El Niño and the ongoing dryness are likely to affect summer temperatures in Philly

The burgeoning El Niño is likely to have at least indirect impacts around here for the next three months, but if the atmosphere’s behavior this summer somehow matches the strangeness of spring, that would be quite a development.

And it would not be a welcome one for farmers and those who aren’t fond of experiencing four seasons in 24-hour periods and wondering when the drought will end once and for all.

With the meteorological summer about to begin, El Niño, which is forecast to mature in the next several weeks, already is having impacts — on the seasonal outlooks. But the timing and intensity of a phenomenon that affects weather worldwide is still in doubt.

In the early going, at least three major commercial services — AccuWeather Inc., The Weather Channel, and WeatherBell Analytics — have said this is unlikely to be an especially punitive summer for heat, with temperatures perhaps only slightly above normal in the Philly region.

Paul Pastelok, AccuWeather’s chief long-range forecaster, foresees fewer sustained 90-degree day streaks than usual.

But don’t hock the air-conditioners or view the delightful start to June — sunny, high temperatures in the 70s — as a harbinger: On average, Philly experiences more than 30 days of temperatures of 90 degrees or better annually. The city has had five already.

The government’s three-month outlook has probabilities favoring above-normal temperatures in the Northeast.

All the outlooks reference El Niño, the atmospheric pot-stirrer that rearranges the pieces that drive day-to-day weather across the globe.

During El Niño, sea surface temperatures remain above normal by a degree or so for several months over a 2.4 million-square-mile expanse of the east-central tropical Pacific. The increased evaporation from the warmed sea surface sets off strong storms that energize the west-to-east winds in the upper atmosphere.

The name is derived from Spanish for the Christ child since Peruvian fishermen noted it frequently appeared off the South American coast around Christmastime, killing the anchovy catch. But this one is getting an early start and might become something special, with temperatures rising to 2 degrees or more above normal.

“When they start so early,” said Pastelok, “the summers across the Ohio Valley and he northern mid-Atlantic states are not very hot.”

Todd Crawford, meteorologist behind the Weather Channel’s outlook, said El Niño has “limited the risk of persistent” heat in the East.

In four of the six years since 1950 that El Niño has ripened to more than 2 degrees during the summer, average temperatures in the June 1-Aug. 31 period — the meteorological summer — were near average or cooler than those in the records dating to 1874.

However, nothing happens in isolation in the atmosphere, and El Niño interacts with other “teleconnections” in the Arctic, North Atlantic, and elsewhere, in ways that aren’t predictable, said Pastelok.

Localized features, such as renegade winds off the cooler ocean and isolated thunderstorms, can have huge effects on temperatures and interrupt heat waves.

The fate of the ongoing drought conditions also may be a major player.

Perhaps lost in the snow and ice of winter and recent rains, particularly on Memorial Day weekend, is the fact that it has been mighty dry.

Officially, May marked the 10th consecutive month that Philadelphia has had below-normal rainfall, according to the National Weather Service. Even with the recent rains, the interagency U.S. Drought Monitor still has most of the region in “severe drought.” Bucks County and half of Chester and Delaware Counties are in “moderate drought.”

No significant rain is in the forecast through at least the first week in June. The soils around here aren’t used to persistent dryness: The region is in the proximity of major water bodies that are rich sources of atmospheric moisture for rain.

If the dryness persists, that would be “concerning,” said Pastelok. “We’re heading into the hotter, higher evaporation months.”

Said Sarah Johnson, warning coordination meteorologist at the weather service office in Mount Holly, “drier air and ground takes less energy to heat up.” Having lived in North Dakota, she said, the effect of dryness on temperature extremes “has fascinated me.”

The lack of rain doesn’t always correlate with heat, she added. The lack of moisture in the air does promote nighttime cooling by allowing daytime heat to escape.

Some research has shown that drought can lead to more extreme conditions, “both heat and cold,” she said. During the summer of 1963, precipitation in Philadelphia was well below normal, and it was the eighth-coolest in records dating to 1874.

By any measure April and May were extraordinary months in the region’s weather history.

Readings hit 90 degrees or better in both months, and this spring marked only the fourth time it has reached 90 on five or more days before June 1. (The all-time champ is 11, in 1991, all of them in May, followed by a sizzling summer.)

The temperature swings were notable. After setting records with 91 degrees April 15 and 16, five mornings later a killer freeze hit local farms and it reached 34 at Philadelphia International Airport. That was the lowest reading ever after a daytime high of 90 in Philly.

In April and May, the temperatures ranged from 31 to 98, a difference of 67 degrees — a gap matched only seven other times in the last 153 years, said Jessica Spaccio, climatologist with the Northeast Regional Climate Center.

Spring and fall are peak commuting seasons for frontal systems that can crash temperatures, said Johnson. The biggest day-to-day change during the meteorological spring this year was 43 degrees, from a high of 83 to a low of 40, a top 10 difference in the period of record. That was on March 10,

That noted, spring behavior is a bad indicator of what’s to come, said Johnson.

Like so many of us, the atmosphere isn’t real big on attention spans. Not a bad thing in this case.