Love it or not we are in our month of transitions, hours of daylight are decreasing and weather patterns will be changing as we head into fall. Meteorological fall begins in two weeks (where did the summer go). I believe our current pattern of above normal temps and below normal rain will persist over the lower peninsula into September though not as extreme as we have seen this summer – perhaps 1° above the mean. We may see closer to normal temps as we get into October and November with the development of El Nino. (May and might are keywords).
From Dr. Judah Cohen (of Atmospheric and Environmental Research) for the coming week – The current weather pattern across North America generally consists of troughing/negative geopotential height anomalies with normal to below normal temperatures centered in Western Canada and ridging/positive geopotential height anomalies and above normal temperatures in Eastern Canada with a cutoff low trapped beneath the Eastern Canadian ridging and normal to below normal temperatures in the Eastern United States (US). However ridging/positive geopotential height anomalies in the Gulf of Alaska are predicted to force downstream troughing/negative geopotential height anomalies in central North America with seasonably cool temperatures. Predicted persistent ridging in the Northeastern US should yield mostly normal to above normal temperatures.
Geopotential Height
Geopotential height approximates the actual height of a pressure surface above mean sea-level. Therefore, a geopotential height observation represents the height of the pressure surface on which the observation was taken.
Since cold air is more dense than warm air, it causes pressure surfaces to be lower in colder air masses, while less dense, warmer air allows the pressure surfaces to be higher. Thus, heights are lower in cold air masses, and higher in warm air masses.
A line drawn on a weather map connecting points of equal height (in meters) is called a height contour. That means, at every point along a given contour, the values of geopotential height are the same. An image depicting the geopotential height field is given below. (note these are not current images)
Source: http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cyc/upa/trgh.rxml

Figure 1
Geopotential height anomalies consist of deviations in the geopotential height field from average values. In Figure 2 below, (which displays the geopotential height anomalies from Figure 1), it is evident that areas with lower geopotential heights correlate with negative geopotential height anomalies. The height anomalies map below indicates that the geopotential heights are much below average for this time of year over the eastern United States, and implies colder than average temperatures across this region.

Figure 2
Below are the norms for SW Michigan:
(click to enlarge)
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We are looking at good chances of wide spread rain and cooler temps this coming week but NOAA is predicting the heat will return for the last week of August. For this weeks system precipitable water values are forecasted to be in the 2 inch range. The NAM and GFS is showing around an inch of rain for most of the area from late Monday through Tuesday. The severe weather should stay south of the state as it has most of the summer.
Yesterday we saw a band of rain set up along a lake breeze line right on 131 from Grand Rapids to Plainwell – we should see something similar today. These cells form and move slow so anyone under them could pick up around a half inch of rain. These are fun to watch on the radar (if you have super resolution like I do with Radarscope). They start as a blue line of moisture from north to south and cells develop along that line.
Looks like more 90s are on tap in the near future. Tally keeps growing.
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Don’t tell me anyone put there AC on today! It was a great summer afternoon!
Working in 100 degree heat 50 hours a week, yes I am going to have our air on. It’s the only way to recharge after getting drained all week. If it got turned off, you would not want to be around the wife and kids. They are even less tolerant than I am when it comes to heat.
Mine was on all day!! It was on yesterday, last night and will be tonight. It will be on till I decide it is not too humid or hot out to be able to do anything. I am really tired of the very hot and humid air.
Good read Michael, although I will say I woke up with a headache this morning so I will have to re-read this later as my brain is not processing so well yet. You have a great way of explaining weather terms that I think many of us have no idea what they are.