Moderately Unstable

The "Mayfield" tornado, as it's being referred to, is *not* just the Mayfield tornado. This tornado was on the ground for potentially over 200 miles. Maybe it cycled once; storm survey teams will determine the continuity of the damage track. But based on the images coming in so far, for Mayfield in particular, upper end EF-3 to middle end EF-4 damage is widespread. The image above from Jeff shows **possible** EF-5 damage. That depends on how well anchored that home was and how well it was constructed (materials). In support (or not) of the EF-5 rating, the survey team will look around that area for ground scouring. EF-5s produce extensive scouring. A good "at home" way to demonstrate this is to take a leaf blower, put it on high, and point it at the ground at close range. The extreme concentrated wind jet will actually physically extricate the grass and soil directly below the blower, like it was dug out with a shovel. That's basically the same thing that happens with an extreme end tornado (on a larger scale). Same thing with debarked trees. When we talk EF-5 damage, we are talking very specific markers of extreme damage that are frankly hard to replicate through any other mechanism. EF-4 damage is devastating, but it's just shy of "complete". The damage images coming in, on large scale, I would also go with in the 170ish range, with exception of that Jeff image. If that is not just a one off and that's what the SW side of town looks like, that would change my perspective significantly. At the end of the day, radar is great for in-situ forecasting but it doesn't beat post storm survey and analysis. Unless you're in a DOW a mile from the storm, radar is not perfect. Partly because the radar beam unless in the above scenario, isn't actually viewing the tornado at the ground. And, partly because while radar is excellent, extreme end things (grapefruit hail, 250mph winds, etc), are more likely to cause issues with the radar beam, the returns, and subsequent digital interpretation. The TBSS illustrates that concept. TBSS occurs when objects in the air cause reflection and scattering of the incoming radar beam, such that they then hit the ground, before reflecting back to the hail (in this case, debris), and then to the radar. Radar calculates distance based on amount of time it takes the beam to return. Longer return time + multiple returns equal that long spike of lower reflectivity seeming to emanate from the storm. But that's obviously not actually what's happening! There's no light precip falling under that spike even though according to the radar's algorithm, there is. All of this is to say, we take the combination of data from radar to understand a storm, not just shear. I will also say, for the most part, the WSRs do a great job with parameterization of wind speeds in tornadoes. I'm simply saying, storm damage survey "wins" versus radar estimated shear when they disagree with one another. Separately, the action that raises debris up 20, 30, 35k feet into the air is not linearly correlated to tornadic wind speed. That's why the study Sam Emmerson did specifies EF-4+ rather than EF-5. There aren't a lot of EF-5s on which to create a strong data set to make that into its own classification. That is much more indicative of the type of devastating damage you talk about with upper end EF-4 or EF-5 storms. If more images like this come out you'll see more mets talking firmly about EF-5 stuff. Central Mayfield is definitely more middle EF-4. This is not. This is more "Joplin". I also think that because the tornado was on ground for so long, there may be other areas where EF-5 intensity is possible. Mayfield is in the spotlight as a fairly big town that got hit near peak strength, but it wouldn't be surprising to learn of ef-5 damage somewhere else on the path, too.

Very good thought. That would make complete sense.

Yeah. It was my error. Though I remain confused. (https://www.nws.noaa.gov/directives/sym/pd03041004s042005curr.pdf): For a power failure to take down an office, it would have to take out the generator. Both the office, and the radar, are supposed to have backup power in the event of commercial power failure (https://www.weather.gov/media/bro/pdf/PressReleaseNEXRADGeneratorSLEP_BRO.pdf). So, something isn't adding up for me. Was that offline for them? Was there storm damage to the generators? Etc.

Not sure if others have noticed but because Paducah is so close to Benton, Springfield MO is currently issuing the warnings for Paducah's CWA. (This occurs when the NWS staff need to take cover. There's a built in shelter in every NWS office). Edit: power failure. Hm. My memory is clearly going bad, I thought they had backups for that.

In light of the debris height, the TBSS, and the fact it basically went through a major town, the odds of finding EF5 damage are actually pretty high. As you know, the surveys done after are looking for degrees of damage. A LOT of the time, there's evidence for a stronger rating, but the tornado didn't hit anything at that time that would be able to score a degree of damage to indicate such wind speed (e.g., the thing would be entirely destroyed, lofted, or otherwise "maximally damaged" at a lower wind speed). Since this hit basically center to a town, many homes were hit. We can reasonably assume this is a multivortex, so, all it takes is 1 subvortex hitting one well built house and sweeping it from the foundation to classify the entire thing as an EF5. The 2020 Bassfield tornado was a potential EF5, couldn't find damage consistent with that intensity. Something tells me this is different.

