Meteorology Basics The study of Weather

Air Masses  Huge masses of air that have uniform qualities of temperature and humidity –cP Continental Polar – dry & cold –mP Maritime Polar – moist & cold –mT Maritime Tropical – moist & warm –cT Continental Tropical - dry & warm

4 Main Weather Controls  Energy from the sun  Earth rotates on an axis  Earth revolves around the sun  Earth is tilted at a 23 ½ degree angle

Energy  Energy from the sun  Most important weather control  Temperature differences –Tropics are hotter than the poles –This causes convection currents between the poles and the tropics  Pressure differences –Warm temps  lower pressure –Cold temps  higher pressure

Earth rotates on an axis  Coriolis Effect –Is a result of the earth spinning –Anything moving in the northern hemisphere in the air moves to the right (clockwise) –Things in the southern hemisphere deviate to the left (counter-clockwise)

Earth revolves around the sun  This helps give the seasons of the year

Earth is tilted at a 23 ½ degree angle  Causes zones of characteristic winds  Causes seasons  Temperature differences drive the whole system

Forecasting Methods  Persistence  Analog  Numerical

Persistence Forecasting  Forecasting for tomorrow the same as what we had today  On the average there are 3 days of the same and 1 day of change (the passing front)  Correct about 75% of the time

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

Numerical Weather Prediction  Uses numerical models  Involved with computers using energy balance  85-90% accuracy

Problems with forecasting  Surface stations are about 100 mi apart and a lot can happen in 100 mi  Atmosphere is three dimensional—what is happening at the surface is often different than what’s happening higher up.  Weather balloons etc only measure a tiny portion of the atmosphere at a time. (400mi temp, pressure, wind speed and direction)

Most important forecasting factor  Air pressure measured by a barometer  Pressure tendency (rising, falling, steady) gives us some indication about temperature and humidity

Anticyclone—High Pressure  One air mass type  Clockwise circulation—due to Coriolis effect  Surface divergence  Descending air  Few, if any clouds  No fronts  Associated with persistent weather –Hot or cold –No precipitation

Wave cyclone—Low Pressure  Counterclockwise circulation  Convergence at the surface  Rising air  Condensation and precipitation common  Different air masses  Fronts between air masses

Comparing Pressure systems