At a Glance
- Warmer-than-average temperatures should dominate much of the Southwest, Plains and East this fall.
- December, however, could trend colder than average in parts of the East.
- A second La Niña and potential blocking Arctic high pressure could play important roles.
Warmer-than-average temperatures should dominate much of the country this fall, but a cooler than average December may be in store for parts of the East, according to an updated outlook from The Weather Company, an IBM Business.
In other words, the typical fall cooldown might be slower than expected in much of the nation. However, there may still be some areas of the country that trend a tad cooler than usual.
Let's take a month-by-month look at the rest of 2021. Keep in mind these outlooks are for each month overall and don't preclude any short-term cold or warm spells.
A warm October is most likely from the southern High Plains to the Midwest and Northeast, particularly around the Great Lakes and northern New England near the Canadian border.
In the southern Rockies and High Plains, that's a continuation of September's heat. A number of cities, such as Denver and Albuquerque, had one of the hottest first halves of September on record, according to data from the Southeast Regional Climate Center.
In the Midwest and Northeast, this warm October outlook is also a continuation of a generally warm pattern that was expected through much of the rest of September.
Parts of Florida and the Gulf Coast, however, could have a slightly cooler than usual October, partly due to the potential for tropical cyclones and other areas of heavy rainfall.
The Northwest and northern Rockies might also trend a bit cooler and wetter than average in October. Both would be welcomed by a region in exceptional drought.
November, however, may see relatively little of the chill the month is known for.
We're not expecting widespread colder-than-average temperatures in November anywhere in the Lower 48 states.
One reason for this mild forecast is La Niña's expected appearance for the second year in a row. This periodic cooling of the water in the eastern Pacific Ocean near the equator drives changes in the jet stream thousands of miles away.
And these changes in the weather pattern tend to favor mild fall temperatures in much of the country, according to Dr. Todd Crawford, Director of Meteorology at Atmospheric G2.
November 2020, also during a La Niña, was mild over much of the country, according to a NOAA analysis.
There's an ingredient that could make for a colder December in the East.
Longer-range forecast models suggest high pressure could be more prevalent by December over parts of the Arctic, including near Greenland.
If that occurs, this blocking high pressure could force more persistently cold air into the East.
For now, our outlook hints at this potential with the Northeast forecast to be slightly cooler than average. If the blocking is stronger and more persistent, December's temperatures would trend colder in the East.
If that blocking chills the East, the pattern could also warm the West, including the Pacific Northwest, more than expected in a La Niña.
The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.