With the mercury reaching the 90s again yesterday, July 1980 -- steamy, sultry and insufferable -- finally ended, passing into Washington weather history as the hottest month ever recorded here.

Sweltering area residents who gasped, sweated and staggered through the 31 searing days and 31 stifling nights of July received confirmation of their agonies from National Weather Service statistics.

The average temperature for the month was 82.3 degrees, the weather service said, the highest monthly average since the weather service started keeping records here 108 years ago.

"It's definitely the hottest," said forecaster Jeffrey Bowman. The previous record average was 82.1 degrees, set in July 1955. The "normal" average temperature for July is 78.7 degrees.

It took the blazing heat of many individual days, each uncomfortable in its own way, to make the month memorable.

When the mercury reached 90 degrees yesterday, on its way to the day's high of 92, it marked the 21st time that temperatures last month had reached 90 or above. While that did not set a record, it equaled one set in 1878.

In addition, on three days, the mercury bubbled up out of the 90s to reach 100 degrees or above.

Yet it took more than the fiery heat of 90- and 100-degree days to set the record.

"What's really made it hot for us is the very warm nights," forecaster Bowman explained.

In an average July, the nightime temperature should cool down to about 69 degrees, he said. On many nights last month, temperatures refused for hours to drop below the 80s and the average low was a relatively high 73.6 degrees.

Bowman attributed July's exceptional heat to the steady arrival here of air flowing east from the Great Plains, which are now in the grip of a scorching heat wave.

Although temperatures here, while high, have been lower than those there, Washingtonians' discomfort may be as great or greater, Bowman said.

In Washington, where humidity comes with the territory, he explained, temperatures in the 90s can produce greater misery than 100-degree temperatures in the drier Southwest.

Forecasters said high temperatures here in August are expected to average near the normal figure of about 86 or 87 degrees.

Today and tomorrow are expected to exceed that, however, with a high of 96 predicted for today and 98 for tomorrow. The record for both days is 98.