# Presentation: 517951

## National Weather ServiceMissoula

- http://www.weather.gov/missoula

## What is Weather??

- The study of the Atmosphere and its phenomenon

## The Water Cycle

## What is the Atmosphere??

- The Earth is surrounded by a thin layer of gases made up of a mixture of molecules. These are mostly molecules of nitrogen, oxygen, argon and carbon dioxide. We call this layer the Earth's atmosphere.
- The layers of the Earth's atmosphere are the troposphere, stratosphere, mesosphere, and thermosphere. They can be defined by their atmospheric temperature profile.

## Slide 5

## We live in the Troposphere! 

- We live in the Troposphere!

## What is Air Pressure??

- Did you know that we are constantly surrounded by tiny air particles that press down on us like a weight? The air particles are too tiny to see, but they take up space all around us. The weight associated with these particles is called air pressure.
- Air pressure can tell us a lot about weather. Can you name two different types of air pressure that relate to weather?
**high pressure**, which usually means sunny and calm weather for Montana.
**Low pressure** is known to bring cloudy and stormy weather. In general, the lower the air pressure outside the stronger the storm will be!
- Air moves from a high pressure area toward a low pressure area. Meteorologists often use an instrument called a barometer to measure air pressure *and* the change in pressure, to track the movement of high and low pressure systems and the weather associated with them.

## Wind Flow around Highs and Lows

## Winds

## Heat Balance

**Notes:**
Earth receives uneven energy distribution.  Like any good system in nature, it tries to come into balance by displacing heat toward the poles.  This energy movement manifests itself in the form of storm systems.

## Global Wind Regimes

## Jet Stream

## Seasonal Position of the Jet Stream

## How do we measure wind??

- We use an Anemometer to measure the wind speed.
- We use a wind vane to measure direction
- Always take the direction the wind is coming from!!

## Air Masses

## Frontal Winds

## Frontogenesis

## Structure of a Cold Front and Wind Shifts

## Lifting Mechanisms

## Frontal Lift

## Convergence/Divergence

- Lift

- Subsidence

## Atmospheric Stability

- The degree of resistance of a layer of air to vertical motion.

## Stable Air Mass

- A state of the atmosphere in which the vertical distribution of temperature is such that an air parcel will resist vertical displacement.

## Unstable Air Mass

- A vertical distribution in the atmosphere that encourages vertical displacement from its level.

## Where will the parcel go?

## Visual Indicators of Stable Air

- Smoke Column drifts apart after limited rise
- Poor visibility in low levels due to accumulation of smoke/haze
- Steady or calm winds

## Visual Indicators of Unstable Air

- Clouds grow vertically and smoke rises to great heights
- Cumulus Clouds
- Gusty winds
- Good visibility

## Valley Inversion

## Thunderstorms

## Thunderstorm Stages

**Cumulus Stage**
- All updraft at this point. Beginning to develop cauliflower appearance.

## Thunderstorm Stages

**Mature Stage**
- Most dangerous stage. Severe weather of all types can occur. Will likely have gusty, erratic winds and cause extreme fire behavior.

## Thunderstorm Stages

**Dissipating Stage**
- Storm still very dangerous. All downdraft now which can lead to gusts in excess of 60 mph.

## Thunderstorm Downburst

## Thunderstorm Downdrafts

## Thunderstorms - Hail

## Lightning

## Lightning

## Lightning

## Cloud Types

## Clouds

## Clouds

- Alto Cumulus Lenticularis
- “Lenticular or Standing Lenticular”
- Caused by vertical wind eddies associated with strong winds aloft