A cool summer

Bananarama sang and Ace of Base redid a song about this, right? No, that was a “cruel summer”, where they stated that the air was “so heavy and dry” (actually correct…dry air is denser than moist air at equal temperature and pressure).

Meteorological Summer is now over, and overall, it was not too hot this summer. We had several unusually strong cold fronts take temperatures down into the 50s, and no significant heat waves.

In Birmingham:
Average high temperature 87.4, 22nd coolest of 114 summers on record, 2.0 degrees below normal.
Average low temperature 68.2, 29th coolest of 114, 0.8 degrees below normal.
Average temperature 77.8, 24th coolest of 114, 1.4 degrees below normal.

Number of days 95 or hotter: 2, normal is 13.
Number of days 100 or hotter: 0, normal is 2.

In general, our cooler than normal summer was brought on by a combination of a wet spring (more of the sun’s energy went into evaporating water than heating the air), more rainy days, and a persistent upper-level ridge in the western US and upper-level trough in the eastern US. Since pressure drops more rapidly with height in cold air than it does in warm air, the height of the 500 mb pressure surface is usually lower in cool air than in warm air.

Take a look at the June 1-August 31 NCEP average 500 mb heights (the upper level flow generally moves along these lines), and the departure from normal of those heights, across the northern hemisphere.

Note (to the left) the cool air troughs in the eastern US, the north Atlantic, and the north Pacific. These are also reflected in the departure from normal of the 500 mb heights (right side), with below normal heights over about the NE half of the US. Also note the area of above normal heights along the Pacific Coast from the NW US into Alaska…they had record heat in Washington and Oregon this year.

Here is a zoom-in on the USA.

Looking ahead…with the sun angle already getting lower and the days getting shorter, the arctic regions are cooling down. Temperatures in the Arctic Ocean (usually peak around 32-34 since ice melts and keeps it from getting warmer than that) are already in the 20s, with the Greenland Ice Cap at 8 below zero early this morning. Temperatures over much of Alaska are still in the 50s, with 30s along the northern coast.

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