Severe storms rumble through the Mid-South early Monday

A squall line of strong to severe storms moved quickly through the Mid-South, including the Memphis metropolitan area, as rush hour began Monday morning. A Tornado Watch was issued shortly after 3am for most of the metro as two lines moved through western and central AR.

Just before 6am, the first Tornado Warning was issued for southern Mississippi County, AR, just west of Tipton County. This was the first sign (locally) that the squall line was capable of producing brief, "spin-up" tornadoes that sometimes occur in severe squalls, verifying forecasts from the previous day that the scenario was plausible.

5:55am A Tornado Warning has been issued until 6:45am for southern Mississippi Co, AR - just west of Tipton Co - for the potential for a brief spin-up tornado. We'll be watching it carefully as it heads towards Tipton. #ARwx pic.twitter.com/U5QgcLvvtD

— MemphisWeather.net (@memphisweather1) October 21, 2019

About the same time, a Severe Thunderstorm Warning was issued for the western half of the metro, including western Shelby County. Over the next two hours, the line crossed the entire metro, then weakened considerably when it reached central Fayette County.

In those intervening hours, no less than four Tornado Warnings were issued in the metro - one in northern Tipton County, one in northern Shelby County, one in southeast Memphis, and one in central Fayette County. Radar showed low-level wind rotation in each, but the southern Shelby storm is the one most likely to have produced a tornado.

6:41am TORNADO WARNING for southeast Shelby Co until 7am. Rotation appearing near I-240 and Perkins moving NE onto the eastern loop and E Memphis. TAKE COVER! https://t.co/N6ylFzYIpx

— MemphisWeather.net (@memphisweather1) October 21, 2019

Wind damage began near Memphis International Airport with trees and limbs down on the west side of the airport, windows blown out in the airport terminal, and damage just east of the airport. The storm's path east-northeast took it parallel to I-240 through Parkway Village, along SR 385 into Hickory Hill, and then into parts of west Germantown near Poplar and Poplar Pike. There were many reports trees down or uprooted, damage to structures (perhaps the worst of which was in the Cottonwood Apartments), and utility poles snapped with wires down. See our Twitter timeline for many reports and photos.

There was also radar evidence of a possible tornado in the form of a "debris ball" - a radar signature that indicates that debris is being lofted into the storm and detected by the radar beam.

pic.twitter.com/GCHCoEbX4k

— Richard Hoseney (@rhoseney) October 21, 2019

MLGW reported that over 43,000 customers (which amounts to more than 100,000 people) lost power during the storms. Scattered traffic light outages were spread across the city. The official peak wind gust at Memphis International Airport was 53 mph, but the storm intensified as it moved east of the airport and rotation in the storm tightened. As of this writing, we are unaware of any major injuries.

An official report from the National Weather Service indicates that the storm produced a preliminary EF-1 rated tornado with maximum wind of 105 mph. Radar evidence and storm damage supports the ground evidence of a tornado. These "QLCS (quasi-linear convective system) tornadoes" - or those that spin up in a squall line and last a short period of time - are very difficult to provide much warning lead time on and frequently are missed completely until after they have done their damage. Fortunately, they also tend to produce damage on the low end of the tornado scale, but that doesn't mean that if one affects you it was no big deal. It is for those affected.

Preliminary EF-1 Tornado damage around Cottonwood Apartment area in Memphis. pic.twitter.com/C1UcXRjwTF

— NWS Memphis (@NWSMemphis) October 21, 2019

A word on "unexpected" storms

Inevitably after a storm that produces damage, we hear that the storm "hit without warning" or was "unexpected." It happened again this morning when MLGW issued a press release calling the storm unexpected.



I understand that there is damage control that must be done when 10% of your customer base loses power. I also understand that perhaps the storm packed more of a punch than what some may have been "expecting." But the presence of a squall line was not unexpected, nor was the timing, nor should have been the potential intensity.

The National Weather Service first mentioned the possibility of Monday's strong storms last Wednesday morning in their Hazardous Weather Outlook - a full five days in advance. By Saturday morning, they had increased their concern level:

.DAYS TWO THROUGH SEVEN...Sunday through Friday

Strong to severe storms are possible on Monday as a cold front 
moves across the Mid-South. Damaging winds, large hail, and
isolated tornadoes will be possible. In addition, heavy rainfall
could lead to flash flooding.

On Sunday, areas along and east of the Mississippi River were included in a Slight Risk (level 2/5) for severe weather on Monday by the Storm Prediction Center. As high-resolution model data got within range of the event, we also posted detailed information Sunday afternoon that had the timing within an hour of the actual event and the mention of a line of storms with damaging wind as the chief concern and an isolated tornado possible. The confidence level was assigned "moderate to high."



By 3am, a Tornado Watch was issued and the line was evident on radar in AR with a history of producing well-publicized tornadoes in the Dallas area. Severe Thunderstorm Warnings were issued well in advance of the line. Tornado Warnings were issued as quickly as possible once rotational signatures became evident.

In my opinion, the squall line was not only NOT unexpected, it was well forecast - down to the hour nearly a day in advance. The potential impact was stated clearly and unequivocally. There is no way to know where and when a tornado will touch down more than minutes in advance. But the possibilities are enumerable and were communicated. Damaging wind was clearly identified as a hazard. It's time to tell it like it is... "a storm system that was well-forecast produced damage that was in line with the potential reasonable worst case scenario and we're doing everything we can to resolve the issues."

