Tuesday will be remarkably warm for the 20th of September with high temperatures in the 90s and lows near 70. For at least Des Moines, it is possible that both values will be the warmest this month. Is it common to have the warmest high or low temperature this late into the month? The featured chart addresses that very question with the daily frequency of the given day having the highest high or low temperature for that month in a given year. Overall frequencies are higher during the first week to ten days as one may expect as the period is closest to summer and features higher receipts of solar energy than the later portions of the month. There is kind of an interesting blip higher during the 17th to 21rst period for high temperature that may be related to the combination of sufficient heating, warm and dry soil temperatures, and lower atmospheric humidity due to senescence, but it could be a coincidence as well!

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