Weather Review
Above normal temperatures dominated this past week and high temperatures warmed back into the upper 90’s to low 100’s. The upper air ridge across the southern Plains built north and east as the week progressed. An upper air trough crossing the northern Plains brought cooler weather to state as the weekend progressed. Unfortunately, widespread precipitation failed to materialize and crop conditions declined for another week as hot temperatures and the lack of adequate soil moisture reserves continued to stress crops and pastures.
By Saturday evening the cold front had reached central Nebraska, but it took another 24 hours for it to clear the areas south of I-80 and east of U.S. Highway 81. This sharp cool down helped reduced average temperature anomalies during the past week across western Nebraska according to Figure 1. A large area of east central and southeast Nebraska was 6-8 F above normal, as well as a small pocket around the McCook area. In general, the western half of the state reported average temperature anomalies 2-6 F above normal compared to 2-8 F above normal across eastern Nebraska. The one exception was the north central through south central Sandhill region, where average temperature anomalies ranged from normal to 2 F above normal.
The daily maximum temperature extremes for airport location provided by the National Weather Service are as follows: 7/1 (103 F: Chadron, Scottsbluff), 7/2 (109 F: Valentine), 7/3 (98 F: McCook, Norfolk, Tekamah), 7/4 (105 F: Chadron), 7/5 (109 F: Chadron), 7/6 (103 F: McCook), 7/7 (100 F: Falls City).
According to published precipitation reports from NERain observers, there was at least one location that reported measurable moisture every day last week. Most of the NERain observers reported less than 0.20 inches of moisture in any individual event and higher totals were limited to less than 3 counties in most instances. The cumulative precipitation received August 2-8 is depicted in Figure 2 and these small precipitation pockets are readily apparent. More importantly, Figure 3 indicates that the only area of the state to receive above normal moisture was around Valentine, Nebraska.
The daily maximum precipitation values reported from NERain observers are as follows: 7/1 (1.20 inches: Harrison 6.4 W), 7/2 (0.60 inches: Bloomfield 0.1 ENE), 7/3 (0.46 inches: Osceola 7.1 W), 7/4 (0.32 inches: Hardy 4.3 E), 7/5 (0.92 inches: Valentine 0.4 E), 7/6 (2.00 inches: Gordon 5.3 E), 7/7 (1.17 inches: Clay Center2.8 W).
Crop Progress
The latest U.S. Drought Monitor (Figure 4) represents conditions through 7 am August 2th, so most of the impacts from last week’s heat and dry conditions will not be reflected until this week’s edition is released August 10h. Although normal conditions are still depicted for the southeastern ¼ of the state, recent visual observations reported to the Nebraska State Climate Office suggest that corn and soybeans are exhibiting moisture stress. Therefore, most of this area is expected to be upgraded to abnormally dry conditions this week, with further deterioration probable over the next two weeks based upon the most current weather forecast.
<>Extreme drought (D3) is currently depicted for the southwest corner of the state, the southern Panhandle border region, extreme northeast Nebraska and parts of the eastern Niobrara river valley. A small pocket of exceptional drought (D4) covers southeastern Chase county, northwest Hayes county and southwest Lincoln county. This past week brought multiple days of high temperatures exceeding 100 F and below normal moisture across western Nebraska. These conditions are expected to lead further expansion of D3 and D4 across the southwest and west central Nebraska, as well as the southern Panhandle.Warm season crops continue to deteriorate on a statewide basis according to the Nebraska Agricultural Statistics Service (NASS) crop progress report issued August 8th based upon survey data through August 7th. Corn, soybeans and sorghum have exhibited a steady drop in crop condition ratings since early July. NASS data indicates that warm season crops rated good to excellent have dropped from the 70 percent range into the 50-55 percent range for corn and soybeans, while sorghum has dropped below 40 percent.
The sorghum crop has the lowest overall crop rating of the warm season crops grown in Nebraska according to NASS. As of August 7th, the sorghum crop is rated 10% very poor, 29% poor, 36% fair, 20% good and 5% excellent. Compared to conditions on July 31st, sorghum rated good to excellent dropped 11 percentage points. Only 4% of the grain heads are showing color, compared to 8% last year and the 5-year average of 7 percent.
