Courtesy: National Weather Service In Huntsville

The April 27th tornado outbreak was a devastating event for the communities of the Tennessee Valley, but it also served as a learning experience. Tornadoes are not uncommon in Alabama and can occur during any month of the year, but this specific event was unique.

Days before April 27th, model data was consistently showing environmental parameters being there for a significant weather event. With data being constant on the parameters and impacts we would see in the region, the National Weather Service (NWS) Offices across the state started identifying the threats as much as seven days in advance.

Weather History: 11 Year Anniversary — April 27th Outbreak

11 years ago, NWS Warning Coordination Meteorologist Jessica Chace was working a the Birmingham office but she noticed what was brewing in the Tennessee Valley.

According to NWS Warning Coordination Meteorologist Jessica Chace “we had three different waves over northern Alabama and southern middle Tennessee, so from the morning squall line or QLCS to that second kind of midday wave to the afternoon supercells.”

Tornado Warnings Issued on April 27th, 2011

During the 18-hour stretch of storm activity in the Tennessee Valley, 92 tornado warnings were issued. In Alabama, a total of 62 tornadoes ripped through the region, 39 of those tracked through northern Alabama. The strongest tornadoes that touched down that day were produced by long-track supercells during the afternoon hours.

What goes into issuing a tornado warning?

Before pulling the trigger on a Tornado Warning, the NWS looks closely at multiple data products. One main data tool that is closely monitored is the storm-relative velocity, which looks at the wind energy and wind pattern within the storm. Another parameter the NWS looks at is the lightning count in a storm. Recent research has shown that storms that produce a tornado tend to have a lightning jump before the tornado develops. A way they are able to look at this product is the GOES-East satellite which shows the lightning density within a storm.

Once the NWS identifies this threat, it is then time for them to write up the warning that is shared with the public. Within the Advanced Weather Information Processing System (AWIPS), an application called WarnGen is how they type up this warning. Within the WarnGen, they will draw out the polygon and add the text information on the weather alert. In times when the tornado is in fact confirmed, they will add cities that will be impacted by the storm.

The relationship between broadcast meteorologists and the local weather service office plays an important role in getting information out to the public. Although the NWS are the only ones that can officially issue a tornado warning, they rely on the broadcast meteorologist and other local partners to get that information out to the public.

Chace mentioned that “whenever I was a young child I was terrified of tornadoes, the only thing that calmed me down was watching my favorite broadcast meteorologist and so you know providing that level of service to our community. Y’all get that message out, y’all get that preparedness information out, and that is crucial for viewers to take that information and apply it when it matters most.”

The April 27th event was eye-opening, showing that even though we have come far with technology we are still vulnerable. Communication ahead of a major weather event is crucial to keeping the public safe and allowing them time to prepare ahead of time! Following this event, the National Weather Service expanded its Decision Support Services. This is a way that they connect with broadcast meteorologists, emergency management, and other partners that can help get that critical information out to the public.

During severe weather events, it is important to have multiple ways to receive watches and warnings that may be issued.