Pennsylvania is impacted by a number of extreme weather events. These include snow and ice storms, nor’easters, heat and cold waves, tropical cyclones, floods, and severe thunderstorms. 

A thunderstorm is basically a rain shower that also produces lightning and thunder. It is classified as a “severe thunderstorm” when it comes with at least one of the following: strong winds exceeding 57.5 miles per hour (50 knots), hail one inch or greater, or a tornado. Roughly 10,000 severe thunderstorms out of the around 100,000 thunderstorms each year hit the U.S., according to the NOAA National Severe Storms Laboratory (NSSL). 

In Pennsylvania, thunderstorms are common during the spring and summer months. They can come with lightning, hail, strong winds, flash floods, and even tornadoes. Outside of this, are thunderstorms in the Quaker State becoming more frequent and severe?

The Answer: Possibly

While we’d love to say “yes” or “no,” the answer to this question is not that simple. There seems to be no definitive data to confirm that thunderstorms are becoming more frequent or severe in Pennsylvania. However, studies have shown that heavy rainfall is becoming more prevalent in the state due to climate change. This intense precipitation can come with thunderstorms, and so, it is likely that thunderstorms could become more frequent and/or severe too. 

Tornadoes in the area have also increased in the last two decades, but more on this below. 

A Look at Past Pennsylvania Thunderstorms & Tornadoes

If we take a look at the thunderstorm events in the last 20 years or so, we’ll find most of them in the earlier half of the last two decades, while the latter half has more tornadoes. Since all tornadoes originate from thunderstorms, we can say that thunderstorms have increased and intensified.  

Table 1. Thunderstorms & Tornadoes in Pennsylvania from 2003 to 2024

Source: National Weather Service

Why Global Warming Matters

The increasing heat in the Earth’s atmosphere could play a significant role in the formation of more frequent and severe thunderstorms in Pennsylvania and elsewhere in the future. Why? You’ll have to understand how thunderstorms are formed.

The Formation of a Thunderstorm

A thunderstorm is made up of different ingredients: moisture, lifting mechanism, and unstable air. But, since climate change can intensify thunderstorm events, let’s focus on how severe thunderstorms are created instead. 

Severe thunderstorms also result from the combination of moisture, unstable air, and a lifting mechanism. However, it adds strong wind shear, or the twisting of the winds, to the mix. 

How Climate Change Affects Thunderstorm Formation

Global warming has created a warmer atmosphere. This leads to the availability of more water vapor, which could result to more intense thunderstorms.  

According to the 2024 Pennsylvania Climate Impacts Assessment, “Pennsylvania is expected to get hotter with dangerous heat waves and droughts, while at the same time experiencing more intense storms and damaging flooding.” The report reviews current scientific findings and climate projections to identify relative risks that were used to inform the state’s Climate Action Plan. 

Compared to baseline conditions from 1971 to 2000, the report expects the annual average temperature to increase by 6.7 degrees Fahrenheit by 2050. This takes into account more frequent and intense heat events and droughts as well as extreme rainfall events. For Pennsylvania, in particular, this means an increase in its total average rainfall but in less frequent but heavier rain events. 

A Continuing Trend

As of 2019, severe thunderstorms and tornado warnings in the Philadelphia region were off the charts, i.e., surpassing 2018’s total warnings for the area. There were 134 severe thunderstorm warnings and 23 tornado warnings for the year compared to 110 and 10 severe thunderstorm and tornado warnings in 2018, respectively. The thunderstorms in 2019 were even labeled “storms on steroids” by some news outlets. 

“No one predicted this would occur now,” Glenn “Hurricane” Schwartz, NBC10 First Alert Weather meteorologist, said of climate models from a generation ago. “Imagine what it’ll be like in 20 years, in 40 years.”