We are always monitoring the current radar during all types of weather events. Knowing how to identify certain features and patterns on a radar image and loop can help increase the time before dangerous weather events may occur. Often a flash flood warning will be issued once heavy rain is, or has, already been detected but knowing certain features that can produce heavy rain could help increase that warning time. One feature that can result in devastating flooding is when rain or thunderstorms continue to develop and move over the same area for an extended period of time. Meteorologists call this phenomenon back-building and/or training thunderstorms.
Looking at the image above if you were in the area receiving the heavy rain and flooding it would seem like it was just a constant rain storm. What is actually happening is that the initial storm actually weakens as it moves downwind and a new storm, or series of storms, develop upwind and move over the same area. Because the storm develops upwind it is called back-building with the training term referring to it moving over the same area on the same track (just like a train on a track). A number of features may cause this. Terrain, atmospheric dynamics, or even outflow from the storm itself. A meteorologists may identify this type of pattern while monitoring a radar loop and put an alert out that there may be flooding if the current situation continues.
Features like this are tough to predict and often National Weather Service offices will not issue a Flash Flood Warning until a significant amount of rain has already fallen. Still an alert meteorologist can recognize this type of pattern developing by monitoring the radar and issuing a special weather statement which would precede a flash flood warning. At Weatherboy we often recognize these patterns and the statements and pass them onto you. Remember if you hear “back-building storms” or “training thunderstorms” and your in the affected area, you have the potential to see significant flooding if the pattern continues.
Stay safe and never drive through flood waters.