(WKBN) — There have already been plenty of windy days across the Valley this fall and winter, and there are more on the way this week. You might have noticed that the wind is often stronger during the winter months, but why is that? We’ll explore the reasons why the wind blows and the factors that affect its strength.

When strong storm systems push into the Valley, they are usually associated with strong winds at the surface. A prerequisite for a strong storm system is large differences in temperature across short distances.

This is called a “temperature gradient” and a simple definition is: a change in temperature over a certain distance. Sometimes, the temperature can be 30-40 degrees different across a 5 mile area due to a cold front. The temperature gradient plays an important role in the location of strong winds.

In fact, the temperature gradient results in strong differences between surface pressure. The gradient of temperature and pressure is often where the jet stream is located. The jet stream is an area of strong winds above the surface that affect the location of storm system tracks.

In the summer months, the temperature gradient across the continental United States is weaker and the jet stream recedes to the north. However, when the seasons change, the temperature/pressure gradient is enhanced once again which brings stronger winds back into the area.

Polar jet streams and subtropical jet streams.
Explainer graphic of the jet stream from the National Oceanic and Atmospheric Administration.

The National Weather Service in Pittsburgh launches a weather balloon twice a day that records temperature, pressure, humidity, wind speed, etc. The data from these balloons are kept for climatology purposes.

We can use these data to asses the seasonal changes in wind speed at the surface and thousands of feet above the surface of the Earth.

First, we can look at how the wind speed changes at an air pressure of 300 mb (between 27,000 and 32,000 feet above the surface).

This graph shows the daily maximum (red), median/mean, and daily minimum value of the 300 mb wind speed from weather balloons launched at the NWS in Pittsburgh.

Notice that the average wind speed (black line) is lower during the summer months of June, July and August. During the winter and fall months, the 300 millibar wind speed approaches 80 knots for an average wind speed.

This trend also shows up in the surface wind.

Same as the first graph but for the surface wind speed.

The average surface wind speed drops from around 7 knots in the winter months to around 5 knots in the summer months.

Now you have learned that the jet stream moves depending on the time of the year and that it has large effects on wind speed. Spread the knowledge!