Thunderstorm activity during the last week produced significant moisture across portions of eastern Nebraska. According to Figure 1, an area extending from just north of Fairbury northeastward through northwestern Lancaster county, then eastward toward the Iowa border received at least 3 inches of moisture. A small area encompassing the Mead to Fremont area exceeded 4 inches. On the flip side, less than 0.50 inches of moisture was received across the northwestern Panhandle, west central sections of the southwestern agricultural district, central Niobrara river valley and the Central City to Aurora area.
During this past week, there was precipitation reported somewhere in the state every day between August 30th and September 5th according to the NERain observation network. The most robust and broad based precipitation event during this period occurred the evening of August 30th through the morning of August 31st east of a line from Valentine to Hebron. Within this region, over one inch of moisture fell north of a line from O’Neill to Columbus to Brownfield. Additionally, over 3 inches of precipitation was reported in a 30 mile wide area extending from Pierce to Nebraska City.
Individual daily maximum precipitation totals from the NERain observation network are as follows: August 30 (Riverton 6 N – 1.50), August 31 (Pierce 3 NNE – 4.85), September 1 (Western 4.5 NNE and Wilbur 7 WSW – 1.41), September 2 (Valentine 12 ENE – 2.45), September 3 (Friend 5 SSE – 4.26), September 4 (Potter 10 NNE – 0.66), September 5 (Elba 2.5 W – 1.29).
Two week moisture anomalies (Figure 2) indicate that the western half of the Panhandle, the southwest corner of the state and the Grand Island-Kearney-Hastings area have received below normal moisture. However, the remainder of the state has received above normal moisture that should help fill grain where crops haven’t reached maturity. Surplus moisture in excess of 3 inches during the past 14 days has fallen in pockets of north central and northeast Nebraska, as well as a large area north of a line from Broken Bow to Omaha.
During this same period, average temperatures were above normal (Figure 3) as Nebraska was positioned south of the upper air troughs that moved across the northern Plains. Any cold front that moved through the state only brought 1-2 days of relief from maximum temperatures reaching the upper 80’s to upper 90’s during this two week stretch. Average temperature anomalies ranged from 2 to 6 F above normal the past 14 days, with 4-6 F anomalies common across southwest, south central, central and east central Nebraska.
As the harvest season rapid approaches, the Climate Prediction Center (CPC) issued the final September national temperature and precipitation outlooks August 31st. Figure 4 (temperature) and Figure 5 (precipitation) replace CPC’s preliminary September outlooks issued August 19th. When the September preliminary and final outlooks are compared, CPC reduced the area of above normal temperatures and below normal moisture across the western United States. CPC has also eliminated the above normal temperature outlook for the northern Plains and Great Lakes region.
In regards to precipitation, CPC added an area of above normal moisture activity in New Mexico, eastern Arizona and southern Colorado in their final September precipitation outlook. All of these adjustments paint a more positive outlook for Nebraska in regards to building soil moisture supplies for the 2022 cropping season by eliminating warmth and dryness across the northern Plains east of the Continental Divide and increasing the probability that September temperatures and precipitation will be closer to normal across the northern half of the High Plains region.
Precipitation activity across the state during the past week helped improve topsoil moisture conditions, but subsoil moisture rating improvements were very limited due to the lingering impacts of drought conditions across the northwestern ½ of the state. Most locations statewide have received above normal moisture during the past two weeks, but crop water demands this late in the growing season are still high enough to offset some of the surplus moisture anomalies.
Nebraska Agricultural Statistics Service (NASS) indicates that for the week ending September 5th, topsoil moisture supplies were rated 7% very short, 25% short, 66% adequate and 2% surplus. In one week, the very short category improved 4 percentage points and the short category improved 11 percentage points. This led to a gain of 15 percentage points in the adequate category. Subsoil moisture supplies on the 5th were rated 14% very short, 40% short, 46% adequate and 0% surplus. The very short category improved 3 percentage points and the short category improved 2 percentage points, while the adequate category improved 5 percentage points.
