More freeze-free days expected in Pittsburgh area due to a warming climate
PITTSBURGH (KDKA) - A large portion of western Pennsylvania and northern West Virginia experienced their first substantial frost and even light freeze of the season on Friday morning.
As usual, the coldest temperatures occurred outside of the Pittsburgh urban heat island with locations like Butler, Washington, Indiana and Somerset dropping to freezing.
Pittsburgh did not have a freeze overnight, which was expected, however, the average first freeze date for Pittsburgh is right around the corner, according to the 1991-2020 climate normal period.
Pittsburgh's average first freeze is October 20, while the average last freeze is April 25.
A freeze marks the end of the growing season, but the length of freeze-free days has been growing over recent decades both locally and nationally.
Let's examine Pittsburgh's first and last freeze date climatology. We will use Pittsburgh International Airport, which has climate records extending back to 1948.
This will allow us to build a better climatology since a climate normal period is 30 years, according to the World Meteorological Organization. Also, Pittsburgh's long-term climate sites shifted several times ranging from the downtown area to the Allegheny County Airport before 1952.
The base period from 1948-2023 has an average first freeze date of October 18 and an average last freeze date of April 27. When calculating new climate normal periods each decade, a practice that is carried out by NOAA's National Centers for Environmental Information (NCEI) to capture changes in a location's climate, we see a decrease in the number of freeze-free days each decade in Pittsburgh.
This can also be interpreted as a longer growing season. The current climate normal period saw an addition of four days to the growing season between 1981-2010 and 1991-2020 in Pittsburgh. This local trend is part of a national trend as climate change is leading 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 across the US is two weeks longer compared to the beginning of the 20th century. Warmer nights will lead to reduced quality of some plants and grains.
Certain plants need a particular number of chill hours in order to go dormant and emerge healthy in the spring, so a longer growing season is not beneficial in that regard.
More pests and disease-carrying insects, such as ticks and mosquitos, are also able to thrive, especially with the ground not freezing as long or as deep.
For those with severe allergies, a later first freeze, and earlier final freeze, leads to a longer and more severe allergy season. Lastly, the long-term trend of warming will ultimately lead to a geographical shift where certain crops and plants have been able to historically grow.
