Weather Update
Hot conditions dominated the Panhandle during the past week as the upper air ridge responsible for the heat slowly built into eastern Nebraska. Overcast skies across southeast and east central Nebraska kept high temperatures below 90 F on Saturday, but as the clouds decreased on Sunday, high temperatures moved into the low to middle 90’s. The northern Panhandle and northwestern Sandhill region had isolated pockets of 100 – 105 F high temperatures on Sunday.
Figure 1 shows the temperature anomalies across the United States for July 19-25. Below normal temperatures covered the southwest, the southern High Plains, the southeast and the northeast. Above normal temperatures were confined to the west coast, the northern High Plains and the northern half of the Rocky Mountain region. Average temperatures were 2-6 F above normal across the northwestern 1/3 of the state, with the north central Panhandle experiencing the largest temperature anomalies. Below normal temperatures were mainly confined to areas south of I-80 and east of a line from McCook to North Platte.
Dew point temperatures increased from the 50’s west to low 60’s east during the first half of last week into the low 60’s west to low 70’s east by Sunday. Human feel like temperatures (heat index) values approached advisory criteria on Sunday with upper 90’s to low 100’s reported statewide. Perhaps the saving grace in regards to moisture stress on warm season crops was that dew point temperatures were high enough to keep evapotranspiration rates below 0.25 inches/day across the eastern half of the state this past weekend.
Normal to below normal temperatures across the central and eastern corn belt (Figure 2) helped to offset the lack of significant rainfall July 19-25. Very dry conditions were common which is leading to concerns in regards to corn pollination and early grain fill, especially as upper 90’s to low 100’s are forecast to cover the western half of the corn belt through July 28. Excessively wet conditions across southern Iowa eastward through Ohio was welcome for the soybean crop that has been displaying poor color due to the lack of dry weather and sunshine.
Most of Nebraska also failed to receive measurable moisture July 19-25 (Figure 3). The exceptions were north central and south central Nebraska, as well as pockets across the northern Panhandle and southwest Nebraska. Readers should be aware that the area impacted by these precipitation events appear greater in Figure 3 than reality due to the large distances between reporting locations used in the mapping process. The most concentrated areas of precipitation fell from Valentine northward and in the counties of south central Nebraska lie along the Kansas border.
Crop Progress
The most significant impacts from the heat and dryness this past week according to the Nebraska Agricultural Statistics Service (NASS) were in the condition reports for pastures and soil moisture reserves. Corn in the good to excellent category declined 2 percentage points, soybeans increased 1 percentage point and sorghum declined 6 percentage points.
NASS reports that as of July 25, pastures were rated 9% very poor, 12% poor, 59% fair, 23% good and 2% excellent. The amount of crop considered in poor shape increased 2 percentage points, while the fair category increased 2 percentage points and the good category decreased 4 percentage points. The very poor and excellent categories were unchanged for the week.
Topsoil ratings declined sharply during the past week according to NASS. Top soil ratings as of July 25 stood at 9% very short, 37% short, 53% adequate and 1% surplus. Soils in the very short category increased 5 percentage points, while the short category increased 10 percentage points. The largest percentage change occurred in the adequate category which decreased 14 percentage points. The surplus category dropped 50 percent from 2% last week to 1% this week.
Subsoil ratings also declined, but not with the intensity seen in the topsoil ratings according to NASS. Subsoil moisture was rated 9% very short, 40% short, 50% adequate and 1 percent surplus. The net change from the July 18 report was that the very short category increased 2 percentage points and the short category increased 6 percentage points. These increases came at the expense of the adequate category which dropped 8 percentage points. Only one percent of the subsoil was rated surplus, unchanged from the previous week.
NASS reports that 84% of the corn crop had reached the silk stage, which compares to 85% last year and the 5-year average of 78 percent. As of July 25, 14% of the crop had reached the dough stage compared to 24% last year and the 5-year average of 17 percent. NASS reports that 76% of the corn crop was rated good to excellent, which compares to 78% last week.
The percentage of the soybean crop in good to excellent condition improved one percentage point from 81% last week to 82% this week. NASS indicates that 85% of the crop had reached the bloom stage compared to 88% last year and the 5-year average of 78 percent. Over half of the crop (52%) had reached the pod setting stage, which compares to 50% last year and the 5-year average of 34 percent.
