Introduction to Weather Chapter 1

A basic understanding of weather and the atmosphere. TV, radio, newspapers, the internet and NOAA Weather Radio

High Pressure 1.Also called an anticyclone 2.Winds blow clockwise and away (diverge) from the center 3.Associated with fair weather 4.Symbol - H Low Pressure 1.Also called a cyclone 2.Winds blow counterclockwise and into (converge) the center 3.Associated with poor weather 4.Symbol - L

An air mass is a huge volume of air covering hundreds of thousands of square miles that is relatively uniform horizontally in temperatures and moisture. The temperature and humidity of an air mass depend on the properties of its source region AND the nature of the surface over which it travels.

AIR MASSES – large volume of air that has a relatively uniform temperature and humidity 1.Continental Polar – cP – cold and dry (Canada) 2.Maritime Polar – mP – cold and wet (Gulf of Alaska) 3.Continental Tropical – cT – hot and dry (Mexico) 4.Maritime Tropical – mT – hot and wet (Gulf of Mexico) 5.Arctic – A – very cold and dry (Northern Canada)

Notes on air masses 1.Tropical air masses show less variation throughout the year compared with polar air masses because solar intensity and duration is more constant in the tropics -This means that cP air is much colder in the winter than in the summer 2.An air mass changes as it moves from its source - The modifications in an air mass depend on the surface that it is moving over – bare land, snow covered land, water

Fronts – the boundary between air masses - a narrow zone of transition. 1.Cold Front a.Generally, a narrow band of precipitation along or just ahead of the surface front, where precipitation is brief (couple of minutes to a few hours) b.Precipitation can be severe c.Boundary between advancing cold air and retreating warm air d.Plotted on a map as a blue line with triangles pointed in the direction of motion

2. Warm Front a.Generally, a wide band of precipitation along or just ahead of the surface warm front, where precipitation can be persistent (12-24 hours) b.Precipitation is generally light to moderate c.Boundary between advancing warm air and retreating cold air d.Plotted on a map as a red line with semi-circles pointed in the direction of motion

Ways to locate a front on a surface weather map: 1.Precipitation/Clouds 2.Wind Shift 3.Temperature Difference 4.Dew Point Difference (change in relative humidity)

A cyclone with the warm and cold fronts extending outward from the low pressure center. Showers generally form along the warm front, while more severe weather can occur along the cold front.

This shows how the warm and cold fronts act as boundaries between different air masses. Notice how the wind directions are different on either side of the fronts, and that the flow is counterclockwise and convergent.

Other Fronts 1. Stationary – a non- moving front where winds on either side blow in opposite directions 2. Occluded – when the air behind the cold front overtakes the air ahead of the warm front

Other Interesting (Non-frontal) Surface Weather 1.Hurricanes and Tropical Storms 2.Lake Effect Snow 3.Land/Sea Breeze – in the summer, areas near large bodies of water are generally cooler during the day and warmer at night

Sensors onboard weather satellites remotely measure two types of radiation: sunlight that is reflected or scattered by and, and infrared radiation that is emitted by earth. Weather satellites are either in geostationary or polar orbits and generate data that are processed into visible and infrared images.

Weather radar continually emits pulses of microwave radiation that are reflected by raindrops, snowflakes, or hailstones… which appear as blotches on a TV-type screen or image. Both intensity and area of precip can be tracked. The new Doppler radars can “see” air circulation inside the storm.