WEATHER

Current map

Pressure Recall the pressure

crushing the pop can from the last unit

The sum of the forces from the moving air molecules over an area

Average Sea level pressure is 1010mb

What do these mean?

L- Low pressure, rising motion

of the air H-High Pressure, sinking motion of the air

So What’s Going on Here?

What is wind?

What would we expect the wind to look like in this example?

H L

WRONG!!!

Instead we see this…

Coriolis Effect

Caused by the Earth’s Rotation Causes the Rotation of air around pressure

centersOpposite effects on southern hemisphereSimpsons video

http://earth.nullschool.net/ Example

• Air rises at a Low Pressure Center

• Associated with cloudy and windy weather

• North Pole Loop

• Air sinks at a High Pressure Center

• Associated with nice and calm weather

Fronts

Isotherm Line of equal

temperature Isobar

Line of equal pressure

Gradient is shown by lines drawn close together Very important to

find fronts!

Fronts Leading Edge of different air mass

Temperature, humidity, wind direction

4 types Cold Front

Warm Front

Occluded Front

Stationary

Cold Front

Brings in colder, drier air with a sudden change in wind speed and direction

Warm Front

Brings warmer, more humid air with change in wind direction

Occluded and Stationary Fronts

Occluded Front• When cold front and warm

front run into each other• Large amount of

precipitation is possible

Stationary Front• Boundary between two

air masses• Neither air mass has

enough force to move the other

Station Model

Reading Pressure

If 1st number is less than 5, you put 10 in front

If 1st number is more than or equal to 5, you put 9 in front

Animation

Weather at Fronts Cold Fronts

Clouds, rain/snow in narrow band right on frontal boundary

Clear skies quickly follow frontal passage with strong N/NW winds

Warm front Thin clouds/blanket of clouds with light rain possible

ahead of the frontal boundary Winds shift to the south

NW (top left) corner of Low Pressure Center Heavy rain/snow fall possible Caused by upper air similar to occluded front

Jet Stream

Pressure Centers control where fronts go

Prevailing winds and the jet stream control where pressure systems go

Link

Clouds

What are clouds made of?

Clouds are made of very small droplets of water or ice crystals.

How do clouds form?

Air cools as it rises, this causes water vapor that is in the air to condense into a liquid

What causesAir to rise?

Types of Clouds

Cumulus “Puffy” with flat base Can grow very tall Time lapse of growth

Another Time Lapse Video

Stratus Clouds Uniform “blanket” layer Usually dark gray Can form at different altitudes

Example: altostratus=middle altitude Cirrostratus=high altitude

Cirrus Clouds Thin “wispy” clouds Very high altitude Made of ice crystals

Special Cases

Precipitation When the cloud drops get too large to stay

suspended Gives the cloud a new name Can be liquid or ice

Cumulonimbus nimbus cloud that is producing precipitation

Nimbostratus Stratus clouds that produce precipitation

Life of a Rain Drop

Link

Fronts can act as LIFTING MECHANISMS to create clouds

Severe Weather When normal weather occurrences (wind,

rain) become more powerful than normal.

This creates dangerous conditionsfor people and property

These storms require very specificIngredients for form

Ingredients for Severe Storms

• High dew points (humid air)

• High Temperature

• Unstable air (cool air aloft)

• Lifting mechanism

(Front)

Squall Line

Line of thunderstorms caused by cold front movement

Several storms may be severe

Cumulus Nimbus

Tallest, most powerful cloud and produces severe storms

Squall line

Super Cell Storms

Cumulonimbus clouds with rotation

Extra ingredient required is wind sheer

Wind sheer is the change in wind speed and direction as you change altitude