Midwest Weekly Highlights - April 15-21, 2014

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Below Normal Precipitation and Above Normal Snow in Upper Midwest

A majority of the Midwest experienced below normal precipitation during the third week of April, with a large portion only receiving less than 25% of normal (Figure 1). Eastern Minnesota, northern Iowa, northern Wisconsin, and Upper Michigan were the only areas with above normal precipitation, with 100% to 300% of normal precipitation. The highest precipitation totals of 1" to 1.5" fell in northern Iowa, eastern Minnesota, and the western Lake Superior basin (Figure 2), with much of this precipitation falling as snow (Figure 3). Much of the snow fell on April 16th (Figure 4), where at least 5" fell across a majority of central Minnesota, northern Wisconsin, and Upper Michigan. The highest totals of 12.5" to 15" fell in northern Wisconsin and eastern Upper Michigan. These snowfall totals were anywhere from 2" to 14" above normal for this time in April (Figure 5). Despite it being the spring season, which is typically the active time of year for severe weather, the third week of April was quiet with no severe weather reports in the Midwest (Figure 6)
 

Widespread Below Normal Temperatures

Average temperatures were below normal throughout the Midwest during the third week of April (Figure 7). The greatest departures of -9°F to -12°F were in Upper Michigan and portions of western Lake Superior. Average temperatures ranged from 50°F to 55°F in the southern Midwest to only 25°F to 35°F in the Lake Superior region (Figure 8). Minimum temperatures were below normal for the entire Midwest as well (Figure 9). On the other hand, maximum temperatures were below normal for the upper Midwest but near normal to slightly above normal for much of the central and southern Midwest (Figure 10).

Record-Setting Late Season Ice Cover on the Great Lakes

As April quickly comes to an end, nearly one-third of the Great Lakes are still covered in ice. According to Environment Canada's Great Lakes ice dataset, this is unprecedented in records dating back more than three decades. The ice dataset, which extends back to 1980-81, shows the current ice extent at a chart-topping 32.8% as of April 22nd. As of April 23rd, the number actually increased to 35% (Figure 11). The year with the next greatest ice extent on this date was 1996, which had about half as much ice (or 16.5% coverage). The normal Great Lakes ice cover for this time of year is 2.2%, meaning there is roughly 16 times more ice than normal right now (source: Washington Post article).

Great Lakes ice cover has been above normal since the late fall, with the maximum extent reaching 94.19% in early March, the second most on record for any month dating back to 1973 in NOAA's dataset.

The shipping industry will be affected by the late season ice cover on the Great Lakes, especially on Lake Superior. On March 20th, the Soo Locks separating Lake Superior from the lower Great Lakes opened for the season. However, it took another 16 days before the first commercial vessel fought its way across Lake Superior (with the aid of several dedicated ice breakers) and down through the locks. Therefore, a negative impact of the late season ice cover is that there is a delayed start to the shipping season. A possible positive impact of the late season ice includes allowing the region to recover from years of historical low water levels since ice cover helps prevent evaporation.

-MW-
Extension Climatologist for Illinois-Indiana Sea Grant and the Midwestern Regional Climate Center.