Frost map

Editor’s note: The following was written by Al Dutcher, Associate Nebraska State Climatologist, for the University of Nebraska Crop Watch website Sept. 12.

Above-normal temperatures during August significantly reduced the freeze risk for timely and late-planted corn.

Because temperatures across the Panhandle were close to or above normal during August, GDD accumulations were also above normal, especially during the second half of the month.

When comparing current conditions to our base normal period (1981-2010) and applying the base normal period to this year’s GDD accumulations for four emergence dates, corn that emerged from May 27 to June 10 now has less than a 50% freeze risk compared to the normal period for varieties of 2,500 GDDs or less.

The latest GDD freeze risk summary indicates corn varieties listed as maturing at 2,500 GDDs or less and which emerged June 10 may fail to reach maturity 60%-100% of the time across the northern third of Nebraska east of the Panhandle. For corn that emerged on May 27, 2,500 GDD varieties would carry less than a 50% risk of freeze damage compared to the 1981-2010 period; 2,700 GDD varieties would have a greater than 80% likelihood of not reaching maturity.

What these statistics tell us is this September needs to be warmer than any September in the comparison period of 1981-2010 to reduce the freeze risk below 50% for corn emerged in late May and early June.

Thus, the temperatures over the next four weeks will ultimately dictate whether late-planted crops escape significant freeze damage.

The latest GFS model run released Sept. 11 indicated warm temperatures would continue as another upper air trough dug into the western U.S. This trough of warm air slowly traversed eastward, impacting the central third of the country.

Unfortunately, the northern third of Nebraska, the Dakotas, Minnesota and northern Iowa also saw excessive moisture. If that is not bad enough, the departing upper air low is forecasted to merge with the upper air trough over the Hudson Bay. The GFS model intensifies the Hudson Bay upper air trough and pulls freezing temperatures southward into the northern Plains and upper Midwest (Dakotas, Minnesota, Wisconsin and Michigan) between Sept. 28 and Oct. 1.

If the GFS model does verify, much of the area of the western Corn Belt north of I-94 — an area that had extensive planting delays — would be impacted. It is entirely possible the GFS is overplaying the extent of cold air that will be pulled southward into the northern Plains, but this pattern bears watching.

If we can escape this forecasted event, it will likely take an additional week or longer for the next surge of cold air to enter the continental U.S.