Over the years while working with the NWS in Southeast Lower Michigan and observing weather patterns; one of the patterns noted was the first hint of autumn (or fall) showing up with somewhat regularity in mid August. So much so, that it even creates a blip in the temperature graph from DTW. Looking at the temperature pattern chart below from Detroit Metro Airport from 1958 thru 2004 shows a small but definite drop in temperatures; maximum-minimum and average or mean.
The timing roughly co-incides with mid August or Julian days 220-232 with its center around 226. Converted to calendar dates non-leap years and leap years that would be;
Julian Day Non-leap Leap Julian Day Non-leap Leap
220 = Aug 8 Aug 7 221 = Aug 9 Aug 8 222 = Aug 10 Aug 9 223 = Aug 11 Aug 10 224 = Aug 12 Aug 11 225 = Aug 13 Aug 12 226 = Aug 14 Aug 13 227 = Aug 15 Aug 14 228 = Aug 16 Aug 15 229 = Aug 17 Aug 16 230 = Aug 18 Aug 17 231 = Aug 19 Aug 18 232 = Aug 20 Aug 19
Enjoy the breath of fall starting Friday into the weekend with high temperatures around 70 to the mid 70s and lows in the mid 40s to mid 50s. Interestingly; these temperatures are the normals for the first day of autumn across Southeast Lower Michigan which arrives on the later side of the autumn window, opening this year @ 10:49 AM EDT on September 22, 2012.
Making weather fun while we all learn,