Current Conditions
Very wet conditions developed across the central Plains during March as two strong upper air lows crossed the region within a ten day period. The first system dropped 4-8 inches of rainfall across the central and eastern Platte River valley in Nebraska March 13-15. Across the Panhandle snowfall rates ranged from several inches in the east to 24 inches along the Wyoming border. The second system delivered 1-5 inches of rainfall over that received excessive rainfall 10 days earlier.
Figure 1 shows the impacts of these two storms on March precipitation anomalies across the United States. Surplus values exist across the central Plains east-southeast through the lower Ohio River Valley. The most significant surpluses are centered over central/eastern Nebraska and Tennessee. These areas are currently the most susceptible to planting delays due to surplus surface moisture conditions.
With a wet trend firmly established for the month of March, the top foot of the profile has adequate moisture for spring planting for all areas showing positive anomalies in Figure 1. Moisture below the top foot of the profile is still a concern across the northern Plains and the western third of the High Plains region. Although short term moisture trends have turned positive recently, deep profile moisture recharge is still behind normal and will require additional activity in April to alleviate short term drought concerns.
Figure 2 shows the precipitation anomalies that have occurred since October 1, 2020 which coincides with the beginning of the soil moisture recharge period (Oct-Apr). If precipitation surpluses from September 2020 are added to this map, then the positive moisture anomalies extend across eastern Iowa, northern Illinois and southern Wisconsin. Therefore, the two areas of the corn belt that have the most significant soil moisture recharge deficits are the northern High Plains (ND, SD, MT) and the western 1/3 of the central and southern High Plains (NE, CO, KS, OK, TX).
Snowpack values for the Rocky Mountains east of the Continental Divide saw significant recovery from the March storm systems. The latest National Resource and Conservation Weekly Weather and Climate update issued April 1 shows all basins running between 88 and 107 percent of normal. Only two basins east of the divide have strong dry trends, both at the extreme ends of the Rockies in New Mexico and the Glacier National Park region of northern Montana.
In order to keep snowpack values in the normal range for the remainder of the snow season, a couple of upper air lows will still need to cross the central Rockies during April. Last year the entire southern Rockies had less than 50% of normal snowpack by early May and drought conditions rapidly expanded northward during the early summer. With snowpack values currently within the normal range, last year’s pattern should be delayed by at least 30 days this year.
Planting Weather Outlook
From the Climate Prediction Center’s (CPC) standpoint, Figure 3 indicates drier than normal conditions are projected for the southern half of the Rockies during April, with slight odds for below normal moisture extending from western Nebraska southeastward through eastern Texas. Additionally, CPC projects below normal moisture to develop across the southeastern U.S. coastal regions. Above normal moisture is projected for eastern North Dakota and northern Minnesota.
Dryness is intensified and expanded in the April-June outlook, which covers the entirety of the spring planting season. CPC indicates in Figure 4 that dryness is expected from California and Oregon east-southeast through Texas. The highest probability for below normal moisture was assigned to the region from northern Nevada and southern Idaho southeast through south central Colorado. Above normal moisture is expected for the Upper Great Lakes, northern Ohio River valley and the mid-Atlantic region.
I will caution everyone that CPC has not handled the impacts of storm systems moving through the southern Rockies very well this entire winter. The forecast for March indicated a strong tendency for below normal moisture across the central/southern Rockies eastward through the western half of the High Plains. Within two weeks these same areas were hit with record rain and snowfall.
Because of the surplus moisture during March, soil temperatures have been slow to respond to above normal air temperatures this past week. With high temperatures through early next week expected to reach the upper 70’s to mid 80’s, coupled with lows above 45 F, daily average 4-inch bare soil temperatures should move into the low 50’s south of the I-80 corridor. Soil temperatures north of I-80 will likely reach the mid to upper 40’s.
Unfortunately or fortunately (depending on your perspective), another upper air low is projected to eject out of the central Rockies April 6 and slowly migrate east northeast through April 9. The weather models are having a difficult time pinning down who will receive significant moisture, but this does appear to be a widespread event from the western through eastern corn belt. Precipitation amounts have been increasing with recent model runs adding higher confidence that widespread moisture will occur.
Once next week’s low passes east of the region, the GFS model indicates a ridge will build back into the central United States and temperatures will rebound back into the 70’s and 80’s across the central Plains by April 11. The warm temperatures will likely take an additional 2-4 days to reach the eastern corn belt. The warm and dry conditions may be short lived as another upper air low is projected to push into the central Rockies by mid-April and then move eastward across the central Plains.
If the GFS model is correct, the combination of these two storm systems should provide enough moisture to slow planting activity across most of the western corn belt. Further east, precipitation from the mid-month precipitation event looks more uncertain. If the system is progressive, then moisture and planting delays will develop there also.
A much drier and warmer trend is likely to develop the third full week of April across the western and central corn belt as high pressure aloft is by numerical weather models to build across the region. If the trend of distinct wet and dry periods that developed across the southern Plains in December and slowly spread northward through March continues, then below normal moisture would be expected through the end of April.
At this point in time I see no dramatic shift from the pattern we have experienced since mid-December. I expect distinct stormy periods lasting 10-14 days, followed by dry and warm conditions lasting equal lengths of time. If I am correct, there will be distinct periods of significant planting activity, interspersed with periodic delays.
It should be noted that if either of the two projected storm systems through mid-April cutoff over the western corn belt, then much of central, south central, east central, and southeast Nebraska would likely experience more significant planting delays due to the excessively wet March conditions. Soil profiles are at field capacity down to 3 feet (or deeper), so it will take longer for surfaces to dry, which increases runoff risks and lowland flooding from elevated river flows.
Al Dutcher, Agricultural Extension Climatologist, Nebraska State Climate Office