Tuesday’s high temperature was just 69 degrees and, according to Evan Webb, meteorologist at the National Weather Service Office in Grand Rapids, temperatures will remain in the upper 60s to low 70s until Thursday.

Webb said the recent cool down is due to the combination of a large, low-pressure system stretching over the Midwest and into southern Ontario and strong northern winds moving through the area at 10 to 20 mph.

He added that temperatures are much cooler than they typically are this time of year.
“Normal temperatures for this time of year are around 80,” Webb said.

NWS Meteorologist William Marino said the low temperatures are “very unusual.” According to his data, over the last 120 years, the chance that any given day from Aug. 1 to Aug. 22 has a high temperature below 70 degrees is just 5 percent.

However, since 2000, lowest high temperatures in that three-week period have been below 70 degrees five times. This includes 2012 when from Aug. 9 to Aug. 22 temperatures were almost exclusively in the high 60s and lower 70s.
For example, last year's high on Aug. 13 was just 71 degrees.

http://www.mlive.com/news/muskegon/index.ssf/2013/08/chilly_august_weather_unusual.html