Chesapeake Bay Climate Impacts Summary and Outlook
Mid-Atlantic Regional Climate Impacts Summary and Outlook: Spring 2021
- Temperatures were above normal across the Mid-Atlantic, with much of the region experiencing temperatures up to 0–2 degrees Fahrenheit above normal and some locations in Virginia, Maryland, Pennsylvania, and New York experiencing some of their warmest spring months on record.
- It was generally dry across the region, with much of Virginia experiencing 50–75% of normal rainfall. Only a small portion of the watershed, primarily in southern New York, experienced above normal (100–125%) precipitation.
- Warm and dry weather across the region was further underscored by low March snowfall, particularly in Scranton, Williamsport, and Harrisburg, Pennsylvania; Binghamton, New York; Baltimore, Maryland; and Washington, D.C.
- The 2021 Atlantic Hurricane Outlook forecasts an above-average probability for major hurricanes for the 2021 Atlantic hurricane season, with NOAA predicting 13–20 named storms, six to ten hurricanes, and three to five major hurricanes.
- A case study of urban flooding in Pittsburgh shows substantially greater rainfall depths and resulting flooding associated with precipitation events estimated with future climate model data than under Atlas 14 estimates.
Part 1: Significant Weather Events and Impacts
This March ranked among the 10 warmest Marches on record at Dulles International Airport, Virginia and among the 20 warmest on record at Baltimore and Salisbury, Maryland; Washington, D.C.; Scranton, Harrisburg, and Williamsport, Pennsylvania; Binghamton, New York; and Norfolk and Charlottesville, Virginia.1
This April ranked among the 20 warmest Aprils on record at Dulles International Airport and Norfolk, Virginia and Harrisburg, Pennsylvania.2 On April 29, low temperatures were particularly warm. Baltimore, Maryland tied its second warmest minimum temperature for the month of April with a low of 68 degrees Fahrenheit (F) while low temperatures of 65 degrees F at Dulles International Airport, Virginia and Harrisburg, Pennsylvania ranked among the top 10 warmest low temperatures for the month of April at both sites.3
This spring was among the 10 warmest on record for Scranton, Pennsylvania; Dulles International Airport and Norfolk, Virginia; and among the 20 warmest on record for Washington D.C.; Harrisburg, Pennsylvania; Baltimore, Maryland; Binghamton, New York; and Charlottesville, Virginia.4 Part 2 of this climate summary shows that spring season temperature trends were above normal for the majority of the region.
Despite a dry start to the season, Binghamton, New York experienced one of its 20 wettest spring seasons on record.5 Despite March ranking as one of the 20 driest on record for Binghamton, April and May both ranked as the 10 wettest on record, and the city also experienced its third wettest April day on record with 2.46 inches of rain on April 29.6,7 Binghamton also had a wet winter 2020–2021 season.8
In stark contrast, the springs months were among some of the driest on record at several Virginia stations. Dulles International Airport, Virginia experienced one of its top 20 driest months for each month this season, March, April, and May, which resulted in this spring season ranking among its ten driest spring season on record.9 Charlottesville, Virginia also experienced its top ten driest spring season, in part due to low precipitation in the month of May, which ranked among the ten driest Mays on record.10 Norfolk and Richmond, Virginia and Williamsport, Pennsylvania also had spring seasons that ranked among their 20 driest on record, with Norfolk and Williamsport experiencing top 20 driest Marches and Richmond experiencing an April that ranked among the top ten driest on record.11
Short-term below normal precipitation and low streamflows led to abnormally dry conditions in a small portion of the watershed starting in late March.12 Areas affected included south-central Pennsylvania, western Maryland, eastern West Virginia, and Northern Virginia.13 Widespread precipitation in early April caused the dryness to ease in these locations by mid-April.14 During the month of May, below-normal precipitation, low streamflow, and declining soil moisture led to the expansion or introduction of abnormal dryness in portions of central Pennsylvania, Delaware, Maryland, eastern West Virginia, and most of Virginia, with moderate drought introduced in part of southeastern Virginia.15 Dry conditions caused some farmers to replant crops and irrigate earlier than usual.16,17
