After a wet winter and spring, it began to dry out again over Upper Michigan with the beginning of summer. However, the rains of the last couple of days, while not abundant everywhere, have brought the monthly total at the National Weather Service (NWS) near Negaunee above average. The total through yesterday is 3.07 inches. The average for the entire month is around three inches, so we??re already there. So far, each month in 2013 has carried a surplus of precipitation.
However, Upper Michigan has been gripped by a long-term dry spell. Each year from 2007 through 2011 had precipitation deficits. The yearly deficits were not extreme. However, it appears that a number of factors went into making this a rather serious long-term situation. With the exception of 2010, summers were dry. The warm season is the time of greatest evaporation from the soil, so dry weather compounds the problem. There is an old saying that ??drought begets drought.?? This has been demonstrated time and time again during Upper Michigan summers of this period. In addition, the storm track in winter was not favorable for wide-spread system snows across the U.P. for a number of years.
This winter was different. Widespread snowstorms fell in every month of the winter into the spring. So soil moisture was at least adequate heading into the warm season. In addition last year, after a dry beginning, turned wet during the summer and fall. The long-term average yearly precipitation at the NWS is 36.32 inches. Last year ended with 36.36 inches??just about average for the first time in six years.
Those U.P. residents who have property on inland lakes that are spring fed are acutely aware of the dry spell. The water table is down and therefore, the lakes fed by the water table are low. For instance, Little Shag Lake in Gwinn reportedly lost over four feet of water from 2007-12. On the Big Lake, water level records have only been kept in an organized fashion by the U.S. and Canada since 1918 (Image 1 above). This is a relatively short record, but combined with less reliable measurements from the 19th century, it shows a cyclical pattern. Levels crashed to their lowest point in the last 95 years in 1926. The low point was nearly equaled during the summer of 2007. During the 30s and especially the 40s and 50s, levels were high. That??s because it was generally wet, especially during the summers around the Lake Superior basin. During the 1960s, levels dropped and were a little below the median during a number of years. Then during the 70s into the 1980s most years were above average with the absolute peak during the last 95 years in 1986. About 2000, water levels dropped and have been somewhat below average ever since.Heavy snows over the entire Lake Superior basin this past cold season melted and brought the lake level up (Image 2). The last data shows the Big Lake only a couple of inches below the long-term average. This is a hopeful sign that the cycle may be turning back to wetter times.