How Cool has the Summer Been?

July 15th marks the halfway point of the Climate Prediction Center's June-July-August outlook. With this in mind, and with all the cool weather lately (record breaking cool weather is some spots!), we decided that it's a good time to take a look at how well the CPC's outlook is panning out. As you can see in the CPC forecast below, on June 1, it was predicted that in the summer months there would be a good chance of below average temperatures here in Wisconsin.

 

So, has it been cool during the first half of this period? Lets take a look at the temperatures in Milwaukee and Madison from June 1-July 14 to find out. In the graphs below, we have information on the observed temperatures for each day in the period in 2014 (solid blue bar), as well as the normal (brown ribbon) and record temperatures (top red for max, bottom blue for min) on those dates.

Indeed, Milwaukee has been below normal.  Milwaukee's average temperatures were 0.4 degrees below normal in June, and have been 2.5 degrees below normal thus far in July. What about Madison? Unfortunately, it's clear that the temperatures have actually been a bit warmer than normal. Madison's average temperature was 3.5 degrees above normal in June. However, so far in July, the average temperatures in Madison have been 2.7 degrees below normal, so overall, the CPC forecast doesn't look too shabby. However, one thing to keep in mind: CPC's forecast runs through August, so there is plenty of time for these numbers to change.

There is another interesting observation in all this; while the average temperature in Madison was a whopping 3.5 degrees above normal in June, the average temperature in Milwaukee was 0.4 degrees below normal. That's a difference in the departure from normal (3.5 - -0.4) of 3.9 degrees. That is the largest difference in the departure from normal between these two sites on record for the month of June!

These two cities are only about 100 miles apart, so why the big difference? Well, throughout this period, the water temperature of Lake Michigan was around 3 to 4 degrees below normal. Those cool lake temperatures coupled with easterly winds off of the lake kept the coastal cities much cooler than the inland cities. For that very same reason, the only month with differences in the departure from normal larger than 3.9 degrees is May. Usually in May, the lake temperatures are quite cool while hot summer air is just beginning to make its way north. The contrast between the cool lake and warm air can make for differences in the departure from normal as large as 10 degrees!

Herzog/Schultz/Hentz



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