By cool front, we are not talking of an early frost.

Cool fronts that move through the region during the fall can bring rain.

The radio on the drive over said the heat wave had broken, that a cooler front was moving in.

"Without this jet stream, no significant cool fronts have passed through."

But a cool front moved through the region last night, and high temperatures today are expected to reach the high 80's or low 90's.

"A cool front is approaching with a band of thunderstorms.

Why couldn't she maintain a cool front too?

The high temperatures will continue until Thursday, he said, when a mild cool front and thunderstorms were expected to move into the city.

He said a cool front in Canada that was moving this way was falling apart even as he spoke.

In fall, cool fronts bring in rainstorms and flooding is not uncommon.

A cool front had moved in from Canada; low, scudding clouds spat wet circles on the pavement.

Ms. Birdsong certainly presents a cool front.

Later that evening a powerful cool front crossed southern Ontario causing further storm damage in Ontario (see below).

Brian Lasorsa, a meteorologist for AccuWeather, said the storm was caused by a weak cool front that combined with warm and humid air.

In the spring, cool fronts moving south from Canada collide with warm, humid air streaming in from the Gulf Coast.

The "sandwich horizon" is the term given to the central region where both cooling fronts met; it is here where the diabase is the most differentiated.

If a substantial number of those jobs could go to residents in the struggling Boston neighborhood, the benefits would spread throughout the area, like a cool front on a muggy summer afternoon.

As Mr. Boyd and his assistant monitored the slow descent of the spinning drill, more anvil clouds rolled in from the west, ushering in the weekend cool front.

A cool front from Canada, tinged with the vestiges of Hurricane Erin, sent the temperature plummeting, said Fred Gadomski, a meteorologist at Pennsylvania State University.

"It's always warmest ahead of a cool front," Mr. Grenci said, explaining that heat-producing winds from the south and southwest are typically driven by a block of cooler weather.

He added: "My impression is that at the end of the weekend or early next week, the jet stream might dip far enough south so a cool front could get into the New York City area."

The lingering effects of a weak cool front from New England pushed temperatures down into the high 80's in the New York region yesterday, but they were expected to rise back into the 90's today.

Chicago nearly recorded a fourth consecutive day at or above 100 F, but the temperature reached 98 degrees at O'Hare in late morning before a slight cool front came through the area and cooled temperatures off slightly.

On August 2, more storms associated with a relieving cool front caused heavy damage over a wide swath of central and eastern Ontario, resulting in 175,000 residents losing power and thousands of felled trees blocking roads.

Though weather forecasters saw little chance of immediate relief for much of the nation, the heat was expected to break in the New York region by midnight, with a cool front from Canada bringing rain and temperatures in the 80's.