It's been nailing things for a long time now. This is definitely turning out to be a very bad night based on the reports and photos coming in so far. Far and away capped by this particular cell, which has gone through several towns and left what seems to be chaos in its wake. Remains to be seen if this is a contiguous single long tracker, or 2-3 shorter, still long trackers. A 3 body scatter off debris is pretty telling. When you get a cell that stays discrete like this one has in an environment like this one is in, you get the type of tornado that gets a wikipedia article dedicated to it. It's very rare. There are plenty of "good ingredients" days, but often on such days you end up with a messy storm mode. Everything and anything that goes up turns into a cell, every cell develops some kind of spin, you get upscale growth and collisions and the integrity of the meso gets disrupted. This is what happens when you take the theoretical "lone" supercell and put it into a dynamically intense environment. Until this thing runs into another cell, or a worse environment, this is going to continue. But, honestly, what just happened to Mayfield might end up being the worst. I'm not entirely sure what to even say at this point.

It would be quite surprising, and unprecedented, to see an EF5, given their rarity here--iirc the strongest Philly area tornado was an EF4 that hit the north broad part of town coming down from Norristown over a century ago. But that radar signature was definitely something else. I stopped what I was doing at work and remarked to a coworker, "this is the strongest tornadic signature I may have ever seen around here"--I am not at all shocked by your report. Certainly seemed EF3+ based on the debris sig and definitely based on the videos. Not something you expect to see in the Philly area. Last year we had a couple strong ish ones from Isias EF2 level...but tonight was just shocking. I will add with that line earlier tonight it felt like everything was rotating to some extent at some point. I went outside a couple of times and in addition to the ground scraping LCLs there was just so much non linear motion on everything. It seems rather clear that there must have been some local enhancement of the low level wind field to cause this degree of widespread and significant damage. It will be interesting to read the storm reports when they come out....honestly I just hope no one died. When I saw that sig earlier that was my first thought. Not something something I'd want to be in.

U.S. Watch/Warning Local Products UPDATE 000 WTNT64 KNHC 300356 TCUAT4 Hurricane Ida Tropical Cyclone Update NWS National Hurricane Center Miami FL AL092021 1100 PM CDT Sun Aug 29 2021 ...HURRICANE CONDITIONS SPREADING FURTHER INLAND... ...CATASTROPHIC STORM SURGE, HURRICANE-FORCE WINDS, AND FLASH FLOODING CONTINUE IN PORTIONS OF SOUTHEASTERN LOUISIANA... During the past couple of hours, a sustained wind of 66 mph (106 km/h) gusting to 111 mph (179 km/h) were measured by a Weatherflow station in Mandeville, Louisiana. SUMMARY OF 1100 PM CDT...0400 UTC...INFORMATION ---------------------------------------------- LOCATION...30.4N 90.7W ABOUT 5 MI...10 KM W OF KILLIAN LOUISIANA ABOUT 30 MI...50 KM ESE OF BATON ROUGE LOUISIANA ABOUT 45 MI...70 KM NW OF NEW ORLEANS LOUISIANA MAXIMUM SUSTAINED WINDS...95 MPH...155 KM/H PRESENT MOVEMENT...NW OR 340 DEGREES AT 9 MPH...15 KM/H MINIMUM CENTRAL PRESSURE...960 MB...28.35 INCHES $$ Forecaster Stewart/Papin // The Lafitte situation is gut wrenching. That is the type of report that can indicate a possible mass casualty event--I hope that doesn't occur. And, let's be clear, being trapped in your attic and drowning is not a peaceful way to go. It's one of the most traumatic and painful ways a person can die. When you actually think about what some people are going through *right now* as you read this.. it's tragic. And that situation is occurring in several areas.

I would frankly be surprised if he's even hit 100. Lots of stuff starts flying once you hit triple digit winds. It's very much "obvious". One easy way to tell--the deciduous trees he's been filming are not toppling over, or even swaying wildly. Those tree types don't handle wind well--palm trees evolved the way they did specifically to handle wind. He's barely seen hurricane strength yet. He will, and he will quickly learn what real strong winds actually look like. His poor estimates are concerning because as a chaser, you need to know what different strength stuff looks like. Also, he should be monitoring the nearby observation sites, have reliable in-situ equipment, and be monitoring radar. If you don't--and I say this having chased before-- you can put yourself into harms way and this isn't a situation where someone can rescue him if he gets into trouble.

Well, it isn't fully over land yet. It brushed the coastline and is now back over water--albeit shallow. Separately, research has indicated that the low-level mesocale environment near the coast in situations like this can be extremely moist and end up largely mirroring the oceanic environment. Another thing to consider is that the part of the circulation that remains over water (including the replacement eyewall), is still able to tap into the oceanic energy. Once the eye firmly crosses land and begins trekking inland, weakening will begin in earnest.

