By Tyler Williams

Like every year in Nebraska, we are concerned about late-summer weather. It just so happens the weather in Nebraska tends to make this time of the year stressful for crops and producers. Many of the crops we grow depend on moderate temperatures and adequate moisture during reproduction to optimize yield potential.

Summer climate impacts
We are challenged every year because the most critical crop stages occur during the most challenging climatological period. The last couple weeks of July and start of August contain our climatological warmest day of the year, and July and August are usually the two warmest months.

Over the last 10 years, Scottsbluff, Holdrege and Columbus have averaged 19, 11 and 11 days, respectively, during the month of July where the maximum temperature was greater than 90 degrees F. In August, the average number of days decreases to 16, eight and eight days over 90 degrees, respectively. These high temperatures are less than ideal, as they fall directly during crop reproduction. Heat stress (often coinciding with moisture stress) during this critical stage may speed up the reproduction period or increase nighttime respiration, if warm temperatures continue at night. Is there any way to avoid this overlap in critical growth stages and high risk of stress?

If we look at precipitation, the wettest month of the year is May for south-central and southeast Nebraska, and June for the rest of the state. This often coincides with planting, which we know wet fields do not provide the best planting conditions. Even though we still get significant moisture during July and August, in most years we wish we still had some of that spring moisture later in the summer. Is there a way we can reduce the impact of too much moisture in the spring and too little moisture in the summer?

There may not be many options for management changes to alter the timing of crop development and the risk of weather impacts due to our growing season window (and potentially many other reasons). We have very little confidence in the variability in our growing season window, due to highly variable freeze dates on the front and back end of our growing season. Even though we have seen some changes in growing season length (especially in western Nebraska), the risk of potential variability from year to year does not allow us to confidently make significant planting date or variety changes; however, adding wheat or changing maturity class may help spread out the risk. No matter what, the growing season weather demands our attention and analyzing the trends and data may help us limit the in-season impacts.

Watching climate trends
The trends in conditions in Nebraska during the summer have been fairly steady over the last 30 years.  There is an increasing trend in spring temperature for most of the state, especially during the early-spring months, but that trend seems to stall out during the summer. We have generally been seeing a slight increase in summer maximum and minimum (nighttime) temperatures, but it is small. Even with this small trend, as mentioned in the previous paragraph, we will continue to get heat events causing stress, since it is our warmest time of the year.

Precipitation trends are steady to slightly decreasing during the summer, which is the opposite trend from the spring. Spring precipitation has been increasing across the state, with the largest increases coming in April. This decrease (or lack of increase) during the summer could increase moisture stress during the point in the season when evapotranspiration (ET) values are the highest. This makes it increasingly important to conserve soil moisture and reduce soil temperatures during the summer. There are multiple options to conserve moisture; however, no-till may be the best (if you have well-drained fields) if you want to minimize the impact of heavy rain in the spring, but reduce evaporation and soil temperatures during the summer.

Looking ahead
The outlooks for the upcoming months are trending toward warmer-than-normal conditions for most of the U.S., including Nebraska; however, the lowest probabilities of this occurring are in the Central Plains. For precipitation, there are increased odds for above-normal precipitation for portions of the Northern Plains; however, our precipitation patterns this time of the year are highly dependent on storm tracks and those are nearly impossible to predict.

The longer-term outlooks rely heavily on the ENSO (El Niño and La Niña) pattern, which is pointing toward neutral conditions to continue through winter 2018. This decreases the skill in the predication, and the forecasters often resort to recent trends for any expected deviation from normal. We have seen a fairly significant warming trend in recent winters, so the initial expectation is for that to continue.

Williams is a Nebraska Extension educator in Lancaster County.