Weather

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Weather
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Weather...

• You cant see me, but you feel me, you cant
  touch me, but I can touch you. I have been
  called the Breathe of the Gods, or the killer
  and giver of life, gentle and fierce, friendly
  and enemy, angry and happy. The Native Americans
  called me Moriah, and Snow Eater (Chinook). The
  Japanese call me Kaze and in Russia I am called
  Veter. I can shatter homes, or wake a child from
  a peaceful sleep or bring relief in times of
  need. I can spread the most dreaded diseases or
  bring a welcome freshness. What am I?

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Weather is....

• The current state of the atmosphere...what is
  happening right now
• BUT Climate is different
• Climate longer time scale (the average
  conditions , temperature, humidity, rainfall,
  winds, and other meteorological elements over a
  long period of time

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Main points to remember as we learn about weather

• The sun warms the earths surface and therefore
  all the air above the surface
• The earth is warmed most at the equator and least
  at the poles---why?
• The air above land is warmed more quickly than
  air above water.
• Warm air expands and rises, creating an area of
  low pressure cold air is dense and sinks,
  creating an area of high pressure

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What are weather variables?

• Temperature
• Barometric (air) pressure
• Wind speed/ Wind Direction
• Humidity (Relative humidity)
• Precipitation

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• The Station Model

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Weather Factors

• Weather The state of the atmosphere at a
  specific time and place
• TEMPERATURE
• the average motion of molecules
• ? TEMP ?movement of molecules feels hot
• ? TEMP ?movement of molecules feels cold

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Instruments to measure weather variables

• Temperature
• Measured with a thermometer
• 2 common scales are Farenheit and Celcius

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Air Pressure- the force exerted by a column of
air at a given point

• Warm air expanding or rising air leaves behind
  L pressure
• Cold Airsinking air leaves an area of H
  pressure
• The higher the altitude the lower the pressure

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Air Pressure

• Air pressure (H or L) is measured with a device
  called a barometer

Units of pressure millibars and inches of mercury
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Air pressure rules

• When air pressure is noted on station model as
  greater than 500, we place a 9 in front of the
  number and a decimal point at the tenths place.
  Ex 506 950.6 mB of air pressure
• When the air pressure is noted as less than 500,
  we place a 10 in front of the number and a
  decimal at the tenths place Ex 467 1046.7 mB of
  air pressure

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Trends in Atmospheric Pressure

• If the pressure is falling stormy weather lies
  ahead
• If the pressure is rising clear skies are coming

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Wind

• -moving air
• Direction and speed are needed to describe the
  wind
• Wind direction is the direction that wind is
  blowing from
• Wind moves from High Pressure to Low Pressure
• Large pressure gradient strong winds
• The knot is a unit of speed equal to one nautical
  mile per hour, which is equal to exactly
  1.852 km/h and approximately 1.151 mph

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What causes winds?

• A wind is a horizontal movement of air from a
  area of high pressure to an area of low pressure
• It is this difference in pressure that makes the
  air movewind

• Winds are measured by direction and speed
• The anemometer is the tool we use to measure this
• Wind chill? cooling the wind causes

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Wind speed

• Wind speed is measured using an anemometer. Speed
  is measured in mph or knots (1.15 mph 1 knot)
• Feathers are used to show wind speed on a station
  model

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Wind direction

• Wind direction is found by using a wind vane.
• Wind direction is always described as the
  direction FROM which the wind moved

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Local Winds

• The land cools and heats faster than the ocean.
  Water holds heat longer than land, and takes
  longer to heat or cool.
• SEA BREEZE

During the day, the land gets hotter faster than
the water. The heated air rises, leaving behind
an area of low pressure. Wind from the cooler
sea blows in to take the place of that warmer
air. These happen during the day!
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Land Breezes

• At night the lands cools off faster than the
  sea. Cool air sinks creating an area of high
  pressure. Wind blows from the land to the sea.

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Wind Speed and Isobars
Isobars- Isolines of equal pressure The larger
the pressure gradient the faster the The closer
the isobars the faster the wind
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Coriolis deflects winds to the right in the
northern hemisphere
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Wind speed (cont)
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Draw the tail feather on a station model

• A. A 5 knot wind blows from the N
• B. A 10 knot wind blows from the N
• C. A 15 wind blows from the N
• D. A 20 knot wind blows from the N
• E. A 30 knot wind blows from the N
• F. A 35 Knot wind blows from the N
• G. Repeat A-F for a Southerly Wind, a North
  Easterly Wind and a South Westerly Wind

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Humidity

• -the amount of water vapor in the air (mass of
  water vapor/total mass of air)
• The hotter the air the more water vapor it can
  hold

