General Observations
It was another dry week across the state with above normal temperatures during the first half of the period. A strong cold front associated with an upper air low crossing the northern Plains brought frost and freeze conditions to the state October 2-4. Although there was measurable precipitation reported with the frontal passage, most locations outside of northeast Nebraska received nothing up to a tenth of an inch. Across northeast Nebraska, precipitation was reported in the 0.10-0.20 inch range, with 0.25-0.30 inches reported from Norfolk to Wayne.
Although temperatures have been consistently above normal the past two weeks, the unusually cold temperatures received Labor Day week overwhelmed these warm conditions across southern and eastern Nebraska (Figure 1). The intensity of above normal temperatures was limited by persistent high elevation smoke from western wildfires. It was not unusual to see the sun completely obscured the first and last two hours of daylight.
Precipitation was hard to come by during September, with the vast majority of it falling Labor Day week. Figure 2 shows that monthly departures from normal were greatest across northeast Nebraska, with departures close to normal across the southern Panhandle and portions of southeast Nebraska.
The cumulative impacts of the dry weather have led to a steady expansion of drought conditions during September. Figure 3 (conditions through September 29) indicates that only a small strip in southeast Nebraska is still considered within normal range. Moderate to Extreme drought covers the majority of the state, with abnormally dry conditions expanding into the Sandhill region at the end of September.
Crop Progress
Warm season crops continued their trend of reaching maturity ahead of last year and the 5-year average. According to the Nebraska Agricultural Statistics Service (NASS), 91% of the corn was mature, 11 percentage points ahead of the 5-year average. Ninety-seven percent of the soybeans were dropping leaves or were mature, 7 percentage points ahead of the 5-year average. Sorghum maturity reached 87%, which is 10 percentage points ahead of the 5-year average. This will be the final maturity information of the 2020 cropping season.
With crops essentially mature across the state, harvest activity proceeded with few interruptions. According to NASS, the soybean harvest saw the most significant increase in harvested acres of the 3 major warm season crops grown in the state. Soybeans harvested stood at 55% as of October 4, compared to 29% September 27th. The 5-year average for soybeans harvested is 25% and last year only 12% of the soybeans had been harvested at this point in the season.
Corn harvested stood at 21%, a gain of 7 percentage points from the previous week. The 5-year average for corn harvested is 15% and last year only 11% had been harvested at this point in time. The sorghum harvest stood at 17%, a gain of 10 percentage points from the previous week. Normally at this point in time 15% of the crop would be harvested using the 5-year average. Last year, only 3% of the crop had been harvested at this point in the season.
Winter wheat seeding was estimated by NASS to be at 80%, compared to 83% last year and the 5-year average of 82 percent. However, the dry conditions are inhibiting emergence as only 33% of the crop was up, compared to 56% last year and the 5-year average of 49 percent. Pasture conditions continue to reflect the impacts of drought conditions and NASS reports that 35% of the state has pasture ratings in the poor or very poor classification.
Finally, with the persistent dry conditions statewide for much of the past 60 days, topsoil and subsoil ratings continue to reflect soil moisture shortfalls. According to NASS, 67% of the topsoil across the state is rated short to very short. Although subsoil estimates are slightly better, they still indicate widespread dryness across the state. As of October 4, 60% of the subsoil across the state was rated short to very short.
Outlook
The Climate Prediction Center (CPC) released its October outlooks for temperature and precipitation September 30th which would indicate that drought conditions should be expected to continue and expand through the month if their forecasts verify. CPC’s temperature outlook calls for above normal temperatures across the western 2/3 of the United States as seen in Figure 4. Unfortunately, CPC indicates that a large are of below normal precipitation is likely, with the highest probabilities assigned to Nebraska and Iowa as seen in Figure 5.
The GFS model released the morning of October 6 indicates that the only precipitation event currently expected to impact Nebraska will occur October 11-13. High pressure is projected to dominate the central Plains through October 10, as a trough across the Pacific Northwest slowly makes its way into the central Rockies. This will push an upper air ridge into the central and eastern U.S., leading to widespread 80’s across Nebraska through October 9.
As the upper air trough approaches the central Rockies, a lead piece of energy will move across the northern Plains on October 10 bringing a slight cool down, with highs topping out in the 70’s. Temperatures are projected to warm slightly on October 11 as the upper air trough begins to move through the central Rockies. High temperatures should warm into the upper 70’s to low 80’s, with cloud cover thickening as the day progresses. Rain is forecast to develop during the overnight hours as the troughing pattern moves into the central Plains.
The GFS model is aggressive with precipitation statewide October 12-13 and has consistently pointed to this event over the previous 7 days of model runs. In fact, the GFS has become more aggressive with precipitation as the event draws closer. This may represent the most widespread statewide precipitation chances since the Labor Day week storm system. High temperatures will cool into the 50’s and 60’s, although eastern Nebraska may see a brief window for thunderstorm development before the cold air sweeps eastward.
As this trough moves toward the Great Lakes region October 14-15, cool air will remain in place across eastern Nebraska, with high temperature primarily confined to the mid to upper 60’s. High temperatures across western Nebraska will likely be 5-7 F warmer. High pressure is forecast to dominate the central Plains October 17-19, with widespread 70’s across eastern Nebraska and low to mid 80’s across the western 1/3 of the state.
The next potential storm system to impact Nebraska is forecast to move across the northern Plains October 20-21. The GFS model keeps the vast majority of moisture across the northern Plains, with only light shower activity projected for the eastern ¼ of the state. The GFS model does hint at hard freeze conditions developing across eastern Nebraska where a killing freeze has yet to occur. At this point in time, the GFS model doesn’t bring hard freeze conditions south of the I-80 corridor in eastern Nebraska.
Al Dutcher, Agricultural Extension Climatologist with the Nebraska State Climate Office