DETROIT – I normally don't do this, but since you may have missed it yesterday, I want to repeat the explanation about why our weather this week is what it is (so many of you are talking about this).
As we've explained on the air, a trough (or dip) in the jet stream has developed over the Great Lakes, maintaining a relatively cooler air mass overhead, and it's going to be a very, very slow process whereby this pattern relaxes. The actual upper level low pressure area is well north of Michigan in Ontario, and the image I want you to picture is a bicycle wheel.
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The center of the wheel is where the upper level low is, and as the wheel rotates, periodic spokes (weak lines of low pressure) cross our state. When one of those spokes coincides with the warmest part of the day, scattered showers, and even a couple of thunderstorms, are possible. Shower coverage is dependent upon how strong the spoke of low pressure is, as well as its timing with the afternoon heat.
If one passes through at 8 a.m., it probably won't trigger more than a few clouds; if one passes through, however, at 6 p.m., then we can expect increased shower activity. In general, though, isolated showers and storms pop up mid-afternoon, and quickly diminish early evening as cooling begins. This is the pattern we'll be in through the weekend, and keep in mind that most of each day will be dry. But the risk is there late each afternoon although, as I'll explain below, I've now taken the rain out of the Sunday forecast.
Tonight, any isolated showers and thunderstorms should die off early this evening (and probably earlier than they did last night). Skies should eventually become partly cloudy. Lows in the mid to upper 50s, with a very light west wind.
Partly cloudy on Thursday, with isolated showers possible between 3 p.m. and 7 p.m. Highs in the mid to upper 70s.
Isolated showers end early Thursday evening, then becoming partly cloudy. Lows in the upper 50s.
Partly cloudy on Friday and Saturday, with scattered afternoon showers and isolated thunderstorms. Highs in the upper 70s, with overnight lows in the low 60s.
As mentioned above, I'm going to take the rain out of Sunday's forecast. Right now, it appears that any upper level spokes of low pressure either won't come through during the warmest part of the day, or will be so weak that it's not enough to trigger showers and storms. This is a tenuous forecast, but I think we should be able to get through Sunday mostly dry. Highs near 80.
Partly cloudy Sunday night, with lows in the low 60s.
Monday features a better chance of afternoon showers and thunderstorms, as an actual cold front approaches. Highs in the low 80s.
Shower and thunderstorm chances continue Monday night, with lows in the mid 60s.
Lingering showers and thunderstorms are still possible on Tuesday, with highs in the upper 70s.
Then look for a partly cloudy day on Wednesday, with highs in the upper 70s.