Why Was It So Dry and Warm? Part III

The answer has many elements. We'll work from the more direct and near-by causes to the antecedent ones.

The pattern across North America was dominated by a "Rex Block" named after Meteorologist Daniel Rex in 1950 who discovered it. You can read about it HERE.

The configuration resembles a backward "S" with high pressure north of low pressure.  These are more common in the western US then over the Great Lakes. The result was a dominant easterly/SE flow which kept the temperatures well above normal not only across Ohio but much of the Great Lakes and Midwest with little rainfall. READ PART I HERE and  READ PART II HERE

Why did this Rex Block form?  I believe the answer lies first in the changing Equatorial Pacific. We have been teetering with a La Nina since last winter/spring.  Most of the summer has been in neutral territory. In the last month, the upwelling of cooler water to the surface is lowing sea surface temperatures especially west.

The pressure changes between Darwin station and Tahiti have been quick.

SOI changes have gone from positive to negative in recent weeks.

Further north in the higher latitudes, the North Atlantic Oscillation also went through changes at roughly the same time. Notice how the jet stream across North America and Europe was strong. Follow the black line across the US, northern Atlantic and Europe.

HUGE low pressure north of the Arctic circle and northern Atlantic with high pressure over Canada and eastern Europe.

As the NAO went negative, the jet stream shifted into southern US and Mexico and east into northern Africa. Little jet stream influence across Canada and the northern Atlantic.

HUGE high pressure ridge developed in eastern Canada north into the Arctic. This extended into the northern Atlantic and into northern Europe.

These changes in the tropics as well as the pattern shift in the higher latitudes among others all contributed to the changes across North America in early/mid September.

What about other years that had similar long stretches of 80+ degree warmth?

Here were the patterns across the US/Canada in east instance: Notice in most instances, the configuration is very similar.