Chesapeake Bay Climate Impacts Summary and Outlook

Chesapeake Bay Watershed Climate Impacts Summary and Outlook: Winter 2018-2019

The MARISA Seasonal Climate Impacts Summary and Outlook is a quarterly series produced by the Mid-Atlantic Regional Integrated Sciences and Assessments (MARISA) program, a collaboration funded by NOAA through RAND and researchers at Pennsylvania State University, Johns Hopkins University, and Cornell University. This series draws information from regional climate centers, news and weather information, and regional-specific climate datasets for the benefit of policymakers, practitioners, residents, and community leaders in the Chesapeake Bay Watershed. Projections of weather and climate variability and change in the Chesapeake Bay Watershed come from the best available scientific information. Part 1 details significant weather events that occurred in the Winter 2018-2019 season. Part 2 characterizes seasonal temperature and precipitation compared to historical averages. Part 3 describes seasonal weather forecasts and pertinent information for the upcoming Spring 2019 season. Part 4 includes an analysis of multi-decadal changes in seasonal precipitation, accompanied by interactive maps of climate projections.

Part 1: Significant Weather Events

From December 2018 through the end of February 2019, extreme weather events caused disruptions, delays, and damages within the Chesapeake Bay Watershed. A December snowstorm dropped up to 15.2 inches of snow on western and central Virginia from December 9th-10th. Richmond, VA, had its greatest daily snowfall for December 9th on record, with 11.5 inches over the storm duration recorded at the Richmond airport.1 The National Weather Service reported that for all stations monitored by the Blacksburg, Virginia weather forecast office, this was the earliest large December snowfall on record2. The storm caused travel delays and power outages.

From January 12 to 14, a winter storm brought up to 13 inches of snow to the region, with the greatest amounts falling in Maryland, northern Virginia, and the Eastern Panhandle of West Virginia.3 Freezing rain and sleet also fell, particularly in parts of central and western Virginia, and the storm caused more than 250 flight cancellations on January 13 at Washington D.C.’s three main airports.4

A week later, from January 19 to 20, another storm dropped up to a foot of snow on the region. Central Pennsylvania saw snow accumulations over the duration of the storm of 12 inches in Wellsboro, Pennsylvania and nine inches in Stormstown, Pennsylvania.5 A flash freeze that accompanied the storm brought dangerous temperatures and unsafe roadway conditions in Pennsylvania and Maryland.6

In late January 2019, the polar vortex (see Figure 1) pushed into the northern Midwest, resulting in cold, windy weather across the Mid-Atlantic region.7 On January 31, Washington, D.C.’s Dulles airport recorded a temperature of 5°F, with wind chill values between -3 to -5°F, prompting the closure or delay of numerous schools in metropolitan D.C.8,9 In Central Pennsylvania, in response to below 0°F temperatures and even lower wind chill values, many schools across the region, including Pennsylvania State University, closed on January 31, 2019.10,11

Figure 1.The Polar Vortex Explained

Source: NOAA, 2019

On February 20, a winter storm brought a mix of snow, sleet, freezing rain, and rain to the region. The greatest storm total snow accumulations were up to 10 inches in south central Pennsylvania12 and western Maryland.13 Impacts from the storm included dangerous travel conditions, thousands of power outages, and schools and government offices being closed.14

On February 24 and 25, wind gusts of up to 81 mph, recorded in Nelson County, Virginia, downed numerous trees and wires, leading to power outages and some closed roads across the Chesapeake Bay region.15

Part 2: Seasonal Temperature and Precipitation

Temperature

An analysis of Winter 2018-2019 average temperature, compared to the normal average from 1981 to 2010, indicates above-normal departures from normal temperature for most of the Chesapeake Bay watershed, including increases above 3°F in winter temperatures in portions of West Virginia and along the Chesapeake Bay. Baltimore, Maryland, for example, had the warmest New Year’s Day since 2005 with temperatures hitting 61°F,16 compared to a normal daily temperature of 42°F.17

Figure 2. December 1, 2018-February 28, 2019 Departure from Normal Temperature (°F)

Note: Normal average temperature is based on temperature data from 1981-2010. Red indicates above normal temperature.

