Chesapeake Bay Climate Impacts Summary and Outlook

Mid-Atlantic Regional Climate Impacts Summary and Outlook: Summer 2023


  • Average temperatures for the summer season were 0-1 degrees below normal for much of the region. This is the first cooler-than-normal season since the start of the MARISA Climate Summary series in 2018.
  • Summer precipitation amounts varied across the region, with some sites experiencing 50–75% of normal rainfall with others experiencing over 150% of their normal amounts of rainfall.
  • In mid-June, 80% of Pennsylvania and 73% of Maryland were in drought. These states last experienced this level of moderate to severe drought in September 2002 and October 2019, respectively.
  • Air quality was a significant issue this season. In June, every state in the Mid-Atlantic had their worst day of air quality from smoke on record.

This summary focuses on weather and climate events in the Chesapeake Bay watershed and provides highlights from the greater Mid-Atlantic region for the summer 2023 season. The summer season is defined as the months of June, July, and August. The MARISA region covers Maryland, Delaware, Virginia, and Pennsylvania and the portions of New York and West Virginia that fall within the boundaries of the Chesapeake Bay watershed, as shown in Figure 1 below. We refer to this region as the Mid-Atlantic region in the rest of the climate summary.

Figure 1. MARISA Mid-Atlantic Region

A map of the Mid-Atlantic regional highlighting the Chesapeake Bay watershed.

A map showing the Mid-Atlantic region.

Part 1: Significant Weather Events and Impacts

Severe Weather

During the month of June there were several instances of severe weather in the Chesapeake Bay watershed, mostly thunderstorm winds downing trees and power lines, as well as localized flash flooding and small hail.1,2 Surry and Prince Edward counties in Virginia saw two-inch hailstones, among the largest on record for each county.3,4 Two tornadoes touched down in the watershed in June: an Enhanced Fujita scale 0 (EF-0) in York County, Pennsylvania, on June 12 and an EF-0 in Isle of Wight County, Virginia, on June 16.5,6 Both tornadoes primarily caused tree damage. 7,8

July was a very active month for severe weather in the region, in fact, severe thunderstorms and/or flooding affected the watershed on more than half of all July days. Due to the number of events, we only discuss a sample of them here.

On July 2, seven tornadoes touched down in central and north-eastern Pennsylvania.9 All were rated EF-0 or EF-1, with wind speeds of 110 miles per hour (mph) or less. 10 The longest path length of the tornadoes was 2.39 miles.11 Storm reports indicated that the tornadoes downed trees and mostly caused minor damage to buildings and other residential properties.12 There was also an area of intermittent straight-line wind damage stretching nearly 20 miles from Juniata County to Dauphin County.13

On July 3, parts of Maryland and Virginia experienced damage from severe thunderstorm winds.14 For instance, straight-line winds of up to 105 mph caused significant damage, particularly to trees, along a 1.3-mile path on Tilghman Island, Maryland.15

From July 13 to 14, over 5 inches of rain from thunderstorms caused significant flash flooding in Lynchburg, Virginia, that inundated roads and submerged vehicles.16,17 Some buildings, including a few rooms at a high school, experienced water damage.18

On July 29, severe thunderstorms with wind gusts of up to 84 mph moved through Maryland, Virginia, and Washington D.C.19,20 The storms knocked down trees and power lines, which blocked roads, damaged homes and vehicles, and left more than 200,000 customers without power.21,22 Storm reports indicated that at least two people were injured and one person was killed due to fallen trees.23

There were two notable severe weather outbreaks during August. On August 7, five weak (EF-0 or EF-1) tornadoes touched down in the watershed: three in central Pennsylvania, one in central New York, and one that traveled from northern Pennsylvania into central New York.24 The greatest tornado wind speeds were near 105 mph and the longest track was 11 miles (in central New York).25,26 Damage mostly consisted of dozens of downed trees, some flattened corn fields, and damage to outbuildings.27,28 Additionally, there were two areas of straight-line winds of up to 90 mph in central Pennsylvania that downed numerous trees and power lines, resulting in many road closures and widespread power outages.29,30 Father south in Caroline County, Virginia, hailstones of 4 inches or larger fell, with the largest stone measuring 4.75 inches.31 The National Weather Service office in Wakefield, Virginia, noted, "This is the largest hailstone ever found in our CWA and the 3rd largest ever in the state of Virginia. The largest hailstone ever recorded in Virginia was 5" recorded both on April 23rd, 1968 in Lee County and July 2nd, 1968 in Loudoun County. That makes this the largest hailstone measured in Virginia in 55 years [...]. A truly remarkable event."32 Over 3.50 inches of rain in an hour during this storm event led to significant flash flooding in Dorchester County, Maryland, where a rare Flash Flood Emergency, signifying a dangerous, life-threatening situation, was issued by the National Weather Service.33 Numerous roads were closed, with waist-deep water in some areas resulting in multiple water rescues. 34 Federal workers in the Washington D.C. metropolitan area were dismissed early due to the severe weather threat.35