The state corn crop also deteriorated according to NASS and as of August 7th was rated 11% very poor, 12% poor, 27% fair, 40% good and 10% excellent. Corn rated good to excellent dropped 4 percentage points from the previous week. In a normal year, corn rated good to excellent at the beginning of August is between 60 and 70 percent. NASS reports that 45% of the crop was in the dough stage compared to 60% last year and the 5-year average of 52 percent.
The state soybean crop continued to deteriorate and NASS rates the crops current condition as 7% very poor, 11% poor, 28% fair, 44% good and 10% excellent. For comparison, conditions on July 31st were rated 54% good to excellent, so soybeans dropped another 4 percentage points last week. NASS reports that 66% of the crop was setting pods compared to 81% last year and the 5-year average of 71 percent. Although soybeans are setting pods, weather forecasts through the end of August would suggest that below normal moisture and above normal temperature will have a detrimental impact on pod fill.
Topsoil and subsoil moisture estimates from NASS deteriorated slightly during the past week, with most of the changes occurring in the adequate and short categories. As of August 7th, topsoil moisture was rated 32% very short, 42% short, 26% adequate and 0% surplus. There was a 4 percentage point decline in the adequate category and a 3 percentage point increase in the short category. Subsoil moisture was rated 30% very short, 41% short, 29% adequate and 0% surplus. There was a 3 percentage point decline in the adequate category, which was offset by 2 percentage point increase in the short category.
Finally, the conditions of pastures and rangeland on August 7th according to NASS was 33% very poor, 28% poor, 30% fair, 9% good and 0% excellent. There was a 1 percentage point expansion for pastures/rangeland rated very poor and no change in the poor category. However, the fair category increased 5 percentage points while the good and excellent categories both decreased 2 percentage points.
Weather Outlook
There would be no greater satisfaction than to say the current short term weather outlook offers significant drought relief. Unfortunately, that doesn’t appear to be in the cards according to the latest GFS weather model issued the morning of August 8th. Heat is projected to return to the central Plains with few precipitation opportunities, which supports further warm season crop deterioration over the next two weeks.
After cooler weather statewide Sunday and yesterday, the upper air ridge that has brought above normal temperatures and below normal moisture to most of the central and southern High Plains is forecast to dominate Nebraska’s weather through August 15th. Currently the GFS model does indicate that this ridge will break down August 16-20 in response to a trough moving across the northern Plains and deepening over the Great Lakes. This will allow a cooler Canadian air mass filter southward before the upper air ridge begins to build back into the region August 21-25 (end of model forecast period).
Maximum temperatures are forecast to warm from the middle 80’s northeast to low 90’s southwest today, then warm into the low 90’s east to upper 90’s west tomorrow. The GFS model indicates that these high temperatures should continue through August 15th and a few 100 F high temperatures may materialize across the western 1/3 of the state this Friday and Saturday. No precipitation is depicted on the GFS model through August 13th.
An upper air trough is forecast to move from the Pacific Northwest to the Great Lakes August 14-18. As this trough moves across the northern Plains August, the GFS model hints that it will interact with monsoonal moisture moving northward through the southern half of the Rocky Mountains. Therefore, isolated to scattered thunderstorms are possible across the Panhandle during the late afternoon and overnight hours of August 14th through the 16th. The most widespread coverage is indicated from the evening of the 16th through the morning of the 17th and total moisture appears to be less than 0.50 inches. Some of this moisture may make it to eastern Nebraska, but currently the GFS model indicates that less than 0.25 inches of moisture is likely.
The GFS model indicates that the upper air trough will strengthen over the Great Lakes August 18-20, which will move cooler air from southern Canada into Nebraska. Daily high temperatures are forecast to cool into the 80’s during the period. Unfortunately, the GFS model lacks any precipitation signal for Nebraska during this cool down. High temperatures appear likely to return to the 90’s August 21-25 as the Great Lakes upper air trough weakens and the western U.S. upper air ridge expands eastward under mostly dry conditions.
Al Dutcher, Agricultural Extension Climatologist, Nebraska State Climate Office