90-day Forecast: Above Normal Temperatues, Below Normal Rain - UNL CropWatch, May 30, 2013

90-day Forecast: Above Normal Temperatues, Below Normal Rain - UNL CropWatch, May 30, 2013

May 30, 2013

It has been an exceptionally challenging spring for producers attempting to seed their 2013 crops across the vast majority of the U.S. Corn Belt. Although Nebraska is faring better than their eastern counterparts, 14% of the corn crop still had to be seeded seeded as of May 26, according to the Nebraska office of the National Agricultural Statistics Service. Depending on location, corn planting and emergence are 10-14 days behind the five-year average.

U.S. map of June-August temperature outlook

Figure 1. Temperature probabilities for June-August. Probabilities for Nebraska range from 33% (light shade) to 40% (medium shade) for above normal temperatures. (Source: National Oceanic and Atmospheric Administration)

U.S. map of June-August precipitation outlook

Figure 2. Precipitation probabilities for June-August. Probabilities for Nebraska range from 33% (outer shaded area) to 40% (inner, darker area) for below normal precipitation.  (Source: National Oceanic and Atmospheric Administration)

Drought monitor for Nebraska

Drought Monitor scale
Figure 3. Nebraska portion of U.S. Drought Monitor for May 28 shows significant improvement, particularly in the eastern half of the state. See map and scale.

Most planting delays can be directly tied to the exceptional cold that invaded the northern and central U.S. in April. A persistent snowpack across Canada and the northern Plains led to Nebraska experiencing its 4th coldest April since records began in 1895. It’s estimated to be the 86th wettest April for that same time period. The chilly weather held through the first week of May before temperatures finally returned to more typical spring conditions.

On a positive note, precipitation has been generous enough across the eastern half of the state to build up soil moisture supplies and lessen drought concerns in the short term. On a less positive note, if we have normal temperatures this summer, corn will likely reach reproduction during mid-July; however, if below normal temperatures continue, the potential for freeze may become an important issue this September.

The Climate Prediction Center has yet to back off its projections for summer heat across the central and southern High Plains region. The two-week forecast for early June indicates above normal temperatures for all of Nebraska, except extreme northeast Nebraska. The entire state is still projected to experience above normal temperatures June through August (Figure 1).

Because standard Growing Degree Day (GDD) calculations for corn and soybeans use an 86°F upper limit and a 50°F lower limit, the best opportunity to reduce the effect of planting delays will be during the first two weeks of June and from mid-August through the end of the crop production season. These are periods when the normal maximum temperature is below 86°F. Otherwise, from mid-June through mid-August, maximum temperatures are above the 86°F threshold and reducing accumulated GDD deficits will require elevated minimum temperatures.

Although severe weather was lacking through mid-May for most of the country, there has been a significant uptick in active weather the past two weeks. If we are to believe the CPC precipitation forecasts for June and June-August (Figure 2), this trend will be short lived. The western two-thirds of the state is projected to experience below normal moisture, while the eastern third has equal chances of experiencing below normal, normal, or above normal moisture during the same time frames.

Short-term model forecasts continue to point toward an active weather pattern for the western Corn Belt through mid-June. The models show continued development of upper air troughs over the western U.S., moving northeast toward the western Great Lakes. This is a perfect scenario for bouts of heavy rain and severe weather for the central and northern Plains. Planting, tillage, spraying, and haying could continue to prove to be a challenge in the short term.

There has been a significant reduction in the drought signature for the western Corn Belt, with the best improvements occurring across eastern sections of this region (Figure 3). The worst drought areas also coincide with the CPC forecast for below normal summer moisture. Thus, this recent stretch of active severe weather has provided us with a unique opportunity to build soil moisture reserves before crop water use begins to exceed the moisture that we normally receive.

Snowmelt in the central Rockies began later than normal this year due to the persistent cold temperatures in April. It is expected to increase over the next few weeks before subsiding during the second half of June. Even with the impressive gains experienced in April, streamflow projections are still expected to be less than 80% of normal. One benefit of the late melt is that it may be providing additional mid-layer moisture for these upper air lows ejecting out of the western U.S. and enhancing their precipitation output across the western Corn Belt.

If the snow can hold on until late June, there will only be a brief period of several weeks before the southwestern U.S. monsoon season kicks into gear (usually late July) and increases atmospheric relative humidity over the western High Plains. Last summer the monsoon season was a bust for western Nebraska due to low atmospheric moisture content over the central Rockies. With the snowpack still holding together, a more normal moisture pattern may develop for western Nebraska during July and August

A second factor that needs to be watched is the intensification and expansion of below normal temperatures across the eastern Equatorial Pacific. If this La Nina-like signal continues to build throughout the summer, the western Corn Belt typically would experience warm, dry conditions in late summer and through fall. This would increase concerns related to the drought and water supplies heading into the 2014 winter.

Al Dutcher
UNL State Climatologist