On August 12, three tornadoes, either EF-0 or EF-1 and with wind speeds of up to 105 mph, downed hundreds of trees in northern/central Pennsylvania.36,37 The longest of the tornado trackes was just over 3 miles in Luzerne County.38 Straight-line winds of up to 90 mph also damaged trees in Pennsylvania. 39,40

Tropical Storms

In late August, Tropical Storm Idalia moved across the southeastern United States, grazing southeastern Virginia on August 31.41 Peak wind gusts ranged from 40 to 60 mph, while rainfall was generally less than 2 inches.42 The Hampton Roads area also saw minor erosion and limited coastal flooding.43


The U.S. Drought Monitor from June 6 showed moderate drought and abnormal dryness covered most of the Chesapeake Bay watershed.44 Dryness intensified through mid-June when severe drought was introduced in south-central Pennsylvania, central Maryland, and northern Virginia and moderate drought and abnormal dryness expanded in multiple locations.45 Conditions peaked at this time, with the June 20 U.S. Drought Monitor showing 80% of Pennsylvania, 73% of Maryland, and 26% of Virginia in drought.46 Pennsylvania and Maryland last experienced this level of drought moderate to severe drought in September 2002 and October 2019, respectively.47,48

Record low seven-day streamflow and/or groundwater levels were noted in parts of the watershed.49 Streamflow on the Potomac River in Maryland dropped to a level low enough to require daily monitoring.50 The low streamflow contributed to an abundance of algae that altered the taste and smell of the drinking water in some areas.51 More than a dozen water suppliers in Pennsylvania asked customers to voluntarily conserve water.52

An uptick in wildfires amid the dry conditions prompted Pennsylvania officials to temporarily prohibit open fires in state forests, while several municipalities and counties in central Pennsylvania enacted burn bans.53,54

Growers in Pennsylvania and Maryland relied on irrigation; however, some crops grew slower than usual, with reduced wheat yields expected.55,56 In eastern West Virginia, some seeds did not germinate, and some crops, such as corn, struggled to establish roots.57

For the week ending June 18, topsoil moisture was rated very short (the lowest rating) for 71% of Maryland and was rated short (the second lowest rating) for just under 50% of Pennsylvania and West Virginia.58 For the same period, pasture and range conditions were rated very poor or poor for just under 50% of Pennsylvania and around 25% of Maryland.59

From late June through July, widespread rainfall allowed drought and dryness to shrink in coverage across the watershed.60 Severe drought was reduced to a section of central Maryland, while moderate drought persisted in an area from northern Virginia and eastern West Virginia through central Maryland and into south-central Pennsylvania.61 Several pockets of abnormal dryness also lingered in the watershed.62

The August 1 U.S. Drought Monitor showed 28% of Maryland, 4% of Virginia, and 2% of Pennsylvania in drought. 63 Even with increased rainfall, residents of Pennsylvania and Maryland were urged to conserve water as indicators such as groundwater levels remained below normal.64,65

Rainfall in early August allowed severe drought to ease in central Maryland and moderate drought and abnormal dryness to contract in multiple parts of the watershed.66 However, the rest of August was generally drier than normal in southern portions of the watershed.67 Severe drought was introduced in northern Virginia, while moderate drought and abnormal dryness expanded or persisted in areas such as northern/western Virginia, eastern West Virginia, central Maryland, and south-central Pennsylvania.68 The August 29 edition of the U.S. Drought Monitor showed 16 percent of Maryland, 12 percent of Virginia, 8 percent of West Virginia, and 1 percent of Pennsylvania in drought.69