No one (in their right mind anyway) expects 43,000 customers to have power restored instantaneously. We just expect hard work towards executing a well-conceived, predefined contingency plan with strong communication on how that plan is evolving throughout the process. I happen to believe MLGW is executing that plan and appreciate the "Memphis grit" that the front line workers are displaying as they work to restore power. Let's not insult the weather community that did an exemplary job attempting to communicate the threat by calling it unexpected.

Erik Proseus
MWN Meteorologist

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Changes to severe weather products coming, including Impact-Based Warnings

There are several recent and upcoming changes to severe weather products issued by both SPC and local National Weather Service (NWS) offices, including Memphis, that you need to be aware of.

SPC Convective Outlooks (effective date: October 2014)

We've talked about the changes made last October to SPC's Day 1-3 convective outlooks in a previous blog. To recap, the three-tier system of Slight, Moderate, and High risk categories has become a five-tier system, adding Marginal and Enhanced categories on either side of a Slight risk. We invite you to read the linked blog above for details on these changes. We'll pair the 5-point numerical value of the forecast category when discussing the risk for the Memphis metro to help eliminate confusion associated with the new names.

In addition to the Day 1-3 outlooks, the Day 4-8 experimental outlooks issued by SPC previously only displayed areas with a 30% probability of severe weather during this period. In December 2014, these outlooks were also modified to display areas under either a 15% or 30% risk of severe storms, which provides meteorologists and the public with a heads up to lower risk severe weather areas in the day 4-8 period that weren't previously highlighted.

Impact-Based Warnings (IBW) (effective date for Memphis: April 1, 2015)

While SPC is responsible for nationwide issuance of Tornado and Severe Thunderstorm Watches, local NWS offices issue the warnings for their area of responsibility. Starting April 1, the Memphis office of the NWS will join many other offices across the nation in an experimental change to the format of Tornado and Severe Thunderstorm Warnings that began a couple of years ago with a handful of offices in the central U.S.

Areas where impact-based warnings will be used in 2015

Called "impact-based warnings," the format change was made in response to the findings of a service assessment done after the Joplin, MO tornado in May 2011. That assessment found that "credible, extraordinary risk signals prompt people to take protective actions." One of the intended outcomes of IBW is to motivate proper public response to warnings by distinguishing between low and high impact events. In addition, it allows the warning system to be optimized within the existing infrastructure, realigning the message in terms of societal impacts, thereby communicating recommended actions more concisely.

The changes will have no effect on the mechanics of warning polygons, but will provide more detailed hazard and action information within Tornado and Severe Thunderstorm Warnings. That detail will include the impacts the severe storm could cause, which will be reflected in the updated format of the warning bulletins. The changes include the addition of "event tags" at the bottom of each Tornado and Severe Thunderstorm Warning. These tags include "Tornado" and "Tornado Damage Threat," which are described below. In addition to those tags, Severe Thunderstorm Warnings will carry maximum hail size and wind speed tags. Tornado Warnings will also carry a maximum hail size tag.

The Tornado tag will have three possible options:

• "Possible" - Reserved for Severe Thunderstorm Warnings, indicating that the storm has some potential to produce a tornado, but forecaster confidence is not high enough to issue a Tornado Warning.
• ""Radar Indicated" - Evidence on radar and near storm environment is supportive of a tornado, but there is no confirmation.
• "Observed" - A tornado is confirmed by spotters, law enforcement, etc.

The Tornado Damage Threat tag will also have three options:

• No tag - Used most of the time when tornado damage is possible, but the tornado is expected to be short-lived.
• Considerable - Used rarely, when there is credible evidence of an ongoing or imminent tornado capable of producing considerable damage. Tornado is expected to be long-lived.
• Catastrophic - Used exceedingly rarely, when a severe threat to human life and catastrophic damage is occurring. Only used when reliable sources confirm a violent long-lived tornado. This tag will trigger the "Tornado Emergency" warning.

The example below summarizes the possible tag options and also shows the Impact bullet in the warning that describes the threat to life and property.

Some additional examples of warnings using the new tags are shown below (changes are highlighted in red).

Severe Thunderstorm Warning with new tags.

Tornado Warning for radar indicated tornado.

Tornado Warning for an observed tornado producing considerable damage

Tornado Emergency for an observed tornado producing catastrophic damage.

More information from the NWS on the 2015 IBW Demonstration is contained within the YouTube video below created by NWS-Memphis and on this website.

Severe weather watches add "Summary" section (effective date: April 14, 2015)

Finally, beginning April 14, all Tornado and Severe Thunderstorm Watches issued by SPC will contain a "Summary" section. According to SPC, the summary will provide a "general 1-2 sentence statement of the severe weather expected in and close to the watch area. This new section facilitates consistent, forecaster-driven, concise communication for public consumption." For more information on this change, please see this page from the SPC.

Erik Proseus
MWN Meteorologist

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Recap of Oct. 2 severe weather, challenges faced, and a word on siren policy

Until last night, it had been a long time since widespread severe weather (not including biblical flooding events) had affected the Memphis metro. Tornado Warnings were last issued in late April. A well-advertised, and well-forecast, squall line moved through the region during the late evening hours bringing many reports of wind damage and several areas of rotation on radar. No reports of tornado touchdowns were received in the immediate area, though possible tornado damage occurred in northeast AR.

