Hi Michael: For the Marine Prediction Center I go to http://weather.noaa.gov/fax/marine.shtml, and then choose the region for which I want charts. Once in the region (say Atlantic) you then go down the list of products to 500mb for whatever timeframe. These are sent out in a strange format and the Marine Prediction Center is in the process of making the 500mb charts more easily accessible. We have a program called Graphic Converter and use it to open the downloaded 500mb files. You can get a copy of this program at http://www.lemkesoft.de/.

Another approach would be to go to http://152.80.56.203/wxmap/web/ which is the website for both the Navy NOGAPs model and the Aviation model. In this case you simply hit the region of the world you want to watch, and then the timeframe (out to 144 hours for NOGAPs) and what data you need (i.e. surface, 500mb, 850mb, etc.). They also have Java movies of the 500mb charts which take a while to load but are really cool. These charts have vorticity shown on them which makes them a little harder to read.

Another good site for 500mb data is http://www.ecmwf.int/services/forecast/index.html. This is from the European Community medium range model. Here you can get surface and 500mb for Northern and Southern Hemispheres as well as the Atlantic for 72 to 144 hours out.

Keep in mind that these are computer-generated models of what is happening and that the professionals always compare different models and then look at the satellite images (especially water vapor) to confirm what the computer is showing.

Good Luck!