Sweltering September heat wave: How long will it last?

The sun shines over Holland on a sweltering day.


GRAND RAPIDS, Mich. (WOOD)  — You wouldn’t guess it if you step outside, but Friday marks the official start of fall.

This week marks the hottest temperatures so far of 2017. The excessive heat forced several West Michigan to cancel or shorten classes Friday. Administrators also delayed Friday’s football games between Northview and Forest Hills Central High School and Rockford and Grand Haven to 7:30 p.m. because of the high temperatures.

The September heat wave that’s settled in West Michigan has already broken a more than century-old record. Thursday’s high of 95 degrees in Grand Rapids blew away the previous record of 92 degrees, set in 1908. It was also hotter than Death Valley, California and any place in Florida, according to Bill’s Blog.

It’s one thing to rewrite the record book for a single event but we will potentially do it for six straight days.

Record highs vs forecast highs

Both the daily high and low temperatures may set records for warmth. Temperatures will be 20 to 25 degrees above average through Tuesday, Sept. 26. However, relief is on the way: A cold front will finally move through Sept. 26, driving down temperatures.

Average high vs forecast high temperatures

One main reason for this prolific heat wave is the jet stream, which shifted well to the north of the Great Lakes after spending much of the first half of September south of us.

The above map shows the jet stream pattern through this weekend.

The lack of rain is also a contributing factor. It has been exceptionally dry since the middle of summer. The monthly rainfall deficit as of Sept. 21 is 2.45 inches. Since July 1, we’re 6.98 inches below the rainfall average; the deficit is 2.85 inches for the year. As a result, the sun’s energy is more efficient at directly heating the atmosphere instead of evaporating moisture that’s in the soil.

This time of year, exceptional heat typically has a short shelf-life. When the pattern change arrives during the middle of next week, it may be a rude awakening. Temperatures are expected to cool closer to average, which will be in the 60s, and they very well could go drop below average.

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