Every county in the metro was under a Tornado Watch and Severe Thunderstorm Warning as the line moved through and several areas were also under Tornado Warnings due to radar-indicated rotation in the fast-moving line. An early recap of the night from NWS-Memphis can be found here. They also discuss areas they intend to survey for storm damage.

Severe weather reports received by NWS as of mid-morning Friday. Most were wind or wind damage, though a possible tornado struck east of Jonesboro.

There are two main issues I want to address in this blog: 1) technology challenges and 2) outdoor warning siren policy.

Technology challenges

Technology. We love it for many good reasons. It allows us to do many things quickly and more efficiently than ever before. It allows us to push specific warning information to you via your smartphone almost as soon as it is issued by the NWS. But it also has its pitfalls. Namely when it doesn't work. Fortunately our critical warnings worked flawlessly last night, but there were other issues.

MWN StormView Radar on the website and mobile apps was one such problem. Due to multiple malicious attacks on multiple weather vendors' servers yesterday, including at least one big name and ours (though not targeting MWN directly), our radar stopped updating. The timing was awful. We apologize for and sincerely regret this major inconvenience; unfortunately some idiots like to "be funny" at other's expense. We're not laughing. If they can be tracked down, they ought to be prosecuted. We will be following up with our vendor on best practices going forward, but the outage was (and remains) completely outside of our control, though we take responsibility for providing the service to you.

In addition to radar issues, MWN headquarters lost internet connectivity as the squall line was moving across the river and Tornado Warnings were being issued (it also remains down this morning). This outage hampered our ability to disseminate information (including critical social media posts and data from our Bartlett weather station), monitor incoming data (including radar), troubleshoot the ongoing issues with our web radar, and communicate with the NWS. I'm not turning this into a bash-fest on our internet provider. This is the first outage we have had in months, perhaps over a year, and the connection handles everything we throw at it on a routine basis. The point is, once again, technology is not flawless and is subject to outage.

I want to take just a minute though to recognize MWN interns Kevin Terry and William Churchill for exemplary service last night as MWN's internet feed went down. Working from Mississippi State (there are advantages to working from disparate locations during severe weather events!), Kevin and William immediately took over nowcasting responsibilities in the middle of the event and didn't miss a beat. I'm guessing that most people watching our Facebook or Twitter feeds last night didn't know a major link in the chain had failed. That is a sign of a well-oiled machine and I thank them for their awesome work and dedication to all of you! My wife loaned her laptop to the cause (thanks honey!) and, courtesy of a smartphone hotspot, I was able to re-engage on a limited basis. Sometimes it takes a team effort and I've got one of the best in #TeamMWN!

Tornado Warnings and outdoor siren policy

The other discussion that needs to be had is regarding outdoor warning siren policies. Truth be told, it's been a relatively quiet couple of years for severe weather in the metro. Sometimes that "lack of practice" results in lack of preparation and awareness. The main issue we saw last night was in Shelby County, but the general principles apply most anywhere. Recall that Tornado and Severe Thunderstorm Warnings are not issued by county. They are "storm-based polygons," meaning they are drawn to reflect the forecast path of the suspect storm. Also recall that outdoor warnings sirens are for OUTDOOR use and aren't designed to be heard inside well-insulated homes with TVs and air conditioners on and storms overhead, and definitely not while you are sleeping. That being said, we recognize that many people are close enough to a siren to hear it indoors.

Siren policy differs by county, and in Shelby County it varies by municipality. The best siren policy is one that limits the activation to times when the community in the path of the storm is the only one alerted. To review, these are the policies in place in Shelby County as of October 2:

• Bartlett, Collierville, and Germantown sound sirens for their cities (the entire city) only if the warning polygon intersects their respective municipal boundaries.
• Shelby County sirens (including Millington, Arlington, Lakeland, and unincorporated areas of the county) sound for the entire county when any part of the county is warned.
• City of Memphis sirens also sound for the entire city when any part of the county is warned.
• However, Memphis is nearing implementation of a brand new system (the change should probably occur in November) that will activate sirens in Memphis only for those areas that are within the warning polygon, plus any sirens outside the polygon that can be heard within the polygon. Details on this policy change can be found here.

A Tornado Warning was issued at 11:13pm last night (shown below) that clipped the eastern side of Collierville. No other part of Shelby County was affected. In fact, the storms had exited all but the southeast corner of the county. However, given the above-stated current policies, sirens should have sounded in Memphis, Shelby County, and Collierville.  Bartlett and Germantown were not affected.

This was a case in which, under Memphis' new policy, sirens would NOT have sounded for any part of Memphis, which is exactly the way it should be. In our opinion, Shelby County should also move to a policy that allows segmentation of the sirens. There really was no reason to warn Shelby Forest, Millington, Arlington, or Lakeland about the storm in Collierville. I checked with Bartlett officials and sirens were not sounded in their city - well done! I also heard multiple reports last night that Collierville siren activation may have been delayed, and then continued after the warning for Shelby County was cancelled at 11:23pm (10 minutes after issuance). We can't corroborate that firsthand however.

