How do storm chasers get so far ahead

How do they find out about the storms days or even weeks before a storm even shows up on the radar??

They don't. You certainly can't forecast where a tornado will be with any accuracy weeks ahead of time, or even days. You can forecast where severe storms will occur days to perhaps a week ahead of time. These days when I chase I run numerical weather prediction models in my hotel room each night, and use them (along with Storm Prediction Center forecasts, etc.) to pick out the day's target area. You then drive to that area and refine your prediction by looking at how fast the clouds are growing, etc. and once the rain starts falling you can use radar data. You should understand that storm chasers are not that accurate. When conditions are right, they might see a tornado one day in every ten that they go out. If they're foolhardy, willing to drive through dangerous areas of a storm to get to where the tornado will form, they might improve their odds somewhat. They will also greatly improve the odds of damaging their car or being injured in an accident.

You should remember when you see tornado videos that they are not showing you all the video from chasers that did NOT see storms.

As a chaser, I use a multitude of resources to forecast severe weather and chasing. A lot of chasers use the weather data from soundings that are gathered from the twice daily weather balloon releases by the NWS. Chasers also use weather and forecast models such as the GFS, NAM, RUC, and HRRR. Some chasers even do their own weather analysis.

Through the use of numerical computer models, synoptic maps, and experience. They will look for the projected areas of best storm development, as well as probable direction of travel. Among the things to look for on the models, are the areas with the best Convective Available Potential Energy (CAPE), lift (Lifted Index, or LI), low convective inhibitors (CINH), good helicity, diverging winds with heights, among other things. Note, though, that the models generally have trouble beyond about five days. You will also study the Storm Prediction Center's convective outlooks, and the upper air soundings.

Here is a good general site with the models, synoptic maps, upper air soundings, and satellite and radar: http://weather.unisys.com/

Here is the Storm Prediction Center's convective outlook page: http://www.spc.noaa.gov/products/outlook…