July 17, 2012: Warm Summer
So far, the summer of 2012 is a warm one. June ended 3.1 degrees above average at the National Weather Service (NWS) near Negaunee. Through yesterday, July is running a healthy 6.1 degrees above the long-term average. In Sault Ste. Marie, the month is just under 7 degrees above normal.
It’s been so warm because the central U.S. remains in the mean upper-level ridge position (Image 1 above). Basically, the mean ridge position has sat over the central portion of the U.S. since spring. In fact, this ridge has been a main stay since last fall. As we’ve shown several times, the ridge is a source of hot, dry weather during the summer. Fortunately, we’re on the northern periphery of the ridge and that means a parade of frontal passages accompanied by showers and thunderstorms.
Will the hot weather continue? Once a pattern is locked in it is tough to break. However, there are signs of some modification over the next couple of weeks. The American computer forecast model, the GFS, shows the ridge holding strong over the Plains on Saturday (Image 2). However, the strong trough over Hudson Bay will tend to suppress the ridge’s heat and humidity. It does look like it will warm as we head toward the weekend, but a front will probably set up over the Upper Great Lakes and could be a source of showers and clouds, which would tend to hold temperatures down. Beyond the weekend, both the European model and the GFS forecast a suppressed ridge and a more westerly flow for us next week (Image 3). This would mean regular frontal passages and a trend toward cooler weather.
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