National Weather Service United States Department of Commerce
When the National Weather Service is Watching Radar...

When there is severe weather across central Alabama, it is the meteorologists of the Birmingham National Weather Service (NWS) office in Calera, AL, who are issuing Flash Flood (FFW), Severe Thunderstorm (SVR) and Tornado (TOR) Warnings. In an effort to better help the citizens of central Alabama understand exactly what we are looking for when we are watching the radar, we have created this page. Along with an explanation of how the radar works, we will highlight certain features of recent storms in order to illustrate what we are looking for when making the decision whether or not to issue a warning. No feature stands alone when making the decision to issue a warning; it is a combination of multiple features which helps us make that decision.


How does the Radar work?

Information the Radar Shows us

Dual Polarized Technology

Key Indicators in Warning Decisions

of the Radar



May 3 Reflectivity
May 3 Velocity


The radar images shown are of a supercell thunderstorm that produced multiple tornado tracks through St. Clair
and Talladega counties on May 3, 2009. The reflectivity is on the left and velocity is on the right.