The dry conditions in August had several impacts. In late August, daily drought monitoring resumed along the Potomac River, which supplies portions of the Mid-Atlantic, including much of the Washington D.C. metropolitan area, with water.70 In Virginia's Shenandoah Valley, Frederick Water and the Town of Strasburg implemented mandatory water restrictions on nonessential water use, while others such as the City of Winchester and the town of Elkton asked customers to voluntarily conserve water.71,72,73,74 Waterways in Shenandoah National Park in Virginia were closed to fishing due to below-normal water levels and above-normal water temperatures, which stressed fish and aquatic populations.75 The dryness led to poor pasture conditions, reduced hay yields, small apples, and drought stress in corn crops in parts of the Shenandoah Valley.76,77,78 Additionally, the dry conditions meant reduced mowing work for landscapers, who pivoted to other projects, such as mulching.79

Air Quality

When someone breathes in the fine particulate matter from smoke, it can penetrate into their lungs and blood, exacerbating asthma and heart conditions.80 Bacteria and fungi that hitch a ride on these smoke particles have the potential to make people sick.81

To communicate about the health effects of the air, the Environmental Protection Agency (EPA) uses the Air Quality Index, or AQI, for some pollutants.82 When the AQI is below 100 (Code Green or Yellow), the air is generally safe to breathe (with some exceptions for unusually sensitive groups).83 If a region is regularly above an AQI of 100, it is out of compliance with national regulations.84 During Code Orange events, between 101 and 150, people who are at particular risk from poor air quality (babies, children, seniors, and anyone with heart or lung problems) should seek clean air. These sensitive groups are even more at risk at "Unhealthy" levels or Code Red, though the general public is also in danger. During Code Purple events, the air is "Very Unhealthy," and everyone is at risk. When there is a Code Maroon event, which corresponds to an AQI above 300 and the EPA labels as "Hazardous," it is considered a health emergency for all.

From June 3 to 10, northerly winds pushed thick smoke from wildfires burning in eastern Canada into the watershed.85 This year has been Canada's worst fire season, with the largest area burned on record.86 Figure 3 shows a modeled simulation of the smoke plume moving to the Mid-Atlantic at the beginning of June. Fires that create particularly large plumes of smoke can launch smoke high into the atmosphere. This smoke can then travel large distances more easily, potentially affecting air quality at locations very far away from ongoing wildfires.87 For example, during June, the smoke from the fires burning across Canada reached Europe.88

Figure 2. A Model of Smoke from Canada June 6-8, 2023

A heat map showing smoke plumes in the atmosphere over the United States. Source: NOAA Global Systems Laboratory, RAP-NCEP-Smoke Model, 2023.

SOURCE: NOAA Global Systems Laboratory, RAP-NCEP-Smoke Model, 2023.89,90

During the June 3-10 event, Air Quality Alerts were in place in the Mid-Atlantic for several days, with the AQI exceeding unhealthy, very unhealthy, or hazardous thresholds in most areas.91,92 Multiple locations experienced some of their poorest air quality since EPA records began in 1999 including Washington D.C. and Harrisburg, Pennsylvania.93,94 Visibilities were reduced to as little as a half-mile at times in parts of central New York and northern Pennsylvania where daily high temperatures were slightly cooler due to the thick smoke.95 In some areas, outdoor activities were cancelled, outdoor spaces such as zoos were closed, and schools dismissed students early.96,97

From June 28 to 30, another significant plume of wildfire smoke moved into the watershed, though this was not as intense as the early June event.98 Air quality alerts were issued as the air quality reached unhealthy levels in many areas.99 At times during this event, Washington D.C. had some of the worst air quality of any major city in the world.100 The poor air quality caused places such as pools to close and sent other outdoor activities indoors.101

The National Weather Service office in Binghamton, New York issued 32 air quality alerts in June, by far their greatest number for any month since records began there in May 2007 (the previous high number for air quality alerts in a single month was 10 in July 2010).102 The National Weather Service offices in State College, Pennsylvania and Baltimore/Washington D.C. also issued their greatest number of air quality alerts for any month since May 2009 and April 2010 respectively.103,104 In June, every state in the Mid-Atlantic had their worst day of air quality from smoke on record.105 Figure 4 shows the highest daily AQI from June 2023 reported at any monitor in each of the states in the Mid-Atlantic.106 Pennsylvania reached an AQI of 309 on June 7 in the Allentown urban area. Meanwhile, hourly AQI readings topped 450 in parts of central New York and central Pennsylvania on June 7 and 8.107,108

Figure 3. Fine Particulate Matter Air Quality Index for June 2023

A line graph showing the fine particulate matter air quality index for June 2023. Source: EPA AirNow, 2023.

