General Observations
This past week started out cool before heat, humidity, and wind built into the region late in the week through the first half of the weekend. A cold front associated with an upper air low situated over the southern Canadian Prairie region that was slowly migrating toward eastern Ontario bringing cooler air into the state on Sunday. This led to several rounds of thunderstorm activity, primarily concentrated across southern Nebraska.
Figure 1 indicates that below normal precipitation was received across the majority of the state from July 13-19, outside of portions of southwest, southcentral, and southeastern Nebraska. A complex of thunderstorms moved across the state during the evening of July 20th and will be incorporated into next week’s report.
Temperatures were slightly above average with most locations reporting normal to 2 F above normal for the week. South central and north central Nebraska were the exceptions with temperatures averaging up to 2 F below normal. Maximum and minimum temperatures July 16-17 were well above normal across the eastern ¾ of the state. High temperatures ranged from the mid 90’s to low 100’s, while low temperatures ranged from the upper 60’s to mid 70’s.
The lack of moisture during June and July has resulted in an expansion of dryness on the latest U.S. Drought Monitor depicted in Figure 3. Conditions reflected in this figure run through the morning of July 13th and do not take into account recent moisture across southern Nebraska.
Expansion of dryness by the Drought Monitor authors included the entire Panhandle into the extreme western Sandhills, along with expansion from northeast into east central Nebraska within the Missouri bluffs region. Further deterioration is likely on the Drought Monitor this week for the southern Panhandle as pasture conditions continue to decline.
Improvements were limited to a small area of central Nebraska, primarily along the Platte River. Further improvements are likely across southern Nebraska due to heavy moisture from July 18-21. Portions of south central and southeast Nebraska received 2-4 inches of moisture during this stretch, with over 6 inches recorded near Du Bois, Hardy, Hebron, and Falls City.
Crop Progress
According to the Nebraska Agricultural Statistics Service (NASS) state crop conditions declined again due to the lack of moisture across most areas north of I-80. Thankfully, extreme heat was limited to July 16-17 and was partially offset by dew points in the upper 60’s to mid 70’s. The most significant deterioration was for pastures, which corresponds to an expansion of dryness across the Panhandle on the U.S. Drought Monitor.
NASS reported that pastures in the very poor to poor category increased to 25%, a gain of 8 percentage points from last week. Only 42% of the crop was rated good and 3% excellent. Some improvements in condition ratings are expected next week due to recent rainfall across south central and southwest Nebraska that should give a small boost to state numbers.
Corn and soybean conditions also declined. Corn in good to excellent stood at66% as of July 19, a decline of 4 percentage points from the previous week. It is likely that dryness across western and northeastern Nebraska is beginning to impact dryland crops and dryland pivot corners. Soybeans declined 2 percentage points in the good to excellent category, dropping to 71 from73 percent.
Soil moisture ratings are reflecting the expanding dryness across western Nebraska. NASS indicated as of July 19 that top soil moisture was 15% very short and 33 percent short. This is an increase of 5 percentage points from last week. Subsoil moisture was rated 11% very short and 32% short, also an increase of 5 percentage points from last week.
Corn in the silk stage increased to 61% as of July 19, compared to 32% last year and the 5-year average of 58 percent. Soybeans in bloom were reported by NASS to be at 75%, compared to 41% last year, and the 5-year average of 61 percent. NASS estimates 31% of the soybean crop is setting pods, compared to 6% last year, and the 5-year average of 15 percent. With both crops in their critical reproductive stages, moisture going forward will be key to yields, especially areas short of subsoil moisture.
Outlook
The upper air pattern for the July 21-August 6 period features the movement of upper air lows into the Pacific Northwest, then shifting them eastward across the northern Rockies and eventually toward the western Great Lakes. In the meantime, high pressure aloft over the southeastern U.S. will be gradually shoved westward in response to the upper air lows deepening over the Great Lakes region.
The subsequent moving of the southeastern U.S. high pressure system toward the southern Plains and Rocky Mountain region will usher in a prolonged period of above normal temperatures for the southern and central Plains region. Nebraska will be on the northern periphery of this expanding ridge, with the southern ½ of the state most likely to experience above normal temperature.
Cool temperatures that are currently in place over the northern Plains will slide eastward through mid-week in response to high pressure building into the central Plains July 24-26. The GFS model indicates precipitation chances are best across western Nebraska July 21, northern Nebraska July 22, and extreme northeast Nebraska July 23. Dry weather is expected statewide July 24-26. Temperatures will gradually warm from the low 80s July 21 to low to upper 90’s July 25-26.
A piece of energy is projected to move along the upper air ridge July 27-28 according to the GFS model. This is projected to develop showers and thunderstorms from north central through southeast Nebraska on July 27 as energy moves southeast along the periphery of the ridge. The GFS keeps scattered thunderstorm chances in the forecast for July 28-29 for southeast and south central Nebraska, but activity is not projected to be widespread.
The GFS model then rebuilds high pressure across the southern Plains and builds it north and northwestward from July 30-August 6. As the ridge builds northward, the GFS model hints at a warm front lifting north on July 30, which generates rainfall statewide, before precipitation chance end of during the first half of July 31.
From July 31 through August 4, the GFS has high pressure centered over the central United States, completely shutting off moisture for Nebraska. The GFS then attempts to break down the ridge slightly August 5-6 by moving energy along its periphery. This in turn increases moisture chances statewide, but since they chances appear at the very end of the model run, confidence in regards to time and location is low. Temperatures from July 24-August 6 are forecasted to be primarily in the 90’s with occasional movement toward the century mark, particularly from August 2-4.
Al Dutcher at the Nebraska State Climate Office