Yes, you do, if you’re going to fly safely. And while there are a lot of websites out there that give you all the information you need, some of them are buried in advertising or not reliably updated.
One that suffers neither of these flaws comes from our own gummint. Yes, the National Oceanographic and Atmospheric Administration have a wonderfully complete and up to date plethora of pages on the subject.
When you’re done here, browse over to http://www.weather.gov/forecasts/graphical/sectors/ and click on your area of interest on the map. Down the left you’ll find a matrix of times and weather parameters. You can easily kill an hour just watching the predicted changes. This series will become a favorite if you’re headed out for lunch in that it shows ground conditions. If you’re going further, you’ll also find links to pages specifically for aviation. As for those other sites? This is where they get their data.
NOAA needs to work on the name though; “Administration” at the end of it implies control of said oceans and atmosphere and that’s a long way off.