Despite the sometimes untimely pitfalls of technology and some initial setup, the best way to receive warning information specific to YOUR location is smartphone weather apps with location-based warning technology. They can be set to warn specific points, regardless of county, and provide the most pertinent information to your location. Because of potential for technology issues, we also strongly advise a secondary means of receiving warning information that will wake you. The best secondary source is NOAA Weather Radio. Despite being county-based (all radios in Shelby County would have alarmed with the Collierville warning above), it's better than nothing, especially when you're asleep and local media is turned off in your home. Outdoor sirens are not to be relied on to wake you up.

We appreciate those who have trusted MWN and our StormWatch+ technology to provide the precision warnings described above. If you're interested in checking it out, click the appropriate link below. It's a fraction of the cost of a weather radio and only alerts you when necessary - plus it will wake you up in the event of the most severe storms. The precision is best demonstrated by an individual who lives on the west side of Collierville and indicated that StormWatch+ did not sound last night. As it turns out, he was less than a mile west of the warned area and not in harm's way. The technology worked as advertised.

To conclude, we thank you for your patronage and support of MWN, we apologize for the radar issues, and we greatly appreciate the dedication of #TeamMWN! If you have any questions, comments, or issues to raise, we would love to hear from you! Comment on this blog, hit us up on social media, or drop an e-mail via our contact form.

Erik Proseus, MWN Meteorologist

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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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Bartlett changes outdoor warning siren policy

As of June 1, Bartlett officials have modified the city's outdoor siren warning system policy to sound less often during adverse weather, just as Germantown did last fall and Collierville did previously. The primary reason for the change is an increase in complacency caused by perceived overwarning of residents, while still letting Bartlett citizens know when their community is threatened. Emergency Management Officials with the City of Bartlett feel that better public response to tornado warnings can be achieved by only sounding tornado sirens in the City Limits of Bartlett if the city is directly threatened by a storm capable of producing a tornado.

A new siren next to the water tower at Rivercrest Elementary School

As with Germantown and Collierville, Bartlett officials will only sound their outdoor sirens when a Tornado Warning (issued by the National Weather Service) intersects or overlays the Bartlett corporate limits, rather than anytime any portion of Shelby County is warned. Bartlett operates twelve (12) sirens with an effective radius of about 1 mile (or 3.5 square miles coverage) to warn their 58,000+ residents in the city limits. (Read the Press Release describing the change.)

In addition, the updated siren policy states that sirens will be sounded for 3 minutes, followed by a 2 minute pause, with the cycle repeated until the Tornado Warning is no longer in effect. This cycle will prevent the siren's mechanical parts from "burning up" that sometimes occurs when they have been running for tens of minutes with no break.

Background on polygon warnings

In 2007, the National Weather Service ceased warning entire counties for tornadoes, severe thunderstorms, and flash floods. Instead, these warnings are now issued on a storm basis. As we've described before, a polygon is drawn around the area in the path of these events, irrespective of county or state boundaries. However, many warning systems including NOAA Weather Radio still send alerts on a county-wide basis, resulting in larger areas being warned than the NWS intended via their polygon system. County-wide alerting result in "perceived overwarning" because people using those warning systems perceive a threat, when oftentimes they are not actually in the warned area. In the cases of Germantown and Bartlett, software designed by Earth Networks will show the polygon warning and the city limits and make the decision whether or not to sound the sirens straight-forward.

A Tornado Warning polygon issued for parts of Shelby County on January 23, 2012, is an example of one that would NOT require the sounding of Bartlett sirens, as the polygon does not touch the city limits. All other sirens in Shelby County would sound if this warning were issued again.

Caveats of outdoor warning sirens 

We cannot have a discussion of sirens though without talking about the main drawback of sirens. They are called OUTDOOR warning sirens for a reason! Sirens are to alert people outdoors that may be away from a news or weather source that dangerous weather is nearby and to seek additional information. They are not designed to wake you up in the middle of the night or be heard in a well-insulated structure over television, air conditioners, heavy rain or wind.


When indoors or asleep, ALWAYS have other sources of severe weather alerts that will grab your attention, such as our MWN mobile apps with StormWatch+ precision weather alert technology or a NOAA Weather Radio. In fact, everyone should have MULTIPLE ways of receiving life-saving severe weather bulletins, as any one can fail at any time.

Bottom line for those in Bartlett and Germantown - if sirens are sounding, you can expect that it is because your towns are within the tornado warned area and you should seek shelter immediately!  (Sirens in both communities are tested on Saturdays at noon, weather-dependent.)

Additional links/info:
Outdoor Warning Sirens page on MemphisWeather.net
Bartlett Fire Department page on City of Bartlett website
Bartlett Fire Department on Facebook

Outdoor warning sirens series on the MWN Blog:

• Part 1 (Role of the EMA)
• Part 2 (Role of warning sirens)
• Part 3 (The warning process & the future of warning systems)

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Germantown residents to hear outdoor sirens less often

Residents of Germantown, TN will be hearing outdoor warning sirens less often, but it's not necessarily a bad thing.  A couple of weeks ago, Germantown flipped the switch on new software and an updated siren policy that allows the city to make their own decisions about warning their residents and visitors during severe weather episodes. [Media release from the city of Germantown]

Background and warning policy

Using a $77,000 grant from the Department of Homeland Security, Germantown installed a complete weather system from Earth Networks (the company that owns WeatherBug) that includes a professional weather station, an HD camera, and Streamer RT software.  The weather station, located on top of fire station #3 adjacent to the Germantown Municipal Center, and HD camera, mounted on top of the city's tallest water tower, provide realtime local conditions and a great view of the sky to Germantown officials and anyone else who visits the WeatherBug website or mobile app. However it is Streamer RT that allowed Germantown to modify their tornado warning policy.