That camera is very impressive. Hats off to John and co. Definitely could offer insights for future ways to construct in situ mesonets for strong future landfalling storms were it needed for a research purpose.

VDM 907 URNT12 KNHC 291626 VORTEX DATA MESSAGE AL092021 A. 29/16:01:50Z B. 28.94 deg N 090.07 deg W C. 700 mb 2517 m D. 931 mb E. 235 deg 10 kt F. CLOSED G. C14 H. 101 kt I. 286 deg 8 nm 15:50:30Z J. 025 deg 111 kt K. 286 deg 8 nm 15:50:30Z L. 114 kt M. 155 deg 5 nm 16:06:00Z N. 228 deg 127 kt O. 146 deg 7 nm 16:06:30Z P. 16 C / 3041 m Q. 20 C / 3014 m R. 3 C / NA S. 12345 / 07 T. 0.02 / 1.5 nm U. AF303 1509A IDA OB 03 MAX FL WIND 127 KT 146 / 7 NM 16:06:30Z ; Quick Links and

Lightning can indicate RI, it is not necessary though conceptually. Also, just to play devils advocate (looking at you Iota and Eta), the plane isn't actually in the eyewall yet (edit: now it is). The forum is convinced due to the sat presentation that it is bombing out--and, yes, anyone looking at that imagery will come to that conclusion. But, the reason we fly into storms is because sometimes the satellite is wrong in either direction--the storm might NOT be bombing as quickly as it looks, or, a seemingly poorly organized storm may in fact have a solid circular closed eye that's just not well discerned on sat imagery. Point is: let's wait for lé plane. That being said if it doesn't find a substantial uptick that accounts both for the current period of intensification and the lack of wind-response to the pressure drops earlier in the day, I would be quite surprised. I was a little surprised that they didn't upgrade to 115 at 10PM frankly but I think the idea was to wait for recon which does seem prudent given earlier sat presentations didn't end up matching the winds that were found. It appears that, yeah, it caught up.

It's actually the same aircraft, 303. Let's hope they fixed the issue--it helps that the base is not a long flight from the storm.

A lot of factors. Various teleconnections feed into the Atlantic basin, and thus their phase and orientation can affect the synoptic environment. Hurricanes are heat and momentum transporters. There is more of both at the equator, and less at the poles. Hurricanes do well as I'm sure you know in barotropic environments. Due to (possibly/probably/degrees-of-relativity), climate change, fundamentally two things are happening: 1) There is more heat in the ocean, and that heat penetrates to a greater depth, on average. 2) The temperature gradient between the equator and poles is weakening. Point 2 has a BUNCH of MAJOR consequences, but, one simple one is, baroclinicity (aka zones of frontal development and the opposite of a barotropic environment), decreases. In simple terms: the temperature difference between the poles, and equator, is decreasing. This reduces frontal strength and makes the environment more homogenous--barotropic--and thus, conducive to hurricane development. It goes without saying that there's more to the story than that, but just taking a big step back, you can certainly note a pattern of destructive, high intensity, rapidly strengthening, water-laden hurricanes hitting the gulf....and everywhere else... over the past few decades. That's not in itself atypical in a vacuum, rather, the consistently increased number of strong storms is the red flag...e.g., the frequency. Another thing that happens with reduced latitudinal temperature gradients is that the steering winds are more prone to break down. Wind--> balance of PGF & Coriolis (assuming you also know this). Less temperature contrast--> less pressure contrast--> less PGF--> less wind--> storms tend to slow down and can "linger" over cities which causes the Harvey-type situation where you get 40" of rain in Houston. With respect to my original point, beyond the physics fundamentals that are responsible for changes to overall hurricane formation patterns, whose trends are beginning to become more evident now, we are in relatively good phases of several teleconnections at the moment. That helps things along. But at the end of the day, this is quite literally the same thing as boiling a pot of water on the stove. Turn up the energy supplied, you will get more steam.

Definitely tightening up a bit.

Unwarned couplet approaching Calhoun on the Huntsville radar.

So, it's difficult to tell, but what you can see on the radar is the *orientation* of the couplet changes. In a handoff, you see two distinct mesos, one weakens, the other strengthens. Here, we have the same meso which was "oriented" "up down" and after passing the radar is now "left right". That's the same circulation. The doppler effect only shows motion towards and away from the radar. Ergo, as you translate around a radar site, the orientation of the couplet can shift as the storm motion is captured in the non-storm-relative base reflectivity with a different relative motion (given a different angle of incidence to the site). Same tornado folks. In fairness, there was one single scan that looked "confusing", so if you just looked then you could go "hm what's going on", but subsequent scans, and playing them back with the prior ones, tell us the whole story.

