I have had several people write in on the same topic: How do we forecast? So for this week's topic we will take a closer look at how we compile that forecast you see on TV.
One word we often mention is models. There are over 20 models that provide data for us to analyze. How do these models happen? First we need observations from weather stations and throughout the atmosphere. These come from weather balloons that are sent up twice a day in over 500 locations all over the world. We also get observations from TAMDAR. TAMDAR are weather observations that are provided by attaching sensors to commercial aircraft. These tools provide observations for temperature, relative humidity, winds aloft and pressure throughout the atmosphere. With surface observations and atmosphere observations we get a snapshot of the weather patterns that are currently happening.
Those observations are then plugged into super computers which can calculate massive mathematical equations and provide outputs of what the atmosphere will do given the initial conditions. It is important to note that certain meteorologist's jobs are solely to build the algorithms ( or code ) that go into the supercomputers. The models in the United States are run by the National Weather Service which houses the supercomputers in Gaithersburg, Maryland. The computers provide four runs a day and were recently updated in September of 2008.
Any individual has access to the model outputs on many different sites on the Internet. Although they may be different sites they have the same data. Models are numerical and graphical and it is from this data that we analyze and make the best decisions possible. What information do these models provide? We see temperatures, wind direction and speed, chance of precipitation, what type and how much accumulations, visibilities, and pressure. On any given day models can agree with each other or disagree. A few items we will look for is how has similar conditions played out in the past and how accurate has a certain model been with a similar situation. On a given day one model may say clear skies and a low of 5 where as another may say mostly cloudy and a low of 15. It is then up to the meteorologist and the knowledge they have acquired throughout their career and schooling to decide what scenario should play out.
If you want to see an example of one model check out any of our forecasts online or on TV and look for our graphic "Futuretrak". This is an example of our own graphical model we use.
Meteorologist Kristen Connolly