The city of Germantown and it's 17.6 square miles and 38,000+ residents are well-covered by 15 outdoor warning sirens with overlapping coverage. (On average, each siren has an audible range of just over a 1 mile radius, or 3.5 square miles.)  Until recently, Germantown followed the siren policy used by the rest of Shelby County and it's municipalities, which required that all sirens county-wide be sounded when any part of the county was affected by a Tornado Warning.

Now, using the graphical overlays available in the software, city dispatchers (whose duties include activating the city's sirens) will look at the display that depicts the Germantown city limits and the warning polygon issued by the National Weather Service (example below) and determine whether to activate the sirens. If the warning polygon does NOT include a portion of the city, sirens will not be sounded.  If any part of the city IS in the warning, sirens will be sounded. And once the warning is lifted for all of Germantown (even if it still encompasses other parts of Shelby County), sirens can be shut off.

Streamer RT software by Earth Networks provides Germantown dispatch and fire with current weather info, as well as warning polygons and the city limits, making the decision to warn the city, or not, an easy one.  In this case, sirens would not be activated. Image courtesy Germantown FD.

Fewer sirens = more trust in the system

In 2007, the National Weather Service ceased warning entire counties for tornadoes, severe thunderstorms, and flash floods.  Instead, these warnings are now issued on a storm basis.  As we've described before, a polygon is drawn around the area expected to be impacted by these events, irrespective of political boundaries (such as the red polygon in the image above).  However, many warning systems, including the NWS' own NOAA Weather Radio, still send alerts on a county-wide basis, resulting in larger areas being warned than the NWS intended via their polygon system.

County-wide alerting result in "perceived overwarning" because people using those warning systems perceive a threat, when oftentimes they are not in the warned area.  Besides weather radio, some commercial radio and TV stations still warn based on counties (though most are moving away from county-based warning), and in most places sirens still warn entire counties, including in Shelby County.  Because the cities of Germantown, Bartlett, and Collierville (as well as Memphis) activate their own sirens, they are able to break away from county-based siren activation simply by changing their internal policies.  Germantown is the first to do so.  Bottom line: going forward, when sirens sound in Germantown, residents can be certain that all or some part of their city is under a direct threat.

The process to transition to this policy actually began two years ago with a search by Germantown Fire officials for companies that would provide the tools to allow them to sound their own sirens.  When asked why Germantown decided to change their siren policy, Chief John Selberg summed it up this way: "I believe in being prepared without over-sensationalizing the emergency."  Ultimately, he expects the change in philosophy to "reduce complacency" since the sirens will only sound for actual threats to the city.

Caveats

Of course, we can't have a discussion of outdoor warning sirens without discussing the caveats.

First and foremost, never rely on sirens when indoors! It's very important to remember that outdoor warning sirens are called that for a reason - they are intended to alert people who are OUTDOORS to go inside and seek additional information on the threat.  Though Germantown's sirens have excellent coverage, if you are asleep with the air conditioner running and it is raining outside, it is doubtful that you will hear the sirens and you place yourself at risk.

Have a programmed NOAA Weather Radio with good batteries and, if you have a smartphone, install a severe weather app that will alert you (and wake you) in case of severe weather.  It should have a feature that will wake you for the most intense storms, allow you to program multiple locations, and preferably have a "follow me" feature for when you are traveling. We highly recommend our MWN app with StormWatch+, which fits the bill perfectly.

One of these methods in and of itself is not sufficient.  Always have multiple ways of receiving severe weather information.  Any one of them can fail at any time and you need a backup or two.

NOTE: Germantown sirens are tested on Saturdays at noon (unless the weather is threatening) and the sirens are all equipped with two-way communication which means the Germantown Fire Department knows, without activating the sirens or being on-site during a test, when a siren is not working properly.

Additional links/info:
Outdoor Warning Sirens page on MemphisWeather.net
Germantown Fire Department page on City of Germantown website
Germantown Fire Department on Facebook
"Weather system to limit siren sounds in Germantown" - Commercial Appeal

Outdoor warning sirens series on the MWN Blog:

• Part 1 (Role of the EMA)
• Part 2 (Role of warning sirens)
• Part 3 (The warning process & the future of warning systems)

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Why you should heed Severe Thunderstorm Warnings

Last Friday morning, a brief tornado touched down in central Tipton County, TN, about 4 miles northwest of Covington.  Two homes sustained significant damage and a shop was destroyed.  In addition, there were downed trees and a grain bin was overturned.  The National Weather Service rated the tornado an EF-1 with approximate wind of 95 mph and a path length of 1.3 miles.   The tornado was on the ground for about 4 minutes from 6:05-6:09am.  There were no injuries.

A grain bin was overturned and 2 homes and other property were damaged from an EF-1 tornado near Covington on Friday, 5-31-13.  Photos from WMC-TV.