There's no specific requirement not to discuss ratings--I think it's reasonable to expect somewhere along path you'll see EF4+ reports...but remember that radars, unless they're DOWs are not measuring the wind AT THE GROUND. That's super critical and why you can't take "wow look at this gate to gate shear" stuff verbatim--that's what's happening a few k feet up. Friction is real, yo. El Reno was an EF5 according to DOW...it's rated EF3. Why? No structures were hit that verified EF5. Same for the Bassfield tornado. Had an EF5 signature at times and would be super easy to believe a monster that big, on the ground that long, produced EF5 winds in a sub vortex somewhere...but clearly didn't do so over a place for which EF5 criteria could be applied. This long track, fatality producing tornado...seems rather clearly destined for EF4+ status with a special wikipedia subsection dedicated to it within the discussion about the overall event. EF5 could have verified if the tornado had gone straight through Brent...looked particularly nasty around then. It may still verify...that's what damage surveys are for. In general though..remember that velocities do not tell you what's happening at the ground unless you're right next to the radar site like now, or using a DOW. It's useful to know what the G2G is, but really the better measure is how high up debris gets lofted. There's a somewhat direct correlation btwn debris height and strength of the tornado.

Yes, he does.

Well, that verified.

Based on the current obs and the earlier modeling I tend to agree with that assessment. As they continue to race NE the downstream environment is highly unstable . They should ingest increasing amounts of SRH so if they stay fairly discrete which seems a reasonable assumption for several reasons, they both do have potential. They're about where you'd expect to see initiation for a cell that was going to take advantage of the environment today and the downstream progs for sig helicity tracks on some of the recent CAMs would, if propagating backward, initiate those cells about in that area. I'll leave it there.

New TOR-W in MS issued. Looks to be going over Chunky right now.

Ding ding ding. For ref, until this AM everyone was talking the evening threat. True instability is lower. But more important (frankly) params are higher. The day ain't over yet. As for critiera: the probability refers to the severe weather type, period. To verify you calculate the density of tornadoes (or wind or hail) in given area and correlate against the percentages delineated. However, hatching verifies separately. That signifies sig severe..sig tor, sig hail, sig wind. To verify that you need requisite # events at the specified threshold per unit area. So far today, neither high risk nor hatching seems to have verified--and particularly that 45% prob did not. Cannot say for certain of course. What is obvious though is, not every tor warning verified (entirely normal), so # tor warnings =/= # tornadoes. Generally, for sig severe vs threat level: USUALLY, the conditions that produce ef4/ef5 and/or long-track tornadoes tend to also be the conditions that produce a lot of tornadoes. It's a venn diagram with significant overlap-- but it is not 100%. In theory you could get 5 EF5s and nothing else and your high risk would bust. You could, conversely, get 100 EF0 and EF1 spin ups, which would verify...given the right delineation of area of couse. It's just that typically (nearly always) we see EF3-5 stuff on days when conditions are outbreak-y. To that end, today has, thus far, had a high end enhanced to mid grade moderate feel to it. If we stopped the clock now, yeah, this isn't the national news event that has been advertised. We've all seen moderate days, and enhanced, that have exceeded what we have seen so far today. To be clear, on a true outbreak day, you (typically) have at least one major tornado hit a populated area and be in the news, with yet more tornadoes ongoing at the time. That's not a rule that pertains to outbreaks and metros--you can of course have 100 tornadoes and have all hit unpopulated forests...it's a probability game. With a true outbreak you almost always get enough tornadoes, several strong, that at least one hits a population center (think Bassfield sized town) and causes major damage. We haven't gotten reports today of mass fatalities. You don't have governors pre declare state wide SOEs unless, being blunt, they expect a body count and a need for S&R and state level disaster recovery resources. That is GOOD, but is an indicator that we probably have not seen a density of tornadoes at any intensity that would verify a HIGH. This is fairly subjective reasoning so take that fwiw, but just my observational experience. But, fun fact, that was round 1. Thermals are more marginal in the evening but the dynamics very much are not. Helicity and such are much higher tonight. That 45% zone...I don't expect it was made for the afternoon stuff. It was made for round 2. I'd bet money on that. Now that may or may not verify vis a vis how discrete the evening cells remain to take advantage of said dynamics but the threat isn't over yet.

Give it 5 minutes. Takes a few minutes to issue a warning (~5-10 if starting from scratch). Have to define the area, define mean storm motion, expiration time, impact based tags (is it confirmed, radar indicated, what's the threat categorization), etc. Once the NWS says "yep gotta warn that" they can't just hit a button.