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Relative Humidity

• -the amount of water vapor in the air compared to
  what the air can hold (before the air is
  saturated)
• Relative humidity is defined as the ratio of the
  water vapor compared to the amount of water vapor
  that the water could hold. Relative humidity is
  expressed as a percentage
• High relative humidity muggy feel or rain

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Relative Humidity

• Relative humidity is described as the amount of
  water vapor in the air compared to the total it
  can hold. (ex. sponge)
• Measured with a sling psychrometer

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Relative Humidity

• -the amount of water vapor in the air compared to
  what it could hold
• Dry air 0
• Saturated 100
• The hotter the air the more water vapor it can
  hold

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Dew Point

• -the temperature at which water vapor condenses
  out of the air
• - the temperature at which air is saturated
• Dew in the moring
• The hotter the air the more water vapor it can
  hold

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Dry air is more dense than moist air

• Humid air is less dense than dry air because a
  molecule of water (mass 1116 18 ) is less
  massive than a molecule of nitrogen (mass 14 14
  28) and a molecule of oxygen (1616 32).

Pressure and Moisture also have an inverse
relationship
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Review

• As altitude, temperature and moisture increases,
  density and pressure decrease

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Cloud Formation

• Clouds form when water vapor condenses on
  aerosols (dust, salt particles in the air)
• Factors needed for cloud formation
• The temperature in which condensation begins is
  called the dew point

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TYPES OF CLOUDS

• Cirrus Clouds wispy, feathery clouds

Form only at high levels, therefore are made of
ice crystals
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Types of Clouds

• Cumulus Clouds are puffy white cotton ball
  looking clouds

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Cumulonimbus Clouds

• These are thunderstorm clouds

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Types of Clouds

• Stratus Clouds clouds that form in flat layers-
  cover all or most of the sky and are low level
  clouds

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Precipitation

• FALLING LIQUID OR SOLID WATER FROM CLOUDS (RAIN,
  DRIZZLE, SNOW, SLEET FREEZING RAIN, HAIL)

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Precipitation

• A rain gauge is used to measure the amount of
  precipitation over a period of time

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Types of precipitation

• Rain- Falls from clouds above Freezing and air
  above freezing
• Drizzle- Small precipitation lt0.5 mm
• Snow- Falls from clouds below freezing and air
  below freezing
• Sleet- Falls from clouds above freezing but air
  below freezing
• Hail-up and down movement of rain in clouds
  multiple freezing as altitude goes up and down
• Freezing Rain-Hail-Falls from clouds and air
  above freezing but ground below freezing

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Haze, Fog and Smog are NOT forms of PRECIPICATION
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Problem Set 3

• Identify the forms of precipiation

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Reading a weather map

• ISOBAR connects areas of equal pressure BAR
  comes from BARometric pressure

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Reading a weather map...

• Isotherm Connects areas of equal temperature
  therm means temperature

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Aim Masses Source Regions
Air Mass is an extremely large body of air whose
properties of temperature and moisture content
(humidity), at any given altitude, are fairly
similar in any horizontal direction.
Source Regions are simply geographic areas where
an air mass originates. Should be uniform
surface composition - flat light surface winds
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Air Mass Classification
4 general air mass classifications categorized
according to the source region. polar latitudes
P - located poleward of 60 degrees north and
south tropical latitudes T - located within
about 25 degrees of the equator continental c -
located over large land masses--dry marine m -
located over the oceans----moist
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Types of Air Masses
cP continental polar cold, dry, stable cT
continental tropical hot, dry, stable air
aloft--unstable surface air mP maritime polar
cool, moist, and unstable mT maritime tropical
warm, moist, usually unstable
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Air Masses

• Air masses are masses of air that have the same
  characteristics of the surface over which it
  develops
• Pressure Systems
• descending (going down)H pressure
• ascending (going up)L pressure

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Fronts Fronts the boundary between 2 air masses
This is the symbol on a map for a warm front

• Warm Front warm air slides over departing cold
  air- large bands of precipitation form

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Cold Fronts
This is the symbol for a cold front

• Cold air pushes under a warm air mass. Warm air
  rises quicklynarrow bands of violent storms form

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Occluded Front
This is the weather map symbol for an occluded
front

• 2 air masses merge and force warm air between
  them to rise quickly. Strong winds and heavy
  precipitation will occur

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Stationary Front
This is the weather map symbol for a stationary
front

• Warm or cold front stops moving. Light wind and
  precipitation may occur across the front boundary

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Problem Set

• What type of weather is associated with each type
  of front
• Draw the symbol for each front

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Wind blows from high pressure areas to low
pressure areas
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The pressure gradient and coriolis force cause
lows to spin counter clock-wise and highs to
spin clockwise