While the foliage around here is rehearsing for its reliably brilliant autumn spectacle, the atmosphere is about to take a short trip down memory lane — to August.
With a balmy southwest breeze due to drive temperatures into the low 90s Wednesday, or about 20 degrees above normal, the record for an Oct. 2 — 87 — appears to be toast.
“It’s almost like a sitting duck,” said Dave Dombek, a meteorologist with AccuWeather Inc. Among the first 10 days in October, that’s the lowest record daily maximum; in 1941, it got to 96 on Oct. 5.
And if the government’s updated forecast for October holds up, the entire month generally should be warm in the eastern half of the country, based on long-term trends and computer-model guidance.
The warmth, however, could be tied to a potentially disturbing development. Anyone who has tried digging in the garden recently likely has noticed a certain resistance. Philadelphia just experienced its driest September in 12 years, with 1.16 inches of rain measured at the airport.
The standing temperature record for an Oct. 2 was set in 2002, the last year that serious drought conditions covered the region, according to data from the Pennsylvania Department of Environmental Protection.
That general lack of moisture is a factor in the impending August flirtation, said Dombek. “The two go hand-in-hand for sure,” he said. "On any given day, you have only so much energy from the sun available. If some of that energy is going to evaporate water, that’s less available for heating up the air.”
Although the long-term average rainfall for September is just over 3.75 inches, that total has been bulked up by the drenching remnants of hurricanes and tropical storms through the years.
This year, although the Atlantic hurricane season has been a busy one, those rains have snubbed the Northeast, and dryness has been making significant gains across the country, according to the U.S. Drought Monitor, a government-academic partnership.
In the last 30 days, the Middle Atlantic River Forecast Center reports, every county in Pennsylvania, New Jersey, Delaware, and neighboring states has experienced substantially below-normal rainfall.
In April, only 2% of the nation was in some state of drought, Brad Rippey, a meteorologist with the U.S. Department of Agriculture in Washington, said Monday. In the Drought Monitor’s most recent survey, the total was 40%.
No significant rain is in the local forecast for the next several days, although showers are possible Thursday as a front replaces the short-lived warm spell, and the government’s Climate Prediction Center has the odds favoring above-normal rains over the two-week period.
October tends to be a transitional month for the atmosphere, as winter begins its intrusions and summer tries to repel them, ultimately unsuccessfully. It can be a month of contrasts, and that will be in evidence this week as temperatures won’t get out of the 60s Thursday, Friday, and Saturday.
As further evidence of October’s caprice, it is worth noting that the latest 90-degree reading occurred on Oct. 10, 1939.
Exactly 40 years later, Philadelphia recorded its earliest snowfall, 2.1 inches.