General Observations
Dry conditions engulfed the state this past week, with the only measureable rainfall confined to northeast Nebraska where totals were less than a tenth of an inch. Average temperature departures shown in Figure 1 indicate that cooler than normal conditions were confined to the southeastern 1/3 of the state. Well above normal temperatures were reported across the western 1/3 of Nebraska.
Once again, an upper air low traversing the northern Plains late last week strengthened as it moved toward the western Great Lakes region. The pulled cooler than normal air southward into eastern sections of the state. In addition to the cool air, wildfire smoke from the western U.S. intensified the cool trend by creating hazy skies which limited solar radiation making it to the surface. At the same time, the western U.S. upper air high pressure system expanded eastward resulting in widespread high temperatures ranging from the mid 80’s to low 90’s.
This past week of dry conditions and above normal temperatures could possibly result in small increases in drought intensity, particularly across Dundy and Kimball counties. However, the full impact of the Labor Day week rainfall event has now been incorporated into the most recent U.S. Drought Monitor depiction seen in Figure 2. All improvements were limited to southeast and east central Nebraska where widespread 1-4 inch totals were reported. At the same time, there was some slight expansion of dryness across the western and eastern edges of the Sandhill region.
Crop Progress
The lack of rainfall this past week allowed producers to begin early harvest activity across the state. However, soil moisture estimates continue to support widespread drought conditions across western, central, and northeast Nebraska. The NASS weekly progress result of conditions through September 20th (indicates that 45% of the topsoil is rated short to very short, down from 73% from the September 6th release. Subsoil moisture levels improved to 53% short to very short compared to 67% last week. Subsoil improvements were most likely associated with areas receiving over one inch of moisture with last week’s storm system.
NASS indicates that corn in the good to excellent condition category improved 2 points from last week to 64%. Soybeans showed a similar improvement of 2 percentage points to 66% good to excellent. Sorghum good to excellent ratings dropped 5 points to 66% largely due to a lack of moisture during late grain fill.
Crop maturity continues to advance ahead of the 5-year normal. Corn in the dent stage stood at 97% as of September 20, compared to 88% last year, and the 5-year average of 94 percent. Corn maturity was at 65%, compared to 32% last year and the 5-year average of 47%. Ten percent of the crop was harvested compare 2% last year and the 5-year average of 4 percent.
Soybeans dropping leaves stood at 82%, compared to 46% last year and the 5-year average of 62 percent. Soybeans harvested were 10% compared to 4% last year Sorghum turning color stood at 93%, compared to 90% last year and the 5-year average of 94%. Sorghum reaching the mature stage stood at 40%, compared to 17% last year and the 5-year average of 36 percent. Only 2 percent of the crop was harvested.
The lack of moisture in early September delayed wheat planting initially, but recent activity after the Labor Day week precipitation event has brought planting percentages in line with historical trends. NASS reports that wheat planting stood at 40%, compared to 42% last year and the 5-year average of 43%. Wheat emergence is estimated to be 4%, which is slightly behind the 5-year average of 7 percent.
NASS reports that pastures showed little change from their impressive gains last week. Pastures in the good to excellent category decreased one point to 40 percent. Pasture ratings for the poor to very poor categories also dropped one point to 33 percent. Even if beneficial moisture is received through the fall period, pasture regrowth will be minimal to non-existent due to how late it is in the growing season. The moisture would help ease concerns in regards to next Spring’s forage growth.
Outlook
The most current model run of the GFS model used for this forecast was issued the morning of September 22 and continues to indicate that the central Plains will be dominated by drier than normal conditions. Therefore, the forecast from September 22 – October 8 offers excellent harvest weather prospects while soil moisture recharge for the 2021 crop season should be virtually non-existent.
The upper air pattern from September 22-28 features the movement of an upper air trough located across the Pacific Norwest into the western Great Lakes region. In advance of the trough moving across the northern Plains, dry conditions and widespread high temperatures in the 80’s is likely through September 25, with occasional 90 plus high temperatures across western 1/3 of the state.
As the upper air low moves across the northern Plains September 26-27, slightly cooler air will filter southward into Nebraska. High temperatures are projected to drop 5-7 F, before temporarily warming back into the 80’s September 28. The GFS hints that a few light showers would be possible across north central and northeast Nebraska September 27 and total moisture is projected to be less than 0.10 inches.
A secondary push of cold air is indicated by the GFS model September 29, as the upper air low deepens over the Great Lakes. Well below normal temperatures are projected by the GFS to invade the central and eastern corn belt. High temperatures across eastern Nebraska may struggle to reach the upper 60’s, with frost conditions possible the morning of September 30. Currently the GFS advertises that areas north and east of a line from central Iowa through central Ohio have the best odds for these conditions to develop.
From September 29 – October 7, the GFS model builds the western U.S. upper air ridge into the central Plains. Dry conditions are projected with a gradual warming trend. High temperatures will warm from the 60’s across eastern Nebraska on September 29 to the middle 80’s by October 5. Western Nebraska will be closer to the center of the upper air ridge and should be consistently 5-7 F warmer than eastern Nebraska.
The GFS model indicates that the upper air ridge will break down October 5-7 as an upper air trough entering the Pacific Northwest begins to move toward the northern Rocky Mountains. Significantly colder air is advertised to begin moving towards the central Plains, but moisture appears to be confined to the northern Rockies and northern High Plains. High temperatures across Nebraska would drop into the 50’s if the forecast verifies, with frost/freeze conditions possible by October 10.
Dryness is expected to persist through the month of October, along with above normal temperatures across Nebraska. Figure 3 shows that the entirety of the continental U.S. should experience above normal temperatures according to the Climate Prediction Center. (CPC). The greatest odds for above normal temperatures have been assigned to the southern High Plains and southern Colorado Rockies region. CPC indicates precipitation will be below normal across the southern and central High Plains region, with Nebraska lying on the northern periphery according to Figure 4. If this forecast verifies, grain harvest should be virtually complete before significant inclement weather moves into the central United States.
Al Dutcher, Agricultural Extension Climatologist with the Nebraska State Climate Office