How are meteorologists able to forecast the local weather 10 to 15 days out?

ShalloWhale

They can't. Their long range forecasts are 7 days, at best and are mostly based on computer generated probabilities. They do a remarkably job, given all the variables of our atmosphere.

derfram

Computers. Vast amounts of data are input to a computer, including current conditions over a wide area, historical data, etc. Then the computer crunches the numbers based on an algorithm and spits out a forcast. They've actually became fairly accurate the last decade.

Joe

looking and measuring wind currents, with radar

Mark

Satellites, and before that, observations about what preceded an event...