Exact Weather forecasts don't exist. Thats why I add the phrase (Not Exact But Close Enough). Just enter your city or zip code to get some information about the weather in your area. This site has hourly weather based on the GFS, ETAMOS And NGMMOS Computer forecast models.
Weather forecasting is not an exact science. It ranges from weather folktale simplicity to elaborate computer simulations that rely on a variety of methods to produce their results.
In attempting a forecast, forecasters rely on a series models. Each model uses a different set of programmed parameters for analyzing upper air data, so readout between them is often different. Confidence in the long-range forecast is much higher when the models are in synchronization , or basically "agree" on what's going to happen.
GFS This is the "Aviation" portion of the Global Spectral Model, also sometimes called the "Global Forecast System" or GFS. AVN looks outward fifteen days, but confidence in accuracy is low beyond eight or ten.
ETAMOS Pronounced "mezzo AY-tuh", this is a short-range model. It looks ahead three days, and is the only model that includes terrain as one of the parameters. When you live near mountains and oceans, terrain is a factor.
NGMMOS (Nested Grid model) (Model Output Statistics) which are statistically derived surface conditions for particular cities. This model gives forecast information out to 48 hours.
Numerical Weather Prediction:
Numerical Weather Prediction (NWP) uses the power of computers to make a forecast. Complex computer programs, also known as forecast models, run on supercomputers and provide predictions on many atmospheric variables such as temperature, pressure, wind, and rainfall. A forecaster examines how the features predicted by the computer will interact to produce the day's weather.
The NWP method is flawed (not exact but close) in that the equations used by the models to simulate the atmosphere are not precise. This leads to some error in the predictions. In addition, the are many gaps in the initial data since we do not receive many weather observations from areas in the mountains or over the ocean. If the initial state is not completely known, the computer's prediction of how that initial state will evolve will not be entirely accurate.
Despite these flaws, the NWP method is probably the best at forecasting the day-to-day weather changes. Very few people, however, have access to the computer data but you don't need to when you can get your forecast from "exact weather." The data is allready compiled and analyzed by the National Weather Service.