2023 Weather in Review: Valley Forge National Historical Park

NPS

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 2023 weather conditions at Valley Forge National Historical Park.

This brief provides county-scale weather data averaged from all of the counties surrounding the park, including data from 1895–2023 (i.e., period of record). These counties include Chester and Montgomery counties, PA. 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 2023 weather placed in the context of long-term climate (i.e., how did 2023 compare to a "normal" year?).

2023 Summary

In all, 2023 was extremely warm but total precipitation was closer to normal. The year ended as the 4^th warmest and 46^th wettest on record (since 1895) for the park. Data indicate that over the long term, annual average temperature and annual total precipitation have both increased in the counties surrounding the park (+0.3°F per decade and +0.33 inches per decade, respectively).

Temperature

In total, 2023 was the 4^th warmest year ever recorded at the park with winter and autumn being particularly warm (Figure 1). Nine months had higher than normal temperatures with December, January, and February all being more than 7.5°F above long-term averages (Table 1).

Figure 1. Seasonal and annual temperature rankings for park counties. 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. Winter = Jan–Mar, Spring = Apr–June, Summer = July–Sept, Autumn = Oct–Dec.

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_{Table 1. Monthly and annual average temperature and departure from long-term averages. Departures from average show how different 2023 was compared to relevant averages from 1895-2022.}

Month/Year	Average temperature (°F)	Departure from long-term average (°F)
January	40.2	+10.8
February	39.3	+8.4
March	42.2	+2.4
April	55.9	+5.4
May	59.5	−1.6
June	67.8	−1.9
July	76.8	+2.3
August	73.2	+0.8
September	67.4	+1.8
October	57.7	+3.5
November	42.6	−0.6
December	40.8	+7.6
2023	55.2	+3.2

Precipitation

The year 2023 was slightly above normal for total precipitation, with a wet autumn and spring and a dry winter. In all, it was the 46^th wettest year recorded at the park (Figure 2), with 47.5 inches of total precipitation (Table 2).

Figure 2. Seasonal and annual precipitation rankings for park counties. 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. Winter = Jan–Mar, Spring = Apr–June, Summer = July–Sept, Autumn = Oct–Dec.

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_{Table 2. Monthly and annual total precipitation and departure from long-term averages. Departures from average show how different 2022 was compared to relevant averages from 1895-2021.}

Month/Year	Total precipitation (in.)	Departure from long-term average (in.)
January	3.62	+0.20
February	1.50	−1.52
March	2.45	−1.34
April	4.16	+0.44
May	0.79	−3.18
June	6.25	+2.20
July	6.42	+1.82
August	2.91	−1.63
September	5.78	+1.79
October	1.56	−1.90
November	3.12	−0.24
December	8.96	+5.28
2023	47.52	+1.94

Temperature and Precipitation Trends
(1895-2023)

Data for Chester and Montgomery counties, PA indicate that annual average temperature has increased approximately +0.3°F per decade and annual total precipitation has increased approximately +0.33 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 3.1–9.0°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.) from 1895–2023 for Chester and Montgomery counties, PA. 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. Data included in this article were obtained from NOAA's NClimDiv dataset (version v1.0.0-20240105).

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