Source: Northeast Regional Climate Center, 2019.

Precipitation

Between December 1, 2018 through February 28, 2019, precipitation departures from normal historical precipitation for the period 1981 to 2010 show that most of the region experienced increases in precipitation compared to historical normal precipitation. Western Virginia, southern and central Pennsylvania and western Maryland experienced the highest rates of precipitation departures—between 150 and 200 percent of normal. Areas vulnerable to flooding in the southern reaches of the Chesapeake Bay also saw precipitation nearly double, compared to historical averages during this period.

Figure 3. December 1, 2018-February 28, 2019 Percent of Normal Precipitation

Note: Normal seasonal precipitation is based on precipitation data from 1981-2010. Brown indicates below normal seasonal precipitation.

Source: Northeast Regional Climate Center, 2019.

Snowfall

An analysis of how total winter snowfall between December 1, 2018 and February 28, 2019 compared to historical averages shows that the region experienced two different trends in snowfall. The majority of the northern two-thirds of the Chesapeake Bay watershed (northern Maryland and Pennsylvania) saw snowfall at 50-75 percent of normal, a decrease in total winter snowfall. Much of Virginia, however, experienced increases in snowfall compared to normal, with snowfall at 150-200 percent of normal or higher. The decrease in snowfall in the northern Chesapeake Bay watershed, combined with increases in total winter precipitation (see Figure 3), suggests that more precipitation is falling as rain, rather than snow, in northern Maryland and Central Pennsylvania.

Figure 4. December 1, 2018-February 28, 2019 Percent of Normal Snowfall

Note: Normal seasonal snowfall totals are based on snowfall records from 1981-2010.

Source: Northeast Regional Climate Center, 2019.

Part 3: Spring 2019 Outlook

Temperature and Precipitation

As of February 5, 2019, NOAA's Climate Prediction Center forecasts a 33-40 percent chance of temperatures above normal. The precipitation forecast shows a 33-40 percent chance of precipitation above normal in the Southern half of the watershed for March–May 2019 in the Mid-Atlantic region.18

Drought Incidence

The U.S. Seasonal Drought Outlook identifies areas of drought across the United States and categorizes them by level of intensity. As of February 21, 2019, the outlook indicates no drought for the Chesapeake Bay Watershed.19

El Niño Watch

NOAA's Climate Prediction Center, which monitors the likelihood of occurrence of El Niño and La Niña climate phenomena, has issued a El Niño Advisory, meaning that weak El Niño conditions have formed and are likely to effect the Northern Hemisphere through Spring 2019.20 El Niño is a climate phenomenon characterized by a warming of the sea surface temperatures in the central and eastern tropical Pacific Ocean that leads to changes in weather across the globe. In the Mid-Atlantic, large storm events are more frequent during El Niño due to warmer ocean temperatures.21 While this generally results in wetter weather, weather impacts to the Chesapeake Bay Watershed can be difficult to predict.

Part 4: Seasonal Precipitation Trends and Projections

The following figures provide detail on how the total precipitation occurring each season has changed over time (Figure 5) and could change into the future (Figure 6). In some areas, such as the northern region of the Chesapeake Bay Watershed, total winter precipitation has increased between 2006-2017 compared to historical averages, while fall total precipitation has decreased. Further, our analysis of future projections of seasonal total precipitation suggests that increases in winter precipitation, compared to historical averages, could continue. Precipitation shifts in magnitude, intensity and timing will likely necessitate changes in management of stormwater systems, reservoirs, agriculture, and urban planning.

Change in Seasonal Total Precipitation from 1976 to Present

Key Findings

  • In general, the region has experienced increases in summer seasonal precipitation from 2006-2017 compared to historical averages, with higher percentage increases in the eastern half of the Chesapeake Bay Watershed.
  • Southeastern Chesapeake Bay has seen notable decreases in winter and spring total precipitation.

How to Use the Tool

Viewing individual locations trends over time:
By holding your mouse over an individual grid cell, a window that shows trends in the seasonal total precipitation will pop up. This data was calculated for each year of the analysis and for each grid cell.

