Weather forecasting is an inexact science, and many different methods are used in combination to make a prediction. These range from common folklore, computer simulations, and radar systems.
The "climatology method" averages weather statistics gathered over many years for a specific region to make a prediction. For example, to predict the weather in New Orleans on July 4th, climatologists will average out all the weather data collected for every July 4th on record, such as temperature and precipitation. But this only works when the weather pattern is similar to what is expected for the chosen time of year.
Taking it to the next level, meteorologists examine a forecast and then look to a day in the past where the conditions were very similar -- and then predict that the current weather is expected to behave like that. But, there are very few days where all the weather variables are very similar in the same locations as before. Even tiny differences can make big differences in the actual weather. Numerical weather prediction uses forecast computer models to make predictions on such variables as temperature, pressure, wind and rainfall.
Radar systems send a signal -- usually microwaves -- towards an object or region, and then analyze how long it takes for the signal to be reflected back. This indicates how far away the object is from the source of the signal. And if the object is in motion when the microwaves hit it, the waves will be shifted in frequency when they are reflected back, telling the system how fast the object is moving. Weather radar detects water particles in the atmosphere, for example, to determine how much moisture is in the air.
SOME WEATHER FOLKLORE:
- If you hear an owl hoot in the daytime, a storm is approaching.
- High clouds indicate fair weather; low clouds mean rain.
- Smoke that curls down and lingers means a storm is nearing.
- Roosting birds are a sign of a storm, because thinning air is harder to fly in.
- A warm November is the sign of a bad winter.
- If fruit trees bloom in the fall, the weather will be sever the following winter.
- If the first snow falls on unfrozen ground, expect a mild winter.