On March 18 severe thunderstorms moved through southeastern Virginia.18 An Enhanced Fujita Scale (EF) EF-0 tornado with estimated peak winds of 85 miles per hour (mph) damaged buildings and uprooted trees in Isle of Wight County, and hail fell in several locations, with the largest stones being golf ball-sized. 19
On April 30, a high wind event with gusts of up to 71 mph knocked down trees and powerlines across Maryland and northern Virginia.20 Trees fell on houses and cars, resulting in a fatality.21 The downed trees also blocked roads, causing an accident that injured three people.22 Downed power lines left at least 65,000 customers without power and likely contributed to a house fire that caused $100,000 in damage.23,24
On May 3 and 4, severe thunderstorms produced six tornadoes, damaging wind gusts, hail, and flooding rain in parts of the watershed.25 An EF-2 tornado moved through Northumberland County, Virginia, destroying a home and damaging several additional homes and outbuildings.26 An EF-1 tornado in Ranson, West Virginia, caused roof and siding damage to several buildings, destroyed a small warehouse, snapped trees, and resulted in one injury.27 In Maryland, an EF-1 tornado in Mt. Pleasant, an EF-1 tornado in Unionville, and an EF-0 tornado in New Windsor snapped or uprooted more than 150 trees and severely damaged or destroyed several farm outbuildings.28,29 An EF-0 tornado briefly touched down near Weedville, Pennsylvania, damaging trees.30 Thunderstorms also produced straight-line wind gusts of up to 90 miles per hour in several locations in Virginia, including Lancaster and Louisa counties.31 The National Weather Service in Wakefield, Virginia noted an 89 mile per hour wind gust was recorded as a part of this system.32 The strong winds damaged buildings, overturned planes, and caused power outages. 33 Dozens of trees were downed, blocking roads and falling on houses and vehicles, resulting in one fatality.34,35 Additionally, about 4 inches of rain flooded basements and roads in parts of Wyoming and Lackawanna counties in Pennsylvania.36,37
On May 26, northern Virginia, Maryland, and central Pennsylvania experienced wind damage and hail from severe thunderstorms.38 Wind gusts reached 83 miles per hour, as recorded at a buoy near Woodbridge, Virginia.39 The strong winds blew down trees and wires, resulting in power outages, and damaging buildings and vehicles, causing an injury in Princes Georges County, Maryland.40,41 One woman was injured by falling hail near Manassas, Virginia. 42
“After February ranked in the top 10 snowiest on record, Scranton, Pennsylvania had its least snowy Marches on record. This March was also the least snowy on record in Baltimore, Maryland; Washington, D.C.; and Harrisburg, Pennsylvania, which each experienced no snow during March.43 It was among the 10 least snowy at Dulles International Airport, Virginia, and Binghamton, New York, and the 20 least snowy at Williamsport, Pennsylvania.44 In contrast, Binghamton, New York received 0.2 inches of snow this May, making it one of the site’s 10 snowiest Mays on record.45
Overall this season, Washington, D.C. recorded no snow while Dulles International Airport, Virginia received only a trace amount of snow. 46 This tied several previous years as the least snowy spring on record for both sites.47 Additionally, this spring ranked among the 10 least snowy on record for Baltimore, Maryland; Binghamton, New York; and Harrisburg and Scranton, Pennsylvania; and among the 20 least snowy for Williamsport, Pennsylvania.48
The snow season (October through May) overall ranked among the 20 least snowy on record for Dulles International Airport, Virginia; and Washington, D.C., but was among the top 20 snowiest for Binghamton, New York and Williamsport, Pennsylvania (largely due to a significant winter storm on December 16-17 and several smaller snow events throughout the month of February).49,50
Part 2: Seasonal Temperature and Precipitation
Figure 2 shows the March through May 2021 average temperature compared with the climate normal—i.e., the average temperature from 1991 to 2020.51 The figure shows that temperatures were above normal across the Mid-Atlantic, with much of the region experiencing temperatures 0–2 degrees Fahrenheit (F) above normal.
Precipitation departures from normal for March 1 through May 31, 2021 are shown in Figure 3. Departures from normal indicate where this spring season’s average daily precipitation was above or below the climate normal—i.e., the average temperature from 1991 to 2020. Figure 3 shows it was generally dry across the region with much of Virginia experiencing 50-75% of normal rainfall. Only a small portion of the watershed, primarily in southern New York, experienced above normal (100-125%) precipitation.