Filtering by geography:
Using the dropdown menu, users should first select a geographic level—the entire watershed, state, county or municipality. A list of states, counties or municipalities will appear, and individual locations can then be selected.

Technical Notes

The ChesWx gridded climate datasets contain daily interpolations of precipitation and temperature observations for the Chesapeake Bay watershed, as well as the broader Mid-Atlantic and surrounding regions. Data are available from 1948 to 2017 at 4km spacial resolution. For this study, we utilized ChesWx daily precipitation data over the Chesapeake Bay watershed from 1976 to 2017. Access ChesWx data and learn more about the ChesWx methodology and input datasets.

Seasonal total precipitation was determined for each season by summing all daily precipitation events that occurred for each three-month season. We calculated seasonal total precipitation for each season for each year and the averaged values for each season across 30-year periods – 1976-2005, 2006-2035, 2036-2065, 2066-2095 for LOCA data for both RCP 4.5 and RCP 8.5 and 1976-2005, 2006-2017 for ChesWx data. To average across climate models for each grid cell in the LOCA dataset, we employed a weighted average provided by the Northeast Regional Climate Center. Both LOCA and ChesWx datasets were masked to the boundaries of the Chesapeake Bay watershed before calculating seasonal precipitation values and the spatial resolution of each dataset was preserved. Winter is defined as December, January and February. Spring is defined as March, April and May. Summer is defined as June, July and August. Fall is defined as September, October and November.

Change in Future Seasonal Total Precipitation

Key Findings

  • All future time periods and emissions scenarios show increases in seasonal total precipitation in the winter and spring across the Chesapeake Bay watershed. This is consistent with increases in precipitation seen in the Winter 2018-2019 season (see Figure 3).
  • Winter precipitation could increase by as much as 30 percent in the northwestern region of the Chesapeake Bay Watershed by the end of the century. Combined with projected changes in spring precipitation, heightened winter precipitation could lead to more dramatic spring flooding as snow melts and spring precipitation increase simultaneously.

How to Use the Tool

Selecting future time periods and emissions scenarios:
The slider bar to the right of the figure under Time Period allows the user to adjust the future time period used to calculate the projected change in precipitation. For each time period, the user can also select a future greenhouse gas emissions scenario under Future Emissions Scenario by selecting Moderate Emissions future, Representative Concentration Pathway (RCP) 4.522, or a High Emissions future, RCP 8.5.23

Viewing individual locations trends over time:
By holding your mouse over an individual grid cell, a window that shows trends in the seasonal total precipitation will pop up. This data was calculated for each year of the analysis, for each grid cell and will change as you select different metrics, years and future emissions scenarios using the instructions above.

Filtering by geography:
Using the dropdown menu, users should first select a geographic level—the entire watershed, state, county or municipality. A list of states, counties or municipalities will appear, and individual locations can then be selected.

Technical Notes

LOCA or Localized Constructed Analogs is a downscaled climate data product available at 1/16thdegree (6 km) resolution over the continental United States. LOCA datasets include the 32 climate models available in the CMIP5 archive, for two future greenhouse gas concentration trajectories – RCP 4.5 and RCP8.5. For this study, we utilized LOCA data over the Chesapeake Bay watershed from 1976-2095. Access LOCA datasets and learn more about the methodology.

Seasonal total precipitation was determined for each season by summing all daily precipitation events that occurred for each three-month season. We calculated seasonal total precipitation for each season for each year and the averaged values for each season across 30-year periods – 1976-2005, 2006-2035, 2036-2065, 2066-2095 for LOCA data for both RCP 4.5 and RCP 8.5 and 1976-2005, 2006-2017 for ChesWx data. To average across climate models for each grid cell in the LOCA dataset, we employed a weighted average provided by the Northeast Regional Climate Center. Both LOCA and ChesWx datasets were masked to the boundaries of the Chesapeake Bay watershed before calculating seasonal precipitation values and the spatial resolution of each dataset was preserved. Winter is defined as December, January and February. Spring is defined as March, April and May. Summer is defined as June, July and August. Fall is defined as September, October and November.

