Marking 40 years, 1983 standard for most 90-degree days annually still stands

Sep. 19—Forty years ago, Sept. 20, 1983, was the 49th and final day that the mercury reached at least 90 degrees that year.

That remains a record in Berks County. At the time it was set, it was a record by far, and it has only been seriously challenged once.

Such a momentous measurement of heat came in an unlikely year embedded in the coldest period on record — the 1970s and '80s — in the 125-year Berks temperature database, showing that Mother Nature can play a few tricks.

Forty years ago in the Reading Eagle, the Reading Fair was just starting a six-day run, Vanessa Williams was recently crowned Miss America, 86-year-old George Burns said, "I'm making old age fashionable," and the search continued for corpses in the Sea Of Okhotsk after a Soviet fighter plane shot down a wayward Korean airliner, Flight 007.

The Baltimore Orioles would beat the Philadelphia Phillies in the World Series in a little more than three weeks, and the bombing of the U.S. Marines barracks in Beirut was a week after that.

The high number of 90-degree days passed with little fanfare as had heat waves from 1953 and again in 1973.

The heat got a late start in 1983, with June 12 the first 90-degree day. The 49 90-degree days were packed into 100 calendar days.

"The prevailing pattern that summer was a persistent upper-level ridge centered over the Northern Plains region, which is where the heat was most anomalous and persistent," said Jeffrey R. Stoudt of Lincoln Park, retired meteorologist and Berks weather historian.

It was a hot and dry period.

"Said ridge and associated heat intermittently extended into the Northeast, only to retreat westward after a few to several days," Stoudt added. "The prevailing northwest flow along the east side of the ridge kept tropical moisture quite limited, thus meager rainfall. And same flow allowed those few cool periods in between the heat. Further, the low moisture that accompanied most of the hot days allowed temperatures to drop rather much during the corresponding nights."

Berks had a similar period this year with hot days and cool overnights in much of June.

About records

You can find only one trace of 1983 in the daily temperature records for heat prior to September: a 98-degree high on Aug. 20.

However, in September there are five dates that set high temperature marks and retain them: 97 degrees on the 6th, 100 on the 10th, 98 on the 11th, 95 on the 19th, and 93 on the 20th.

With setting such records amid nine 90-degree days in September, it would seem logical that the month overall would rank highly among warmest Septembers, but not so. It's not even in the top 10 because there was so much offsetting cold.

Sept. 26, 1983's high temperature of 38 degrees remains a Berks record for coldest high for that date, for an example of the weather whiplash. The 100 on Sept. 10 is the latest 100 in a year.

The hottest September on record was in 1961, with nine 90-degree days, with little offsetting cold.

As an example of the offsetting cold, there were 11 days in July 1983 that the temperature bottomed out in the 50s. Even with 16 90-degree days, July 1983 can't be found near the 10 warmest Julys on record by average temperature.

A close call

The one run at 49 was in 2010, and it was close. There were 48 90s that summer.

The stage was set for one more warm day on Sept. 25 before a cold front pushed through and summer weather would come to an end. The mercury raced past a forecast high in the low 80s and topped out at 89 degrees at Reading Regional Airport.

It was 1 degree away from tying 1983 at 49 90-degree days.

Since then there have been many months with high average temperatures, some records and some not, but 39 is the most individual days in a year since. This year has seen 20, and that seems very likely to be the final number.

These are the most 90-degree days in a year, with 40 such days as a minimum: 49, 1983; 48, 2010; 41, 1944 and 1980; and 40, 1943 and 1966.

In terms of overall cold, each month not only has a warmest 10 but a coldest 10. Taking a whole year into consideration, there are a total of 120 months on coldest 10 lists.

Of that total, an outsized 40 are from the 1970s and 1980s. The first decade of the 20th century had 17 and the 1990s, primarily 1990 through 1996, has 13.

This century has only nine, and none since February and March 2015.

Conversely, most of the warmest months are in the periods not mentioned for the coldest.