08-20-2006, 05:36 PM
The National Weather Service runs a long range numerical weather forecast called the GFS. You can see the output here: http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/ . They use other techniques such as 'ensemble forecasting' (running multiple forecasts starting with small perturbations of the initial forecast) to assess the forecast spread and determine how predicatable the weather situation is currently. I'm not saying the 16-day forecast is going to be accurate - but it would serve as a basis for the extended forecast you (h') saw.
Of course the global forecast models provide mainly a larger-scale picture of how weather will evolve. A good forecaster who knows how local conditions (topography, prevailing winds, etc) impact on the weather can make better forecasts than those provided by model guidance. Then again there are some times when it isn't really possible to provide a good forecast - the exact track of a storm system determining whether you get a rain, icy mix or snow (a dusting or a foot of snow!) so I expect that we have to allow the forecasters their misses once in a while.
Of course the global forecast models provide mainly a larger-scale picture of how weather will evolve. A good forecaster who knows how local conditions (topography, prevailing winds, etc) impact on the weather can make better forecasts than those provided by model guidance. Then again there are some times when it isn't really possible to provide a good forecast - the exact track of a storm system determining whether you get a rain, icy mix or snow (a dusting or a foot of snow!) so I expect that we have to allow the forecasters their misses once in a while.