The tornado is one of the type that meteorologists refer to as a "spin-up" tornado, which typically occur along a line of thunderstorms, not from a supercell.  Lines of storms, which can be called squall lines or quasi-linear convective systems (QLCS), can occasionally produce these brief, weak tornadoes and this was a classic example.  A bow echo in the line (named because it arches forward like an archer's bow) pushed out as it crossed Tipton County and on the north end of the bow (a typical place for some rotation), the tornado formed, touched down, produced minor damage, and quickly disappeared.

Radar loop of squall line (QLCS) as it marched across Tipton Co around 6am on Friday, 5-31-13.  The bow echo is visible moving across northern Tipton Co. (center of image).

The NWS NEXRAD Doppler Radar system nominally takes about 5 minutes to produce each set of images  for the forecaster to analyze.  In cases of QLCS tornadoes, most of the time the tornado may show up on one set of imagery, then disappear in the next set.  This tornado lasted 4 minutes, so the forecaster would have had no more than one set of data to look at to spot the tornado.  With QLCS tornadoes, literally by the time the warning meteorologist sees the radar data indicating a possible weak tornado and issues a warning, the tornado is gone.

(Top) Reflectivity (or precipitation) data as the tornado touched down - 6:04am.  The twister occurred in the favored area for QLCS tornadoes, at the northern edge of the bow echo.
(Bottom) Velocity (or wind) at the same time. Rotation is observed in the wind data.

 This can create a dilemma for the NWS on how to warn on these scenarios. Issue a tornado warning after seeing the spin-up on radar for a storm that likely won't produce another tornado after the warning is sent out, hence warning needlessly and after the fact? Warn on every QLCS that hints at possible rotation, likely with the result of a high number of false alarms? Don't issue a Tornado Warning, but allow a Severe Thunderstorm Warning to cover the possibility of brief spin-up tornadoes that produce minor damage in a short path?

(Top) Reflectivity data at 6:09am, about when the tornado lifted.  This panel look less ominous.
(Bottom) Velocity data at 6:09am. The rotation has weakened considerably.

In the case of the Covington tornado, a Tornado Warning was not in effect, but a Severe Thunderstorm Warning was issued well before the line of storms reached the affected area, due to the likelihood of damaging wind. In addition, there was not a Tornado Watch because the threat of tornadoes over a large area was very low (and since this was the only report of a tornado, it makes sense that a Tornado Watch was not in effect).

This event does raise some points worth considering by the public:

• Because of their transient nature, QLCS, or squall line, tornadoes (which are almost always EF-0 or EF-1 in strength and produce minor damage and typically no injuries) are extremely hard to produce timely Tornado Warnings for.
• Whether a Tornado Watch is in existence or not, and no matter how small the tornado threat might be, severe thunderstorms can, and occasionally do, produce tornadoes. If a squall line is heading for you, you must be mindful that a brief tornado is possible.  Not the big monster EF-4/5's that come from supercells, but a 80-100 mph wind producer.
• Severe Thunderstorm Warnings indicate the likelihood of imminent severe weather, which can and often does include damaging wind of at least 60 mph.  Whether it originates from a tornado or straight-line wind, 60-100 mph wind ins a squall line will cause damage.
• Tornado Warnings are NOT always issued for every remote tornado possibility.  Meteorologists have a hard enough time getting people to heed Tornado Warnings with false alarm rates hovering near 75%.  If every possible spin-up in a squall line got a Tornado Warning, the public would become even more siren-weary and nobody would pay attention when there was a serious threat.

The point of this post is to remind you that all severe weather can be dangerous and damaging - not just supercells with big tornadoes.  If a Severe Thunderstorm Warning is issued, go inside, stay away from windows, and if it gets real ugly out, get in your safe place.  Don't wait for a Tornado Warning.  Your time to take action may be limited, especially with fast-moving squall lines that can hit and be gone within a matter of minutes.

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EF-1 tornado confirmed in Fayette County Saturday night

After surveying the damage earlier today, NWS officials deemed the damage to the Belmont community of northwest Fayette County (a few miles southeast of Mason in Tipton Co) to be caused by a high-end EF-1 tornado with maximum sustained wind estimated at 105 mph.

According to the damage survey, the tornado touched down at 9:13pm just northeast of Exit 35 north of I-40 in the Belmont community.  It stayed on the ground for 5 minutes, lifting 1 mile east of the touchdown point at 9:18pm in a wooded area north of Old 59 Drive.  There was one minor injury in a residence near the end of the tornado path. Maximum wind was estimated at 105 mph with a path width of 250 yards (0.14 miles). The most significant damage was to a large barn that housed K9 Savior, where well over 100 animals were kept. This barn was about where the tornado touched down.  In addition, many trees were uprooted or snapped and a rural church that was resting atop brick pilings just off the ground was moved about 15 feet off it's foundation at Belmont Cemetery on Old 59 Drive.

Tornado path (1 mile) of the Belmont tornado. Click here for KML file to view in Google Earth.

The entire area, including Fayette County, was under a Tornado Watch at the time. The National Weather Service issued a Tornado Warning for far southeast Tipton County and northern Fayette County at 9:19pm CDT that was in effect until 10:00pm.  At 9:24pm, the Tornado Warning was cancelled for Tipton as the storm had left the county. The section of Fayette around where damage occurred was removed from the warning at 9:36pm as the storm had left that part of the county. The remainder of the warning was allowed to expire at 10:00.

