2021 Weather In Review: Gettysburg National Military Park and Eisenhower National Historic Site

"Gettysburg" by Matt Evans (Flickr / CC BY-NC 2.0)

In order to better understand ecosystem health in national parks, the Mid-Atlantic Inventory and Monitoring Network measures ecosystem "vital signs" across the Mid-Atlantic region. One of those vital signs is weather and climate. Below is a summary of 2021 weather conditions in Gettysburg National Military Park and Eisenhower National Historic Site.

This brief provides county-scale weather data for Adams County, PA, including data from 1895–2021 (i.e. period of record). Data and analyses herein are courtesy of the National Oceanic and Atmospheric Administration's (NOAA) Climate at a Glance Program.

Weather vs. Climate

First of all, what is the difference between weather and climate? Weather consists of the short-term (minutes to months) changes in the atmosphere. Weather is what is happening outside at this very moment, be it rain, snow, or just a warm sunny day. Climate is what you expect to see based on long-term patterns of over 30 years or more. An easy way to remember the difference is that climate is what you might expect, like a hot summer, and weather is what you get, like a warm rainy day.

The following information includes a discussion of 2021 weather placed in the context of long-term climate (i.e. how did 2021 compare to a "normal" year?).

2021 Summary

In all, 2021 was an extremely warm year with precipitation that was near normal. The year ended as the 4^th warmest and 61^st wettest on record. Data indicate that over the long term, annual average temperature and annual total precipitation have both increased (+0.21 °F per decade and +0.28 inches per decade, respectively).

Temperature

In total, 2021 was the 4^th warmest year at the parks since 1895 with all seasons being much warmer than normal (Figure 1). Ten months had higher than normal temperatures with March, August, October, and December all being more than 4 °F above long-term averages (Table 1).

Figure 1. Seasonal and annual temperature rankings for Adams County, PA. An arrow at the top of the figure would represent the warmest year/season on record (since 1895); at the bottom, the coldest year/season on record.

_{Table 1. Monthly and annual average temperature and departure from long-term averages. Departures from average show how different 2021 was compared to relevant averages from 1895-2020.}

Month/Year	Average temperature (°F)	Departure from long-term average (°F)
January	32.6	+3.8
February	30.7	+0.3
March	44.2	+4.6
April	52.8	+2.6
May	60.3	-0.4
June	71.6	+2.5
July	75.1	+1.5
August	75.7	+4.1
September	67.4	+2.6
October	60.3	+6.8
November	41.8	-0.5
December	39.5	+7.2
2021	54.3	+2.9

Precipitation

Total precipitation in 2021 was near normal (i.e. 61^st wettest year recorded; Figure 2). That said, the summer was very wet though the other seasons were dry. In all, the county received just 0.09 inches more than the long-term average (Table 2).

Figure 2. Seasonal and annual precipitation rankings for Adams County, PA. An arrow at the top of the figure would represent the wettest year/season on record (since 1895); at the bottom, the driest year/season on record.

_{Table 2. Monthly and annual total precipitation and departure from long-term averages. Departures from average show how different 2021 was compared to relevant averages from 1895-2020.}

Month/Year	Total precipitation (in.)	Departure from long-term average (in.)
January	1.47	-1.62
February	3.37	+0.56
March	2.82	-0.81
April	2.76	-0.80
May	3.60	-0.42
June	2.90	-1.11
July	4.14	+0.17
August	5.43	+1.50
September	10.55	+6.75
October	3.41	-0.03
November	1.47	-1.62
December	0.76	-2.50
2021	42.68	+0.09

Temperature and Precipitation Trends
(1895-2021)

Data for Adams County, PA indicate that annual average temperature has increased
approximately +0.21 °F per decade and annual total precipitation has increased approximately +0.28 inches per decade since 1895 (Figure 3).

National Park Service scientists have forecast future changes in climate too. Models estimate that by 2100, annual average temperature at the park will increase by 3.1–9.2 °F (from a best-case to worst-case scenario, respectively). Annual total precipitation is expected to increase by 7–14% (see Gonzalez et al., 2018 for details).

Figure 3. Annual average temperature (°F) and annual total precipitation (in.) for Adams County, PA, from 1895–2021. Dashed lines represent linear estimates of change.

Climate Change

Today's rapid climate change challenges national parks in ways we've never seen before. Wildlife migrations are altered, increasingly destructive storms threaten cultural resources and park facilities, habitat is disrupted—the list goes on. Go to the NPS Climate Change site to discover how climate change is affecting our nation's treasures, what the National Park Service is doing about it, and how you can help.

A summary of the Mid-Atlantic Network's weather and climate monitoring program can be found here. For more information, contact Mid-Atlantic Network Biologist, Jeb Wofford.

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