I almost hesitated writing this piece this week because I have already written it before in this space. In December and January I remarked how models were trying to force cold, arctic air into the United States with the aid of a weakened Polar Vortex. Only, the models would trend warmer with time and make me look like a fool.
This no longer appears to be the case. After a week of fair consistency, and even trending colder during the last few days, I am more certain that a long-duration burst of arctic air will slide into the U.S. east of the Rockies.
The active jet stream is the mechanism by which this will occur, aided by blocking high pressure over Greenland. The high will "pinch" the jet stream off at the North Pole, while a strong storm forces the cold air to move southward through the continent.
And this will have a dramatic change to our weather that we have been experiencing this winter. Yes, there has been snow and as far south as Louisiana this winter, but the cold has not arrived in any meaningful way just yet and certainly not with any duration. Temperatures for November through January were all well-above normal across the majority of the country with little exception.
The change is on the horizon. A system will move through the country Feb. 3-5 and will be the catalyst for bringing cold air southward as it will push above-normal temperatures out of the way. But it will be a secondary system Feb. 6-8 that will do the heavy lifting, or rather pulling, of the cold air. Temperatures will go below zero Fahrenheit over the Northern Plains and Midwest and may not make it into positive territory for a couple of days. Temperatures are also likely to fall into the negative values in the Central Plains, with chances as far south as Wichita, though that chance is somewhat remote.
It is here that we should direct attention. There has been some snowfall over Nebraska and northern Kansas recently, but bare ground still exists for much of the Central and Southern Plains. Warm weather this week will help to shave off some of that snowpack as well. With temperatures nearing or falling below zero Fahrenheit, winter wheat is under increased risk for winterkill.
A similar impact could be felt in the Midwest wheat belt, with the primary risk for southern Illinois. Drought over the Plains has already had a negative impact on winter wheat as January's crop ratings fell for each state except for Oklahoma. Winterkill would only worsen what is already a sub-optimal outlook for wheat this growing season.
La Nina has weakened during the last month, but is still in the moderate category going into the new month. Models continue to suggest that La Nina will weaken through the spring, but not go away entirely. This typically means lower-than-normal precipitation for this portion of the Plains and would compound upon the recent conditions.
John Baranick can be reached at firstname.lastname@example.org
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