Friday, August 8, 2014

Unusual Upwelling in Lake Superior

Anyone who has gone swimming in Lake Superior this summer has noticed how cold the water is.  The main reason is that almost 95 percent of the lake was covered in ice last winter.  The ice continued well into the spring.  At the end of July the situation became worse as winds caused upwelling and shifting of the water along the shorelines.   The water temperatures along coastal regions of Lakes Michigan and Superior dropped up to 30 degree overnight!  According to NOAA, sections of Lake Superior bottomed-out at 38°F, while parts of eastern Lake Michigan hit 41°F. These temperatures are more common in April than the last week in July.

This shifting of water occurred due to upwelling, which occurs when cold waters from the bottom of the lake rises towards the surface.  The strong winds pushed the surface water toward the middle of the lake, causing deeper and colder water to rise to the surface along the shoreline.  In Grand Marais as well in other areas along Lake Superior and Lake Michgan, the rapidly-chilled water created a thick layer of fog where temperatures dropped the most. The cold water cooled the air above it through conduction, dropping the air temperature to its dew point and condensing its water vapor.  This colder water is rather dramatic considering that the average surface water temperature in Lake Michigan at the end of July is around 68°F, and the average temperature for Lake Superior surface water is 60°F. 

The chart below shows the differences over the last few years.  The chart is in Centigrade.  If it was calibrated in Fahrenheit, then the graph lines would be even more dramatic.

Some of the NOAA surface water temperatures are shown in the charts below.  First August 2, 2012.  Most of the temperatures are in the upper 50s and low 60s.

The next map below shows the surface temperatures of Eastern Lake Superior on July 29th of this year.  Near Grand Marais, the temperatures were in the 40s and into the 50s along the Pictured Rocks.

After the upwelling the end of July, the surface water temperatures of a large section of
the center of Lake Superior dropped to  the 30s.

One of the results of this colder water is that there will be less evaporation.  As a result, the level of Lake Superior is expected to rise up to 10 inches.  The lake level is also up due to high snow levels last winter.  As of the end of June, the level of Lake Superior was up five inches in past month and 15 inches in the past year. 

The graphic below shows the dramatic increase of Lake Superior's water level since 1994. Since the low water level in March 2013, Lake Superior has risen 30 inches.

Change of subject:  here is the latest agate window that I made.  I have made custom agate windows for people before that have hand-crafted frames with no glass, but this is the first I made for sale in the museum's gift shop.  


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