A IR F RONTS

Q UESTIONS What’s the difference between weather and climate? What’s an air mass? What’s an air front? What is humidity? How do we measure it? What it isWeatherSymbol Cold front Warm front Stationary front Occluded front

B ACKGROUND INFORMATION Weather: What happens that day at a particular place Rain, snow, sun, etc Climate: The average weather conditions of an area over a long period of time. Good for weather forecasting Determined by 2 factors Temperature Precipitation

C LIMATE There are 3 main climates in the world (all of which can be divided down further) Tropical Characterized by constant high temperatures (over 65F) all year Polar Characterized by constant low temperatures (under 50F) all year Temperate Characterized by both high and low temperatures with distinct seasons We live in a temperate climate!

A IR MASSES Air mass: A large body of air that has similar temperature and moisture throughout. Warm and cold air masses move through the US in both the summer and winter. Influences both the weather AND climate

C OLD A IR M ASSES Cold Air Masses : Comes from the polar regions and down over Canada, bringing cold air Cold air sinks because the molecules in the air clump closer together Cold air is more dense!

W ARM A IR M ASSES Warm Air Masses : Comes from the tropics, and brings warm air Warm air rises because the molecules in the air expand and move farther away from each other Warm air is less dense!

D EMONSTRATION TIME ! In one beaker, heat up 150 ml of water until bubbles form At the same time, get ice and put it in another beaker with 100 ml of water Put the bottle with the balloon in the hot water first, then the cold water. Repeat several times What’s going on with the balloon?

F RONT Front: where different air masses meet. Weather is usually cloudy and stormy where fronts meet. Fronts only happen at middle latitudes where there is both warm and cold fronts Doesn’t happen at the tropics or the polar regions

C OLD F RONT Cold front : Cold air meets and pushes up a warm front Causes thunderstorms, heavy rain, and snow. Symbol for a cold front:

W ARM F RONT Warm front: Warm air meets and pushes down the cold air. Generally brings a rainy drizzle. Symbol for a warm front:

S TATIONARY F RONTS Stationary front: A cold air mass meets a warm air mass and little movement occurs. Rainy drizzle The symbol for a stationary front:

O CCLUDED F RONT Occluded front: A warm front is caught in the middle of two cold fronts Cool temps and lots of rain Symbol for an occluded front:

H UMIDITY Fronts bring different weather conditions when they meet One such result might be humidity Humidity - The amount of water vapor or moisture in the air – Humidity is what makes your hair frizzy! When there is more water in the air, your hair absorbs water and becomes longer

R ELATIVE HUMIDITY – As air temperature increases, the amount of water it can hold increases – Humidity is generally given as a percentage – The most water air can hold is 100% humidity, which means rain!

C ONDENSATION Condensation —Gas that has cooled to become a liquid – The air must have a 100% relative humidity for condensation to occur – Examples: The water on the outside of a glass Dew on the grass

H OW TO FIND RELATIVE HUMIDITY Sling Psychrometer —The instrument used to measure relative humidity – It contains two thermometers – One thermometer is covered with a wet cloth, the other one is normal – The water evaporates from the wet bulb, lowering the temperature of the thermometer – This tells us how humid the air is based on how much water is actually evaporating from the wet cloth

H OW TO FIND RELATIVE HUMIDITY 1. Take the temperatures of the wet bulb and the dry bulb 2. Subtract the wet bulb temperature from the dry bulb temperature. 3. Use the relative humidity chart to find the humidity