Ag Weather Forum

Today is Oct. 1 and it may be hard to believe, given the recent warmth, but the average temperatures take quite a dive during the month. The first frosts and freezes just occurred in parts of the northwestern Plains this morning and we should not be surprised to find frosty air coming through the country from now on, even if temperatures are above normal for the next few weeks.

Outside of mountain areas, the median first frost dates, when the low temperature for the day reaches 32 degrees Fahrenheit, range from late September near the Canadian border to late October or early November near the southern end of the Corn Belt. It may take until late November or later for areas around the Gulf of Mexico.

Temperatures will drop throughout the month, even if the setup is for a continued supply of warm air. For example, Minneapolis goes from an average low of 47 F on Oct. 1 to 34 F on Oct. 31, or a drop of a degree about every two days. By the end of the month, snow could be falling. For Nashville, TN, low temperatures drop from 56 on Oct. 1 down to 44 for Halloween. The first frost almost always comes well before the average low reaches 32 degrees. For Minneapolis, the average low of 32 occurs on Nov. 6 while the first frost date is Oct. 16. For Nashville, Tennessee, the average low of 32 F happens on Dec. 23, while the first frost date is Nov. 4. Outlying areas away from the city centers almost always have earlier frost dates.

So, during October, it should come as no surprise that frost will become a regular part of weather discussions. But will this year be late?

As mentioned above, parts of the western Dakotas, western Nebraska, Wyoming and Montana have already seen their first frost. For some spots, it was on time. But for others, it was a bit late. According to data from the Midwest Regional Climate Center, some spots from central Nebraska through Michigan and across the Northeast are already late as well.

The setup for the next two weeks is a little chaotic, but otherwise warm. An upper-level ridge of high pressure has found its way into the West and looks to stick around at least through the middle of the month, supplying areas east of the Rockies with warm air. Although it is stout, there are some weaknesses to it and disturbances will be moving through Canada, bringing cold fronts rather frequently across the U.S. These fronts do not have access to a lot of cold air, but could bring a brief burst of near-normal or even slightly below-normal temperatures for a day or possibly two behind them before the warmer air rushes back in from the ridge. In those cases, patchy areas of frost will be possible across northern areas of the country through next week if aided by clear skies and calm winds. Such was the case in the northwestern Plains this morning.

A shakeup in the weather pattern may come for the second half of October. Some models are suggesting that the warm ridge gets pushed westward into the Pacific and up into Alaska. If it does so, it would be more likely to bring down colder air for those of us east of the Rockies. There is no guarantee here that some areas in the southern Corn Belt would see an early frost, but that would be possible after enduring a warm start to the month. Early November first frost dates range from the southern Texas Panhandle through central Oklahoma east through North Carolina.

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John Baranick can be reached at john.baranick@dtn.com

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