2020 Weather In Review: Valley Forge National Historical Park

"Cabin and Sunrays at Valley Forge" by Garen Meguerian (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 2020 weather conditions at Valley Forge National Historical Park.

This brief provides county-scale weather data averaged from all of the counties surrounding the park. These include Chester and Montgomery counties, PA. Individual weather station data may vary from what is reported here. Data are available from the National Climate Data Center.

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 2020 weather placed in the context of long-term climate (i.e. how did 2020 compare to a "normal" year?).

2020 Summary

In all, 2020 was extremely warm and precipitation was also above normal. The year ended as the 3^rd warmest and 23^rd wettest on record. Weather data collected from surrounding areas indicate that annual average temperature and annual total precipitation have both increased over the last century (+0.25 °F per decade and +0.34 inches per decade, respectively).

Temperature

In total, 2020 was the 3^rd warmest year ever recorded at the park with all seasons being very warm except the spring (Figure 1). Ten months had higher than normal temperatures with January, February, and March all being more than 6.0 °F above long-term averages (Table 1).

Figure 1. Seasonal and annual temperature rankings for Chester and Montgomery counties, 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 2020 was compared to relevant averages from 1895-2019.}

Month/Year	Average temperature (°F)	Departure from long-term average (°F)
January	36.4	+7.0
February	38.9	+8.1
March	46.0	+6.2
April	49.0	-1.5
May	59.0	-2.0
June	71.3	+1.8
July	79.1	+4.7
August	75.3	+3.0
September	66.2	+0.6
October	56.3	+2.2
November	48.9	+5.8
December	36.0	+3.0
2020	55.2	+3.2

Precipitation

It all, 2020 was the 23^rd wettest year ever recorded at the park (Figure 2). In all, 51.6 inches of precipitation fell, almost 6 inches more than the long-term average (Table 2).

Figure 2. Seasonal and annual precipitation rankings for Chester and Montgomery counties, 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 2020 was compared to relevant averages from 1895-2019.}

Month/Year	Total precipitation (in.)	Departure from long-term average (in.)
January	3.0	-0.4
February	2.8	-0.2
March	3.9	+0.1
April	4.9	+1.1
May	3.0	-1.0
June	3.2	-0.9
July	5.6	+1.0
August	8.4	+3.9
September	3.2	-0.8
October	4.1	+0.6
November	4.0	+0.6
December	5.5	+1.9
2020	51.6	+5.9

Temperature and Precipitation Trends
(1895-2020)

Data for Chester and Montgomery counties, PA indicate that annual average temperature has increased approximately +0.25 °F per decade and annual total precipitation has increased approximately +0.34 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 1895–2019 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. Click here 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 or Valley Forge Natural Resource Manager, Amy Ruhe.