What does the National Weather Service look at to issue tornado warnings?


MOBILE, Ala. (WKRG) – In the wake of several recent severe weather days, News 5’s Caroline Carithers spoke to Jason Beaman, the Warning Coordination Meteorologist at the National Weather Service (NWS) in Mobile about how the NWS decides to issue warnings, how tornadoes form, and the differences in a tornado watch and a tornado warning.

Beaman explains, “Even before a severe weather event develops, we are looking at the conditions in the atmosphere that could be favorable for the development of severe thunderstorms and tornadoes.” He then explains that they look wind shear (change of wind speed/direction with height), instability (how quickly the air can rise) and “trigger” (a cold front or weather disturbance) that could set everything into motion.

When storms start evolving, the radar meteorologists at NWS start keeping an eye on storms that look to be rotating and areas where the ingredients listed above are coming together. On the radar, meteorologists typically look at velocity, among many other things, for tornado detection. Velocity on the radar shows wind speed and whether the wind is blowing to or away from the radar. When winds of different directions are very close together and strong, you can see the rotation, usually indicating a tornado.

Tornado formation can get a bit complicated. It all has to do with wind shear, instability, and lift (the same things meteorologists look at before an event). Other than the environment, it also depends on the thunderstorm itself. If the updrafts and downdrafts and other processes interact in a certain way, it intensifies and stretches the low-level circulation to produce a tornado.

It is also important to remember then difference in a tornado watch and a tornado warning. A tornado watch means that the environment is favorable for tornadoes, but one has not yet occurred. A tornado warning means that a tornado has been spotted by an observer on the ground or has been detected by radar. Because severe weather season can last through the fall, winter and spring you must always be prepared.

Check out the video for visuals and more information.

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