SOURCE: Data from Source: EPA AirNow, 2023.

Multiple air quality alerts were issued in July, with the National Weather Service office in Binghamton, New York issuing more alerts this July than any other July on record.109 The alerts were mostly centered around July 17 and 18 when a plume of smoke from wildfires burning in western Canada reduced air quality and produced hazy skies around the watershed.110,111 In fact, Washington D.C. had some of the worst air quality of any major city in the world on July 17. 112

Canadian wildfire smoke passed through southern parts of the watershed in early August.113 The smoke was mostly aloft, creating hazy skies; however high-risk populations were advised to reduce outdoor activities.114,115

Figure 4. Poor Air Quality at the National Weather Service office in Binghamton, New York on the morning of June 7, 2023

Poor air quality at the National Weather Service office in Binghamton, New York on the morning of June 7, 2023. Photo by National Weather Service, Binghamton, New York.

SOURCE: National Weather Service, Binghamton, New York

A study by the Centers for Disease Control indicated that between late April and early August 2023, there was a 17 percent increase in asthma-related emergency department visits in the U.S. associated with days with significant wildfire smoke (generally equating to an Air Quality Index of 101 or higher).116 The U.S. Department of Health and Human Services' Region 3, which includes most of the Chesapeake Bay watershed, had five wildfire smoke days, the greatest number of any region, and observed a marked increase in asthma-related emergency department visits during the major early June smoke event.117

Part 2: Seasonal Temperature and Precipitation


Figure 5 shows the summer 2023 average temperature compared with the climate normal, which is defined as the average summer temperature from 1991 to 2020.118 The figure shows that most of the region experienced below-normal temperatures. We have not seen a season with largely below-average temperatures since the start of the Climate Summary series in 2018. This was driven by cooler temperatures in June, which more than balanced out warmer July temperatures. The difference between these months is further illustrated in the site temperature rankings below in Table 2.

Figure 5. June 1 – August 31, 2023 Departure from Normal Temperature (degrees Fahrenheit)

A heat map showing departure from normal temperature in the Mid-Atlantic region from June to August, 2023

SOURCE: Northeast Regional Climate Center, 2023 ( Used with permission.

NOTE: Normal temperature is based on the summer season's average temperature data from 1991–2020. Yellow, orange, and red indicate above-normal temperatures. Blue indicates below-normal temperatures. The boundaries of the Chesapeake Bay watershed are outlined in bold black. Average departure from normal temperature is based on a station's normal temperature for summer compared with the same station's summer 2023 average temperature. Station-level departures from normal are spatially interpolated across the region. Both are produced by the Northeast Regional Climate Center. These can be found at

Summer 2023 was the ninth coolest on record for Martinsburg, West Virginia, but the 15th warmest on record for Dulles Airport, Virginia. It was generally cooler than normal for the region, which is illustrated in Figure 5 above.

Additional temperature-related events are discussed in the Monthly Temperature Rankings section below.

Table 1. Summer Season (June – August) Temperature Rankings

Station Name Avg. Temp (degrees F) Normal Temp (degrees F) Rank (coolest)
Martinsburg, WV 71.1 73.5 9
Station Name Avg. Temp (degrees F) Normal Temp (degrees F) Rank (warmest)
Dulles Airport, VA 76.0 75.2 15

SOURCE: Northeast Regional Climate Center, 2023 ( Used with permission.

Monthly Temperature Rankings

The first few days of June were generally warm, with Binghamton, New York recording a high of 91 degrees F on June 2, which ranked among the site's 10 warmest high temperatures for June on record.119 However, the month turned cooler, allowing this June to be ranked among the 20 coolest months of June on record for three sites (Table 2).120

After a cooler than normal June, temperatures warmed up for much of the region during the month of July and, to a lesser extent, August. The most intense heat of the season was at the end of July. Excessive heat warnings were issued by the National Weather Service for July 27 through 29 in Washington D.C. and portions of Maryland and Virginia as high temperatures pushed into the 90s and heat index values reached up to 110 degrees F.121,122 Baltimore, Maryland, declared its first "Code Red Extreme Heat Alert" of the season.123 July was ranked among the 20 all-time warmest months on record for multiple sites in the watershed: Dulles Airport, Richmond, Charlottesville, and Norfolk, Virginia; Binghamton, New York; Baltimore and Salisbury, Maryland; Harrisburg, Pennsylvania; and Washington D.C.124

This August ranked among the top 20 warmest Augusts on record for four Virginia sites. August did not rank among the top 20 coolest or warmest for other locations in the watershed.

