Weather Update: Much Variance from Norms, but Good Soil Moisture

Weather Update: Much Variance from Norms, but Good Soil Moisture

Extension State Climatologist Al Dutcher gives his forecast for the coming week on the Sept. 19 Market Journal.

It has been a challenging growing season, to say the least.  Portions of Nebraska saw a late freeze during the middle of May, along with several hail and tornado outbreaks.  June brought record rainfall to northeastern Nebraska, only to flip to one of the top 10 driest July's on record.  Dry conditions continued through mid-August before wet conditions redeveloped with localized flooding reported across portions of eastern Nebraska.

To add insult to injury, frosts Sept. 13-14 damaged crops in the western half of the state.  Eastern Nebraska reported frost, but assessments so far suggest that damage was limited to areas susceptible to cold air drainage or fields that were replanted due to the hail events in mid-May through early June.

Whether crops will reach maturity prior to another freeze remains an open question, especially when the first half of September has seen average temperatures running 4-8°F below normal across the state.  Short-term models continue to hint at above normal temperatures to finish out the remainder of the month, but recent models are showing another surge of freezing temperatures in the northern US  during the first third of October.

In addition, last week's models pointed toward a warm, dry forecast for the last 10 days of September while more recent models point toward a wetter forecast.  Even with a cooler temperature forecast, it appears there will be enough warmth to bring most of Nebraska's non-replanted soybean and corn crop to maturity before the next freeze invades the state.  If freezing temperatures hold off until the second half of October, there is a strong probability that replanted acres that weren't freeze-damaged last week will make it to maturity.

The good news with recent active weather is that soil moisture reserves are at or above long-term trends for most locations across the state.  An examination of the High Plains Regional Climate Center's soil moisture monitoring network indicates that 39 of the 48 locations across the state are at or above the long-term available soil moisture average for mid-September.

The two driest locations are Beatrice and Smithfield with soil moisture readings suggesting a 2-3 inch deficit in available soil water compared to long-term averages for this time of year.  Sites in southwest Nebraska and the northeastern Sandhills are showing deficits of 0.50 to 1.50 inches below long-term averages for mid-September.

The largest available soil moisture reserves in comparison to normal are located north of a line from Kearney to Omaha, where surpluses are in the range of 2-4 inches. The remainder of the state — outside the dry areas previously listed — has available soil moisture values that are normal to 1.5 inches above normal.

For areas east of the Panhandle, available soil moisture supplies are greater now than they were in mid-April.  If we are fortunate enough to receive normal precipitation during the fall and spring recharge periods, soil profiles down to 5 feet will likely reach at least 80% of field capacity.  This would translate to at least 8 inches of available water in our heavier soils and 5 inches in our lighter soils going into spring planting of warm season crops.

Wet conditions in June and late August have improved 2015 irrigation allocations from Lake McConaughy water delivered by the Central Nebraska Public Power (CNPPID) irrigation canal system.  CNPPID board meeting minutes from September 2 indicate irrigation allocations will increase to 12 inches based on Sept. 1 storage levels.  Current Lake McConaughy lake levels are 12 feet higher than one year ago.  Currently the lake has 1.036 million acre-feet in storage, a 260,000 acre-foot increase from last year.

Upstream reservoirs on the northern branch of the Platte have also exhibited a dramatic rise in water levels from a year ago.  Seminoe, Pathfinder, and Glendo reservoirs currently have a combined storage of 1.037 million acre-feet, up 262,000 acre-feet from last year.  If the upper Platte basin receives normal snowfall this winter, it's likely that upstream reservoirs from Lake McConaughy will reach full pool prior to the onset of the 2015 irrigation season.

Al Dutcher
Extension State Climatologist

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