Weather Update
During the past week, the western 1/3 of the state experienced anywhere from 3 to 5 consecutive days of high temperatures reaching or exceeding 100 F July 26-30. Preliminary data from airport locations around the state that are reported through the National Weather Service indicate that the highest statewide maximum temperatures were: 7/26 (Chadron: 105); 7/27 (Chadron: 105); 7/28 (Chadron: 107), 7/29 (Imperial: 101); 7/30 (McCook: 100); 7/31 (Valentine: 91); 8/1 (Chadron: 90).
Dew point temperatures were consistently in the 65 F (west) to 75 F (east) during the hottest stretch of weather last week (July 27-30), which helped reduce evapotranspiration demands slightly (0.05 inches/day). An additional factor that may have kept high temperatures from exceeding 100 F across eastern Nebraska was the wildfire smoke that was pulled southward from northern Canada. Air quality and visibility issues were most pronounced July 29-31, with north central and northeast Nebraska having the most significant impacts. Regardless, most of the eastern half of the state was under air quality alerts during this stretch.
With daily maximum temperatures consistently above 100 F across the western 1/3 of the state, it is no surprise that average temperatures were above normal (Figure 1). Most of the northern Panhandle, southwest, northeast and east central Nebraska saw average temperatures 2-5 F above normal. An additional pocket of 2-5 F average temperature anomalies was located in a narrow band from north central through south central Nebraska. The remainder of the state average had normal average temperatures to anomalies approaching 2 F above normal.
Most of the precipitation received during the past week was associated with the cold frontal passage that occurred July 30-31. Figure 2 indicates that localized precipitation totals exceeded two inches in pockets that included the southeastern Panhandle, southwestern Sandhill region, south central and east central Nebraska from Columbus to the Iowa border. Areas with above normal precipitation (greater than 0.75 inches) during the past week are depicted in Figure 3. It should be noted that even for areas depicted as receiving above normal moisture, precipitation variability was high over short distances.
Crop Progress
Widespread heat occurred statewide July 26-30 before a cold front associated with a trough of low pressure pushed the heat south of the state July 31. Unfortunately, precipitation with the cold front was not very widespread with much of the southwestern ½ of the state failing to receive significant moisture (less than 0.50 inches). Warm season crop condition ratings fell for a second consecutive week as pockets of drought developed and/or expanded across the western half of the northeast, east central, southeast and southwest climate districts.
Although maximum temperature soared above 100 F across the Panhandle July 26-29, the cold front dropped high temperatures back into the lower 90’s. The 100 F plus high temperatures shifted into the western half of the state east of the Panhandle July 29-30 before the cold front dropped maximum temperatures back into the upper 80’s to low 90’s. Dew point temperatures during this stretch of heat were consistently between 65 and 75 F, which partially offset crop water demands and kept in canopy relative humidity levels high enough to offset pollination concerns for the corn crop.
Nebraska Agricultural Statistics Service (NASS) indicates that corn and sorghum showed large declines in the good to excellent ratings due to continued dryness issues coupled with maximum daytime temperatures in the middle 90’s to just shy of 110 F (location dependent). NASS indicates that corn in good to excellent condition was 71% as of August 1, which is a drop of 5 percentage points from the July 26th crop report. Sorghum in good to excellent condition stood at 64%, which is an 11 point drop from the previous week.
NASS reports that as of August 1 corn in the silk stage had reached 97%, while 41% of the crop was in the early dough stage. At this time last year 41% of the corn was in the dough stage compared to the 5-year average of 32%. Soybeans in bloom reached 97% with 66% of the crop setting pods. Last year at this time 62% of soybeans were setting pods compared to the 5-year average of 53 percent. Sorghum heading reached 49%, which is behind last year’s pace of 61% and the 5-year average of 49 percent.
