Keep Your Christmas Tree From Getting Crispy

For the final month of summer and into the first two months of fall, near- or slightly below-average temperatures may infiltrate the central and eastern United States while above-average warmth remains locked in the Southwest and West, according to the latest three-month outlook from The Weather Company, an IBM Business.

Meteorologists typically divide the seasons into the three-month periods that best define them, meaning meteorological summer runs from June 1 to Aug. 31 – the three average hottest months of the year – and meteorological fall runs from Sept. 1 to Nov. 30 – the three transition months between summer and winter.

(MORE: Why Seasons are Different to Meteorologists Than the Rest of Us)

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The following map depicts the overall temperature expectations for the three-month period from August through October. We'll dive into the month-by-month details below.

August

As we transition into August, the potential emergence of El Niño and its impact on tropical activity in the northwestern Pacific Ocean may influence the jet stream pattern downstream in the United States, and therefore, temperatures as well.

(MORE: Increasing Chance of El Niño Later This Year)

"The pattern flip towards cooler conditions across much of the eastern U.S. is in progress, and we expect this new pattern to persist into August, with the coolest temperatures relative to normal across the north-central U.S.," said Dr. Todd Crawford, chief meteorologist with The Weather Company.

As a result, the Great Lakes and upper Midwest are expected to see below-average temperatures in August, with near- or slightly below-average temperatures in many other central and eastern locations. In the West, the opposite is expected, with widespread hotter-than-average conditions forecast, particularly in Southern California and south Texas.

September

Looking ahead to September, a large swath of the nation is forecast to see near- or slightly above-average temperatures.

Northern and central California into the Great Basin, Pacific Northwest, northern Rockies and northern Plains, as well as South Florida, are the most likely locations for above-average warmth.

Meanwhile, parts of the Southwest may be near or slightly cooler than average.

October

"We expect a much different start to the heating season this fall compared to last year, with an El Niño base state helping to drive western North American ridging and cooler risks in October through the major heating demand regions of the eastern U.S.," Crawford said.

What this means is that an upper-level trough, or southward dip in the jet stream, is expected to set up in the East, yielding below-average temperatures across the region. An upper-level ridge in the West should keep temperatures mild there.

Cooler-than-average temperatures in October can be quite chilly in the northern tier of states, where average highs for the month are in the 50s and 60s and average lows are in the 30s and 40s.

(MAPS: Average Monthly Temperatures)

Keep in mind, these outlooks are overall trends for an entire month or a three-month period. An individual cold front or an upper-level ridge of high pressure can lead to a brief period of colder or warmer weather, respectively, that doesn't match up with the outlook.

Brian Donegan is a meteorologist at weather.com. Follow him on Facebook, Twitter and Instagram.