North Carolina Weather and Climate

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Information about North Carolina Weather and Climate

Published on August 30, 2008

Author: EdgrT


North CarolinaWeather and Climate : North CarolinaWeather and Climate Tom Shields NCST 2000 Fall 2008 Weather versus Climate : Weather versus Climate Weather: “. . . state of the atmosphere at a given time and place with regard to temperature, air pressure . . . , wind, humidity, cloudiness, and precipitation.” “The term weather is restricted to conditions over short periods of time; conditions over long periods, generally at least 30—50 years, are referred to as climate.” Climate: “. . . average condition of the atmosphere near the earth's surface over a long period of time, taking into account temperature, precipitation . . ., humidity, wind, barometric pressure, and other phenomena.” Source: Columbia Encyclopedia. Yahoo Education. < reference/encyclopedia/>. North Carolina Weather : North Carolina Weather Air Masses Affecting North Carolina : Air Masses Affecting North Carolina Air masses are controlled by the Westerlies, especially the Jet Stream. The air masses that effect North Carolina most often are: Maritime Tropical Air Masses from the Gulf of Mexico Maritime Tropical Air Masses from the Caribbean Sea Arctic and Continental Polar Air Masses from Northwestern Canada and Alaska Types of Precipitation : Types of Precipitation Orographic Precipitation Convectional Precipitation Cyclonic Precipitation Orographic : Orographic Occurs in the mountains and western piedmont The mountains serve as orographic barriers (from the Greek óros, meaning mountain) Tropical air masses reach the mountains and cool as they rise along the mountains. When they reach the dew point (100% humidity), the result is rain or snow. Convectional Precipitation : Convectional Precipitation Primarily a warm weather phenomena—isolated summer thunderstorms. Most summer rain comes from convectional precipitation. The heat of day on the air and land heats an already warm maritime Tropical Air Mass. As the heated and moist air rises, it cools and its water vapor turns into rain. Cyclonic Precipitation : Cyclonic Precipitation Conventional low pressure storms, often from the meeting of Arctic and Continental Polar air masses with Maritime Tropical air masses. Generally move west to east across the United States. Generally fall, winter and spring in North Carolina. Warm fronts tend to provide light, prolonged precipitation. Cold fronts tend to provide brief, heavy showers. Exceptional Weather : Exceptional Weather Hurricanes Floods Winter Storms Ice Snow Tornados Heat Waves Drought Hurricanes : Hurricanes Hurricane trends are beginning to be measured but are not fully reliable However, there may be cycles of 25-50 years that affect hurricanes 1911-1930—few storms affected North Carolina A slow increase in the number peaking in the 1950s 1961-1980—quiet period A rise in the number, especially beginning in 1989 until the present An Example of Hurricane Effects : An Example of Hurricane Effects A radar picture of Isabel as it came across the Albemarle Sound and struck Edenton. Floods : Floods Flash Floods—large amounts of water into river basins Summer thunderstorms Winter rains on frozen ground (especially in mountains) Hurricanes can also bring large amounts of rain and flooding Winter Storms : Winter Storms Winter storms come as snow, ice, and/or freezing rain Snowstorms are most frequent in the mountains, and several occur each year. Ice and freezing rain regularly occur throughout the state Ice occurs when the atmosphere is slightly warmer than the ground and super-cooled rain hits an object that is at or below freezing Freezing rain occurs when the air and ground are just at the point between freezing (snow) and above freezing (rain) Tornados : Tornados North Carolina is affected by tornadoes, but not as frequently or as strongly as in the Midwest Most are associated with isolated thunderstorms (though they arise within hurricanes as well) North Carolina averages 10 to 20 tornadoes per year. Extreme Tornado Outbreaks : Extreme Tornado Outbreaks Tornadoes can hit anywhere in the state (see The North Carolina Atlas, figure 2.18), but are most frequent in the Coastal Plains The 1984 outbreak illustrates the sort of extreme tornado event that can occur. More complete information on North Carolina tornados can be found at < climate/ tornadoes.html>. Heat Waves : Heat Waves A heat wave is an extended period of high heat and humidity Measured by the heat index Two consecutive days of a daytime heat index over 105 and a nighttime heat index over 80 is one measure The Coastal Plain seems most susceptible to heat waves, especially since the 1980s Note that there has never been a heat wave recorded in Asheville Drought : Drought Drought is usually felt the most severely in late summer and early fall More water loss through evaporation in summer The convectional rainfall typical of summer is more variable and scattered than the cyclonic rain dominant the rest of the year. While there have been swings in droughts in North Carolina, there does not appear to be a specific pattern to them. For current information on drought in North Carolina and elsewhere, see the US Drought Monitor at <>. North Carolina Climate : North Carolina Climate Climatic Measures : Climatic Measures Average Temperatures Frost-Free Seasons Average Annual Rainfall January Average Temperatures : January Average Temperatures Note that average temperatures go from higher in the east to lower in the west. The main factor in average temperatures across the state is altitude, warmer at lower altitudes and cooler at higher ones. July Average Temperatures : July Average Temperatures Aside from altitude, some other factors can affect average temperatures. For example, in the east the water can help moderate temperatures, particularly right along the coast. And as illustrated above, the makeup of the Sandhills can hold extra heat during the summer. However, the main factor affecting in average temperature across the state is altitude. Average Frost-Free Days : Average Frost-Free Days The average number of frost-free days follows the same pattern as average temperatures. Climate Change Issues : Climate Change Issues No overall trend in average state temperature Most of the state has a few days longer growing season than a century ago. A few places have as much as a month longer season Another few have shorter seasons Average Annual Precipitation : Average Annual Precipitation Average annual precipitation is affected by topography, but differently from temperature The highest average annual precipitation is in the southeastern mountains, caused by orographic precipitation from Maritime Tropical Air Masses from the Gulf of Mexico and Atlantic. The smallest average annual precipitation is in the mountains. Orographic precipitation falls along the mountains surrounding the Asheville Basin before it can reach the basin, causing a rain shadow. Changes in Precipitation : Changes in Precipitation Precipitation Trends Drier summers Wetter falls Less water supply available Climate Change: North Carolina : Climate Change: North Carolina Global Warming No warming trend in North Carolina and the southeastern United States (Only one other similar region in the world in southeast China) Seasonal Changes Drier summers Wetter falls Results in less water available than 100 years ago. Changes in frequency of extreme events may be a matter of shorter term patterns (e.g. theorized 25-50 year cycles of hurricanes) and better observation of events.

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