shoveling snow
© GLEN STUBBE / STAR TRIBUNE VIA AP
A Saint Paul Hotel doorman clears snow during a mid-April snowfall in Minneapolis. It was a cold, snowy month across the nation.

The evidence of a spring-deferred lay in a yellow layer on Thursday atop a Center City building.

Donald J. Dvorin, the region's official pollen counter, noticed it on the roof, above his office, where he collects samples to calculate the daily count. "We saw the pollen looking yellow," said Dvorin, a physician with the Asthma Center, a sure sign that "it's accumulating."

Since last week, the tree-pollen counts have been "extreme," the fallout from a particularly chilly April - around here and across the nation - that delayed the pollen season a good 10 days, he said.

Temperatures in the contiguous United States were 2.2 degrees below 20th century averages last month, making it the coldest April in 20 years, according to a government analysis released Tuesday.

Overall, it was the ninth-chilliest April in Pennsylvania in records dating to 1895, said the National Center for Environmental Information.

In Philadelphia, 21 of the 30 days were cooler than normal, and the official temperature was 2.2 degrees lower. The month also featured a significant snowfall.

crocus
© MARI SCHAEFER / STAFF
Snow covers a crocus in Villanova on April 2.

Nationally, it was the 13th-coldest April, with Iowa and Wisconsin registering their frostiest on record.

Generally, overnight minimum temperatures have been creeping upward in recent decades; however, in April it was the overnight lows driving the departures, NCEI said.

April also was particularly generous with snowfall nationally. The calculated monthly snow cover was the fifth-largest in the 52-year data set, according to the Rutgers University Snow Lab.

The center won't be releasing its global surface-temperature report until later in the month - that analysis is far more complicated - but we'll go out on a limb and say the rest of the world didn't cool very much in April.

The NASA/University of Alabama satellite data posted last week had the planetary temperature holding fairly steady in the first four months of the year but still above the 30-year normal.

While the global temperature tends to change ponderously month to month, warm and cold air masses slosh around the planet capriciously and sometimes dramatically.

In an area over the Arctic Ocean, northeast of Russia's Lyakhovsky Islands, temperatures were close to 10 degrees above normal. Meanwhile, North America was favored for the chill in April, according to the satellite analysis.

All that chilly weather around here pushed back the annual tree reproductive frenzy.

As allergy sufferers are well aware, however, the trees have been making up for last time with a vengeance.

And just to add insult to misery, the grasses also are popping, and the counts Wednesday were in the "moderate" range.

Conditions recently - dry and warm - have been ideal for this annual reproductive frenzy.

But while they might not be welcome by everyone, pollen-dampening showers are possible Thursday.