The 90-degree day, the hallmark of Washington in the summer, is unlikely to become an endangered species. It’s just that to the regret of few, it hasn’t been around much this season.

At Reagan National Airport, traditionally one of the warmest spots in the region, the average temperature for July was a little less than normal. Four-tenths of a degree less, to be exact.

That fractional dip at the official measuring station for Washington was enough to make last month the capital’s coolest July of this decade — the coolest since July 2009, according to National Weather Service figures.

To be sure, the month has not been without its days in the 90s. In fact, nine were recorded, with one day, July 2, reaching the summer’s top temperature of 99.

With the mercury falling only a single degree short of 100 so early in the month, it seemed as if no amount of sweltering might be ruled out for the succeeding days.

But it did not turn out that way. As it happened, the 99-degree reading was more the exception than the rule. The second-hottest July day, the 8th, was 96. For the rest of the month, the mercury climbed to 90 or above seven times. None of those days was warmer than 94.

Moreover, the last half of the month seemed to suggest the climate of a different season or a different city from Washington in the summer. Since July 14, only a single day was characterized by a 90-degree reading at National — the 23rd, when it was 94.

In fact, with Saturday’s high at National of 84 — four degrees below normal for the date — a 90-degree reading was made only once in the past 19 days. And on one particularly memorable occasion, July 29, the thermometer not only shunned the 90s, but it did not even reach the 80s.

The high temperature that day was only 78, leaving many Washington residents almost giddy with appreciation of the uncharacteristic meteorological gift.

If summer seemed free of the season’s usual oppressiveness in the District, and was surprisingly devoid of both searing heat and wet-blanket humidity, the western parts of the area were even more so.

It was the coolest July since 2001 at Dulles International Airport.

July’s temperature averaged 2.5 degrees below normal at Dulles, according to weather service figures.

The month’s highest temperature was 95 degrees, on the 2nd. That was one of only five 90-degree days.

On the 29th, the mercury managed to reach only 74 degrees, and the next morning, dipped to 48, just 16 above freezing. That was the coolest July reading at Dulles since 2002.