Monday, September 22, 2014

New siren activation policy coming to the city of Memphis

In Shelby County, there are five entities responsible for outdoor warning sirens to alert the populace that a Tornado Warning has been issued for Shelby County. Those are the cities of Memphis, Collierville, Bartlett, and Germantown, plus Shelby County. Each of the four cities are responsible for warning systems within their municipal jurisdiction, while the Shelby County Emergency Management Agency covers unincorporated Shelby County outside the aforementioned 4 cities, plus the towns of Arlington, Lakeland, and Millington.

Municipal boundaries within Shelby County. Bartlett, Germantown, Collierville, and Memphis all activate their own outdoor warning sirens. Shelby County is responsible outdoor sirens in unincorporated areas, as well as Millington, Lakeland, and Arlington city limits (grey).

As has been discussed on this blog before, Bartlett, Germantown, and Collierville all sound their outdoor sirens based on an imminent threat to their particular municipality, using the Tornado Warning polygon (or warmed area) issued by the National Weather Service. The city of Memphis and Shelby County have warned their entire area of responsibility for a Tornado Warning that includes any part of Shelby County. That policy will be changing in the city of Memphis.

Under an agreement with American Signal (an outdoor warning siren manufacturer), a brand-new state-of-the-art warning system has been developed and is in a test phase at the Memphis Office of Emergency Management (OEM), a division of Memphis Fire Services, which is responsible for activation of the city's 108 outdoor warning sirens. This new system, with multiple layers of redundancy and the ability to be triggered manually from multiple locations including via mobile by key personnel, will allow the city to modify its policy such that only the portions of the city that are under a threat of a tornado will be warned. Using software automation, polygon notification to specific areas of the city will be possible, thus reducing over-stimulation and siren fatigue of the public and ensuring that those that hear an outdoor siren during inclement weather in or very near the warned area as defined by the National Weather Service (NWS). (Note that the new system has not been implemented and no date has been set at this point for implementation.)

Location of the city of Memphis' outdoor warning sirens on Google Maps.

So how will the new system work? The software will ingest weather alerts as soon as they are issued by NWS-Memphis. When a Tornado Warning is issued that intersects any part of the city of Memphis, sirens will be automatically activated by the software. The sirens that sound will be those within the NWS polygon/warned area, as well as those that can be heard within a portion of the warned area, even if they are outside of the warned area. This "buffer" will mean that some areas that are just outside the warned area could hear the sirens, but it will significantly cut down on the overwarning of the entire population when a small section of the city is affected.

In addition to the software-driven activation, sirens can also be sounded (in whole or in part) manually. All activities of the system are also logged and displayed on the user interface so that key personnel will know when and which sirens activated and whether each siren is in a functional state.

The approach taken by Memphis is a bit different from those in Bartlett, Collierville, and Germantown. In the new Memphis system, parts of the city may be warned, while other areas are not, due to the large geographic area within the city limits. In the other three municipalities, the entire municipality is alerted if any part of their city limits are within the warned area. This approach, while it may still result in some overwarning, is certainly satisfactory given the smaller geographic area that these cities cover.

At this time, we are unaware of any planned modifications to the Shelby County policy, which warns all of their area of responsibility for any threat to the county (meaning a Tornado Warning for Collierville would result in sirens sounding countywide). Shelby County is responsible for sounding sirens for areas outside Memphis, Bartlett, Collierville, and Germantown, including Arlington, Lakeland, and Millington.

Our take

I am strongly in favor of the more modern, and conservative, approach to warning that is now being developed by Memphis and is in place in the other three municipalities. It has been nearly 7 years since the National Weather Service transitioned from county-based warnings to storm-based polygon warnings for Tornado, Severe Thunderstorm, and Flash Flood Warnings. The goal was to offer more clarity on areas the storm would affect and warn fewer people, only those most likely to be in harm's way.

While media outlets and, more recently, smartphone apps like StormWatch+ properly warn only those who are within the storm's path (polygon), there are several warning methods that a vast majority of the public still rely on that do not have this capability, including NOAA Weather Radio and many outdoor warning siren systems. These systems MUST be upgraded to produce a consistent message across warning methods. While the NWS has done their part to attempt to reduce overwarning, technology must now catch up or the efforts of the NWS will be moot. Too many warnings, whether from true false alarms or "perceived" false alarms due to poor communication, result in complacency by the public who are then put in greater jeopardy of injury or death. We say "bravo!" to those communities who are addressing the issue with modified outdoor warning siren policies.  (Now it's time to get NOAA Weather Radio on board.)

Erik Proseus, MWN Meteorologist

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