS speaks highly of you.

By John Dee on Thursday, December 20, 2007 - 01:10 pm: Edit Post

Tom is a great guy and loves to hear about our interesting weather up here in the Keweenaw.


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