The full set of monthly rankings, locations, and temperatures are shown in Table 2.

Table 2. Monthly Temperature Rankings

June Temperature Rankings (coolest)
Station Name Avg. Temp (degrees F) Normal Temp (degrees F) Rank (coolest)
Martinsburg, WV 65.8 71.1 2
Lynchburg, VA 68.8 72.0 7
Dulles Airport, VA 70.6 72.5 18
July Temperature Rankings (warmest)
Station Name Avg. Temp (degrees F) Normal Temp (degrees F) Rank (warmest)
Dulles Airport, VA 80.1 77.2 4
Charlottesville, VA 80.4 79.0 8
Salisbury, MD 79.9 77.9 10
Binghamton, NY 71.6 68.9 12
Baltimore, MD 80.6 78.3 13
Richmond, VA 81.2 79.4 13
Harrisburg, PA 78.5 77.3 15
Norfolk, VA 82.1 81.1 15
National Airport, D.C. 81.6 81.0 16
August Temperature Rankings (warmest)
Station Name Avg. Temp (degrees F) Normal Temp (degrees F) Rank (warmest)
Dulles Airport, VA 77.2 75.7 13
Charlottesville, VA 78.0 76.9 17
Norfolk, VA 79.7 79.2 17
Richmond, VA 78.9 77.5 18

Source: Northeast Regional Climate Center, 2023 ( Used with permission.


Figure 6 shows how the total precipitation for the summer season differed from normal, with normal being defined as the average summer precipitation from 1991 – 2020. Central Maryland and much of northern Virginia experienced 50-75% of normal rainfall whereas some of central Pennsylvania and central Virginia experienced more than 150% of normal precipitation.

Figure 6. June 1 – August 31, 2023 Percentage of Normal Precipitation

A heat map showing departure from normal precipitation for the Mid-Atlantic region for June to August, 2023. Source: Northeast Regional Climate Center, 2022

SOURCE: Northeast Regional Climate Center, 2023 ( Used with permission.

NOTE: Normal seasonal precipitation is based on precipitation data from 1991–2020. Brown shades indicate below normal seasonal precipitation. Blue shades indicate above normal seasonal precipitation. The boundaries of the Chesapeake Bay watershed are outlined in bold black. Average departures from normal precipitation are based on a station's normal precipitation for summer compared with the same station's summer 2023 average amount of precipitation. Station-level departures from normal are spatially interpolated across the region. Both are produced by the Northeast Regional Climate Center. These can be found at

Precipitation amounts were unevenly distributed throughout the watershed this season, with some areas receiving more rainfall than normal while others saw less than normal precipitation. This is visible in both in Figure 6 and in the seasonal precipitation rankings. Two sites in Virginia experienced summers that ranked among their top 20 driest on record. Meanwhile sites in Pennsylvania, New York, and southern Virginia experienced summers that ranked among their top 20 wettest on record.

The details of these rankings are included in Table 3 below.

Table 3. Summer Season (June - August) Precipitation Rankings

Station Name Precipitation (inches) Normal Precipitation (inches) Rank (driest)
Charlottesville, VA 5.85 11.62 4*
Dulles Airport, VA 9.24 11.98 18
Station Name Precipitation (inches) Normal Precipitation (inches) Rank (wettest)
Williamsport, PA 21.81 12.66 3
Binghamton, NY 18.27 12.59 4
Norfolk, VA 23.38 16.39 6
Scranton, PA 16.15 11.26 14

* Four days of precipitation data is missing from Charlottesville, VA record this summer.

SOURCE: Northeast Regional Climate Center, 2023 ( Used with permission.

Monthly Precipitation Rankings

Compared to this season's temperature trends, precipitation was much more variable across months and the watershed. This June ranked among the 20 driest months of June on record for two sites, but among the 20 wettest on record for 2 different sites.125

Williamsport, Pennsylvania tied its wettest July day on record with 3.29 inches of rain on July 15.126 Lynchburg, Virginia received 5 inches of rain in a single storm event (July 13-14) and experienced significant flash flooding as a result (see Part 1), which contributed to the site logging its wettest July on record.127

Conditions were split geographically for the month of August, with two Virginia sites and one Maryland site experiencing Augusts that were among the top 20 driest on record while three sites in New York and Pennsylvania experienced Augusts that ranked among their top 20 wettest on record.

