AccuWeather forecasters say a massive shift in the weather pattern is on the way for North America next week. Summerlike heat is expected to build over the western United States as a surge of Arctic air is projected to plunge into the eastern half of the nation. Both high and low temperature records could be broken amid the extreme weather setup.
Cold wave for the eastern half of the US
An outbreak of the coldest air since last spring will sweep across much of the Plains, Midwest and part of the interior South next week.
"The change in the pattern will come in two waves," said AccuWeather Long-Range Meteorologist Tyler Roys. "After a warmup during the second half of this week, an area of low pressure sweeping across southern Canada will usher in an initial cooldown."
The first wave of cooler air will settle over the northern Plains and Great Lakes this weekend and then will filter into the Northeast early next week. The cooldown will be preceded by a substantial warmup with widespread highs in the 80s late this week and this weekend in the Eastern states.
The first push of cooler air will serve to bring temperatures back to near normal, or a little below normal for late September, and it will be limited to northern areas. Across the Southeast, temperatures will remain a few degrees above normal.
Normal highs are generally in the middle to upper 60s in the northern Plains, Great Lakes and Northeast during late September. Farther south, temperatures typically climb into the lower to mid-70s in the mid-Atlantic through the Ohio Valley and into the mid-Mississippi Valley, and upper 70s to low 80s across much of the Southeast and lower Mississippi Valley this time of year.
A second wave of cool air will follow and will be much more dramatic and longer-lasting than the first wave and should result in much lower daytime highs than prior air masses from earlier in September.
"The real cold shot will be ushered in later next week as a stronger storm system pushes from the northern Plains through the Great Lakes," Roys explained. "High pressure building down from northern Canada and a deep dip southward in the jet stream will bring a continuous flow of cold air straight from the Arctic."
The core of the cold is expected to be aimed from the Midwest and Mississippi Valley to the western slopes of Appalachians. From Wisconsin to Louisiana and from eastern Kansas to West Virginia, temperatures are forecast to be 10-20 degrees Fahrenheit below normal during the height of the cold shot during the first weekend of October.
Interior portions of Louisiana, Mississippi, Alabama and Georgia, areas weary from the record-setting tropical season, could have afternoon temperatures topping out in the 60s and overnight lows dropping into the 40s. Some communities still cleaning up and without power from Laura, Sally and now enduring flooding rainfall from Beta will face chilly weather.
Frosts and freezes could threaten sensitive agriculture from as far south as parts of the Ozarks in northern Arkansas to the Blue Ridge Mountains straddling Tennessee, North Carolina and far northern Georgia.
Even in Atlanta, low temperatures could drop to the mid-40s, with near-40-degree readings in some outlying areas. The normal low in Atlanta at the end of September and beginning of October is around 60 degrees.
"While the Great Lakes and interior Northeast were hit with a cold snap that led to the end of the growing season last week, this next shot of cold will target areas farther west, and will likely end the growing season across much of the Midwest and Ohio Valley," Roys said.
Afternoon temperatures are expected to be stuck in the 40s and even some in the 30s across the Upper Midwest and northern Great Lakes. Lake-effect rain showers and a raw, gusty wind will also add to dreariness and the feeling of chill. During the overnight hours during the height of the cold, some parts of the Great Lakes may see their first snowflakes of the season.
Overnight lows will plunge with widespread temperatures projected to be in the 30s and 40s and even some 20-degree readings for locations from the eastern Plains.
"Moisture generated in part by the Great Lakes may keep the sky overcast at night in portions of the Appalachians, upper Midwest and interior Northeast," according to AccuWeather Senior Meteorologist Alex Sosnowski.
"A breeze may remain active at night as well later next week and the first weekend of October, and both the breeze and cloud cover could prevent frost by only allowing low temperatures to be in the upper 30s and lower 40s in the cold spots," Sosnowski added.
Along the Eastern Seaboard, the cooldown will be felt, but the core of cold will grip areas much farther to the west. "Most locations east of the Appalachians and along the Interstate 95 corridor will be around 5-10 degrees below normal," Roys said.
During the first full week in October, this extreme kink in the jet stream is expected to ease, bringing conditions back closer to normal across the nation. However, that could also mean a return in activity in the record-setting 2020 hurricane season.
"Computer forecasts continue to show the development of a large counterclockwise wind pattern over Central America, commonly referred to as a gyre, later next week. This could lead to the development of an organized tropical system in the southern Caribbean during early October," said AccuWeather's lead hurricane expert Dan Kottlowski.
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