Meteorology BasicsMeteorology Basics

The study of WeatherThe study of Weather

Air MassesAir Masses

Huge masses of air that have uniform Huge masses of air that have uniform qualities of temperature and humidityqualities of temperature and humidity– cP Continental Polar – dry & coldcP Continental Polar – dry & cold– mP Maritime Polar – moist & coldmP Maritime Polar – moist & cold– mT Maritime Tropical – moist & warmmT Maritime Tropical – moist & warm– cT Continental Tropical - dry & warmcT Continental Tropical - dry & warm

4 Main Weather Controls4 Main Weather Controls

Energy from the sunEnergy from the sun Earth rotates on an axisEarth rotates on an axis Earth revolves around the sunEarth revolves around the sun Earth is tilted at a 23 ½ degree angleEarth is tilted at a 23 ½ degree angle

EnergyEnergy

Energy from the sunEnergy from the sun Most important weather controlMost important weather control Temperature differencesTemperature differences

– Tropics are hotter than the polesTropics are hotter than the poles– This causes convection currents between the This causes convection currents between the

poles and the tropicspoles and the tropics Pressure differencesPressure differences

– Warm tempsWarm temps lower pressure lower pressure– Cold tempsCold temps higher pressure higher pressure

Earth rotates on an axisEarth rotates on an axis

Coriolis EffectCoriolis Effect– Is a result of the earth spinningIs a result of the earth spinning– Anything moving in the northern hemisphere in Anything moving in the northern hemisphere in

the air moves to the right (clockwise)the air moves to the right (clockwise)– Things in the southern hemisphere deviate to Things in the southern hemisphere deviate to

the left (counter-clockwise)the left (counter-clockwise)

Earth revolves around the sunEarth revolves around the sun

This helps give the seasons of the yearThis helps give the seasons of the year

Earth is tilted at a 23 ½ degree angleEarth is tilted at a 23 ½ degree angle

Causes zones of characteristic windsCauses zones of characteristic winds Causes seasonsCauses seasons Temperature differences drive the whole Temperature differences drive the whole

systemsystem

Forecasting MethodsForecasting Methods

PersistencePersistence AnalogAnalog NumericalNumerical

Persistence ForecastingPersistence Forecasting

Forecasting for tomorrow the same as what Forecasting for tomorrow the same as what we had todaywe had today

On the average there are 3 days of the On the average there are 3 days of the same and 1 day of change (the passing same and 1 day of change (the passing front)front)

Correct about 75% of the timeCorrect about 75% of the time

Analog ForecastingAnalog Forecasting

Going back in history to find similar Going back in history to find similar conditions and predicting what the “next” conditions and predicting what the “next” day brought in historyday brought in history

Numerical Weather PredictionNumerical Weather Prediction

Uses numerical modelsUses numerical models Involved with computers using energy Involved with computers using energy

balancebalance 85-90% accuracy85-90% accuracy

Problems with forecastingProblems with forecasting

Surface stations are about 100 mi apart and Surface stations are about 100 mi apart and a lot can happen in 100 mia lot can happen in 100 mi

Atmosphere is three dimensional—what is Atmosphere is three dimensional—what is happening at the surface is often different happening at the surface is often different than what’s happening higher up.than what’s happening higher up.

Weather balloons etc only measure a tiny Weather balloons etc only measure a tiny portion of the atmosphere at a time. (400mi portion of the atmosphere at a time. (400mi temp, pressure, wind speed and direction)temp, pressure, wind speed and direction)

Most important forecasting factorMost important forecasting factor

Air pressure measured by a barometerAir pressure measured by a barometer Pressure tendency (rising, falling, steady) Pressure tendency (rising, falling, steady)

gives us some indication about temperature gives us some indication about temperature and humidityand humidity

Anticyclone—High PressureAnticyclone—High Pressure

One air mass typeOne air mass type Clockwise circulation—due to Coriolis effectClockwise circulation—due to Coriolis effect Surface divergenceSurface divergence Descending airDescending air Few, if any cloudsFew, if any clouds No frontsNo fronts Associated with persistent weatherAssociated with persistent weather

– Hot or coldHot or cold– No precipitationNo precipitation

Wave cyclone—Low PressureWave cyclone—Low Pressure

Counterclockwise circulationCounterclockwise circulation Convergence at the surfaceConvergence at the surface Rising airRising air Condensation and precipitation commonCondensation and precipitation common Different air massesDifferent air masses Fronts between air massesFronts between air masses

Comparing Pressure systemsComparing Pressure systems