Although sites such as Hepburn’s Tropo Forecast and the Mountainlake APRS maps have good intentions, they can be highly inaccurate. The Hepburn site is weather forecasting, the Mountainlake site can be easily misdirected by a single signal.
The only reliable method to accurately detect Tropo is by observing “false” echoes on National Weather Service weather radars.
http://radar.weather.gov/Conus/RadarImg/latest_Small.gif
Refresh to Update
National Weather Service radars do not filter out “false echoes”, nor also what is known as “ground clutter”. To the weather observer looking for storms, these false echoes can be confusing, but to the Ham looking for the potential of Tropo enhancement, it will guide them to point in the right directions. The conditions that enhance the troposphere to bend VHF/UHF signals over the horizon are the exact same conditions that create the images on these radars.
First of all, determine where the real storm systems are located on a radar map that does not filter clutter. Use a commercial national weather radar site display, such as the one linked.
Storms DO NOT create Tropo.
Notice that once the sun sets, many of the radars sites (usually those close to water) have a light blue image surrounding it. Later in the evening, the light blue images become much darker as Tropo develops and intense signal reflections will be colored yellow and red. These are the areas that strongly favor enhanced conditions. Again, check the commercial site to verify where the real storm systems are. If you are located underneath an area of a false image, point your antenna towards like and adjacent areas, the potential is there.
Once you have watched this map and experienced a Tropo opening, the patterns are quite apparent.
Good luck….