Thanks to a conspiracy of generous cloud cover and persistently wet soil, this June will end up being the coolest in 12 years.

The official Philadelphia temperature for the month will come in right around 71 degrees, and while that's less than 1.5 degrees below normal, that's a lot chillier than some recent Junes, especially last year's.

The relative coolness has a lot to do with the frequent cloud cover, which has obscured the sun, and the rains, which have dampened the ground and blunted the sun's energy, says Todd Miner, a meteorologist at Pennsylvania State University.

Rainfall for the month has been about 150 percent of normal, however the most-prominent June feature has been the lack of extreme heat.

It never got as warm as it was at the end of April. At Philadelphia International Airport it reached 90 on only one day, last Friday. Normally it hits 90 at least five times in June.

It's not just here. A chill has covered the entire Northeast, Miner said, with Boston and New York also having one of their coolest Junes ever.

In Philadelphia it looks to be the coolest June since 1997, which also finished at 71.1. Until the temperature hit 88 degrees this afternoon - 4 degrees highern than predicted - this June looked to be coolest since 1985, when the average temperature was 68.8. June 2008 was one of the warmest ever, finishing at 76.4.

Throughout the Northeast this has been the year of the trough, a broad area of lower-than-normal pressures that has favored clouds and storminess.

As for the future, no serious heat is in the forecast for the next several days, however, the pattern could shift sometime next week, said Dean Iovino, a meteorologist at the National Weather Service office in Mount Holly. That would favor a warm-up.

"My gut tells me we could pop out of this and have a really steamy end of the summer," said Miner. "But that's just my gut."

Contact Anthony R. Wood at 610-313-8210 or twood@phillynews.com