More frost-free days are expected in the Pittsburgh region due to the warming climate

PITTSBURGH (KDKA) – Much of western Pennsylvania and northern West Virginia experienced the first hard frost and even light frost of the season Friday morning.

As usual, the coldest temperatures occurred outside the urban heat island of Pittsburgh, with places like Butler, Washington, Indiana and Somerset falling to freezing.

There was no frost overnight in Pittsburgh, which was expected. However, the average first day of frost for Pittsburgh is imminent, according to the 1991-2020 climate normal period.

Pittsburgh’s average first frost protection is October 20th, while the average last frost protection is April 25th.

A frost marks the end of the growing season, but the length of frost-free days has increased both locally and nationally in recent decades.

Let’s examine the climatology of the first and last freeze dates in Pittsburgh. We will use Pittsburgh International Airport, which has climate records dating back to 1948.

This will allow us to build a better climatology since, according to the World Meteorological Organization, a climatic normal period is 30 years. Additionally, Pittsburgh’s long-term climate locations shifted from the city center to the Allegheny County Airport several times before 1952.

The base period from 1948 to 2023 has an average first frost day of October 18 and an average last frost day of April 27. When calculating new climatic normal periods each decade, a practice conducted by NOAA’s National Centers for Environmental Information (NCEI) to capture changes in a location’s climate, we observe a decline in the number each decade in Pittsburgh frost-free days.

This can also be interpreted as a longer growing season. In the current climatic normal period, the growing season increased by four days between 1981-2010 and 1991-2020 in Pittsburgh. This local trend is part of a national trend, as climate change leads to warmer, shorter winters, among a host of other changes.

While some see the benefit of a warmer winter due to lower heating costs and more opportunities for outdoor recreation, there are long-term consequences.

According to Climate Central, the growing season in the U.S. is two weeks longer compared to the early 20th century. Warmer nights lead to reduced quality of some plants and grains.

Certain plants require a certain number of chill hours to enter dormancy and emerge healthy in the spring. Therefore, a longer growing season is not beneficial in this regard.

More pests and disease-carrying insects such as ticks and mosquitoes also thrive, especially when the ground doesn’t freeze as long or as deeply.

For people with severe allergies, a later first freeze and an earlier last freeze results in a longer and more severe allergy season. Finally, the long-term trend of warming will ultimately lead to a geographical shift in which certain crops and plants were able to grow in the past.