Pasture rating changes this week offer a mixed bag with improvements across eastern Nebraska and declines across parts of the Panhandle and southwest. NASS reports that as of September 5th 14% of the pastures were rated very poor, 18% poor, 40% fair, 23% good and 5% excellent. The very short and short categories increased 2 percentage points over the August 29th report, while the fair category declined 12 percentage points. Not all of the fair category declines moved into the poor and very poor categories, as the good category increased 5 percentage points and the surplus category gained 3 percentage points.
Crop ratings for corn and soybeans declined this week, while sorghum improved slightly. NASS reports that corn in good to excellent conditions stood at 64%, a decline of 3 percentage points from the August 29th report. Soybean ratings this week are 67% good to excellent, which is a decline of 2 percentage points from last week’s crop report. Sorghum in good to excellent condition is 51%, which is an increase of 3 percentage points from last week’s crop report and likely due to localized heavy precipitation across the eastern half of the southwestern agricultural district.
With the calendar moving into September, warm season crops are reaching maturity and combine activity will likely commence on early corn this week. NASS reports that 18% of the corn crop is mature, compared to 25% last year and the 5-year average of 14 percent. Seventy-eight percent of the crop was in the dent stage, compared to 83% last year and the 5-year average of 75 percent.
NASS reports that soybeans are closing in on maturity and 20% of the crop is now dropping leaves, which compares to 34% last year and the 5-year average of 18 percent. Sorghum still has several weeks to go before widespread harvest activity commences. As of September 5, 6% of the crop had reached maturity, compared to 11% last year and the 5-year average of 9 percent.
The latest GFS model run released the morning of September 8 hints at limited opportunities for moisture over the next two weeks and that they will occur in conjunction with the passage of upper air troughs moving from the Pacific Northwest toward the western Great Lakes region. At present, the GFS model forecast suggests that upper air trough passages will occur September 13-14, 19-21 and 23-24.
Since high pressure aloft is forecast to dominate the southwestern ¼ of the United States eastward through the southern High Plains, the return of low level Gulf of Mexico moisture will be limited ahead of approaching cold fronts. During the September 8-24 period, the trough passage September 23-24 appears to have the most potential to deliver moisture across the entire state. The precipitation currently projected for the September 13-14 currently indicates that the southwest and northeast corners of the state have the highest probabilities to receive measureable moisture. The September 19-21 precipitation chances are currently most favored for the southeast eastern corner of the state.
With the lack of widespread precipitation events predicted by the GFS model over the next two weeks, there should be extended periods of favorable harvest weather. Although maximum temperatures this time of the year can breach 90 F, the amount of hours in any given day above this threshold is considerable smaller than in August due to the declining hours of daylight available to heat the atmosphere at the surface.
From the GFS model standpoint, it appears that jet stream forecast over the next two weeks will produce periods of summer and fall like temperatures as upper air troughs move across the northern third of the United States. The GFS model forecast indicates that high temperatures will breach the 90 F across the Panhandle on September 9, with low 80’s across extreme eastern Nebraska. A trough moving across the northern Plains will cool temperatures slightly on the 10th, cooling highs into the 80’s statewide, then warming into the middle 80’s north to low 90’s south on the 11th.
As the upper air trough moves toward the Great Lakes, high temperatures are forecast to range from the low 80’s northeast to upper 80’s south September 12-13. Another upper air trough crossing the northern Plains on September 14 will drive a sharp cold front through the state bringing fall-like temperatures to the central High Plains. High temperatures are forecast to range from the middle 60’s across northeast Nebraskan’s to the upper 70’s along the southern border.
From September 14th through the 19th, high pressure aloft will allow for above normal temperatures to build across the southern and central High Plains region. High temperatures on September 14th will range from the low 70’s northeast to the upper 80’s across the northwestern Panhandle. High temperatures will move into the low to middle 80’s east and into the upper 80’s to low 90’s west.
On September 20th the GFS model indicates that an upper air trough approaching the northern Plains will begin to impact high temperatures and much cooler weather will build into the central Plains through September 24th. On September 20th, the GFS forecast is for high temperatures ranges from the upper 70’s north to the upper 80’s south, then cooling into the low to middle 60’s north to upper 70’s south September 21-24.
Al Dutcher, Agricultural Extension Climatologist, Nebraska State Climate Office