Weather Update
Air temperatures this past week started out below normal, but gradually increased to above normal conditions over the Holiday weekend. High temperatures June 28-30 ranged from the upper 70’s to middle 80’s statewide as an upper air trough over the Great Lakes region kept Nebraska in a northwesterly flow aloft. By July 1, the Great Lakes low began moving toward the east coast which allowed high pressure over the central Great Basin to build over the central High Plains.
By July 3, daily high temperatures across the western 1/3 of the state moved into the upper 90’s to low 100’s, while central and eastern Nebraska experienced high temperatures in the low 90’s. The heat continued July 4th, but a cold front began to enter northwestern Nebraska during the evening and hen slowly progressed through the state July 5-6. The cooler temperatures were appreciated, especially after June average temperature were above normal statewide (Figure 1). Average temperature anomalies were up to 4 F above normal across the southern 2/3 of the state and 4-8 F above normal over the northern 1/3 of Nebraska.
Even with the widespread moisture across southern and eastern Nebraska, coupled with cooler average temperatures this past week, soil moisture and pasture ratings continue to show that dryness is a concern across northeastern and western Nebraska according to Nebraska Agricultural Statistics Service (NASS). Even with a weekly pasture rating decline, crop ratings in the good to excellent category continue remain at 80% or higher for corn, soybean and sorghum.
Unfortunately, precipitation was spotty during the past week with the most of the concentrated precipitation falling across the southern tier of counties bordering Colorado and Kansas. Even this area had widely varying totals over short distances, but most locations received at least 0.25 inches of moisture June 28 – July 4 and exceeded 2.50 inches in the Beaver City and Potter areas. The cumulative impact of this scattered and not widespread precipitation events for the month of June can be see in Figure 2.
Normal weekly precipitation during the last 7 days of June ranges from 0.60 inches across the Panhandle to just over an inch across the eastern ¼ of the state. The lack of widespread moisture across the northern half of the state and the spotty nature of precipitation across southern Nebraska solidified the June precipitation trend of below normal moisture for most of the state (Figure 3). With corn and soybeans beginning, or closely approaching reproduction, below normal moisture coupled with above normal temperatures during July will lead to concerns crop stress will materialize from declining soil moisture reserves.
Crop Progress
The lack of widespread moisture across the northern half of the Nebraska this past week led to declines in topsoil, subsoil, and pasture condition ratings in the latest Nebraska Agricultural Statistic Service (NASS) crop progress report issued July 6th on conditions through July 4th. Ratings declines were likely most substantial across central, north central, and south central Nebraska based upon precipitation totals last week.
Pockets of short term dryness (< 90 days) exist across the central Panhandle region, the eastern Sandhill region and the immediate Fairbury area. Long term precipitation deficits (> 6 months) are occurring in the same general areas, along with areas north of the Niobrara river valley along the South Dakota border. If below normal moisture continues during July, these general regions and areas in close proximity, will likely experience crop moisture stress. The amount of stress will be dependent on whether maximum temperatures consistent breach 95 F and minimum temperatures remain above 70 F.
Topsoil moisture conditions declined last week after improvements the previous week. NASS indicates that as of July 4 topsoil conditions were rated 6% very short, 36% short, 56% adequate and 2% surplus. There was a 2 percentage point increase in the very short rating and a 11 percentage point increase in the short rating. These increases came at the expense of the adequate and surplus ratings which declined 9 and 2 percentage points, respectively.
Subsoil moisture conditions also declined according to NASS, but the most significant change was the decline in the adequate rating by 8 percentage points. Subsoil conditions ratings increased 2 percentage points in the very short category and 4 percentage points in the short category. Surplus moisture ratings remained unchanged. As of July 4, NASS reports topsoil moisture was 8% very short, 38% short, 53% adequate and 1% surplus.