The full set of monthly rankings, locations, and amounts of precipitation are shown in Table 4.

Table 4. Monthly Precipitation Rankings

June Precipitation Rankings (driest)
Station Name Precipitation (inches) Normal Precipitation (inches) Rank (driest)
Charlottesville, VA 1.22 4.38 7*
Dulles Airport, VA 2.30 4.30 18
June Precipitation Rankings (wettest)
Station Name Precipitation (inches) Normal Precipitation (inches) Rank (wettest)
Norfolk, VA 7.10 4.43 13
Binghamton, NY 5.04 4.69 18
July Precipitation Rankings (driest)
Station Name Precipitation (inches) Normal Precipitation (inches) Rank (driest)
No sites experienced precipitation that ranked in their top 20 driest months of July on record.
July Precipitation Rankings (wettest)
Station Name Precipitation (inches) Normal Precipitation (inches) Rank (wettest)
Lynchburg, VA 10.39 4.19 1
Williamsport, PA 10.05 4.64 2
Scranton, PA 6.85 3.61 11
Binghamton, NY 5.90 3.80 12
Dulles Airport, VA 5.09 4.15 15
August Precipitation Rankings (driest)
Station Name Precipitation (inches) Normal Precipitation (inches) Rank (driest)
Charlottesville, VA 0.86 3.87 7
Dulles Airport, VA 1.85 3.53 14
Salisbury, MD 2.02 5.27 17
August Precipitation Rankings (wettest)
Station Name Precipitation (inches) Normal Precipitation (inches) Rank (wettest)
Binghamton, NY 18.27 12.59 4
Williamsport, PA 8.61 4.17 4
Scranton, PA 6.42 3.85 11

* Missing 3 days of data

Source: Northeast Regional Climate Center, 2023 ( Used with permission.

Part 3: Fall 2023 Outlook

Temperature and Precipitation

As of August 17, 2023, the NOAA Climate Prediction Center forecasts a 33-40-percent chance of above-normal temperatures for Virginia and western Pennsylvania and western Maryland and a 40-50-percent chance of above-normal temperatures for the rest of the rest of the region for September, October, and November 2023.128 This forecast means that the Mid-Atlantic is leaning towards having a warmer than normal fall season.129 The precipitation forecast calls for equal chances of above-normal, below-normal, or near-normal fall season for New York and Pennsylvania. The forecast for Maryland, Delaware, Washington, D.C., and Virginia shows a 33-50 percent chance of wetter than normal conditions.130

Drought Incidence

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 August 31, 2023 the Outlook indicates that drought conditions are likely to improve and be "removed" during the 2023 fall season in central Maryland, Northern Virginia, and the panhandle of West Virginia.131 Drought is not likely in the rest of the region.

Climate Circulation Patterns

NOAA's Climate Prediction Center, which monitors the likelihood of occurrence of El Niño and La Niña climate phenomena, has an El Niño Advisory active as of August 10, 2023, with a greater than 95 percent chance of El Niño conditions continuing through winter 2023-2024.132 For the Mid-Atlantic, El Niño generally produces wetter winter weather, but does not generally indicate an above or below normal winter for temperatures across the region.133 In the Washington, D.C. and Baltimore areas, El Niño has produced warmer, wetter and snowier than normal winters.134

ENSO conditions are one of the factors taken into account in NOAA's long-term forecasts and seasonal outlooks such as the one included in this climate summary.135 However, other regional climate dynamics and natural climate variability also influence weather in the Mid-Atlantic. Additional information on La Niña and El Niño is available from the Pacific Marine Environmental Laboratory (La Niña, El Niño).

The North Atlantic Oscillation (NAO) can enhance or counteract El Niño's influence on weather in the Mid-Atlantic. A higher NAO index can lead to milder winters in the North Atlantic, while a lower index can lead to more severe winters.136 137 Short term forecasts of the NAO index are made by NOAA's Climate Prediction Center (CPC), which suggests a negative NAO index is likely through late September.138 NOA index values are, however, highly variable within a season and are not yet suggestive of winter weather in the Mid-Atlantic.