If you look carefully at the timeline above, you'll see that the NWS indicates the tornado was on the ground prior to the issuance of the warning.  In fact, it was issued one minute after the tornado lifted, however strong rotation was still evident on Doppler Radar imagery of the storm well after the tornado had lifted.  This is a sobering reminder of how storms can and occasionally do produce tornadoes, especially weaker ones, with little notice, especially when a Tornado Watch is in effect.  A Tornado Watch means conditions are favorable for storms to produce tornadoes. People should keep a close eye to the sky and monitor local weather sources anytime storms are present, especially when a watch is in effect.

A church at Belmont Cemetery was shifted about 15 feet off it's foundation.
Click here for more pics on our Facebook page.

It is certainly fortunate that no one was seriously injured or killed and that population density was low where the tornado struck, or damage would have also certainly been more extensive. Please keep those affected in your thoughts and prayers.

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11 Reasons why Mid-South tornadoes are so insidious

While Tornado Alley may be the Hollywood backdrop for storm-chasing worthy tornado action, those of us living in the south know that Tornado Alley's redneck cousin, Dixie Alley, is where the real action is when it comes to deadly tornadoes!  In fact, statistics show that Dixie Alley is where the majority of killer events occur.  

The graphics below show that, while the frequency of tornadoes is highest across the Plains from the Corn Belt to north Texas, killer tornadoes are most likely in the Mid-South and Tennessee Valley.  In fact, the highest frequency of significant (EF-2+) tornadoes stretches from a peak in the Red River Valley east into the mid-lower Mississippi Valley, including the Mid-South.

In light of the statistics above, here are 11 reasons why Dixie Alley tornadoes, as compared to those in Tornado Alley, are more insidious (in no particular order).

1. High frequency overall - While Tornado Alley boasts the greatest number of overall tornadoes in the nation, and perhaps the world, the south is no slouch. And in fact, when considering "significant tornadoes" (EF-2+), Dixie Alley and the Mid-South in particular are just behind Oklahoma and the Red River Valley and exceed most of the Plain states. The average annual number of tornadoes in Dixie Alley per 10,000 square miles is 6-9+, rivaling just about any other area in the nation.

2. Frequency of nocturnal tornadoes - Just about anyone living in Dixie Alley for any length of time can tell you that the sound of tornado sirens wailing or Weather Radios screeching in the middle of the night is enough to either frighten or frustrate nearly everyone, especially when it occurs on a relatively frequent basis. In fact, AR, TN, MS, and AL all have 50% or more of their tornado deaths at night, with TN at 73.3%! Due to the likelihood of more tornadoes in transitions seasons (more in #3 below) than other areas, more tornadoes also occur after dark. When is the most likely time to die in a tornado?  When you can't see it coming or are sleeping through a warning (at least until it's too late).

3. No well-defined tornado season - Alluded to above, unlike Tornado Alley when tornadoes are generally concentrated during "tornado season" from roughly April-June, Dixie Alley sees an abundance of tornadic storms in the "cool" or transitions seasons.  In fact, there is a notable severe weather peak (albeit lower than spring time) in November and early December in the South that exists nowhere else in the U.S. However, it is not unusual (despite post-storm media reports to the contrary) to see tornadoes in winter and even summer (one of the best "off-season" examples being the Super Tuesday Outbreak of February 2008).  When tornado season is spread out over the course of the year, preparedness and awareness tend to be low.  In Tornado Alley, the preparedness level in the spring is at an all-time high.

Comparison of strong & violent tornadoes by month for Tornado Alley (red) and Dixie Alley (green). Gagan  et al, 2010.

4. Fast storm motion - Because of the nature of Dixie Alley storms to occur more often in the spring and fall, the storms that develop tend to be pushed by a stronger jet stream than in the late spring/summer when jet streams are typically less vivacious. A stronger jet results in faster moving storms. Faster moving storms mean A) less time for forecasters to react and warn the public (though southern meteorologists take this into account and by and large do a fantastic job at providing excellent lead time) and B) less time for the public to process the threat and respond accordingly. When a tornado is moving at 40-50+ mph, it doesn't take long to cross the typical county and residents must be ready to take cover when the warning is issued. Some of the videos of Dixie Alley tornadoes appear to be time-lapsed when in reality the funnels really are moving THAT fast!

5.  Rain-wrapped funnels - This refers to the nature of southern tornadoes to tend to be less "visible" to the public due to having rain surrounding the funnel.  In Tornado Alley, moisture is often not nearly as abundant as in the South, where southerly wind off the generous Gulf of Mexico provides ample moisture for heavy rainfall.  In addition, higher low level humidity also means lower cloud bases.  These factors result in tornadoes in the Plains that are "picturesque," with their funnels easily identifiable from a long distance, while in Dixie Alley, what appears to be a heavy shower could actually be masking a deadly swirl of air lurking inside. 

Where's the tornado?  (Hint: where the transformer is blowing.) Photo credit: Dr. William T. Hark.

6. Terrain / trees - The South loves it's trees. They're everywhere and they make for great scenery, ample lumber, and cool shade in unbearably hot and humid summers.  Hilly terrain (at least moreso than the Plains - outside of the Mississippi Delta region) also provides for scenic Sunday drives and interesting local effects on the weather.  However, vegetation and terrain also make for a great game of hide-and-seek with tornadoes.  Visibility, as in #5, significantly affects the ability to survive a twister.

