It’s no secret: This year has been a bad one so far for severe thunderstorms around Pittsburgh. In fact, it has been quite an active season throughout the Ohio Valley and a large part of the Midwest.

How bad has it been? In the months of March, April, May and June 2026, Pennsylvania saw a whopping 852 reports of severe weather. By my calculations, that is for the same four-month period during the past 30 years.

These severe weather patterns are similar to 2025 as well, so it’s no wonder that Pittsburghers feel there’s been a lot of severe weather recently. There has been.

My research over the past 40 years has focused on different kinds of weather phenomena. Knowing why weather events happen can give additional guidance to forecasters and improve the models we use to predict it – and help everyday people prepare for severe storms that may affect their daily lives.

How severe thunderstorms happen

Multiple factors come together to create severe storms. Generally, the winds 2-3 miles above the ground need to be at least 30-40 miles per hour greater than they are near the ground. This difference is called the vertical shear.

To form a severe storm, the air near the ground also needs to be warm and moist. These conditions make the initial clouds that form buoyant, so they accelerate upward. Strong updrafts result from this acceleration, often more than 50 mph (80 kph). That creates the billowing, deep clouds that characterize thunderstorms.

In the presence of strong vertical shear, updrafts start to rotate, which is a common precursor to large hail, tornadoes and severe winds.

The science of severe weather in 2026

In the case of the severe storm days in Pennsylvania, you may notice a few days with a large number of severe weather reports and many days with few or none. You might wonder about what is different on these days with many severe storms.

For the 11 days with at least 20 severe weather reports in Pennsylvania during the period between March 2026 and June 2026, I computed how different the meteorological conditions were compared to the average for 1996-2025.

The departure from the average is often called an anomaly. I combined all 11 severe weather days to look at the anomalies that more often repeated from case to case. The anomalies on individual days don’t look exactly like the composite, but they generally have elements in common.

High above the ground, these days shared a distinctive pattern: stronger than normal winds from the southwest. Winds at lower levels were also from a similar direction, although weaker nearer the ground. Winds from the southwest near Pittsburgh tend to bring warmer and moister air into the region, and, indeed, the moisture was considerably greater than normal on these severe weather days. And where the winds change significantly with height, we saw enhanced vertical shear.

The combined weather maps for these severe weather days revealed something else: cooler and drier air well to the west of Pittsburgh over the upper Midwest and Great Lakes, pushing eastward. This air mass contrast meant that a cold front was present to the west of Pittsburgh when the severe weather occurred. As cold fronts move in, they help lift the air ahead of them. Therefore, we had all the ingredients for severe weather: anomalously warm and moist air, enhanced vertical wind shear and a mechanism to lift air to start thunderstorm development.

What this means for next spring

Between March and June 2026, it appears that frequent strong fronts were passing through Pennsylvania more often than usual. My recent collaborative research indicates that atmospheric rivers – giant, invisible rivers in the sky made of concentrated water vapor – frequently transport moist air northeastward ahead of cold fronts. This moisture transport often coincides with days of severe weather.

What seems to have made 2026 unusual is the strength and number of frontal systems passing through, where Pennsylvania repeatedly got warm, moist air ahead of a front. This past spring, cold air over central Canada and warm air over the southern U.S. created a persistently strong jet stream and storm track just to the north of Pittsburgh, creating one severe weather setup after another.

El Niño, a natural climate pattern characterized by the episodic warming of sea surface temperatures in the central and eastern equatorial Pacific Ocean, may bring some good news for Pittsburgh residents. The one developing now could lead to less cold air over southern Canada and a jet stream farther south over the U.S.

If that pattern develops as expected and lasts into next spring, the Pittsburgh area may get a relative reprieve from severe weather. That doesn’t mean there won’t be any severe weather in later 2026 and in spring 2027, but it could be less frequent.

Read more of our stories about Pittsburgh and Pennsylvania.

Christopher Davis receives funding from the U.S. National Science Foundation, the National Aeronautics and Space Administration, and the State of California.