Saturday, July 21, 2012

A few observations on 2012 weather so far

Even though our temperatures here in Central Illinois have seemed consistently above normal since last winter, I thought it might be interesting to look at the data to see just how warm it's been.  The data behind both the charts shown here is the daily mean temperature as measured at the Peoria International Airport; the mean temperature being a simple average of the daily high and low temperatures.

The first chart shows the actual daily means plotted as the red curve, and the historical average daily means plotted in blue.  Since the chart begins at January 1, the mild temperatures we experienced in October, November, and December 2011 are not obvious in this data.  January of this year had a couple of brief cold snaps, February had even fewer days below normal, and most of March was part of a 35-day string of days whose means were significantly above average including 6 record daily highs.  Below normal rainfall accompanied our current 24-day string of above normal temperatures to create drought conditions as severe as any I can remember.

(click to enlarge)

This next chart shows the deviation of the actual mean temperature from the historical mean as the light blue bars that in 2012 have been warmer than the historical mean over 81% of the days so far.  Although the temperature has been much hotter lately, this chart makes it obvious how much warmer than normal the temperatures in March were.  Some days were over 30 degrees F hotter than normal!  No wonder the plants started budding early this spring!

(click to enlarge)
The darker blue dotted curve on the chart represents the cumulative average deviation of the actual mean from the historical mean temperature.  As we approached the end of the warm streak in March and April, the deviation of the cumulative average reached almost 11 degrees F, and even now at July 21 is over 7 degrees F higher than normal.  A year of historically normal temperatures would have zero deviation from the  historic mean, but this year has been so hot that our temperatures have AVERAGED over 7 degrees hotter than normal EVERY DAY!  That's not just statistically significant, that's very unusual!  For reference, 2009 averaged 0.12 degrees F warmer than normal, 2010 averaged 1.85 degrees F warmer than normal, and 2011 averaged 2.07 degrees F warmer than normal, but none of them came close to the 7 degree average deviation so far this year.

I don't predict the weather, but unless the next five months are much colder than normal, our cumulative average should remain significantly above historical levels throughout 2012.


  1. I agree; the daily temperature certainly has been mean.

  2. Hmmm... Kathryn read the post far enough to see the word "mean." Someone must have hacked her account...