A Look Back at Temperatures During

the First Half of Meteorological Winter

Meteorological winter began very cold across the Upper Mississppi Valley. North and northwest winds aloft brought several polar and arctic air masses into the region. During the first nine days of December 2005,  temperatures averaged from 10 to 15 degrees below normal across northern Wisconsin and northern Minnesota, and from 15 to 20 degrees below normal across the remainder of the Upper Mississippi Valley.  This was the coldest start to a meteorological winter since the mid to late 1970s. 
 

The National Centers for Environmental Prediction (NCEP) upper air chart above shows that our winds aloft were originating from northern Canada on December 5, 2005. This type of flow brings arctic
and polar air masses southward into the Upper
Mississippi Valley; thus, temperatures were well
below normal.

The figure above is from the Midwestern Regional Climate Center. It shows the December 1-9, 2005 temperature departure from normal.
 
From December 10th through December 20th, temperatures remained below normal; however, not to the same extreme as they were earlier in the month. This was mainly due to our air masses originating over western Canada instead of the arctic. Temperatures during this period averaged from 1 to 5 degrees below normal across northern Wisconsin and northern Minnesota, and from 5 to 9 degrees below normal across the remainder of the Upper Mississippi Valley.
The National Centers for Environmental Prediction (NCEP) upper air chart above shows that our winds aloft were originating from western Canada on December 15, 2005. This type of flow brings polar air masses southward into the Upper Mississippi Valley; thus, temperatures were below normal, but not to the same extreme as they were earlier in the month. The figure above is from the Midwestern Regional Climate Center. It shows the December 10-20, 2005 temperature departures from normal.
 
Since December 21st, the Upper Mississippi Valley has been seeing well above normal temperatures. Abundant thunderstorm activity in the tropical regions of the western Pacifc Ocean and Indian Ocean has result in the east Asian jet to be shifted further noth than normal. In addition, this jet extended east into the western United States. Typically this jet does not extend too far east of the International Dateline. This jet brought a continual stream of low pressure systems into the western United States (especially Washington) and western Canada. This resulted in Pacific air masses moving east across much of the United States, and western and central Canada. These air masses are typically warmer than normal; thus, this is the main reason why the Upper Mississippi Valley has been seeing much warmer than normal temperatures since the first day of Astronomical Winter (December 21st). Temperatures during this period averaged from 16 to 20 degrees above normal across northern Wisconsin and northern Minnesota, and from 12 to 16 degrees above normal across the remainder of the Upper Mississippi Valley. In many cases the low temperatures have been warmer than the normal high temperatures.
The National Centers for Environmental Prediction (NCEP) upper air chart above shows that our winds aloft were originating from western Canada on January 4, 2006. This type of flow brings Pacific air masses eastward into the Upper Mississippi Valley; thus, temperatures are either normal or above normal. The figure above is from the Midwestern Regional Climate Center. It shows the temperature departures from normal from December 21, 2005 to January 15, 2006.
 

La Crosse, WI

During the first nine days of December 2005, La Crosse had an average temperature of 9.6 degrees. This was 16.4 degrees below the normal of 26 degrees. This was the 4th coldest start to a December and the coldest since 1976 when the average temperature was 8.4 degrees. The coldest start to a December occurred back in 1972 when the average temperature was 7 degrees. Below is a list of the top five coldest starts to a December.

Rank
Year
Average Temperature
1
1972
7.0F
2
1919
7.3 F
3
1976
8.4F
4
2005
9.6F
5
1977
10.1F

From December 10th through December 20th, the average temperatures was 16.6 degrees. This was 5.3 degrees below the normal of 21.9 degrees. During the first 21 days of December 2005, La Crosse had an average temperature of 13.5 degrees. This was 10 degrees below the normal of 23.5 degrees.

From December 21st through January 15th, there was a sudden reversal in our temperatures. This was due to the area seeing mainly Pacific air masses moving into the region. The average temperature was 31.9 degrees which was 15.1 degrees above normal of 16.8 degrees. This was the second warmest start to an Astronomical Winter.

Rank
Astronomical Winter
Average Temperature
1
1877-78
32.04F
2
2005-06
31.9F
3
1986-87
29.2F
4
1991-92
28.9F
5
1931-32
28.7F

In most cases, our low temperatures have been above our average high temperatures. Since December 21st, only 6 nights were colder than our average high temperatures. The figure below shows the actual daily high and low temperatures and the average high and low temperatures from December 1, 2005 to January 15, 2006.

From December 1, 2005 to January 15, 2006 (fist half of meteorological winter), the temperarture averaged 23.9 degrees which is 4.1 degrees above the normal of 19.8 degrees.

Rochester, MN

During the first nine days of December 2005, Rochester tied 1977 for the 5th coldest start to a December. Through the first nine days, Rochester had an average temperature of 5.6 degrees. This was 15.7 degrees below the normal of 21.3 degrees. This tied 1977 for the 5th coldest start to a December and it was the coldest start to a December since 1978 when the average temperature was 3.5 degrees. The coldest start to a December occurred back in 1972 when the average temperature was 0.3 degrees. Below is a list of the top five coldest starts to a December.

Rank
Year
Average Temperature
1
1972
0.3F
2
1978
3.5 F
3
1919
4.7F
4
1886
4.9F
5
2005
5.6F
1977
5.6F

From December 10th through December 20th, the average temperatures was 14.7 degrees. This was 2.6 degrees below the normal of 17.3 degrees. During the first 20 days of December 2005, Rochester had an average temperature of 10.6 degrees. This was 8.5 degrees below the normal of 19.1 degrees.

From December 21st through January 15th, there was a sudden reversal in our temperatures. This was due to the area seeing mainly Pacific air masses moving into the region. The average temperature was 29.5 degrees which was 16.6 degrees above normal of 12.9 degrees. This was the warmest start to an Astronomical Winter.

Rank
Astronomical Winter
Average Temperature
1
2005-06
29.5F
2
1991-92
26.4F
3
1986-87
26.2F
4
1959-60
25.1F
5
1931-32
25.0F

In most cases, our low temperatures have been above our average high temperatures. Since December 21st, only 5 nights were colder than our average high temperatures. The figure below shows the actual daily high and low temperatures and the average high and low temperatures from December 1, 2005 to January 15, 2006.

From December 1, 2005 to January 15, 2006 (first half of Meteorological Winter), the temperatures averaged 21.1 degrees which is 5.7 degrees above the normal of 15.4 degrees.


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.