The days are getting shorter and autumn is approaching, but when will cooler conditions return -- and will snowflakes fall before Halloween? Get the answer to these questions and more with AccuWeather’s annual fall forecast.
Widespread heat has shattered records from coast to coast throughout the first half of summer, but the longest days of 2023 are in the rearview mirror and cooler weather is on the horizon.
Astronomical autumn officially arrives on Saturday, Sept. 23, at 2:50 a.m. EDT, a few weeks after the arrival of meteorological fall. Regardless of which date you celebrate the start of autumn, it may take some time before fall weather takes hold across the country.
A woman walks past autumn foliage during snow flurries, Tuesday, Nov. 12, 2013, at Independence Mall in Philadelphia. (AP Photo/Matt Rourke)
AccuWeather's team of long-range forecasters, led by veteran meteorologist Paul Pastelok, has analyzed weather patterns around the globe to piece together the weather forecast for the United States this fall.
One of the driving factors behind the weather patterns across the U.S. this autumn will be El Niño, a regular climate pattern that can reshape the jet stream. El Niño developed early this year when the water near the equator in the eastern Pacific Ocean warmed to at least 0.9 F above the historical average. The pattern replaced its cooler counterpart, La Niña, which persisted for three consecutive years.
Other factors have weighed on the minds of forecasters, including sea surface temperatures in the Atlantic and what has transpired in previous years when conditions were similar.
So get ready for hoodie weather, pumpkin spice lattes and vibrant fall foliage with a region-by-region breakdown of the seasonal forecast:
October to bring major shakeup to weather in Northeast, Midwest
Meteorological fall kicks off on Sept. 1, but summery weather will linger into the start of the new season for millions of people across the Northeast and Midwest.
The temperature could top out around 90 degrees in New York City and Philadelphia during the first week or two of September, slightly later than the historical average for the latest 90-degree day. In Chicago, the final 90-degree day of the year might not occur until the latter part of September.
Lingering heat could be good news for folks planning trips to the beach after Labor Day weekend, but the warm weather will begin to break down as the calendar flips from September to October.
Fall foliage colors the Franklin D. Roosevelt Four Freedoms Park, Thursday, Nov. 8, 2018, in New York. The Manhattan skyline is across the East River. (AP Photo/Mark Lennihan)
A "big transition" in the weather will usher in chillier air around the end of September across the Midwest and Northeast, Pastelok explained. The clash of much cooler air with warmth and humidity will ignite thunderstorms, including the risk of a more significant severe weather event.
The change in the pattern could also bring an early frost to parts of the Midwest near the end of September or early October, including in major metro areas such as Chicago, Milwaukee, St. Louis, and Minneapolis.
The first frost of the season will hold off until October for the Northeast, and perhaps even early November for areas closer to the coast, which is more than a week later than the historical average. This could extend the growing season for farmers and gardeners across the region.
The arrival of cooler air across the Midwest and Northeast will also open the door for snowflakes to fall for the first time in months.
"I think we could start to see some flurries in the higher elevations as we get into very late September and October, but lower elevations may wait until later October or November," Pastelok said. It is not rare for flurries to fall in these areas in October, but it is about two weeks ahead of the historical average for the first snowflakes of the season.
The snow will likely be limited to just flurries before the potential of widespread accumulating snow forces folks to dig snow shovels out from storage.
Hot water will be 'very critical' to Atlantic hurricane season
A strengthening El Niño tends to put a cap on tropical activity across the Atlantic basin, but people in hurricane-prone regions of the U.S. should not let their guard down this season.
The biggest factor in the hurricane forecast apart from El Niño is the water temperatures across the Atlantic basin, which are running well above average in many areas. Warm water is the fuel for tropical systems. The warmer the water, the more energy is available for the storms to tap.
Sea surface temperatures have been particularly noteworthy in Gulf of Mexico waters, where a marine heat wave is ongoing near Florida. Water temperatures just off the coast of South Florida and around the Florida Keys have been as high as the upper 90s to 100 F in July.