Nearby tornado hidden by trees, Photo credit in image.

7.  High population density - While it may seem that there are lots of rural areas in the South, when compared to the miles upon miles of deserted farm and pasture land of the Plains, the population density of Dixie Alley is actually much higher than in Tornado Alley.  If a tornado touches down in the middle of nowhere in Kansas and no chasers are there to record it, does it even count?  Try doing that in the South.  If it's not brushing up against a mid-size or larger city, there are likely at least 2-3 hamlets or single-stoplight towns in the path. Bottom line: nearly every tornado in Dixie Alley will affect SOMEBODY.

8. Low quality construction - Hate to say it, but it's a fact. Housing stock in the southeast U.S. is, on average, poorer than the Plains.  In particular, the abundance of mobile homes, manufactured homes, or trailers (or whatever you want to call them), means that even the weakest tornadoes can wreak havoc on the occupants of one of these dwellings. Here are the facts: from 2001-2005,  nearly 57% of all tornado fatalities occurred in non-permanent housing and the number has consistently been rising. Stick-built, or permanent, houses accounted for just over 25% of tornado deaths. In AR, AL, GA, MS, and TN from 1985-2005, 52% of all tornado deaths occurred in mobile homes. Add to that that the southeast U.S. has the highest percentage of mobile homes east of the Rockies and you have a recipe for disaster. More mobile homes = more death.

Mobile home park after a tornado. Photo credit: http://thetornadoallie.blogspot.com.

9. Lack of basements and storm shelters - Anecdotally, we know that there are very few underground places of shelter in the southeast.  Due primarily to construction costs among other factors, basements are very rare.  In addition, storm shelters are also rare, likely due to their relatively high cost as compared to demographics.  In Tornado Alley, a large percentage of the population has either a basement or a storm shelter. Some tornadoes are only survivable if you are underground, plain and simple.  Even the most well-constructed homes are Lincoln Logs to an EF-4/5. 

Germantown, TN tornado, originally posted on the MWN Blog. Photo credit: Edgar Babian.

10. Demographics - It is what it is.  The "social vulnerability" of those living in Dixie Alley is higher than in other tornado-prone areas of the country. Poverty is higher (which likely factors into #8 above) and the age of the populace is higher.  Both likely contribute to the fatality rate. In fact, the percentage of tornado fatalities of those over age 50 is higher than the percent of the population of that age, suggesting that older people are more vulnerable.  On the other hand, the percentage of tornado deaths of those under 30 is much lower than the percentage of the population in those age brackets, meaning younger people tend to do a better job of heeding the storms and sheltering appropriately.

Percentage of tornado fatalities vs general population by age.  Ashley 2007.

11. Apathy - Perhaps the hardest, and easiest, reason to understand, there's no getting the fact that we tend to be apathetic. "It'll never happen to me." "The sirens are always sounding." "Tornadoes don't happen at this time of year/day."  Helen Keller said, "Science may have found a cure for most evils; but it has found no remedy for the worst of them all - the apathy of human beings."  True, the false alarm rate for tornado warnings is high - but which would you rather have, a few extra warnings or one that truly does his "without warning?"  The science is improving and false alarms are decreasing, but we have to counter apathy with education and information.

The bottom line

Mississippi, Alabama, and Tennessee lead the nation in terms of tornado deaths per square kilometer AND killer tornadoes per square kilometer. Most of the other states in Dixie Alley also have averages well above the rest of the nation. While we don't see as many tornadoes by sheer number, Dixie Alley is the most vulnerable part of the nation when it comes to severe weather, due to all of the factors described above.  Most of these factors won't change, but an apathetic populace is inexcusable. The National Weather Service offices across the south know exactly what they are dealing with and do a fantastic job warning the public when severe weather is possible, sometimes days in advance.

Every home must have a NOAA Weather Radio programmed for the county in which it resides. We need to stop relying on outdoor sirens to be the sole warning of impending storms. Technology now allows us to reduce apathy by targeting warnings to those in the path of the storm. Our mission at MemphisWeather.net and Cirrus Weather Solutions is to do whatever we can to get the body count down and the awareness up. Whether you use our services, or someone else's makes no difference to us. But the information is there. It's time to put on your big boy/girl pants and make sure that you survive the next tornado!

References:

Ashley, W., 2007: Spatial and Temporal Analysis of Tornado Fatalities in the United States: 1880-2005. Weather & Forecasting, 22, 1214-1228. Available online at http://journals.ametsoc.org/doi/pdf/10.1175/2007WAF2007004.1

Gagan, John, et al, 2010: A Historical and Statistical Comparison of "Tornado Alley" to "Dixie Alley." National Weather Digest, 34, 145-155. Available online at http://www.nwas.org/digest/papers/2010/Vol34No2/Pg145-Gagan-etal.pdf

Husted, R., 2012: Mid-South Severe Weather Climatology. Available online at http://www.srh.noaa.gov/images/meg/Mid-SouthSevereClimatologyStudySummary2012.pdf

National Climatic Data Center, 2012: U.S. Tornado Climatology. Available online at http://www.ncdc.noaa.gov/oa/climate/severeweather/tornadoes.html

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