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Great Lakes Article:

Extended dry spell reflected in lake level forecast
By Jack Storey
The Soo Evening News
Published June 2005


UPPER GREAT LAKES - A rainfall deficit of roughly six inches across northern Michigan and the Eastern Upper Peninsula so far in 2005 is slowly finding a reflection in Upper Great Lakes water levels.

A run of late-spring thunderstorms may bring rainfall closer to the historic average but a Corps of Engineers official last week said hydrologists have already dialed back their forecasts for a recovery in lake levels.

Carl Woodruff, hydrologist with the Corps' Detroit District, said late last week that forecasters have shaved two to three inches from summer lake level peaks because of continuing dry conditions.

He said even heavy rains through the spring and summer may have little effect on Upper Great Lakes water levels, mainly because the ground is so dry. He said dry soils tend to soak up even copious amounts of rainfall, sending relatively little downstream to the Lakes.

At the start of June, monthly comparisons of Great Lakes water levels were beginning to reflect several months of lighter than normal rainfall. As of June 1, Lake Superior stood at three inches below its long-term average and just an inch higher than the same time last June.

The early-June level on Lake Superior showed a slowing in the Big Lake's gradual rise from near-record lows in 2001. The slowing rise came despite a relatively wet May around the Lake Superior watershed, during which rainfall was 120 percent of the average, Woodruff said.

He accounted for the apparent disparity between higher rainfall and lower overall water supply to the Big Lake with the dry soil observation.

To the south, Lake Huron and Lake Michigan had no disparity last month. The watershed feeding the two lakes received less than half its average May rainfall as near-drought conditions continue throughout the two lakes' watershed.

At the start of June, the Corps reported Lakes Michigan and Huron were running about 13 inches below their long-term average after gaining on the norm through several months late in 2004 and early 2005. The two lakes rose just one inch in May compared to an average May rise of three inches.

While lake levels are beginning to reflect rainfall or lack of it, Woodruff said experts do not expect the lakes to bottom out if rainfall does not improve. He said hydrologists recently adjusted the normal summer peak in Michigan-Huron water levels about two inches lower than forecast in April.

The two lakes usually reach their highest levels of the year in early July.

"We don't expect a severe drought, but you never know," Woodruff said of the forecaster's conundrum. Though Lake Huron and Michigan have fallen roughly half-way to their recent low point - 23-24 inches below their long-term average - Woodruff said officials do not expect a repeat even if the light rainfall pattern persists through early summer.

A similar prospect appears for Lake Superior, which usually peaks in August or September.

Woodruff said if dry conditions continue to prevail across the Upper Lakes region, runoff water supply will be negligible and the only replenishment the lakes can expect from rain is from precipitation on the lakes themselves.

With thunderstorm potential in the weather forecast for several days this week, the rains have some considerable ground to make up throughout the region. Year-to-date deficits prevail across the north, even though respective Great Lakes watersheds are much larger.

A report early last week showed Sault Ste. Marie and Traverse City running very nearly six inches below average for the year and several other locations across northern lower Michigan in excess of five inches beneath their averages for the time of year.

Whatever may be in the precipitation cards for the balance of the summer, Woodruff said a collapse of water levels to those seen in 2001 and 2002 is not likely in 2005. Compared to datum, or the low-water minimum for shipping channels across the Great Lakes, Lake Superior was still five inches above the chart minimum in May and Lakes Michigan-Huron were eight inches above datum.

At the height of the early-century water level drop, lake levels on all three of the Upper Lakes fell below datum for months at a time. As recently as February and March 2004, the Upper Lakes slipped below datum again, only to recover by some 12 inches later.

Summarizing the Corps' expectations for the balance of summer on the Upper Lakes, Woodruff said, "Water levels are a little lower than last year but a lot higher than 2003."

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