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A Climate Primer for New England New England weather and climate are arguably among the most varied in the world. It includes extremes of both hot and cold temperatures, droughts, heavy rainfall, hurricanes, tornadoes, blizzards, and more. These great variations in New England weather are influenced by many factors relating to the physical geographical setting, including the region’s latitude and coastal orientation. To understand the dynamic New England climate, it is important to have a basic understanding of the larger scale general circulation of the atmosphere. Figure 2.1 depicts the surface and upper air flow for the northern hemisphere, and there is an identical set of cells for the southern hemisphere. The Hadley Cell to the south primarily controls tropical and subtropical climates, and only indirectly influences climate in this region. The mid-latitudes, however, are dominated by westerly circulation at the surface, which is fed by the subsiding air from the Hadley Cell in the subtropics. These northward-directed winds are deflected to the right (toward the east) in this hemisphere because of the rotation of the earth. As a result, the zone of the "westerlies," which are winds that come from the west and blow toward the east, is created across the middle latitudes. At the other end of the spectrum, the polar easterlies dominate the very high latitudes and are made up of extremely cold air that is transported away from the polar region. The westerlies and polar easterlies frequently converge between 40o and 60o North latitude. The boundary between these contrasting air-masses forms the polar front , which divides warm and moist air to the south from cold and dry air to the north. The jet stream resides aloft over this dividing line delineating the location of the polar front at earth’s surface. This dynamic boundary generally lies near New England and the region can fall on either side of the boundary at any time of the year, thereby shifting us frequently from one air-mass to another. In winter, the polar front is typically located on the south side of New England and the region is dominated by colder and drier air-masses from Canada. In summer, the polar front relocates farther north, placing New England south of the boundary in warm and more humid air (Figure 2.1 ). This is one of the reasons that New England seasons are so distinct. New England summers are not that dissimilar from locations much farther to the south, e.g., Miami, Atlanta, or Washington, D.C., because these areas are typically all imbedded in the same air-mass. These locations can differ greatly in winter, however, when New England mostly falls on the north side of the polar front. It is also important to realize that the polar front is always shifting, and New England can find itself basking in warm and humid air even in winter, but these incursions are infrequent at that time of year. There are four important components that dominate New England climate, some of which relate to the previous discussion. First, the area is located about halfway between the equator and the north pole, which is why it serves as a battleground for warm-moist air from the south and cold-dry air from the north. The surface air-mass boundaries are made up of warm, cold, and stationary fronts, which frequently traverse the region, bringing us from one air-mass to another in rapid succession. Second, the region is dominated by a cold water current along its east coast (coastal Maine, New Hampshire, and eastern Massachusetts) and a warm water current along the south shore (coastal Connecticut, Rhode Island, and southern Massachusetts). These currents and corresponding water temperatures affect summer recreation in the form of swimming comfort and a cooling sea breeze. Sea breezes are generated by the temperature difference between the cooler water and warmer land. The sea breeze circulation, particularly along New England’s east coast, tends to mitigate frequencies and intensities of thunderstorms in the coastal zone, while bringing relief in the form of mild temperatures in the peak summer heat. In winter, coastal waters remain warm relative to land areas, thereby influencing snow-rain boundaries, which are difficult for forecasters to predict. Third, since New England falls primarily in the zone of the westerlies, the area is dominated by drier continental airflow from various areas across North America, rather than having a prevailing flow from off of the Atlantic Ocean. So, despite the coastal orientation of New England, it does not have a maritime climate like those found on the west coast of the United States. Fourth, New England has mountainous topography which also influences weather patterns. Mountains can enhance precipitation on the windward side, and create drier conditions on the downwind slopes, known as the "rainshadow" effect. Increases in elevation also lead to cooler air temperatures. Figure 2.1 also depicts air-mass characteristics of New England, based on source regions. As noted, the prevailing wind across most of New England has a westerly component, while southeast winds are least common region-wide. However, winds can, and do, come from all directions on the compass. North and northwest winds deliver to New England cold and dry air from Canada. Moving counterclockwise, westerly winds transport Canadian air to the region, but the air is generally modified (warmed slightly) as a result of passing over the Great Lakes. Southwesterly winds are very common in New England, but are highly variable in character. These winds can be generated by a high pressure area in the mid-Atlantic states, in which the air is Canadian in origin, but has been modified from the long trajectory over the American Midwest. In this case, the air is generally cool and dry, but can be hot and dry in summer. However, southwest winds are also common after the passage of a warm front, which can carry warm and humid air from the Gulf of Mexico and Caribbean. South and southeast winds are hot or warm and humid, though these winds have low occurrence rates over most of New England, with a notable exception along New England’s south shore. East and northeast winds are cool and humid, as the air takes on the characteristics of the cooler water of the Labrador current and northern Atlantic Ocean. Northeast winds in New England are frequently associated with coastal nor’easters. As a result of New England's position relative to the polar front, it’s continental climate type, it’s coastal orientation, and the mountainous topography, the region’s weather is notorious. It is known for its diversity over short distances and changability in a matter of minutes. New England has recorded temperatures up to 107 o F and down to -50o F (Ludlum, 1976). The high is hotter than the all-time high temperatures ever recorded in Miami, Florida or Atlanta, Georgia. The low is colder than the record low temperature in Anchorage, Alaska or International Falls, Minnesota - which is commonly the coldest location in the conterminous United States. The region also has rainstorms that rival those in the southeastern United States. As a result, the splendors of New England weather and its bountiful variety were noted by many authors ranging from Robert Frost to Mark Twain. Twain captured the richness of New England weather in his speech at the New England Society’s seventy-first annual dinner in New York: "Now as to the size of the weather in New England - lengthways, I mean. It is utterly disproportionate to the size of that little country. Half the time, when it is packed as full as it can stick, you will see New England weather sticking out beyond the edges and projecting around hundreds and hundreds of miles over the neighboring States. She can’t hold a tenth part of her weather" (Twain, 1935, p. 1110). Many locations in the United States have the saying " if you don’t like the weather, wait a minute," but nowhere is this more true than in New England. Yet despite the richness of the weather here, and the abundance of severe weather types, little research has concentrated on understanding the dynamic climate of the region. Ludlum, D. 1976. The Country Journal: New England Weather Book. Houghton Mifflin: Boston. Twain, M. 1935. The Family Mark Twain. Harper and Row: New York. Prepared by: Dr. Barry Keim, New Hampshire State Climatologist and Assistant Professor in the Department of Geography and the Climate Change Research Center in the Institute for the Study of Earth, Oceans and Space. |
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