June 25, 2010

The seemingly endless stream of storms rolling across the central U.S. in June has led to some impressive precipitation totals in Nebraska. Rainfall reports from volunteer observers indicate that a broad area of central and eastern Nebraska received 8 inches of moisture, with an area extending from Broken Bow southeast through Omaha receiving 9.5 to 12 inches (Figure 1). A couple isolated locations reported rainfall over 15 inches.

An analysis of June moisture levels through the 23rd showed no reporting site with below normal precipitation. Surpluses of 3-5 inches are common over the eastern two-thirds of the state, with the hardest hit areas indicating surpluses of 8-12 inches (Figure 2). I fully expect that many of these locations will show June 2010 precipitation totals that exceed the records set in June 1993.

Wet or Dry for July?

The question going forward is whether the moisture continues unabated or a drier weather becomes established as we head into July. Current weather models indicate a return to drier weather as we enter the week, but by late week things become more uncertain as an upper air trough is projected to slide across the northern Plains.

The latest models indicate that this trough could sink far enough south to bring a return to heavy thunderstorm activity, especially over northern Nebraska; however, the models have been oscillating between keeping the moisture across the Dakotas or shifting it further south across Nebraska and Kansas. A shift south would certainly create additional concerns as river basins will likely still have above normal flows and soils will not have dried out sufficiently to absorb intense rainfall.

Potential for Shallow Corn Root Syndrome

If a drier trend does develop, irrigators may need to closely monitor their growing corn crop. It is not clear how well roots have developed with all of the June moisture that fell on soils that were already near or at field capacity. Poor rooting structure (shallow root syndrome) concerns are being raised in portions of Iowa, Illinois, Indiana, and Ohio. There have been isolated reports of corn plants falling over because their anchor roots were in saturated soil and hadn't gone deep enough to support the plant.

It is possible that the same conditions may develop in Nebraska, but so far I haven't been aware of any reported instances. If roots have not developed deep into the soil profile, stress will likely occur with a couple of weeks of dry weather. Periodic field scouting should be conducted to monitor plant health so that irrigators can keep ahead of crop water demands, instead of trying to play catch-up during the mid-July through August period. For dryland producers, the crop will be at the mercy of Mother Nature.

Reservoirs Filling

On a positive note, the abundance of late season snows and heavy spring moisture have resulted in full pools for all Wyoming Platte River reservoirs. In fact, there is currently 200,000 acre feet of water being stored in their flood pools to mitigate flooding upstream from Lake McConaughy.

Lake McConaughy had 1.45 million acre feet in storage as of June 24, nearly 500,000 acre feet more than at this time last year. Inflows have been running close to 5,000 cubic feet per second, about five times the normal flow for this time of year. The latest projections indicate that high flows will likely continue well into July, with an outside chance that it will reach capacity before the end of this summer. Even if it doesn't fill completely, it is likely to reach at least 90% of capacity, barring the development of an intense drought.

Climate Prediction Center Forecast

The latest Climate Predication Center forecast would suggest there will be additional inflows into McConaughy. The two-week lead forecast for July indicates above normal moisture in the eastern two-thirds of the state, coupled with below normal temperatures. CPC currently anticipates that June conditions will continue during July, although recent temperature trends would suggest that their forecast is too cool.

Much of the area south and southeast of Nebraska has been experiencing a prolonged period of temperatures in the 90s to low 100s coupled with high dew point temperatures. We have been on the northern fringe of this region and shared the oppressive heat several times in the past 10 days.

With the abundance of June rainfall and full to saturated soil profiles, evaporation and plant transpiration will be adding additional moisture to the lower atmosphere, increasing the risk for heat stress for livestock producers. An absence of wind could easily produce a scenario similar to last June when temperatures soared into the 90s and, coupled with dew points in the low 70s, produced consecutive days of heat indices in the 105°F to 120°F range.

Al Dutcher
Nebraska Agricultural Meteorologist