May Features Peak Tornadic Activity and Chance of Tropical Weather

As the calendar flips from April to May, this is a good time to take a look at what the fifth month of the year generally brings for weather. In short, you can find a little bit of everything during the last month of the meteorological spring. Here is a deeper dive detailing what to expect in the month ahead.

Peak Tornadic Activity

May is distinguished as being the peak month for tornadoes across the U.S., coming in with an average of 260 twisters. A number of atmospheric elements make this month more likely to be a prolific producer of tornadoes. The month is sandwiched between the second-highest month for tornadoes with an average of 202 in April and the third-busiest month of the year in June with 186 accounts.

What makes May different than March and April is where the twisters are more likely to erupt. The southern tier of the U.S. tends to see more of the early-season tornadoes in March and April due to the warmer temperatures in this part of the country. However, the focus of the tornadic activity shifts to the more traditional "Tornado Alley" in the Plains and the Midwest during May.

Although the nation's heartland tends to see the most activity in May, you cannot rule out twisters forming in the South and all the way to the East Coast.

In addition to May being the peak month for the number of confirmed tornadoes, the events are also most likely to be the most destructive at this time of the year. This is evident in the statistics that show that the highest number of EF4 and EF5 tornadoes happens in May when compared to other months.

This is important to note as these violent tornadoes are also responsible for the highest fatality counts. For instance, nine of the 25 deadliest tornadoes to strike the U.S. happened in May. April and May are tied with seven each.

Forecasters also note that the tornado count in May can vary widely, making this an inexact science to predict. For example, May of 2024 notched 530 tornadoes, equating to more than double the historical average and just slightly below the May record of 542 tornadoes, dating back to 2003.

Conversely, May of 2023 only saw 169 tornadoes spring up. Likewise, May of 2020 recorded a mere 126 twisters.

So what causes a more active May as it relates to the prevalence of tornadoes? The answer lies in the amount of moisture coming up from the Gulf of Mexico. The amount of moisture-rich air filtering to the north from the Gulf is what fuels the development of thunderstorms that go on to produce tornadoes. The more pervasive temperatures in the 80s and 90s in May, when compared to earlier in the spring, also make this month more active on a widespread basis.

The position of the jet stream also promotes greater twister development in May. The energy in the jet stream is still powerful enough in May to generate strong wind shear across the Plains states, causing storm cells to spin around and produce tornadoes.

In that same vein, if the jet stream dives farther south across the eastern U.S., the end result will be cooler temperatures and less moisture for the Plains and the Midwest. Chillier temperature readings and an absence of moisture are mitigating tornadic factors, leading to the years that see less activity.

Preparing for the Start of Tropical Weather Season

The Atlantic hurricane season officially starts on June 1. However, tropical weather events have been known to roam the basin before this start date. The zone from the western Caribbean Sea and over to the southeastern coastline of the U.S. is the area most likely to see early-season development.

Going back to 1851, there have been 37 storms that have come to life in the Atlantic prior to June 1. This equates to an average of one early storm erupting every four to five years. That said, hurricane experts warn that the season has been starting earlier and earlier due to the impacts of global warming.

The most recent named storm to form before June 1 was in 2021 when Ana roamed the basin. While Ana never made landfall, 2020's Arthur and Bertha both impacted the U.S. in the month of May. Additionally, Tropical Storm Beryl came just short of reaching a hurricane designation before making landfall in northeast Florida over Memorial Day weekend in 2012.

Snow Still Hanging On

The true dichotomy of May weather is further illustrated by looking at average snowfall events in May. While most of the nation is in the clear and thinking along the lines of thunderstorms and tropical weather this time of the year, some of the higher elevations of the western U.S. are still seeing snow at times. There have also been times when late-season snow has made its way across the Plains, the Midwest, the Appalachian region, and into the Northeast.

Donner Summit, California, picked up 26.4 inches of snow over two days in early May last year. This snow event ended up being distinguished as the snowiest 24-hour period over the course of the entire season.

May of 2023 was a particularly snowy month for the top terrains of West Virginia and central Pennsylvania. Measurable snow fell during this time, catching residents off guard.

Drastic Swing in the Temperatures and Precipitation Amounts

One of the most noticeable changes that happens in May is the natural upswing in temperatures. Places such as Chicago see a climb of about 10 degrees from the beginning of the month to the end, going from an average of 65 degrees to 76 degrees. It is even hotter to the south, where Phoenix sees the mercury average temperatures around 100 degrees by the end of the month.

The shift from the wet to the dry season is another meaningful change that happens in places such as California. The dry season in the Golden State lingers throughout the summer and into the fall months.

It is an opposite situation in Florida. The Sunshine State says goodbye to the dry season in May as tropical moisture makes an appearance, signaling the start of the wet season for the peninsula. The warmer temperatures and the increasing humidity levels also support the development of more afternoon and evening thunderstorms at this time across Florida.

It is important to remember that these statistics are just trends. Nearly anything can happen during the transitional month of May.

Did you find this content useful? Feel free to bookmark or to post to your timeline for reference later.