A strong push of autumnlike air will invade the North Central states later next week and will bring the risk of frost, as well as the chance of a bit of snow to some locations.
The chilliest air since last spring will push southward from Canada and across the northern and central Plains, Midwest and the eastern slopes of the Rockies, prior to the middle of September.
The chilly air will follow an expanding cooldown already in progress and will follow a large area of rain forecast to sweep out of the Southwest.
A patchy light frost will visit portions of the northern tier states over the Central states beginning next Friday.
According to Senior Meteorologist Dale Mohler, "The frost will be mostly a concern for backyard gardens, where tomatoes, squash and other sensitive vegetables and flowers are flourishing."
Temperatures are forecast to dip into the 30s in rural areas of the Dakotas, Minnesota, Wisconsin and Nebraska.
In the coldest spots near the ground, temperatures can drop close to freezing for a few hours.
On a broad-term agricultural standpoint, crops such as corn and soybeans are maturing about a week behind average, but with such a bumper crop anticipated, no significant impact is expected by the light spotty frost unless temperatures dip significantly lower than currently forecast.
Patchy cloud cover and a breeze can have a positive impact on low temperatures and are expected in part of the North Central states during the chilly air outbreak. Clouds act as a blanket, preventing warmth from escaping, while a breeze causes the air to be well-mixed and prevents cold air from collecting near the ground.
In the East, temperatures may get low enough in portions of upstate New York, northern Pennsylvania and northern New England for spotty light frost later next weekend. However, the air masses coming eastward early in the season are likely to be significantly modified by the warm waters of the Great Lakes.
The potential for an early jump start on the cold and frost for the autumn in the North Central states was first discussed in early August by the AccuWeather.com Long Range team.
Spotty Snow Possible
While some snow already fell on Alberta, Canada, during the first couple of days of September, another round of snow is forecast to fall on the eastern slope areas of the Canada Rockies and Prairies during the upcoming week.
According to Canada Weather Expert Brett Anderson, "A change to snow is likely in the Alberta mountains and foothills Monday into Tuesday."
As this cold air settles southward later in the week, spotty snow may fall on eastern slope areas of of the northern and central Rockies of the United States as well. There is a slight chance of wet snow mixing in with rain showers in portions of northern Minnesota and Wisconsin late next week.
The amount of snow, if any, in the U.S. will be dependent on the amount of moisture available and the magnitude of the cold air.
Anderson pointed out that any snow that falls outside of the high elevations is likely to be very wet and melt on roads.