Early Cold Shot
Having a big cold front roll into the United States during the month of September is not unusual. However, most September cold shots come during the third or fourth week of the month.
This week, a very strong surge of cold air will move into the Northern Rockies and the Northern Plains. There will be many areas that experience the first snowflakes of the fall season as well as the possibility of the first frost/freeze. Some growing seasons may come to an end in the Northern Plains and Northern Rockies.
The graphic below (courtesy of the Midwest Regional Climate Center) shows the average first fall freeze date based on the thirty year average from 1981 to 2010.
Areas of North and South Dakota and Wyoming show the average first 32F (outside of the mountains) happening between September 11 through September 20th (darker blue) with the rest of the region having the first 32F between September 21 through September 30 along with areas of the western Corn Belt.
Those areas are likely to have 32F or colder by late this week. For areas farther to the south, such as Nebraska and northeast Colorado, the average first 32F is during the first 10 days of October. Portions of western and southwestern Nebraska and northeastern Colorado may have temperatures close to 32F by the end of week. We will also need to keep an eye on temperatures across the Dakotas, Minnesota, Wisconsin and Iowa.
With the cool summer that many areas have experienced this summer season, an early frost/freeze could impact hay crops, beans and corn in the northern and western plains this week.