KANSAS CITY, MISSOURI, U.S. — U.S. flood damage in March reached well over $1 billion in Nebraska alone and that was through March 27. Many other states in the Midwest and lower Mississippi River Basin have sustained damage as well, but the assessments have only begun because high river flows and flooding are still under way in many areas.
Weather conditions actually improved in the latter part of March and early in April, but you would not know it looking at some satellite and low altitude imagery. The saddest part of the current situation is that the atmosphere is regrouping for another round of significant rain later this month and in May.
Despite commentary from some news media that this bout of flooding is because of climate change, it is extremely important to note that floods like this have been happening periodically since the 1700s. The only difference with this event and those of the past is the record-setting river flows in some areas. But changes in river flows may be at least partially attributed to increased urbanization that raises runoff. The flood event in March culminated after significant precipitation events occurred while the ground was frozen and while snow was melting across the central United States. It was a bad combination of events that resulted in this situation.
Mississippi river flooding is not unprecedented. One of the early recorded historical events came from Hernando DeSoto’s expedition in 1543 near the confluence of the Mississippi and Arkansas rivers. Serious flooding, like that of this year, seems to happen periodically. According to one mathematician they tend to be closely associated with the 22-year solar cycle. Flooding of great significance was recorded in 1809, 1825, 1844, 1851, 1927, 1945, 1973, 1983 (lower part of the river), 1993, 2011 and now 2019. There have been other floods on at least a part of the river, but these were the greater floods that have been recorded. There are many other weather associations with solar minimums, and 2019 is the latest solar minimum.
The weather pattern that generated frequent precipitation during the winter comes from the lunar cycle, which tends to occur in a little more than 18-year intervals. Since the lunar cycle and the solar cycle are somewhat similarly timed, it does make sense that the pattern of extreme rainfall and flooding would occur near the anniversary of these two events. The 1983 flooding on the lower Mississippi river was part of a very wet spring that impacted the lower Midwest, Delta and southeastern states, and the rainy pattern was perpetuated through the entire spring season. Unfortunately, the rainy pattern in 1983 ended in a serious summer drought in the same areas that were flooded a few months earlier.
Before there can be any consideration of drier-biased summer weather in the central and eastern United States, the nation needs to prepare for more rainy weather. The lunar cycle dictates that the wet bias will continue for at least the next two months. The good news is that seasonal warming is under way and faster drying rates will take place between rain events, which might help reduce some of the flood severity. However, changes are expected in April that will raise some concern over the frequency and rain intensity that takes place.
The changes expected this month include the development of a high-pressure ridge over the southeastern United States and the development of a northwesterly flow aloft across Canada’s Prairies and into the north-central United States. The northwesterly flow pattern aloft will bring cooler air temperatures to the north-central United States at the same time that the ridge in the southeastern United States brings on warmer temperatures. The jet stream likely will be split during April and a part of May with one branch coming from the northwest across Canada to the north-central United States and the other coming from the southwestern United States as a result of the lunar cycle.
The southern branch of the jet stream will flow across the southwestern corner of the nation. Immediately off the Baja California coast is a large pool of warm water. That warm water will see that storm systems forming in the southwestern United States have ample moisture as they move inland. The storms will then move from southwest to northeast into the heart of the Midwest, at which time cooler air from Canada and the northwesterly flow aloft will meet and small weather systems suddenly will grow large in size as they move through the Midwest, inducing significant rain and snow events. The new moisture will be significant at times and its frequency will be great enough to limit farming activity in portions of the Midwest, Tennessee River Basin and lower Mississippi River Basin. Spring planting delays are expected to be most significant in these areas.
Both El Niño and a warm pool of ocean water in the Gulf of Alaska will help to promote the northwesterly flow of air aloft from northwestern Canada into the north-central United States, keeping sufficient amounts of cool air available for storm development farther to the south. Most of the storms that come into the southwestern United States are expected to be weak systems, but the moisture they drag into the middle of the United States from both the eastern Pacific Ocean and Gulf of Mexico will be sufficient to induce rapidly developing storm systems capable of producing heavy rainfall in a short period of time.
Concern about the upper Midwest flooding remains high, but late March and early April precipitation was minimal in the region, and temperatures failed to warm enough to induce a sudden meltdown of snow. The end result has been a lack of flooding in the Red River Basin. The threat of significant flooding is not over, though. Significant snow melt is still under way in eastern North Dakota and Minnesota as well as Manitoba, Canada, and there is still some potential for serious flooding, especially if significant precipitation evolves.
The northern branch of the jet stream is not expected to be very strong until near and shortly after mid-April. That raises the potential for at least one storm, and possibly a couple may move across the upper Midwest and southeastern Canada’s Prairies, resulting in some significant runoff that might worsen flood potentials. The development of a negatively phased Arctic Oscillation is supposed to evolve near and beyond mid-month. Once that takes place the northern branch of the jet stream is expected to become stronger, and that should help force storm systems farther to the south across the United States once again. Pushing the storm systems into the heart of the Midwest may not bode well for spring planting in that region, and more flooding may result, but the change will reduce the potential for more serious flooding in the upper Midwest and southeastern Canada’s Prairies.