Weather Review and Crop Progress
Below normal temperatures dominated the state April 11-18. The warmest day on a statewide basis was April 11th with high temperatures in the sixties. A strong upper air low moved across the northern Plains April 12th pulling cold Canadian air into western Nebraska. The cold air spread eastward on the 13th resulting in average temperatures dropping 10-20 F below normal.
As the northern Plains upper air low slowly drifted southeastward toward the Great Lakes, a piece of energy rotated around the low and formed a strong trough over the northern Rockies on April 17th. By the evening of April 18th, precipitation in the form of snow began to fall across the northwestern Panhandle. Western Nebraska never saw a reprieve from the cool air, but southeastern Nebraska was able to reach the low 60’s as the trough strengthened and pulled warm air northward from the southern Plains.
Figure 1 shows the average temperature departure from normal April 13-19. The most significant departures from normal occurred across the Panhandle, but everyone experienced below normal average temperatures during the period. Maximum average temperatures were impacted to a greater degree due to the extensive cloud cover and Figure 2 shows average departures from normal exceeded 15 F below normal across the Panhandle.
Nebraska Agricultural Statistics Service (NASS) reported 4.6 days of suitable field work conditions for the week ending April 18th. Only 2 percent of the corn crop was reported planted. This compares to 2% last year and the 5-year average of 4 percent. Average high temperatures across the western half of the state ranged from the upper 30’s to mid 40’s April 14-17, while eastern Nebraska ranged from the low to upper 40’s. With these types of temperatures, it is not surprising that little corn planting was accomplished in the past week.
To add insult to injury, precipitation reports from the April 14-15 storm event produced widespread 0.25 – 0.75 inches of liquid equivalent moisture south and west of a line from Blair to Ord to the South Dakota border. A few small pockets of 1.00-1.50 inches of moisture were reported in the Platte Valley of the Panhandle, as well as, central and south central Nebraska. Figure 1 shows the accumulated moisture for the April 13-19 period, while Figure 4 depicts the precipitation departures from normal for the same time period.
Snowfall with the April 14-`15 event ranged from 3-7 inches across the Panhandle, southwest and southern half of west central Nebraska. Snowfall totals dropped off quickly across central and south central Nebraska, with most locations reporting nothing to less than two inches. Since the northeastern ¼ of the state saw less than 0.20 inches of moisture, if any at all, oat planting progressed rapidly. NASS reported 70% of the crop was planted compared to 30% last week. Last year 51% of the crop had been planted compared to the 5-year average of 52%. Twenty-six percent of the oats had emerged compared to 14% last year and the 5-year average of 16%.
Although warm season crop planting was virtually non-existent this past week, the moisture received across western Nebraska helped improve topsoil and subsoil moisture ratings slightly. Nass reported that topsoil moisture on a statewide basis was 4% very short, 15% short, 77% adequate, and 4% surplus. Subsoil moisture was rated as 5% very short, 28% short, 65% adequate and 2% surplus. Compared to last week’s subsoil ratings, the very short category shrank four percent, while the short category increased by the same amount.
Winter wheat condition improved slightly according to NASS. As of April 18, 5% of the wheat crop was rated very poor, 12% poor, 40% fair, 40% good and 3% excellent. The very poor and poor categories improved 1 percentage point from last week, while the good category improved 2 percentage points. With additional snowfall occurring across the Panhandle and southern border region after the NASS weekly crop reporting deadline, further crop improvement would be expected in next week’s NASS release.
Weather Outlook
There finally appears to be a window for corn and soybean planting across the state, potentially lasting through April 26th, before the GFS model indicates a strong upper air trough will cross the central Plains April 27-28. In fact, if the GFS model is correct, a significant convective outbreak should develop across eastern Nebraska and Kansas, as well as western Iowa and Missouri.
The upper air pattern forecast from April 19-26 as depicted by the GFS model moves the upper air trough responsible for our recent cold weather into the eastern Great Lakes. A piece of energy from this trough will sag into the southern Rockies. Upper air ridging will develop between these two systems through April 23. Further north across north central Canada, an upper air low will pivot energy southward toward the northern Plains.
On April 24th, the GFS model begins to push the southern Rockies energy eastward and it merges with the Canadian upper air low to form a trough that progresses eastward toward the Great Lakes. At this time, the GFS model indicates the southern portion of the trough will touch off some light showers across east central and southeast Nebraska April 24th. The most concentrated area of precipitation with the northern Plains energy will fall across northern Montana, North Dakota, and Minnesota.
High temperatures are projected to move from the 40’s April 19th into the 60’s April 23rd. Even warmer temperatures are depicted for April 24-26, with highs in the 70’s to low 80’s. This warming is in response to an upper air low moving toward the central Rockies and increasing southerly flow from the Gulf of Mexico in advance of the surface low predicted to form the April 27th over southeastern Colorado.
The GFS model indicates that there will be strong low level atmospheric flow northward from the Gulf of Mexico ahead of the surface low. On the backside of the surface low, cold air aloft should be sufficient to initiate severe weather the afternoon of the 27th, with wrap around moisture predicted for the 28th. If the GFS model is correct, the entire state will see precipitation, with heavy rainfall in excess of two inches possible east of Grand Island.
As this system moves toward the Great Lakes on the 29th, high pressure will quickly build back into the central Plains through May 1. Yet another upper air low is forecast to move into the Pacific Northwest April 29th. High temperatures return to the 70’s and 80’s from April 30 – May 2. The GFS model shows a piece of energy will eject out of the western U.S. upper air trough and cross the central Plains May 2-3. At this time, modeled precipitation looks to be widespread, but on the light side.
The main upper air low is projected by the GFS to move into the central Plains May 4-5, bringing widespread moisture from northern Texas northward through the Dakota’s. Severe thunderstorms are indicated for the southern and central Plains, with moderate to heavy rainfall for the upper Plains. The GFS model develops this trough into a cutoff upper air low over North Dakota and Minnesota, broadening it out from May 6-8 over the upper Midwest. Nebraska would lie at the boundary between this system and warm air to the south. If the GFS were to verify, active weather would continue into the second full week of May, statewide.
Weather models are notorious fickle at this time of the year. What is certain is that temperatures will warm into the middle of the next week before a system moves into the region with the potential to drop heavy rainfall across eastern Nebraska. Warm temperatures will return after that, but several additional weather systems may develop and slow planting activity across the state. If the GFS is wrong about the early May activity, then the open planting window will extend into early May.
Al Dutcher, Agricultural Extension Climatologist, Nebraska State Climate Office