What a difference a year makes...literally! Winter 2011-2012 is certainly getting off to a lackluster start...temperatures so far this month have averaged nearly 6°F per day above normal in Chicago...and 15.4°F warmer than first week of December last year! In fact...so far this month our average low temperature has been 30°F while in comparison 4 out of the first 7 days of December 2010 didnt even see high temperatures that warm. In fact...by this time last year we had already seen lows in the single digits.
The coldest temperature we have seen so far this year in Chicago was 24°F back on nov 17th! Going back through the 138 years of weather records in Chicago there have only been 4 winters that have failed to produce colder temperatures up this point in the year. The only 4 winters where we saw later dates for the first time reaching 23°F or colder in Chicago are:
1) Dec 31 1923
2) Dec 21 1998
3) Dec 14 1939
4) Dec 9 2001
The average first date for seeing a temperature at or below 23°F in Chicago is november 17th. By this time last year Chicago had already seen 2 days with high temperatures colder than the coldest low temperature so far this year!
In addition...if Chicago fails to get measurable snowfall tonight then all indications are that the threat of measurable snowfall will be very low through next wednesday Dec 14th...which would put the record latest measurable snowfall record for Chicago in very real jeopardy. The latest first measurable snowfall in Chicago was Dec 16 1965.
In Rockford...the coldest temperature thus far this year has been 21°F back on november 30th and again on Dec 7th. There has only been one other year in Rockford weather history that there hasnt been a colder temperature yet up to this point in the year and that was back in 2001. In 2001 the first day with temperatures at or below 20°F in Rockford was December 9th. The average first day for seeing temperatures at or below 20°F in Rockford is November 13th...so we are running nearly a month late!
The opening week of December in Rockford...like Chicago...has been abnormally mild with temperatures averaging 4.8°F above average. The first week of this December in Rockford is running 13.7°F warmer on average than the opening week of December 2010. In fact...by this time last year Rockford has already seen 2 days with high temperatures colder than the lowest low temperature so far this year!
There is a change in the pattern taking place and the regions first shot of truly winter-like air will arrive by Friday...however all indications are this will be short lived with temperatures rebounding to above average by sunday. The climate prediction center is forecasting a high probability of temperatures averaging above normal December 13th through 21st...so current indications are that the overall pattern of this winter looks likely to continue for another week or two.