Why so steamy? Winter’s lack of snow may be one factor

Posted: June 30, 2012

Mary Catherine Dabrowski recalled similarly sparse turnouts at her senior center - but under radically different circumstances.

Two winters ago, snow deterred the usual crowd from making the trek to socialize or play ping-pong at the Havertown Surrey Center in Delaware County. Traffic was light Friday, but snow wasn't a problem.

"It was too hot to move," Dabrowski said.

The elderly weren't the only ones baked into lethargy.

The official high was 98, well shy of the record. But the late-afternoon heat index shot up to 104, making it the most uncomfortable day of the year so far. In Washington, the high was 104; the heat index, 112.

After another steamer Saturday as a hot blob of high pressure continues to ooze eastward, Philadelphia is going to set a record for the warmest Jan. 1-June 30 period since the government began keeping track in 1874.

The average temperature for the six-month period - 54.8 - would beat 1991's by 0.4 degrees.

In the last week, 57 all-time-high-temperature records nationwide have been tied or broken - extraordinary for June. The high hit 105 in Denver on Monday and Tuesday, as hot as it has ever been there.

Evidently, the extreme heat is related to the aforementioned snow, or lack thereof.

"It's been a really warm period," said Jake Crouch, a climatologist with the National Climate Data Center.

What has been so unusual, he said, is the way in which spring heat has lapped into summer. Typically, like many human beings, the atmosphere has a notoriously short attention span. Spring conditions often have little relation to summer's.

Not this time.

The general lack of snow cover in the nation meant a paltry snow melt, Crouch said. That, in turn, allowed the ground to dry out, priming it for heating, particularly in the middle of the country.

That has permitted the sun to go right to work heating the ground, rather than wasting energy on evaporating water. A hot ridge of high pressure has been able to grow and expand.

Meanwhile, drought conditions have expanded rapidly across the country, according to the U.S. Drought Monitor, and that has contributed to the Western wildfires.

The crops also are feeling the heat, said David Streight, founder of Commodity Weather Group, an agricultural-forecasting service in Washington.

"The real concern is that heat may resurge late next week in the Upper Midwest," he said. This is the critical pollination period, and a heat burst could cut into yields 30 percent, he warned.

In the spring, the consensus among commercial forecasters was that summer temperatures would end up close to normal around here. That still could happen. June, in fact, will end up coming in quite close to normal, noted Mark DeLisi, the National Weather Service climate specialist in Mount Holly.

However, the longer-range models continue to suggest heat in the Midwest, and some of that could leak eastward at any time, said Streight.

Heat heading into July is hardly unprecedented.

But, as Dabrowski observed, "this is a little bit too warm."

Contact Anthony R. Wood

at 610-313-8210 or twood@phillynews.com.

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