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This summary is the start of a series of climate summaries produced by MARISA for stakeholders, decisionmakers and water managers in the Chesapeake Bay watershed. For any questions or comments, please contact Krista Romita Grocholski at Krista_Romita_Grocholski@rand.org.

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Footnotes

  1. https://www.washingtonpost.com/weather/2018/12/10/historic-mid-atlantic-december-snowstorm-heres-how-much-fell/?utm_term=.18c8489a8763 /a> Return to text ⤴

  2. Including Roanoke, Lynchburg, Danville, Bluefield and Blacksburg, Virginia. Lynchburg is located in the Chesapeake Bay Watershed. https://www.weather.gov/rnk/2018_12_9_10_WinterReturn to text ⤴

  3. https://www.wpc.ncep.noaa.gov/storm_summaries/storm1/stormsum_10.html Return to text ⤴

  4. https://www.nbcnews.com/news/us-news/least-7-dead-after-winter-storm-pummels-mid-atlantic-n958176 Return to text ⤴

  5. https://www.wpc.ncep.noaa.gov/storm_summaries/storm2/stormsum_11.html Return to text ⤴

  6. https://www.nytimes.com/2019/01/20/us/winter-storm-flash-freeze.html Return to text ⤴

  7. https://www.washingtonpost.com/weather/2019/01/29/polar-vortex-descends-midwest-with-life-threatening-wind-chills/?noredirect=on&utm_term=.935687d26a57 Return to text ⤴

  8. https://www.washingtonpost.com/weather/2019/01/31/dc-area-forecast-bitter-arctic-air-today-with-snow-showers-possible-tomorrow/?noredirect=on&utm_term=.edd3449d4caf Return to text ⤴

  9. https://www.washingtonpost.com/local/school-closings-and-delays-for-jan-31/2019/01/30/98ae9020-2499-11e9-90cd-dedb0c92dc17_story.html Return to text ⤴

  10. https://news.psu.edu/story/556688/2019/01/30/campus-life/university-park-early-dismissal-jan-30-cancellation-jan-31Return to text ⤴

  11. https://www.heraldmailmedia.com/weather/closings/weather-related-delays-closings-and-cancellations---jan/article_6548d936-7b23-529f-8ffc-3e3584855355.html Return to text ⤴

  12. https://www.usatoday.com/story/news/2019/02/20/winter-storm-snow-ice-heavy-rain-set-hit-39-states/2921511002/Return to text ⤴

  13. https://www.weather.gov/lwx/pnsmap?type=snow&date=20190220&option=snow Return to text ⤴

  14. https://www.washingtonpost.com/local/no-signs-of-snowflakes-for-close-in-dc-region--yet/2019/02/20/630310e8-34f9-11e9-a400-e481bf264fdc_story.html?noredirect=on&utm_term=.58132f248a08Return to text ⤴

  15. https://www.wusa9.com/article/weather/weather-blog/damaging-winds-in-dc-maryland-virginia-monday-heres-how-high-the-winds-gusted/65-0b1067af-e56d-4e18-842f-d5a2273411d1Return to text ⤴

  16. https://mesonet.agron.iastate.edu/sites/hist.phtml?network=MD_ASOS&station=BWI&year=2019&month=01Return to text ⤴

  17. https://www.weather.gov/lwx/bwinme#jan Return to text ⤴

  18. http://www.cpc.ncep.noaa.gov/products/predictions/long_range/seasonal.php?lead=2 Return to text ⤴

  19. http://www.cpc.ncep.noaa.gov/products/expert_assessment/season_drought.png Return to text ⤴

  20. https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html Return to text ⤴

  21. https://www.weather.gov/media/akq/cliSUM/ENSO_CPC_Presentation.pdf Return to text ⤴

  22. More information on RCP 4.5 can be found in: Thomson, A.M., Calvin, K.V., Smith, S.J. et al. Climatic Change (2011) 109: 77. https://doi.org/10.1007/s10584-011-0151-4 Return to text ⤴

  23. More information on RCP 8.5 can be found in: Riahi, K., Rao, S., Krey, V. et al. Climatic Change (2011) 109: 33. https://doi.org/10.1007/s10584-011-0149-yReturn to text ⤴

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