It has been a difficult spring season across most of the United States east of the Rockies. Unusually warm weather during March quickly gave way to cold air intrusions during April and May, making row crop planting a challenge at best. Heavy rains, several unusually late snow events, and severe temperature oscillations have producers wondering what conditions will develop during this upcoming summer.
The official outlook by the Climate Prediction Center indicates their target area for above-normal precipitation is centered on the western High Plains and Rocky Mountain states. In fact, CPC points toward a wet pattern for the central High Plains in each three-month period starting from June to August and running through the August to October timeframe. Temperatures for our region are expected to be near normal until a weak tendency for above-normal temperatures develops in the August to October period.
At this point in time, I can find little disagreement with CPC’s depiction for the western United States. Sea Surface Temperature departures from normal continue to depict an anomalously cold pool in the Gulf of Alaska that has persisted since late last summer. Upper air lows continue to shoot energy into the western U.S., and we have seen strong surface low formation the past two months in the southern High Plains. I would expect this trend to lift northward over the next 45 days, putting Nebraska and the Dakota’s in the crosshairs of the active pattern experienced south of us the last two months.
Another cold pool recently has developed in the western Atlantic basin and will bear watching for development into the eastern Atlantic. Currently the Atlantic is considered to be in its warm phase and when coupled with the cold phase of the Pacific, precipitation tendencies for Nebraska are weighted toward the wetter side of normal. If the Atlantic moves into a cold phase and the Pacific remains cold, precipitation tendencies move toward a drier pattern for the central High Plains.
At the current evolution pace of the Atlantic toward colder conditions, it will be the end of this summer or early this fall before the Pacific and Atlantic are both in a cold phase. Therefore, the warm pool in the eastern Equatorial Pacific likely will continue to supply an abundance of atmospheric moisture into the southwestern and south central U.S. This will likely be a major contributor to an aggressive Monsoon moisture season during July and August, with spill over into the western half of the High Plains region.
The remaining cold pocket in the central Equatorial Pacific has dissipated over the past 90 days, but there are a few small pockets of cold that appeared recently in the eastern part of this basin. It is too early to tell whether this area will grow and expand westward, as it may be simply a function of increased convective activity cooling ocean surfaces. If this pocket were to develop, it is likely that the development will be slow and shouldn’t impede the Monsoon moisture feed during the summer months.
Based upon the current evolution of ocean anomalies in both the Atlantic and Pacific, I would expect that the current moisture pattern for the western Corn Belt will continue through the first half of the summer. Climatology would suggest that moisture pattern will shift northward from the southern Plains to the north Plains, increasing the likelihood that rainfall will alleviate short-term dryness across the western half of the Dakota’s.
Areas of the central and eastern Corn Belt are a more difficult call. Much of the persistent cold that has created havoc in regards to planting, emergence, and delays in growth of warm-season crops can be tied directly to upper air lows stalling over the northwestern Great Lakes after they eject of the western U.S. If this pattern persists, periodic heavy rainfall will continue for areas that have battled wet conditions all spring.
A second scenario would be that these upper air lows will weaken as we progress into the heart of the summer season. These upper air lows would lose their strength the further they move east of the High Plains. Being weaker, these lows would not be able to draw as much moisture northward from the Gulf of Mexico and heavy precipitation events would subsequently decline. This would not likely occur until we move past the month of June.
Tornadic activity across Nebraska has been very limited, with the major outbreaks remaining south and east of the region. At present, only three confirmed tornadoes have occurred through the end of May, according to the Storm Prediction Center. We have yet to consistently see dew point temperatures above 60 F, which has limited the amount of energy available for convective outbreaks across the state.
With the abundance of moisture that has fallen across the state from mid-April through the end of May, we would expect humidity levels to increase as crops begin to actively grow and surface temperatures increase. There continues to be a regular sequence of upper air lows ejecting out of the western U.S. and coupled with cold air aloft, the necessary ingredients for active severe weather during June appear to be in place.
If the current pattern holds, Nebraska will likely see active severe weather during June, with occasional bouts of heavy rainfall. Western Nebraska will likely be in a beneficial location to tap into the Monsoon moisture during July and August. Further east, precipitation during the second half of the summer will depend on whether this Monsoon moisture can ignite convective complexes that can hold to together and reach the eastern half of the state.
If we are to see drier conditions, the most likely scenario is for it to develop as we enter the second half of this summer, with the highest odds placed for the eastern half of the state. It appears to me that the real wild card in U.S. corn and soybean production will be whether cool and rainy conditions will continue for areas severely impacted the past 60 days or whether warmer and drier conditions develop. Both scenarios place a higher weather premium on the central and eastern corn belt than the western corn belt.