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 centers

Opposite effects on southern hemisphere

Simpsons 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 FrontsOccluded Front

• When cold front and warm front run into each other

• Large amount of precipitation is possible

Stationary Front

• Boundary between two air masses

• Moves very slowly

Animation

Station Model

Reading Pressure

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 configuration similar to occluded front

Current Weather! http://www.hpc.ncep.noaa.gov/

! http://weather.cod.edu/satrad/

! http://www.aviationweather.gov/

! http://www.noaa.gov/

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?! Rising air cools as it rises, this causes water

vapor that is in the air to condense into a liquid

! What causes Air 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 layer Usually dark gray Can form at different altitudes ▫ Example: altostratus=middle altitude

! Cirrostratus=high altitude

! Cirrus Clouds Thin wispy clouds Very high altitude (7-18km) ▫ 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. How do these form in non severe cases? How can we make them severe?