Atlantic Hurricane Outlook

As of August 3, 2023, researchers at Colorado State University (CSU) predicted an above-average season (130% of a regular season) due to abnormally warm Atlantic sea surface temperatures working to increase the likelihood of hurricanes and tropical storms despite El Niño conditions which usually decrease the likelihood of tropical storm activity.139 They note that this dynamic between the warm ocean temperatures and El Niño is causing there to be more uncertainty than normal in their forecast.140 The CSU team predicts 18 named storms total with nine of those becoming hurricanes and 4-5 becoming major hurricanes (category 3-5).141 Their forecast has a 25% chance that a major hurricane will make landfall on the U.S. East Coast.142

NOAA's CPC predicted an above-normal season.143 For the June 1 to November 30 Atlantic hurricane season, NOAA is forecasting 14–21 named storms, out of which 6–11 could become hurricanes and 2–5 of those could become major hurricanes, meaning that they would be category 3, 4, or 5 with winds of at least 111 mph.144 A normal Atlantic hurricane season is defined as having 14 named storms, seven hurricanes, and three major hurricanes (Category 3, 4, or 5).145

As of September 12, there have been five hurricanes in the Atlantic, including Hurricane Idalia, which degraded to a tropical storm by the time it reached the Mid-Atlantic.

Part 4: Air Quality in the Mid-Atlantic

While this was a record-breaking season for poor air quality in the Mid-Atlantic, wildfire smoke may become more common in the region into the future. Globally, the fire season is lengthening and there is a greater area with hot and dry conditions prone to fire.146 Climate projections for North America indicate that there will be both more wildfires and that these fires will burn a greater area than in the past.147

The interactive data tool shown in Figure 7 shows how air quality has changed over time based on a range of air quality thresholds. The figure plots the maximum days within a month for each year from 2000 to present with an AQI above the selected threshold.

Key Findings

  • 2023 is the first year on record that the Mid-Atlantic region had air quality rated as hazardous to human health.
  • The summer months have historically produced the worst air quality in the Mid-Atlantic.
  • Most states experienced at least one month each year with all days at or above the moderate threshold until 2010.
  • For many years, cities saw improved air quality as regulations on emissions from trucks and cars reduced particulate matter pollution. The number of days above the "Unhealthy for Sensitive Groups" has been decreasing in many regions between 2000 and about 2016. Wildfire smoke could cause this trend to reverse or stagnate.148

Figure 7. Air Quality in the Mid-Atlantic from 2000-Present

How to Use the Tool

Selecting Air Quality Threshold Use the checkboxes to select which air quality threshold to display.

Selecting State Use the checkboxes to select which state or states to display.

Technical Notes

The U.S. Environmental Protection Agency began recording air quality data for fine particulate matter (PM2.5) in 1999. Data from January 1, 2000 to May 31, 2023 are submitted by monitoring organizations and certified by the EPA's Air Quality System. Data after June 1, 2023 are from the EPA's AirNow system and are not certified. Counties with the worst air quality are listed based on those with the most days above a selected threshold in the tool. Maximum days above the AQI threshold are calculated as the greatest number of days in a month in any county within the selected state. In the tooltip, the average number of days is an average of all stations within that state. Due to data availability, data is missing for some years and states (e.g., Pennsylvania in 2003).

Data were processed by the RAND Corporation to calculate AQI above certain thresholds.

Back to top

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, the Virginia Institute of Marine Science, Morgan State University, and Carnegie Mellon University. This series is specifically designed to support policymakers, practitioners, residents, and community leaders in the Mid-Atlantic by serving as a data and information resource that is tailored to the region. It draws information from regional climate centers, news and weather information, and regional-specific climate data sets. 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

This edition of the MARISA Seasonal Climate Impacts Summary and Outlook was authored by Michelle E. Miro (RAND Corporation), Krista Romita Grocholski (RAND Corporation), Sophia Charan (RAND Corporation), Jessica Spaccio (Cornell University), Samantha Borisoff (Cornell University), and Arthur T. DeGaetano (Cornell University).

Citation: Miro, Michelle E., Krista Romita Grocholski, Sophia Charan, Jessica Spaccio, Samantha Borisoff, and Arthur T. DeGaetano, Mid-Atlantic Regional Climate Impacts Summary and Outlook: Summer 2023. Santa Monica, CA: RAND Corporation, 2023.

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  89. This is the modeled vertically integrated smoke with data initialized at 5am EDT on 6/6/2023 using the Rapid Refresh model by the National Centers for Environmental Prediction. Return to text ⤴

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  118. 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 Return to text ⤴

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  129. For more information on how NOAA defines at, above or below normal and determines percent chances, see: Return to text ⤴

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