3WHY DO WE HAVE THE WEATHER ? Just think about it!Why is there wind? Why does it blow from one direction one day and another the next?Why is it rainy one day and dry the next?How come it’s cold in the winter?How can we have hail in the summer?What causes snow and freezing rain?video
4Let’s take a look at the weather picture and why we have weather!
5You might pick heat or sun….but another good choice would be If we were to pick one term to help explain why we have weather, what do you think would be a good word?You might pick heat or sun….but another good choice would beConvection
6Convection is the transfer of heat, usually in gases or liquids.
7After the atmosphere is warmed by radiation and conduction, the heat is transferred throughout the atmosphere by convection.Since warmed air has more space between the molecules, it’s less dense and risesCooled air is more dense and tends to sinkIn general, air near the equator tends to rise and air near the poles tends to sink
13The Weather HighwaysThe rotation of the earth creates the Coriolis effect.The Coriolis effect causes the air and water to be deflected to the right north of the equator.This creates global weather highwaysvideo
14The WesterliesBecause of our latitude, most of our weather comes from the westLooking at the weather map, what type of weather might we expect?What type of weather might we expect in a few days?
15Let’s break for a short review 1.Transfer of heat in liquids or gases_____2. _____ air is dense and tends to sink.3. Band of clouds found around the equator______4. Cold air holds _____ moisture than warm air5. The Coriolis effect causes the air and water in the Northern hemisphereto be deflected to the _____ of the equator
16How did you do?1. CONVECTION2. COLD3. ITCZ4. LESS5. RIGHT
17Winds You’ve read about Global Winds: Trade Winds Westerlies 0-30°WesterliesBetween 30-60°Polar Easterlies60-90°The Doldrums & Horse LatitudesAreas of weak and variable winds
18Local Winds Land surfaces heat up faster than water surfaces Sea Breeze:Cool wind from water to landLand Breeze:Cool wind from land to sea
19Valley Breezes Mountain Breezes: Warm air from the valley moves upslopeDuring the dayMountain Breezes:Cool air descends from the mountainsDuring the night
20Now What?Ok, so we know that the weather moves around on these highways and that warm air rises and cold air sinks.But why is it sunny one day, and rainy the next?
21Let’s take another look at the weather map Notice that there are H’s and L’s on the mapThere are also blue lines with spikes and red lines with half circlesLet’s take a closer look!
22High Pressure AreasWhen cooler air sinks and is warmed, the air can hold more moistureThis usually means sunny skiesWinds tend to move clockwise around a high
23Low Pressure AreasWhen warm air rises and is cooled, the air can not hold as much moistureOften, these areas are associated with precipitation and stormy weatherWinds tend to move counter clockwise around the low
24So, if you see a big H on the weather map over the area you live, you can expect fair weather
25Surrounding these "highs" and "lows" are lines called isobars. "Iso" means "equal" and a "bar" is a unit of pressure so an isobar means equal pressure.We connect these areas of equal pressure with a line. Everywhere along each line is constant pressure.The closer the isobars are packed together the stronger the pressure gradient is.
26When you see a big L in your area, there will probably be stormy weather
27These highs and lows move or less along the jet stream and bring us our weather changes
28Fronts and Air MassesAn air mass is a large body of air whose temperature and moisture are fairly similar at a given altitudeFronts are boundaries separating different air massesThere are four different air masses that affect the United States
29The Air Masses cP( continental polar) : cold, dry stable cT( continental tropical) : hot, dry, stable air aloft, unstable at the surfacemP( maritime polar) : cool, moist, unstablemT( maritime tropical) : warm, moist, unstable
30This map shows the air mass source regions and there paths
31Ok, now we see the difference in the air masses Let’s look at the different fronts and their impact on weatherCan you see the four different types of fronts on the map?
32Warm Fronts A warm front is when warm air is moving towards cold air. The shallow leading edge of warm air must “overrun” cold airThese are usually slow moving
33Cold Fronts Cold air is moving into a region of warm air Intensity of precipitation greater, but short livedClearing conditions after front passesUsually approaches from W or NWanimation
34Stationary FrontsWhen neither a warm or cold air mass is moving very muchOften a region of clouds
35Occluded Fronts Cold front overtakes warm front Often found close to the low pressure centermap
36Ready for a little quiz? You’ll need a sheet of paper Write your answers as we goHere we go!
371.Winds in a low pressure system move _____ around the low
382.What type of front can be found close to point D ?
393.Which of these fronts would you expect to have greater precipitation, but be short lived as the front passes?
404.Give the name of the air mass that would have the following characteristics:cool, moist, unstable
415. That important weather word that refers to the transfer of heat
426. In general, air near the equator tend to_____ ( rise or fall )
437.It causes air and water to be deflected to the right north of the equator
448. Which of the weather highways usually controls our weather
45Warm air holds ( more or less ) moisture than cold air 9.Warm air holds ( more or less ) moisture than cold air
4610.If there is a big H on the weather map where you live, would you expect fair or stormy weather
47Let’s check the answers! How did you do?Let’s check the answers!