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Wet and Windy: Delmarva's unique weather - November 30, 2014

 If you have ever seen a weather map of Maryland you might have noticed a division between the weather on the western shore and the eastern shore. It might be snowing in Baltimore but in Salisbury and Ocean City it only rains. This change in weather from the mainland to the Delmarva peninsula is in part due to the distance between the western shore and the eastern shore but also because of multiple unique environmental conditions. Surrounded on three sides by water, the Atlantic Ocean on one side and the Chesapeake Bay and its tributaries on the other, the Delmarva peninsula has many different environmental aspects. These environmental aspects create unique local weather on Delmarva as opposed to the mainland. Wet, foggy and windy conditions dominate our fall and winter seasons while the western shores of Virginia and Maryland get hit with snow, sleet and freezing rain. The summer and spring seasons on the eastern shore tend to have more rain and a higher humidity than the mainland however we tend to have cooler summers with fewer extremely high temperature days.
 
Large bodies of water, such as the Chesapeake Bay and Atlantic Ocean, have a direct effect on temperatures and the local weather in coastal areas. Proximity to large bodies of water creates a kind of buffer which stabilizes temperatures in that area and leads to less dramatic temperature fluctuations. This means that while inland regions can quickly decrease in temperature from the fall to winter seasons, coastal towns are kept warmer by the water's effect on the air. This is due to water's high heat capacity compared to both air and land. This higher heat capacity means that coastal towns and areas, like Ocean City, will experience warmer winters and cooler summers than inland communities because the surrounding water heats up and cools down slower than the air and land do.
 
Shoreline communities also experience an interesting dynamic between the air over water and the air over land. Air tends to move from cooler areas toward warmer areas, and the sun and seasons often dictates whether the land or water is cooler. During the day, the air onshore is warmer than the air over the water, so the wind usually blows from the water to the land. At night, the opposite occurs since the air over the water is warmer. Winds also tend to be stronger and more prevalent here on Delmarva as opposed to the mainland. This is because when wind travels over land there is more air resistance than over large bodies of water. Forests, buildings, hills and mountains create air resistance which slows down or blocks wind on land as opposed to bodies of water which create little to no air resistance until the wind meets the shore.
 
Bodies of water not only affect how much precipitation a shoreline gets, but also what type of precipitation falls there. The Gulf of Mexico, for example, brings warm moist air over the Gulf Coast region, which results in thunderstorms, heavy rains, fog and, most notoriously, hurricanes. This severe precipitation occurs when the warmer, moist air collides with a mass of cooler, dry air. Here on the Eastern shore of Maryland we find that we generally tend to have more rain than the western shore. During the winter months when cold weather systems move across Maryland it might snow on the western shore however due to the heat capacity and evaporation from the Chesapeake and Atlantic Ocean the same weather system will produce rain for the Delmarva peninsula.
 
The direction of oceanic currents also greatly affects the climate of coastal towns and areas as well. The Gulf Stream brings warmer water from the Caribbeans upward along the United State's Atlantic coast, eventually ending across the Atlantic near England. The Gulf Stream brings slightly warmer water to the Atlantic coastal states, which can lead to more precipitation, but is also a possible pathway of hurricanes and tropical storms. These storm systems move from the Caribbean or west coast of Africa toward North and South America making landfall near the Florida peninsula and Gulf of Mexico. Hurricanes and tropical storms can gain strength, size and heavier precipitation from warmer waters which means if they encounter the Gulf Stream while moving along the United States East Coast then they can be more powerful and dangerous to the states in their path. Since 2004, scientists have seen a reduction in flow speed of the Gulf Stream along the Atlantic coast. While not dramatic, this slower flow speed has been attributed as one of the reasons for higher sea-level rise along the Atlantic. Normally, the Gulf Stream helps to pull water away from the shore. Due to climate change and the addition of more fresh water into the ocean, currents such as the Gulf Stream are slowed. This means that the Gulf Stream no longer pulls as much water away from the coasts as it would normally, resulting in an increase in sea-level rise due to a higher water volume in the coastal areas.
 
Delmarva's unique weather and location has allowed the creation of an amazing diversity of ecosystems, animals and plants. Unfortunately, if current trends continue, there will eventually be shifts in our global climate that will change our weather patterns, creating change in our local ecosystems that could be irreversible.
 
Harrison Jackson is the Coastal Stewards Coordinator for the Maryland Coastal Bays Program.


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