The weather pattern across the northern tier of the United States has been pretty active so far this summer, with a lot of rain. The amplified weather pattern shaping up for the first half of this week will be much different, and rather unusual, for this time of year. It will feature a large and cold low pressure area moving south from Canada into the Great Lakes region. The cool, Canadian airmass will bring well below normal temperatures to our area for the middle of this week, with temperatures slowly warming up toward normal levels by the end of the week.
The animation below shows temperature at the jet stream level from this past Saturday morning through Friday morning. The blue/purple colors are cooler temperatures, and the yellow/orange colors are warmer temperatures. Notice the blob of cooler air that gets pushed down from Canada into the Great Lakes region. It moves over Wisconsin today, then retreats back northward as the week progresses.
Unseasonably cool temperatures are expected through Wednesday morning across southern Wisconsin. The last time we had a cool period like this in the summer across Wisconsin was July 2009, when it was in the mid 60s across the state. Today's forecast high temperatures may approach or break the record low maximum temperature for July 15th, which is 68 degrees at Madison, and 64 degrees at Milwaukee.