Part 3: Summer 2021 Outlook
Temperature and Precipitation
As of May 20, 2021, the NOAA Climate Prediction Center forecasts a 50-60-percent chance of above-normal temperatures for the majority of the Chesapeake Bay watershed and Mid-Atlantic region for June, July and August 2021.52 The precipitation forecast shows a 40-50-percent chance of wetter than normal conditions in the majority of the region for the same period.53
The U.S. Seasonal Drought Outlook identifies how drought might change across the United States and categorizes areas by whether drought could develop or become more or less intense. As of May 20, 2021, the outlook indicates no tendency toward drought for the Mid-Atlantic region.54
Atlantic Hurricane Outlook
Researchers at Colorado State University (CSU) have predicted an above-average probability for major hurricanes for the 2021 Atlantic hurricane season.55 As of June 3, 2021, CSU’s forecast anticipates 18 named storms and eight hurricanes for 2021, with a 45-percent chance of at least one major hurricane (category 3–5) making landfall on the eastern U.S. coastline.56 NOAA’s Climate Prediction Center, which issues a hurricane outlook for the Atlantic at the end of each spring season, is forecasting a 60-percent chance of an above-normal 2020 Atlantic hurricane season. NOAA’s outlook forecasts 13–20 named storms, six to ten hurricanes, and three to five major hurricanes.57 According to NOAA, “an average hurricane season produces 14 named storms, of which seven become hurricanes, including three major hurricanes.”58
NOAA’s Climate Prediction Center, which monitors the likelihood of occurrence of El Niño and La Niña climate phenomena, has a Final La Niña Advisory active as of May 13, 2021 with El Niño-Southern Oscillation (ENSO-neutral) likely to continue through the summer.59 ENSO-neutral conditions occur when tropical Pacific sea surface temperatures are close to normal and neither El Niño or La Niña conditions are present.60 ENSO-neutral conditions factored into the forecast for an above-average hurricane season.
Part 4: Future Precipitation Impacts on Stormwater Management—A Case Study of Pittsburgh, Pennsylvania
Global climate models provide projections of future precipitation conditions across the Mid-Atlantic that can serve as key inputs for stormwater management in the region. Other MARISA tools have examined these trends and made this data available, including changes in future seasonal precipitation and future extreme precipitation. Figure 4 presents the results of related analysis carried out by the MARISA team that examined how changes in future precipitation events lead to urban flooding in Pittsburgh, Pennsylvania.
This figure is based on an analysis of three projections of future precipitation, shown by the three models in the figure, compared to estimated historical precipitation events from NOAA’s Atlas 14.61 Using each dataset, the study team compared recent estimates of climate adjusted precipitation depths for combinations of event duration (e.g. 1-hour to 24-hour) and frequency (e.g. 100-year return period).62 These are shown in the top panel of Figure 4. These estimated projected and historic precipitation depths were then used as inputs to a stormwater model that calculated runoff and inundation depths across an urban catchment in Pittsburgh – Negley Run. The maps shown in Figure 4 show a selection of streets and intersections in the catchment area prone to flooding that could be represented in the simulation model. While specific to Pittsburgh, this study shows how increases in extreme precipitation events translate into urban flooding and offers a case study of solutions that may be relevant to other locations.
The Mid-Atlantic Regional Integrated Sciences and Assessments (MARISA) Seasonal Climate Impacts Summary and Outlook is a quarterly series produced by the MARISA program, a collaboration funded by NOAA through the RAND Corporation and researchers at Pennsylvania State University, Johns Hopkins University, Cornell University, and the Virginia Institute of Marine Science. This series draws information from regional climate centers, news and weather information, and regional-specific climate data sets for the benefit of policymakers, practitioners, residents, and community leaders in the Mid-Atlantic region. Projections of weather and climate variability and change in the Mid-Atlantic region come from the best available scientific information. For any questions or comments, please contact Krista Romita Grocholski at Krista_Romita_Grocholski@rand.org.
This edition of the MARISA Seasonal Climate Impacts Summary and Outlook was authored by Jordan Fischbach (The Water Institute of the Gulf and RAND Corporation), Michelle E. Miro (RAND Corporation), Krista Romita Grocholski (RAND Corporation), Jessica Spaccio (Cornell University), Samantha Borisoff (Cornell University), and Arthur T. DeGaetano (Cornell University).
Climate normals, as defined by the National Oceanic and Atmospheric Administration (NOAA), are “three-decade averages of climatological variables including temperature and precipitation.” The latest climate normal released by NOAA is the 1991–2020 average. See https://www.ncdc.noaa.gov/data-access/land-based-station-data/land-based-datasets/climate-normals#:~:text=Climate%20Normals%20are%20three%2Ddecade,variables%20including%20temperature%20and%20precipitation Return to text ⤴
For more information on how NOAA defines at, above or below normal and determines percent chances, see: https://www.cpc.ncep.noaa.gov/products/predictions/long_range/seasonal_info.php Return to text ⤴
https://www.cpc.ncep.noaa.gov/products/expert_assessment/season_drought.png; The Mid-Atlantic has experienced severe to extreme droughts in the past, most notably in the mid-1980s, the late 1990s, and the 2000s. https://onlinelibrary.wiley.com/doi/pdf/10.1111/1752-1688.12600 Return to text ⤴