Monitoring the Weather Air Pressure: the highs and lows Fronts: cold and warm Weather Symbols Clouds © AMS

highs and lows highs and lows © AMS

Hand twist H L highs and lows http://www.youtube.com/watch?v=yds8exoCFT8 © AMS

“Rules” for Highs and Lows High and low refer to air pressure High pressure area is relatively high compared to surrounding air Low pressure area is relatively low compared to surrounding air Highs Fair weather Clockwise rotation of sinking air (in Northern Hemisphere) Generally track toward the east and southeast Lows Stormy weather Counterclockwise rotation of rising air (in Northern Hemisphere) Generally track toward the east and northeast Lows tracking across the northern U.S. or southern Canada produce less moisture than lows tracking across the southern U.S. Weather to the west and north – usually cold Weather to the south and east – usually warm © AMS

highs and lows © AMS

© AMS

Weather Systems & Weather Maps A. clockwise and outward flow from a high-pressure system. B. counterclockwise and inward into a low-pressure system. © AMS

Weather Symbols © AMS

© AMS

© AMS

© AMS

Pressure Systems 2 Types High Pressure Systems or “Anticyclones” Low Pressure Systems or “Cyclones” © AMS More of this next week…..

Weather Systems & Weather Maps Air Masses Huge volume of air covering hundreds of thousands of square kilometers Horizontally relatively uniform in characteristics Temperature Humidity Gathers characteristics from its source region Cold, dry air masses form at higher latitudes over continents Cold, humid air masses form at higher latitudes over maritime surfaces Warm, dry air masses form over continents in subtropical regions Warm, humid air masses form near the equator or in the subtropics over maritime surfaces © AMS

Weather Systems & Weather Maps Air Masses Polar air masses are colder in winter, milder in summer Tropical air masses have less seasonal variation, due to nearly uniform sunlight duration and intensity Air masses modify as they move away from source region Taking on the characteristics of the area passing over © AMS

Fronts Warm Front Cold Front © AMS

Weather Systems & Weather Maps Fronts are 3-dimensional Where the front intersects the Earth surface is shown with the front symbol on the map. Warm front clouds and precipitation occur over a wide band May occur 12-24 hours or longer Usually light precipitation Cold front clouds and precipitation occur over a narrow band, May occur over minutes to hours May be very heavy precipitation Wind directions are different on the two sides of a front © AMS

Weather Systems & Weather Maps Some fronts have no clouds or precipitation Passage indicated by wind shift, temperature/humidity changes Fronts anchored to lows on a weather map Counterclockwise flow brings contrasting air masses together to form fronts Thunderstorms/severe weather often occur in the warm, humid air mass located between the cold and warm fronts © AMS

Weather Systems & Weather Maps In coastal areas Lake/sea breezes may lower summer temperatures May push 10-50 km (6 -30 miles) inland from the coast/shore Heavy lake-effect snow on Great Lakes or Great Salt Lake Late fall and winter Downwind (eastern and southern shores) Central US Most common location of tornadoes in the spring Thunderstorms Common in FL, western High Plains and eastern slopes of the Rockies Rare along Pacific Coast and in HI Tropical storms and hurricanes impact Atlantic and Gulf coasts Mostly August through October Rare on West Coast © AMS

Describing the State of the Atmosphere Maximum Temperature Usually occurs in early to mid-afternoon Minimum temperature Usually occurs around sunrise Dewpoint (frost point) Temperature when air is cooled, at constant pressure, so it is saturated with water vapor; dew (frost) forms Relative humidity Percentage/ratio of actual water vapor concentration of air vs water vapor concentration if air was saturated Relative humidity changes through the day as temperature varies Generally highest around sunrise and lowest when warmest Precipitation amounts General rule: 10 in. of snow = 1 in. of precipitation © AMS