This article was written by Emily Bowers, Minneapolis Park and Recreation Board Naturalist at North Mississippi Regional Park
One of the more exhilarating aspects of summer is the opportunity to experience the tremendous nature of thunderstorms. A warm, sunny day can quickly transition to an increasingly dark and cloudy afternoon until the sky bursts with pouring rain, flashes of lightning and claps of thunder. Then as effortlessly as it arrived, the clouds break enough to allow the sun’s evening light to set the sky aglow with orange and pink hues. Creatures resume their daylight tasks; muskrats foraging in the water, toadlets hopping for safety, nighthawks and swallows catching a last feast of insects for the day before the cover of night blankets the world. Summer storms truly provide an opportunity to marvel at the spectrum the natural world offers.
Thunderstorms are short-lived, but tumultuous weather events are typically associated with dense clouds, heavy rain or hail, lightning, thunder and strong winds. These storms form in a three stage cycle: developing (or cumulus), mature and dissipating. Throughout the day, the sun heats Earth’s surface and warms the surrounding air. Since warm air has a lower density than cool air, it rises creating an updraft. When that air contains a lot of moisture, as it usually does during the muggy days of summer, the humid air current condenses as it reaches the cooler temperatures higher up and this forms a cumulus cloud.
As condensation builds, the cloud grows vertically and develops into a towering cumulus (cumulus congestus) with a top that looks like cauliflower heads. The cloud becomes very large and the condensed water in it becomes heavy. The updraft can no longer support the weight and raindrops fall through the cloud creating a downdraft. Upon entering the mature stage, the cloud becomes a cumulonimbus because it has an updraft, a downdraft, and precipitation with an anvil-shaped top. Electrical charges accumulate on water droplets inside the cloud until they become strong enough to discharge in the form of lightning. The heat of lightning passes through the air with such speed and intensity that shock waves are produced, which are heard as thunder. The thunderstorm begins to dissipate after large amounts of precipitation have been produced and the updraft is overcome by the downdraft. The storm dies out with light rain as the cloud disappears from bottom to top.
An estimated 16 million thunderstorms occur each year worldwide, and roughly 2,000 thunderstorms are in progress globally at any given time. Thunderstorms occur in almost every region of the world, though they are rare in polar regions. The United States experiences about 100,000 thunderstorms each year with the highest frequency happening in Florida at more than 90 thunderstorm days per year. Minnesota’s location in the upper Midwest provides some of the widest variety of weather in the United States. The heat and humidity that predominate our summers help to initiate thunderstorm activity 30–40 days per year. In fact, rainfall during the summer months accounts for almost half of our annual precipitation due to the frequency of summer storms.
Minnesotans tend to feel that the majority of the year is dominated by the icy cold of winter and that the warmth of more temperate seasons is fleeting. However, rain alone (not mixed with snow) is the most common form of precipitation for nearly nine months of the year, from early March through late November. The sunniest and warmest part of the year is from May through September, but it is also the middle of the wet season. June is the wettest month in Minnesota with the most rain falling during the 31 days centered around June 18. The average total accumulation for the month is 4.3 inches, which puts us right in the middle compared to other U.S. states. In Minnesota, the date with the highest percent chance of rain for the year is this month on June 19.
While thunderstorms are one of the more thrilling types of weather phenomena, they can also be dangerous. Ordinary thunderstorms are the common summer storm that involve rain, occasionally small hail, and last around an hour. Severe thunderstorms however, can last several hours and are capable of producing large hail, strong winds, intense rain, flash floods and tornadoes. On average, 44 tornadoes touch down in Minnesota each year with June being the peak tornado month. Weather-related sirens are triggered when the National Weather Service has issued severe weather warnings. If a storm hits, find shelter away from windows, preferably on a lower level or in a basement, making sure you have a way to get up-to-date info. Find out more from the National Weather Service at weather.gov to receive notifications or preparedness plan information.
Minneapolis Park and Recreation Board program buildings remain closed to the public until further notice due to the impacts of COVID-19. The MPRB’s priority is the health and safety of our park visitors and our employees. The MPRB urges park users to follow park use guidelines:
- Do not visit parks or trails if you feel sick.
- Take social distancing seriously. Stay at least six feet apart from other park users not part of your household.
- Wash your hands immediately before and after visiting a park.
- Walk to local parks. Do not drive across the city or metro to visit popular park attractions.
- Do not hang out at the park all day. Visit to walk, bike or roll, then return home.
Visit minneapolisparks.org/coronavirus or sign up to receive email updates at minneapolisparks.org/subscribe by selecting “COVID-19” in the “News Updates” section.
Do you have a question about nature in your own backyard? Then send it our way by emailing northmississippi@minneapolisparks.org and it could appear in a future article. Like us on Facebook to stay in the loop about what is happening at your park.