The amount of sorghum rated good to excellent dropped sharply from the previous week according to NASS. As of July 25, sorghum was rated 75% good to excellent compared to 81% last week. Since the majority of crop acres planted to sorghum is located across south central and southwest Nebraska, it is not surprising to see declines, especially considering that most of the southwest climate district has received less than 0.50 inches of moisture during July.
With hot temperature expected to hold through July 28 (west) and July 29 (east), further crop rating declines are likely next week barring an unexpected increase is the moisture projected to fall primarily across eastern Nebraska this weekend. Heat stress is expected to subside through the middle of next week before returning to the central Plains the first full weekend of August. Therefore it will be critically important for precipitation events to materialize statewide to reduce the likelihood of more significant crop rating declines as we move through the month of August.
Weather Outlook
The upper air ridge responsible for the current outbreak of heat and humidity in the central Plains is expected to be pushed south and west by this weekend in response to an upper air trough that will shift from the northern Plains into the Great Lakes region. This trough is then forecast to deepen and pull a cooler Canadian air mass southward behind the surface cold front. The GFS model indicates normal to below normal temperatures will hold through the middle of next week before the upper air ridge builds back into the central Plains and brings a return to heat and humidity as early as August 6.
Upper 90’s to low 100 F maximum temperatures are forecast statewide through July 28, before cooler air pushes southward from southern Canada. Maximum temperatures will decline into the upper 90’s across southern Nebraska July 29, with upper 80’s possible across the northern 1/3 of the state. By July 30 high temperatures should range from the mid 80’s northeast to the mid 90’s southwest. The GFS model then holds high temperatures in the 80’s through August 6, except for the southwestern corner of the state where high temperatures could reach the low to mid 90’s by August 5.
Unfortunately, the GFS model doesn’t portray a robust precipitation pattern during the cool down currently forecast. Most of the precipitation indicated by the GFS model through the end of next week is directed toward the southeastern ½ of the state which lies at the forecast intersection of the Great Lakes upper air trough and the southwestern U.S. upper air ridge. This will create a northwest flow aloft and waves of energy moving southeast may generate rounds of thunderstorm activity during the late afternoon and overnight hours.
Further west, the GFS model does not show any widespread precipitation chances, but does allow for isolated thunderstorm development, particularly for the western half of the Panhandle. These isolated thunderstorms will be on the northeast edge of monsoon moisture that is forecast to develop widespread precipitation activity across the southern half of the Rockies. Southwestern Nebraska is currently depicted with the lowest overall odds of receiving moisture through the end of next week.
The GFS model issued the morning of July 27 indicates that the ridge from the southwestern desert region will expand north and east into the central Plains beginning next weekend and hold through August 11 before an upper air trough moves across the northern Plains August 12 and pulls a surface cold front through the state. If the GFS model is correct, expect widespread mid 90’s to low 100’s July 7-11 across the western half of Nebraska July 9-11 east.
The only moisture that the GFS model is showing for Nebraska August 8-12 occurs August 11-12 south of of the I-80 corridor and east of a line from McCook to North Platte. That being said, the GFS model does indicate that high temperatures will drop back into the low 80’s northeast to upper 80’s southwest August 12. Usually a 15-20 F forecast drop in maximum temperatures will generate thunderstorm activity, so it is possible that the GFS is underplaying moisture if the pattern change does develop.
Longer term, the Climate Prediction Center issued their preliminary August outlook for temperatures and precipitation (Figures 5-6) and they have reduced the odds of dryness and warmth for the Pacific Northwest east-southeast into western Nebraska, South Dakota and North Dakota. There probability odds are slightly tilted toward warm and dry conditions, but are considerable lower than their outlooks issued in June.
We have been fortunate in Nebraska for the most part in not having the weather pattern lock into place like last summer. It has been pretty much two weeks of above normal temperatures followed by considerably cooler temperatures the next two weeks. Hopefully the atmospheric pattern continues for the second half of August and cooler temperatures and more widespread precipitation chances materialize.
Even though recent precipitation events have not been widespread, when they have developed, the quantity and areal coverage has been greater than initially forecast by weather models. With a strong monsoon season underway in the southwestern desert region, some of this moisture should move around the high pressure dome and enhance lift for frontal boundaries moving through the state. Otherwise, crop deterioration and drought expansion across the state will be rapid and widespread.
Al Dutcher, Agricultural Extension Climatologist, Nebraska State Climate Office