Sunday, December 18, 2016

Strong storms precede Arctic cold & a commentary on storm warnings

As we predicted in our Friday evening blog, this was indeed a wild and wacky weekend in Mid-South weather. An Arctic cold front, bringing a surge of the coldest air felt yet this winter, sparked widespread thunderstorms along and just behind the front. Wind, both ahead of and behind the front, was a significant issue and the thunderstorms caused scattered wind damage of their own as well.

As the storms entered the metro from the north, cold air from the Arctic front started to out-run the storms and "cut off" their supply of warm air from the bottom, resulting in a lot of lightning and thunder (even as precipitation changed to sleet about 3 hours after temperatures started plummeting from the mid 70s) but little damage. However, in north MS, storms re-developed on the front and tapped into the warm air, as well as a little extra vorticity, or spin, provided by the front itself, and funnel clouds and possibly brief tornadoes resulted. (Tornadoes are unconfirmed at this time, as the National Weather Service has not completed storm surveys.)

Following the storms, temperatures were quick to fall. At MWN on the north side of Bartlett, the mercury fell from 75° at 7:20pm to 53° in twenty minutes, 44° in less than an hour, and into the 30s in less than two hours. The graphs below show the precipitous drop in temperature and subsequent rise in pressure behind the front.


Fortunately, precipitation tapered fairly quickly once the frozen stuff began to mix into the rain and only light amounts of sleet occurred. By Sunday morning, roads were mainly dry, or at least just a bit damp, with temperatures in the mid 20s and a biting north wind.

Moving on to the aftermath, the greatest damage I have seen via social media and news reports is a series of power poles snapped and an apparent fire at the Gateway Tire store on McIngvale Road in Hernando, across the street from Hernando High School on the east side of I-55, and some minor roof damage in an adjoining neighborhood.
Re-creating the timeline of events, the first report of something suspicious in the area was actually an aircraft on final approach to Memphis International about 10 miles south of the airport at 8:45pm. The flight crew reported seeing a "possible tornado." There are some discrepancies with the report in that the pilot report (PIREP) location was provided as 10 miles south of MEM, but the actual text of the report stated "2 mile short final [approach to MEM]." Either way, something fishy was occurring in storms south of the airport. Within a couple of minutes of the report reaching the National Weather Service, a Severe Thunderstorm Warning was issued for the storm, at 8:54pm. Then a couple minutes later, public reports of power lines down (as described above) were received. Subsequent storms, beginning about a quarter past 9:00, prompted Tornado Warnings for eastern DeSoto County and points south and east (Marshall and Tate Counties in particular). However, a Tornado Warning was never issued for the storm that produced damage in Hernando.

Commentary

I have received several reports of "sirens not sounding" and an eyewitness in the news report above seemed to indicate that the storm hit without warning. I have a handful of comments. I'll try not to lose followers with these comments, but be forewarned, this part is commentary.

  1. "Sirens didn't sound for this storm" is true. I have not (yet) talked to DeSoto County EMA, which is the agency responsible for the sirens, but there was no Tornado Warning, therefore they (properly) didn't sound. (A Tornado Warning WAS issued for eastern DeSoto County about 9:15pm for a different storm. I'm not sure if sirens sounded for that storm, or if not, why not. I'll try to find out.)
  2. I'll be blunt. If sirens are your primary means of taking action in the face of a possible tornado, and you're inside, you're doing it wrong. Sirens are for outdoor use. With pounding rain, thunder, and strong wind, their range is limited and sound muffled. DO NOT RELY SOLELY ON SIRENS FOR YOUR WARNING SYSTEM. They serve a purpose. It isn't for indoor warning, even if one is not far from where you are. They are to let those outside know that they are in a dangerous situation and to go take shelter or, at the least, gather more information on the threat.
  3. I had stated yesterday in social media posts that the tornado threat would be primarily limited to brief tornadoes that would likely occur in the line of storms. These types of non-supercell tornadoes are quick to touch down and lift and exceptionally hard to warn for given current technology. The NWS does a fantastic job, but if they were to warn for every thunderstorm that rotates, the false alarm rate would be close to 100% (because the vast majority of rotating storms don't produce tornadoes with damage) and more people (than already do) would not pay any attention to them. 
  4. I'm assuming there was no Tornado Warning for the storm in question because the tornado (assuming one occurred, which isn't confirmed at this point) was brief and had lifted before the warning forecaster had even seen it on radar. Again, I haven't spoken to the NWS, but I have good friends who work there and I've observed warning operations in person before. The storm was at the least producing strong wind and a Severe Thunderstorm Warning was issued for those in the path of the storm moments later.
  5. Blunt, again... I'm getting tired of hearing people say that the storm "hit without warning," or in this case, "I don't think anybody expected it at all." Now, MAYBE the person who said this in the article above meant that she (and "anybody" else, whoever that is) didn't expect it could actually happen to her. But all of the local (and even national) weather folks had been talking about the real potential for severe weather in our area at least since Friday (and it was mentioned by us a couple days before that). There was a Tornado Watch issued mid-afternoon, many hours before the storms arrived. For gosh sakes, it's December and the temperature is 75° with very humid air and a strong wind! If you somehow didn't know you were in a watch box, the conditions should've been enough to tell you that maybe you should be paying closer attention to a weather source! That particular storm doing damage in that section of Hernando might've not been predicted, but the fact that it COULD happen means it was not completely unexpected. 
  6. It's 2016. You all have multiple options for staying abreast of rapidly changing weather conditions. I can tweet until my fingers fall off and the TV weatherman can talk until he runs out of breath, but if the public doesn't take some amount of personal responsibility for becoming a knowledgeable consumer, then our efforts are for naught. 
  7. There's a massive push underway to put more "social science" in meteorology. Not only producing accurate forecasts and warnings, but creating and disseminating the products in a way that will result in the most eyes and ears taking notice, comprehending, and taking action against. I'm all for this. But I also know that there are some folks out there that you can tell a tornado is going to hit their house in 5 minutes with 100% certainty and they still won't respond. Lack of personal responsibility will always result in some people saying they "didn't know" that xyz was going to happen. It hit without warning! If you're reading this blog, I assume you're not one of those people. 
  8. I'm all for better products and services that can reach the most folks and end in response and preparation, but I also believe that we (the scientists) can't sacrifice improving the science and accuracy of our products in the name of trying to figure out a way to personally hit some people over the head to try and get them to respond. The response is up to the individual, based on their individual risk and tolerance level, assuming they get the information. Personal responsibility says don't rely solely on sirens (or any single source, they'll all fail you at some point). Personal responsibility says you must take action if the information you have gathered results in a threat that exceeds your risk/tolerance level.

Be safe, be prepared, and be responsible.

Erik Proseus
MWN Meteorologist

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3 comments:

Anonymous said...

You guys did a great job!! If anyone wasn't aware, they had their heads in the sand. I couldn't agree with you more.

Sam Rikard said...

Thanks Erik, for the commentary. Great points made as always. I posted about both warnings in Desoto. The second warning included portions of the City of Olive Branch, and was issued around 9:15pm. My post carries a timestamp of 9:18pm and the sirens were activated both inside the city limits and outside. I have followers that noted sirens were going off at 9:24pm. They had been going off for a several minutes by then in my area. Your points are well made and valid. One should not rely upon warning sirens as their only source of notification and there was not a tornado warning issued for Hernando, therefore, the sirens would not have been activated for that area.

Meteorologist Erik Proseus said...

Thanks for the insight, Sam. The sirens were activated as I suspected they probably were, when the warning was issued. Appreciate what you do for DeSoto County! Merry Christmas!