A map of the Atlantic hurricane basin showing sea surface temperature anomalies. Areas of yellow, orange red and pink show where water temperatures are above the historical average. Areas of blue and green show where water temperatures are below the historical average. (NASA Worldview)
Last year, Hurricane Ian was supercharged by unusually warm water off the coast of Florida, helping the system rapidly intensify before making landfall as one of the most powerful hurricanes in Florida's history. A post-storm analysis found that Ian had briefly intensified into Category 5 strength while over the Gulf, but made landfall as a Category 4 near Fort Myers, Florida.
"We could see one or two systems getting into this warm pool of water and exploding," Pastelok said. "There could be a rapid development, and that could be proved to be the biggest impact that takes place in this tropical season."
This satellite image taken at 3:06 p.m. EDT and provided by NOAA shows Hurricane Ian making landfall in southwest Florida near Cayo Costa, Fla., on Wednesday, Sept. 28, 2022, as a catastrophic Category 4 storm. (NOAA via AP)
The most active period for the tropics could be late August and September, around the traditional peak of the Atlantic hurricane season. If El Niño strengthens throughout the autumn, it may limit tropical development in October and November.
Thunderstorms could also drench the Southeast on a regular basis between tropical threats. At times, stormy weather could reach areas farther north as well.
"The transition period in late September and October could be very active for parts of the southern Midwest, western Ohio Valley and extending down into the mid-Mississippi and lower Mississippi Valley," Pastelok said.
Pastelok added that summerlike weather will hang around the Southeast through the first part of autumn before eventually giving way to cooler and less humid conditions late in the season.
Big changes to follow mild start to autumn in central US
The central U.S. and Rocky Mountains are in for a major shakeup following a mild start to autumn.
When crafting weather forecasts for an entire season, meteorologists look at the past to help predict the future. "We look at other years and try to match up the current pattern or what we expect to happen over the next couple of months," Pastelok explained. These are known as analog years.
One analog year that stands out is 2009. That year featured a major snowstorm on Oct. 8 that unloaded over a foot of snow in Nebraska.
"There is a good chance that we're going to see something similar to that [this year]," Pastelok said. "A pattern change that takes place could produce a lot more cold across the north-central Plains states and getting back into the northern Rockies."
Even if snow is not prevalent in the central U.S. during October, temperatures across the region are projected to be lower than last October, including in Denver, Dallas and Kansas City.
Even if snow falls over these areas in October, the opportunity for snow will likely decrease some in November. Temperatures across the Rockies and Plains may also rebound a bit in November with widespread temperatures slightly above the historical average.
Wildfire season in West to 'build up quickly'
It has been a hot summer across most of the western U.S., and that theme will continue right into the start of autumn.
"Summer probably will hang around for a little bit longer, especially in the Southwest," Pastelok said. "California, the central valleys, the deserts, they probably should stay hot at least until October."
However, a much different story will unfold across the Pacific Northwest. "There is the possibility of some wet weather coming in very quickly in September, maybe even the potential for an atmospheric river to develop," Pastelok said.
A pedestrian huddles under an umbrella near a tourist shop during a steady rain Monday, Nov. 26, 2018, in Seattle. (AP Photo/Elaine Thompson)
While the wet pattern will not be persistent across the Pacific Northwest throughout the entirety of autumn, an early rainstorm or two could help curtail the wildfire season across the region.
The U.S. wildfire season had a slow start in part thanks to a prolific winter season that saw many moisture-laded storms slam the West with historic snowfall amounts and drenching rainfall. However, this slow start to the fire season may not last.
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"Even though we're having a late start, and the season may be shorter this year compared to other years, we may see the acreage really build up quickly," Pastelok explained.
The highest fire risk this year is expected in Northern California, eastern Oregon, eastern Washington, Idaho, and parts of Nevada.
Additionally, there could be more Santa Ana wind events in October than last year, helping to fan the flames of fires across Southern California.
Pastelok said a few fires could flare up in October as winds fan the flames, causing fires in California to grow.
AccuWeather meteorologists say wildfires will likely burn between 5 and 6.5 million acres across the U.S. this year, below the historical average of 7 million and less than last year's total area scorched of 7.5 million acres across the country.
Looking forward to seeing colorful foliage this autumn? Check back on Friday, Sept. 1, for the release of AccuWeather's U.S. fall foliage forecast.
Fog sits in the valley of the White Mountains as leaves change colors, Sunday, Sept. 28, 2014 in this photo taken from Milan Hill in Milan, N.H. (AP Photo/Jim Cole)
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