It finally felt like summer in Pittsburgh yesterday, but the high temperatures aren't expected to stay. It's likely to feel like spring again next week, according to forecasters.

Last month, a cool breeze swept through Pittsburgh, making it the fifth-coldest July ever recorded in Western Pennsylvania.

With an average temperature of 69.4 degrees -- about 4 degrees below normal -- and some nights plummeting into the low 50s, July in Pittsburgh sometimes felt more like spring than summer.

And the region wasn't alone. Across the country, more than 1,100 weather stations reported new records for daily low temperatures in July, mostly in the Northeast and Midwest. An additional 1,200 reported readings that tied record lows.

Several cities in the Midwest that reported record-breaking low monthly averages included Cincinnati, Chicago and South Bend, Ind.

Things are looking up, mercury-wise, but just for a while: Temperatures this week may be the summer's highest, with 90-degree days in the forecast. Yesterday, the high reached 90 degrees.

"There are some signs that summer may pay us a visit" from now until Aug. 18, said Rich Kane, a meteorologist for the National Weather Service.

But then it's back to relatively cool temperatures for the rest of August, he said.

Meteorologists blame the uncharacteristic summer weather on a low-pressure system that has pushed cool, dry air from Canada and the Great Lakes into the northeastern part of the country.

High-pressure systems, which rotate counterclockwise, usually bring warm, moist air from the Gulf of Mexico during the summer. The low-pressure system is related to El Nino, an abnormal warming of surface ocean water in the eastern tropical Pacific that can affect weather all over the world.

In other parts of the country, particularly the West and the South-central plains, July produced record-breaking temperatures on the opposite end of the scale. According to a report released by AccuWeather.com last week, a heat wave on the Pacific Coast broke numerous records for highs in the last week of July, including the highest temperature ever recorded in Seattle on July 29: 103 degrees.

"This is kind of an abnormal summer," said AccuWeather.com meteorologist Kate Walters.

While the National Weather Service and AccuWeather.com agree that August in Pittsburgh is likely to be relatively cool and produce normal precipitation amounts, they disagree on what El Nino will bring to the area for the rest of the year, especially the winter months.

The National Weather Service predicts that El Nino will also bring mild weather this winter.

"El Nino effects are much more pronounced in the winter time," Mr. Kane said.

He added that this year's El Nino has been classified as moderate to weak, meaning that average winter temperatures most likely will be slightly above average.

"But we still might have some cold spells in there," he warned.

AccuWeather.com, on the other hand, predicts Pittsburgh is in for an especially cold and snowy winter.

Its forecast shows El Nino fading, a transition that will bring harsher weather to the Northeast and shift winter-storm patterns.

Harsh storms passing to the east of Pittsburgh would make the region much more susceptible to frigid weather and snowfall than last year's storm track, which passed to the west.

"[Pittsburgh] will be on the backside of the storms, which would be much colder. Last year, they were on the warmer side," Ms. Walters said.

AccuWeather also forecasts a cooler-than-average fall here, while the National Weather Service believes fall will be slightly warmer than usual.