WEATHER is a short-termcondition of the atmosphereWeather is the result oftemperature, humidity, air pressureand winds
Air Temperature: measured witha thermometer.Complete the questions on page 142.
Humidity:• Humidity measures the amount of moisture in theair.• Dew point: the temperature at which the air issaturated with moisture.• As the dewpoint temperature reaches the airtemperature, the chance of precipitation increases.• When the dew point is reached, it precipitates.• Relative humidity how much moisture in air.
As the dewpoint temperature reachesthe air temperature, the chance ofprecipitation increases
A psychrometer is used to determinedewpoint and relative humidity.
How to determine dewpoint andrelative humidity• Find the dry bulb temperature (the airtemperature).• Find the wet bulb temperature.• Subtract to find the different.• Use the ESRT charts on page 12
As relative humidity increasesthe chances of rain increases.
WHICH STATION MODEL SHOWS THEHIGHEST HUMIDITY? HOW DO YOU KNOW
THIS STATION MODEL BECAUSE THE AIRTEMP (DRY BULB) & THE DEWPOINT ARECLOSE IN NUMBER.
Air pressure• The air presses down on us, this is called “airpressure”.• Air pressure is measured with a barometer.• The units are millibars (mb) and inches ofmercury (Hg).• Isobars are lines that connect equal air pressurereadings.• High pressure brings good, clear weather• Low pressure brings bad weather.
Winds (and breezes)• Winds are movements of air caused bypressure differences.• Wind speed measured with anemoemter• Winds ALWAYS blow from high pressure to lowpressure.• Winds are named for where they come from.• In the USA the prevailing westerly tends tomove weather from west to east.
In the USA winds bring weatherusually from west to east.
Clouds: are made of tiny waterdroplets or ice crystals that float in theair.• Clouds need condensation nuclei to form.• Condensation nuclei are dust particles, dirt particlesthat float in the atmosphere on which waterdroplets can form.
Clouds and precipitation form on thewindward side of mountains.On the windward side:warm, moist air:• Rises• Expands• Cools to the dewpoint• And thus a cloud isformed.
The water cycle: The continualmovement of water thru the Earth’ssystems• Precipitation: water falling from sky.• Evaporation: liquid water into gas (watervapor)• Transpiration: water from the leaves of plants.• Together called “evapotranspiration”• Infiltration: water soaks into ground.• Run off: water flowing over land.
Water Infiltration happens whenground is NOT saturated and the slopeis gentle.
WATER INFILTRATES (SOAKS IN) GENTLESLOPE & SOIL IS NOT SATURATED.
Water run off happens when groundis saturated and the slope is steep.