2020 Weather in Review: Assateague Island National Seashore

Assateague Island National Seashore

NPS/Baranowski

Weather and climate play significant roles in driving both physical and ecological processes. For example, the active processes that shape the North Atlantic coastline are largely the result of meteorological events such as wind-driven waves. For research and long-term ecological monitoring, weather and climate data provide the potential for correlations to be made with observed physical and ecological pattern data.

This resource brief provides a summary of both historic and current (2020) weather data for Assateague Island National Seashore (ASIS), Maryland (MD). Information in this brief represents county-scale weather data averaged from the county surrounding the park, Worchester County, MD. Because tide levels and wind can be significant for coastal parks, the annual water level and wind data are included. Individual weather station data may vary from what is reported here. Data are available from the National Climate Data Center.

Temperature

Overall, 2020 was the 2^nd warmest year on record with an average temperature of 59.4 °F — 3.1 degrees above average (Figure 1). Spring nearly reached “above normal” temperatures, while summer, autumn, and winter seasons fell within “much above normal” temperatures. 2020 had the 2^nd warmest winter on record. The warmest month was July with an average of 81 degrees — 4.7 degrees over the monthly average. Every month had higher than average temperatures, except May at 1.4 degrees below average (Table 1).

Figure 1. Worcester County, Maryland annual and seasonal temperature rankings from 1895-2020. Of the 126 records, 2020 was the 2nd warmest year. Seasonally, it was the 2nd warmest winter, 48th warmest spring, 7th warmest summer, and the 4th warmest autumn.

Table1. Worcester County, Maryland average monthly, average annual, and departures from long-term average temperatures. Departures from average are based on a comparison of 2020 average temperatures to relevant averages from 1895-2019.

Month (2020)	Average temperature (°F)	Departure from long-term average temperature (°F)
January	43.0	+6.8
February	43.6	+6.7
March	50.5	+6.3
April	53.6	+0.5
May	61.4	-1.4
June	73.5	+2.1
July	81.0	+4.7
August	78.3	+3.2
September	70.1	+0.9
October	62.4	+3.7
November	53.8	+5.6
December	42.2	+2.8
Annual	59.4	+3.1

Precipitation

Overall, 2020 was the 12^th wettest year on record with a total of 54.57 inches of precipitation (Figure 2, Table 2). Seasonally, winter and summer fell within “above normal” levels, spring fell to a “below normal” level, while summer reached a “much above normal” level. Eight months had higher than average amount of precipitation. August had the greatest amount of precipitation in 2020 at 7.52 inches — 2.92 inches over the average monthly rainfall. May had the lowest amount at 1.9 inches — 1.43 inches below average.

Figure 2. Worcester County, Maryland annual and seasonal precipitation rankings from 1895-2020. Of the 126 records, 2020 was the 12th wettest year. Seasonally, it was the 45th wettest winter, 22nd driest spring, 16th wettest summer, and 2nd wettest autumn.

Table 2. Worcester County, Maryland monthly and annual total precipitation and departures from long-term average totals. Departures from average are based on a comparison of 2020 precipitation levels to relevant averages from 1895-2019.

Month (2020)	Total precipitation (in)	Departure from long-term average precipitation (in)
January	3.34	-0.14
February	4.42	+1.07
March	3.78	-0.25
April	3.35	+0.02
May	1.90	-1.43
June	2.22	-1.34
July	5.67	+1.42
August	7.52	+2.92
September	3.93	+0.30
October	5.41	+1.97
November	5.73	+2.75
December	7.20	+3.74
Annual	54.47	+11.03

Temperature and Precipitation Trends (1895–2020)

Temperature and precipitation data are gathered from the U.S. Climate Divisional Database, which stores data from January 1895 to the present, and can be accessed via the National Oceanic and Atmospheric Administration’s (NOAA) National Centers for Environmental Information (NCEI) website (Figure 3). Users can choose different geographic scales (i.e., global, national, statewide), different temporal scales, and display them in various types of graphical formats. Temperature and precipitation data presented in this brief are for Worcester County, MD.

Figure 3. Worcester County, Maryland yearly average temperature and precipitation from 1895 to 2020. Dashed lines represent the 1895-2020 trend for each parameter; +0.2°F/decade for temperature and +0.45 in/decade for precipitation.

Wind

Wind data (wind speed and direction) is collected from the NOAA National Water Level Observation Network (NWLON) station 8570283 located at the inlet of Ocean City, MD. Each direction is divided up into categories called bins that are color coated to represent the frequency of a certain wind speed. The length of the bin represents the number of times wind comes from a given direction as well as the speed of the wind. The longer the length of the bin, the more frequent the given speed was recorded (Figure 4).

Figure 4. Wind charts reflecting both the seasonal and annual wind direction and speed at the NOAA NWLON station 8570283 located at the inlet of Ocean City, Maryland during 2020.

Tide Levels

Water level data is also collected from the NOAA NWLON station 8570283 in the vicinity of the inlet at the northern end of the island. Located at the inlet of Ocean City, MD, this station has records dating back to 1978. The data is graphed to show the difference in the predicted tide level verses what was observed (Figure 5). The offsets in height reflect the effect from storm surge on the normal, astronomically driven tide level.

Figure 5. This bar graph depicts the difference in the predicted and observed tide levels at Ocean City Inlet, Maryland for 2020.

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