Pasture ratings dropped ever so slightly from last week according to NASS. As of July 4, 4% of the crop is rated very poor, 10% poor, 57% fair, 25% good and 4% excellent. The very poor category remained unchanged from last week, while the poor and fair categories increased 1 and 2 percentage points, respectively. The increase in the lower ratings came at the expense of the good category, which declined 3 percentage points from last week. The surplus category remained unchanged from last week.
Corn, soybean, and corn ratings continue to be strong as of July 4 according to NASS, although good to excellent categories for soybeans and sorghum ratings slipped 3 percentage points from the previous week. As of July 4, corn and soybeans are rated 80% good to excellent, while sorghum is slightly better at 83 percent. Corn good to excellent ratings were unchanged from the previous week, while soybeans and sorghum dropped 3 percentage points.
Both corn and soybeans are now entering their reproductive stages according to NASS. NASS indicates that corn silking stood at 2% as of July 4, compared to 4% last year and 9% for the 5-year average. Soybeans in bloom reached 46%, compared to 39% last year and the 5-year average of 27 percent. NASS indicates that soybeans setting pods was 2%, behind last year’s pace of 4%, but ahead of the 5-year average of one percent.
The winter wheat harvest is in full swing across south central and southwest Nebraska, while just beginning across the Panhandle. As of July 4, NASS indicates 7% of the winter wheat had been harvested, compared to 14% last year and the 5-year average of 16 percent. The condition of the wheat crop declined slightly due in part to above normal temperatures and below normal moisture across a majority of the Nebraska Panhandle.
As of July 4, 3% of the winter wheat crop was rated very poor, 8% poor, 31% fair, 50% good and 9% excellent. The fair category increased 7 percentage points from the previous week, mostly due to a 2 percentage point decline in the good category and a 4 percentage point decline in the excellent category.
Weather Outlook
The GFS model issued the morning of July 7th indicates that the best opportunities for moisture through July 23 (end of the model forecast period) will occur across eastern Nebraska during the first week of the model run, but it also indicates significantly conditions over the western half of the state. From July 7-13, upper air ridging will be in control from the Rockies westward, while an upper air trough impacts the central and eastern corn belt.
The GFS indicates that a trough will cross the northern Rockies July 8-9, eventually deepening as it approaches the northern Plains. As this trough deepens, a surface cold front will dive southeastward toward Nebraska and initiate strong thunderstorm development. The GFS model indicates that convection will develop across north central and northeast Nebraska the afternoon of July 9 and clear the state by July 10th. Precipitation of 0.50-1.50 inches is forecast east of a line from Valentine through Red Cloud, with the heaviest totals forecast to fall across northeast Nebraska.
As the upper air trough reaches the western Great Lakes, the GFS stalls the troughs eastward movement and forms a semi-cutoff upper air low. Eastern Nebraska will lie on the backside of this trough and the GFS model indicates that weak waves will move through the state on a daily basis from July 12-15. Isolated to scattered thunderstorms will be possible, but widespread coverage on any given day should be small.
Unfortunately, the GFS model is not depicting widespread moisture for the western half of the state during this period as it will lie on the front edge of the western U.S. upper air ridge. Therefore, isolated thunderstorms are possible, but significant widespread moisture does not appear likely. High temperatures will be primarily in the middle 80’s to low 90’s east and upper 80’s to upper 90’s west.
There is high chance that exceptionally warm conditions will develop across the central Plains July 16-23 as the western upper air ridge shifts eastward. In fact, the GFS model does forecast thickness levels that would coincide with 100 F plus high temperatures for the western half of the state, with mid to upper 90’s across eastern Nebraska. Relative humidity levels will be elevated during this period, especially across eastern Nebraska.
What is even more concerning is that the GFS model does not currently show a significant breakdown of this hot pattern at the end of its 16-day model run. It does show a trough entering the Pacific Northwest, but wants to slow down its eastern progress. If this occurs, the heat currently depicted by the GFS would last at least several days longer. Pastures and soil moisture would be expected to see further deterioration over the next two weeks, while warm season crop ratings will likely shrink from their current lofty levels.
Al Dutcher, Agricultural Extension Climatologist, Nebraska State Climate Office