During the mid afternoon hours on Friday, July 27th, waterspouts were observed over Lake Michigan, offshore of the Port Sheldon/Holland areas.
Below is a picture taken from near Holland of two waterspouts that formed offshore around 2:52 pm on 7/27. Click on image to enlarge. Photo is courtesy of Derek Dennis.
The waterspouts formed as a strong wave of low pressure and associated cold front pressed through the area. A line of showers and embedded thunderstorms formed along the cold front, and helped to produce the waterspouts. The waterspouts were reported between 2:50 pm and 3:00 pm on Friday 7/27. A radar loop from 2:39 pm to 3:13 pm is shown below.
A lot of ingredients came together just right for the waterspouts to occur. One of the most important ingredients in producing waterspouts is having relatively warm water temperatures. Obviously, this summer has been quite warm, and has allowed water temperatures to warm to above normal values for this time of the year. A recent article about the above average water temperatures this summer on the Great Lakes can be found here: http://www.climatecentral.org/news/great-lakes-water-temperatures-at-record-levels/
Another ingredient that is necessary for the formation of waterspouts include temperatures around 5,000 feet much cooler than the water temperatures. This was definitely the case on Friday as a wave of low pressure associated with the cooler air at 5,000 feet came in. Temperatures at 5,000 feet were around 56-57 degrees F, while water temperatures on Lake Michigan were around 75-76 degrees F. This big difference in temperatures, or instability over the lake is very important in the formation of waterspouts. Instability occurs when warm air is positioned below cold air. The warm air would tend to rise, leading to clouds and precipitation. A good example of this is a boiling pot of water on a stove, producing steam since the room temperature is much cooler compared to the boiling water.
The next ingredient that was present on Friday was some sort of boundary for the waterspouts to develop. The waterspouts developed in association with showers and embedded immediately ahead of a cold front that was moving through the area. An image of the observations and position of the cold front at the time can be seen below:
The showers/storms developed where winds were coming together, or converging. Winds ahead of the cold front near Holland were from the west. Winds behind the cold front near Muskegon were from almost the north. The cold front was likely just north of Holland at the time of the waterspouts. This change in wind direction over a short distance combined with the other ingredients listed above, helped to produce the waterspouts when the showers/storms developed upward into the sky on top of the wind change. This term is called "stretching" by meteorologists. The change in wind direction at the surface is stretched up into the sky by the developing showers/storms. If this change in wind direction is maintained vertically and all of the other ingredients are present, rotation occurs, and a waterspout develops.