Published April 30, 2013
The same storm bringing heavy snow to Denver and Cheyenne Wednesday will regroup farther east later this week and has the potential to bring a swath of heavy, wet snow from eastern Nebraska to northwestern Wisconsin and the western Upper Peninsula of Michigan.
The upcoming storm, like many in recent weeks, seems to be ignoring the date and, if all the right pieces were to fall into place, could bring 6 inches to a foot of snow on its northwestern flank Wednesday night and Thursday over the central Plains and more so later Thursday into Friday farther north over the Upper Midwest.
Such an unprecedented storm could not only bring heavy snowfall to non-paved areas, but also slippery travel conditions and even downed trees and power outages.
Forecast Challenge: In order for it to snow and accumulate, let alone bring this sort of snowfall away from the higher elevations this time of the year, conditions have to be perfect with just the right balance of warm, moist air and cold, dry air.
Typically in this situation, a very narrow band or a small area of heavy snow falls, rather than a broad leaf of snow that is often observed during the middle of winter. Most often, the snow this time of year last only a few hours, changes to rain or melts as it falls.
In May, accumulating snow must also overcome a warm ground, sun effect and marginal temperatures.
It must snow hard for a small accumulation to occur away from the High Plains and Rockies, especially in the area of eastern Nebraska, neighboring Kansas, Iowa, southeastern Minnesota and the lower part of northwestern Wisconsin. In order for there to be a foot of snow, it must snow extremely hard for a long period of time.
The position of this band of intense snow is critical. A shift in the estimated track of the anticipated heavy band by 50 to 100 miles would mean the difference between a heavy accumulation, snow melting as it falls and heavy rain.
As a result, there is a much greater chance of error with a May snowstorm as opposed to a similar storm during the middle of the winter. Odds favor much less snowfall, on the order of a few inches in a narrow band.
The accumulation of snow would vary tremendously in a local area from hilltops to shallow valleys, as well as from road surfaces to grassy areas to tree tops.
The snow is more likely to melt on most warm road surfaces but could cling to tree limbs. Cars would have to be cleaned off. Patches of roads and sidewalks that don't receive direct sunlight on a clear day might be more receptive to the snow in this situation.
May Snowstorms: A Historical Perspective There have been some snowstorms in May in the region, but they are rare. 1907 sticks out as a benchmark year for a number of locations. However, multiple years during the mid-1940s also brought snow events to the region for several years in a row.
According to National Weather Service records for May, there have never been more than 2.0 inches of snow in Omaha, Neb. On May 9, 1945, 2.0 inches of snow fell. There have been two snowfalls on May 3 over the years in Omaha. One was 1.3 inches in 1907 and another was 1.0 inch in 1967.
The heaviest May snowfall on record for Des Moines, Iowa, was during 1907, when 1.2 inches fell on the third day of the month. There has been measurable (0.1 of an inch or more) snow as late at May 15, which was set the same year.
So it seems the odds are greatly stacked against a heavy snowfall for areas this far south with this storm.
Farther north, the odds increase for more substantial snow.
About 100 miles north of Des Moines, along I-35, in Mason City, Iowa, there has been 4.0 inches of snow as late as May 28 in the year 1947. That storm continued into the next day and brought a grand total of 4.5 inches.
Meanwhile, the Minneapolis-St. Paul area has received measurable snow as late as May 15, during 1907. On May 11, 1946, a storm brought 2.8 inches of snow.
Records for the area date back into the late 1800s.
In Eau Claire, Wis., records only date back to 1949. The only measurable snowfall during May since then was 0.7 of an inch on the ninth day of the month in 1960.
Get Ready for a Snowstorm: While the storm is likely to bring accumulating snow, a swath of 6 to 12 inches of snow would be unprecedented this late in the season from Omaha to Minneapolis and vicinity.
Given the weather pattern of recent weeks and months, such a snowfall is a strong possibility in this case. Despite a recent warm surge, cold air has been lingering in southern Canada and is again dropping southward, ready to dive into the storm.
At the very least, while the storm will bring another dose of needed moisture to some areas on the Plains, it will also add to planting delays and flooding problems in areas that have received an overabundant amount of moisture in recent weeks.
Stretches of I-29, I-35, I-80 and I-90 could be adversely affected by this storm. Delays are possible on these highways and others. Flight delays could occur at airports in the region due to deicing operations.