With most of the state receiving below normal moisture and above normal temperatures during the past week, subsoil moisture ratings declined sharply compared to topsoil moisture ratings. NASS indicates that subsoil moisture as of August 1 was rated 12% very short, 47% short, 41% adequate and 0% surplus. The very short category increased 3 percentage points and the short category gained 7 percentage points. The percent of subsoil with an adequate rating decreased 9 percentage points and the surplus category declined 1 percentage point.
Topsoil condition ratings as of August 1 were 11% very short, 37% short, 52% adequate and 0% surplus according to NASS. The net change from the July 26 crop report was an increase of 3 percentage points for the very short category and a loss of 1 percentage point in the adequate and surplus categories. Topsoil moisture for the short category was unchanged from last week.
There were sharp decline in pasture ratings this week when compared to the July 26th release from NASS, due in large part to 3-5 days of 100 plus readings (location dependent) across the western 1/3 of the state coupled with below normal moisture. NASS reports that as of August 1st eight percent of pastures were rated very poor, 12% poor, 61% fair, 18% good and 1% excellent. The very poor category increased 4 percentage points and the poor category was unchanged. There were decreases in the fair to excellent categories according to NASS with the fair category decreasing 2 percentage points, while the good category decline 5 percentage points and the excellent category decline 1 percentage point.
Weather Outlook
Nebraska got a brief taste of below normal temperatures to start the month of August, but numerical weather models indicate that the heat will return to the central Plains as this week progresses with high temperatures returning to the upper 90’s to low 100’s by this weekend. The GFS model indicates that high temperatures should remain and will
The first half of August currently appears to favor above normal temperatures as the upper air ridge to out west-southwest begins building east and northward into the central High Plains this week. Although there are weak chances for isolated thunderstorms to develop across northern and eastern Nebraska August 4-6, the GFS model indicates that more widespread convection is possible August 8-9 in association with a cold front that will work southward across the state as an upper air trough slides across the northern Plains towards the western Great Lakes.
High temperatures August 5-9 will warm from the mid 80’s into the upper 90’s, before cooling back into the upper 80’s to low 90’s August 11-13. From August 13-15 the GFS model indicates another upper air trough will move across the northern Plains and pull in cooler air into the northern half of the High Plains region. High temperatures are forecast to drop into the upper 70’s to low 80’s.
The base of the trough August 13-15 is currently projected to lie across northern Nebraska and monsoon moisture from the southwestern United States is projected to lift northeast and interact with this upper air trough. Currently, the GFS model aggressively points toward widespread precipitation chances for the eastern 2/3 of the state, with the highest odds pointing toward south central, east central, and southeast Nebraska.
The GFS model then builds the upper air ridge back into the central Plains August 16-19 under mainly dry conditions. High temperatures are forecasted to warm into the mid 80’s to low 90’s, but another upper air trough appears to take aim at the northern and central High Plains August 20-22. Normal maximum temperatures are in the upper 80’s and the beginning of August and cool into the lower 80’s by the end of the month. Based upon the current GFS model, average temperatures the first 19 days of the month should average 3-6 F above normal, with the greatest heat anomalies assigned to the western 1/3 of Nebraska.
The Climate Prediction Center (CPC) released their final August temperature and precipitation outlooks (Figures 4 and 5) on July 31 and they indicate that below normal precipitation is favored for the northern half of the High Plains region, including Nebraska. The highest probabilities of dryness are assigned to the Dakota’s. This dry area was shifted eastward from the Pacific Northwest and northern Rockies in the preliminary release issued July 22nd.
The August temperature outlook issued by CPC is very similar to the preliminary temperature outlook issued in July. Above normal temperatures are favored for the western United States, the northern half of the High Plains region, as well as the Great Lakes and the northeast. The highest probability of occurrence is forecast for the northern half of the Rockies eastward through Minnesota. Below normal temperatures have been relegated to Texas, Oklahoma, Arkansas, Louisiana and Mississippi.
Al Dutcher, Agricultural Extension Climatologist, Nebraska State Climate Office