UNL CropWatch May 26, 2010: GDDs Catching up From Early Season Fluctuations

UNL CropWatch May 26, 2010: GDDs Catching up From Early Season Fluctuations

May 26, 2010

It certainly has been a challenging start to the 2010 production season as much of the Corn Belt has seen remarkable temperature swings since mid-April.

Record warmth during the second half of April led to rapid planting across the central and eastern Corn Belt, followed by colder temperatures (4-10 degrees below normal), rain, snow, and some freezing temperatures the first two weeks of May. The pattern shifted back during the latter half of May to temperatures 5-15 degrees above normal, depending on your location in the Corn Belt.

Closer to home, the early May cold snap had many producers concerned that we would see a repeat of 2009. Remember that in 2009 corn and soybean planting progressed at an unusually fast pace due to an extended warm, dry period. This year is still in line with the five-year average. (Sorghum planting is trailing the five-year average by about a week.)

GDDs Catching Up to Normal

 High Plains Map -- 30 days

Figure 1. Percent of normal precipitation for April 26 to May 25 for the High Plains Region.  (Source:  High Plains Regional Climate Center)

 High Plains Map -- 60 days

Figure 2. Percent of normal precipitation for March 27 to May 25 for the High Plains Region.  (Source:  High Plains Regional Climate Center)

I conducted a quick analysis of the growing degree day unit accumulations (Base 50/86) for all Nebraska reporting locations using emergence dates of May 1 and May 15. I found GDD running 40-70 units behind normal for a May 1 emergence, and from 20 GDDs ahead to 20 GDDs behind normal for a May 15 emergence. Based on the daily GDDs expected for May 25, the 70-unit departure from normal represents five days. This can easily shift — over the last seven days, GDD departures were cut by 30-50 GDDs.

Weather models continue to point toward normal to slightly above normal temperatures for the next two weeks (May 26 – June 8). If the models verify, GDD departures will be cut an additional 30-50 units. In other words, virtually all GDD departures accumulated from the May 1 emergence date would be eliminated, leaving the crop one to three days behind normal. For the May 15 emergence date, crops would be only one to three days ahead of schedule.

Dry Pattern Persists in Several Areas

A more important concern is a dry pattern that has developed across portions of the state in the last 30 to 60 days. Drier than normal conditions are evident in Figure 1 for the past 30 days. Where moisture has fallen, it has been abundant; however, large areas of north central, northeast, and east central Nebraska have not seen the heavier moisture. Only portions of the Panhandle and southern Nebraska had received above normal moisture through 7 a.m. May 25.

The 30-day precipitation tendencies force us to concentrate on dry areas and the potential for drought. Sixty-day precipitation tendencies (Figure 2) show that a dry pattern is well established in north central and northeast Nebraska. The exceptional moisture we had last winter more than offset the lack of precipitation this spring so we don’t expect any problems for the time being.


If this trend continues during the next 30 days and as crop water use increases to 1/4  - 1/3 inch per day, I wouldn’t be surprised to see the U.S. Drought Monitor authors suggest abnormally dry to moderate drought conditions for this area. I am hopeful that the recent wind activity will begin to subside; otherwise, temperatures in the 90s and consistent winds in the 20-30 mph range could increase water demands by up to 25% and increase the risk for flash drought conditions.

Streamflows to Lake McConaughy Up 150%-300%

On a positive note, the early May cold conditions have delayed the Rocky Mountain snow melt. Coupled with recent precipitation across eastern Wyoming and western Nebraska, streamflow rates entering Lake McConaughy have been in the 2000 to 4000 cubic feet per second range (150% - 300% of normal). Lake McConaughy gained almost 30,000 acre feet during the last seven days and stands at 1.25 million acre feet (71.2% full). Based upon current snow pack, I expect all Wyoming reservoirs to fill this spring, with Lake McConaughy possibly reaching 80% of capacity (1.4 million acre feet).

Allen Dutcher
Nebraska State Climatologist, Lincoln

 

Online Master of Science in Agronomy

With a focus on industry applications and research, the online program is designed with maximum flexibility for today's working professionals.

A field of corn.