the winter storms because of the generally higher winds. Because of the 

 significance of low-pressure systems in the overall scheme of coastal 

 processes and erosion, the number of low-pressure systems passing across 

 Lake Michigan was obtained from the number of lows on daily weather maps 

 of the National Weather Service (Table 2). These data indicate that late 

 fall through early spring is the time when cyclonic systems pass most fre- 

 quently. During the 3-year study period, the rate of cyclone occurrence 

 was fairly constant. From 1970 to 1973, the annual number of cyclones was 

 36, 44, and 40, respectively, or an average of 40 cyclones per year which 

 is close to the annual average of 43.2 cyclonic systems passing over the 

 Lake Michigan area between 1938 and 1970 (Seibel, 1972). 



Because of the general consistency in the total number of storms that 

 pass through the area annually, and the relative uniformity in the seasonal 

 nature of the distribution of cyclonic systems during each year, this is 

 not an important variable with respect to the annual or long-term period- 

 icity of coastal erosion. However, the above discussion of cyclonic sys- 

 tems does not consider the intensity of the storms which is a variable that 

 must be considered. 



Typically, the most intense storms develop during late fall and winter; 

 however, because of the winter ice cover, November and December storms are 

 most effective in coastal erosion. Although there may be extremely intense 

 storms during summer, they are not common. One such storm in July 1969 

 caused severe erosion on the southeastern coast of Lake Michigan (Fox and 

 Davis, 1970b). 



Fetch is a limiting factor in wave development in Lake Michigan. The 

 relatively shallow nearshore area also causes waves to break at a consider- 

 able distance from the beach. As a result, breakers rarely exceed 5 or 6 

 feet, although local residents and newspapers have reported 12- to 20-foot 

 waves. Because of the elongate nature of the lake in a north-south direc- 

 tion, there is a considerable fetch difference between the north and south 

 end of the lake with respect to the two primary wind directions. For ex- 

 ample, winds from the southwest have a long fetch toward the northern part 

 of the study area but the fetch is short for those locations in the south- 

 ern part; winds from the northwest cause the opposite situation. 



Wind velocity and direction data were obtained from the U.S. Weather 

 Bureau at the Muskegon County Airport, Muskegon, Michigan. This station 

 is located nearly 3 miles from Lake Michigan on a flat plain approximately 

 40 feet above lake level. Although trees are present on the lake margin, 

 there are none about one-half mile immediately adjacent to the weather 

 station. Because of the station's central location along the eastern coast 

 of Lake Michigan and the absence of any other first-order weather stations 

 nearby, all data were compiled from this location. Wind roses for each of 

 the 3 years show the expected similar patterns with two modes, one from the 

 southwest and one from the northwest (Fig. 4). This pattern is similar to 

 that found for a 10-year period from 1960 to 1969 (Seibel, 1972). 



Climatological data show that the prevailing winds are from the south- 

 west and the predominant winds from the northwest. The predominant winds 

 are generated by the trailing side of the cyclonic system as it passes 

 over Lake Michigan. 



17 



