The Hottest Week in Rockford's History

The Hottest Week in Rockford’s History

The year of 1936 was the peak of the Central Plains Dust Bowl and it was also a year of extremes across the region…particularly at Rockford. These dry conditions extended into northern Illinois where Rockford saw month after month of below normal precipitation. The month of March recorded only 0.43” of rainfall. From December of 1935 through the end of July 1936, there was only one day that recorded over an inch of precipitation when 2.85” of rain fell on the 2nd of June. This one day rainfall accounted for 23% of the total precipitation over this 8 month period. On top of this, temperatures over the winter were the 4th coldest on record (actually, they were the coldest at the time only to be surpassed by the winters of 1976-77, 1977-78, and 1978-79). The average temperature for February of 1936 of 10.2 degrees was the coldest on record and still stands today. Snowfall for the season was above normal by today’s standards by 15.1 inches. Needless to say, the residents of northern Illinois were ready for a warm up…and boy did it warm up.

 Surface Map from July 6th 1936

Fig 1: July 6th1936 Surface Map

June was still below normal temperature-wise, but things started to change shortly after the 4th of July. A low pressure system over the northern Plains lifted a warm front northward through northern Illinois on the 6th of July. With the warmer air surging northward, it began a stretch of 9 days in a row (would have been 12 had the high temperature been one degree higher on the 15th) of the high temperature reaching 100 degrees or higher at Rockford. This is far and away the warmest stretch ever in Rockford’s history as the southwesterly surface winds continued throughout the hot spell with the surface low stuck in the Dakotas.

July 1936 High Temperature Graph from Rockford

Fig. 2: High Temperature Chart for July 1936 in Rockford

The span from the 11th through the 14th recorded the four highest temperatures in Rockford’s history. What is remarkable is the fact that the overall average temperature for the month of July was not the warmest ever. Due to the start of the month being slightly “cooler” in 1936, the July of 1921 actually ended up being the warmest ever averaging 80.3 degrees, while the July of 1936 averaged 80.0 degrees. However, the high temperature did top 100 degrees 15 times total that summer (3 times in August) with the only nearest rival being the year of 1934 when it topped 100 degrees 11 times. Overall, since 1906, there have been 101 occurrences of the high temperature reaching 100 degrees or higher in Rockford.

Average Temperature for July of1921 and 1936 at Rockford

Figure #3: Average Daily Temperatures for July 1921 and 1936 at Rockford

In recent years, 100 degree highs at Rockford have been much scarcer. The last time that 100 degrees was topped was on July 10th of 1989. In 1988, the high reached 100 degrees 7 times, but before that you have to go back all the way to 1957 for the last time that 100 degrees had been hit.

As we reach the hottest portion of the summer here across northern Illinois and Indiana in 2008, there luckily does not appear to be any 100 degree days on the horizon.
Tim Halbach
Climate Focal Point 

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