My wake-up call on Sirens

This seems like a very long day.

And maybe that's because a weather radio shattered our silent slumber at 4-something. Later, just as I was peeking out my window at some really ominous stuff, illuminated by almost constant lightning, the sirens started blaring. So like any other self respecting Midwesterner, I'm thinking, `Holy cats, it's a twister,' wake up my wife and kids and head for the basement, dog on a leash. And coffee. Essential.

Maybe some of you did the same. Yawn, all together now.

But the weather guys soon told me that the sirens are blowing for straight line winds of over 70 mph, not a tornado. Pretty serious weather, to be sure, but I thought the siren threshold was a tornado warning. So now I know.

I found this on the Linn County Emergency Management site. Not sure what year the change was made, because the release isn't dated. But clarifies the siren guidelines, so we're all on the same page. Looks like big hail is also siren-worthy.

Changes to Outdoor Siren Activation Guidelines

The Linn County Emergency Management Agency has implemented changes to the use of the outdoor alert warning (siren) system. After a review of the system's capabilities, it has been determined that EMA can activate a series of individual sirens. This is a temporary solution until additional siren grouping can be completed next year. Current programming has one grouping containing all 109 sirens in the emergency planning zone.

“Activating a series of individual sirens may help align the siren soundings with the actual warning area but it takes additional time before the warnings are heard,” stated Mike Goldberg, Linn County Emergency Management Director. “Activating a series of individual sirens will be the exception and not the rule. We will always default towards activating over the broader area and getting the alert to the public as quickly as possible.”

Another change is that the sirens will be sounded for those severe thunderstorms (NWS warning or spotter observed) that have a potential of winds of greater than 70mph* or golf ball size hail**. “These conditions create the potential for significant personal injury and property damage”, stated Goldberg. These conditions are a higher severity than the NWS threshold for issuing a severe thunderstorm warning (potential of > 58 MPH winds or 1” hail).

The sirens are used to promote situational awareness of radiological, severe weather, hazardous material incidents, and other situations. People should take shelter and tune to their local broadcast media for more instructions when they hear the alert system.

These changes are based upon a review of the system's capabilities and new activation thresholds recommended by the National Weather Service (NWS). The system, owned and maintained by NextEra Energy-Duane Arnold as part of the radiological response plan, is used by Linn County EMA for other situations to alert the public.

KEY CHANGES:

• Re-sounding of sirens every 10-15 minutes while the condition continues

• Activating for severe thunderstorms with dangerous conditions of winds=> 70mph or hail=> golf ball size

• Possible activation of series of individual sirens (exception not the rule)

Background

* Most fatalities during tornadoes or severe thunderstorms occur due to falling trees or large branches. 70 mph is the typical threshold at which large branches and small trees break. (Additional background for this threshold is available in the engineering document for the Enhanced Fujita damage scale: www.spc.ncep.noaa.gov/efscale)

** Hail begins to break windows when it reaches or exceeds golf ball size.