Hook slicing: What do you think?

[Rob H]

Deleted! The point of a hook slice is to drive through the precipitation until you're in the bearcage, and then staying in the bearcage next to the tornado until the road network or damage prevents you from going any further. This is the complete opposite of relaxing, fun, and safe.

 

[Shane Adams]

I guess I've always tried to avoid "hook slicing" despite the fact I never knew it was called hook slicing. I always called it "what you have to do when you screw up and get on the wrong side of the storm." I've done the traditional core punch fairly often, because most times my screw ups land me on the north side of storms. I rarely get caught back west behind the action, because I did this once very early in my career, and spent all day chasing down storms from the backside. Very frustrating. Also, for me, I've always been far less comfortable with a hook slice, because IMO it's more difficult to have to crane your neck south or southwest, to ensure you've not driven too far east ahead of the tornado's position, putting yourself directly in the path (assuming a NE motion for the purposes of this example). I can only think of a handful of successful hook slices I've done, and neither were (1) intentional or (2) got me real close to the tornado. In both cases I was probably a few miles N/NNW of the tornado, and gained a view after a lot of heavy precip (no hail) and then eventually ended up in precip-free air with a decent view. Here's a few images from some of these type encounters/views:

June 6, 1996. My first tornado, with horrible contrast. Small white tube angling down right to left over the "6 1996" portion of the time stamp:

October 9, 2001. First saw the tornado through heavy rain, which gradually stopped completely:

Initial view

After the precip cleared, from a static location NNW

I guess my chasing style is cautious, because in my cases, hook slices have been done (relatively) well-away from the tornado itself.

 

[Bob Schafer]

Rob and others: That explains it (mostly). My assumption was that the whole goal of the hook slice is to get under the RFB to the ENE of the tornado, directly in its path. Like Shane's scenario I have found myself behind (W of) storms/tor's many times, frustrated, seeing nothing but rain and anxiously waiting for the storm to get farther NE or N so that I could proceed E to get back into a position where I could view the action. It never dawned on me that by driving through that vision-obscuring rain one could get into that little zone between it and the tornado, and that some people not only do this but have a name for the strategy! Brilliant! LOL

Now, I would call that strategy of stopping at Position 1 the "Truncated Hook Slice", since you haven't completely sliced the hook.

When I mentioned TWISTEX it was in the knowledge that they were, indeed, NE of the tornado just before the tragedy, so they did not do a "Truncated Hook Slice", but rather a "Full Hook Slice". I am making another assumption, of course, as to what they had done prior to ending up there.

...and I'm not encouraging anyone to do any such thing, just for the record. Hook slices are not for me, either.

 

[Rob H]

Now, I would call that strategy of stopping at Position 1 the "Truncated Hook Slice", since you haven't completely sliced the hook.

The hook is just the RFD precip reflectivity, so once you pass through that into the bearcage, you're through the hook. You could drive out through the inflow notch and not intersect the hook again. With "full" vs. "partial" that seems like it's more having to do with the distance traveled through the bearcage. The "full zoo tour" if you will

 

[Dan Robinson]

Bob's post also raises the point that not every west to east passage through a storm's core is a dangerous "hook slice" if you're far enough north. The majority of times I've made such a move, it's probably more like a west-east "core punch" with the tornado at least 2 miles to the south/southeast of me and in clear view with a very wide gap once I popped out of the rain. At that point it's not much different than the north-to-south move, as it puts you in a similar position well downstream of the meso/tornado. Again, whether or not it's a safe move depends on the situation, and is usually only an option if you have a full handle on what's going on and know you have plenty of room.

 

[Bob Schafer]

Okay, I will cede you that point.

The hook is just the RFD precip reflectivity, so once you pass through that into the bearcage, you're through the hook. You could drive out through the inflow notch and not intersect the hook again. With "full" vs. "partial" that seems like it's more having to do with the distance traveled through the bearcage. The "full zoo tour" if you will

 

[JamesCaruso]

As Paul said, traditionally this has been called "core punching". "Hook slice" is a term I hadn't first heard used until last June after El Reno. From what I understand, hook slice refers to a west-to-east transection of the hook to the north of the meso. Core punching is also a common move from north to south through the forward flank precip east of the meso, done if you find yourself on the wrong side of the storm (to its north).

Isn't it any west-to-east transection of the hook, not necessarily north of the meso? Not saying you'd want to approach any other way, but setting aside the level of risk of various approaches, just from a straight definition standpoint, I would think hook slicing is any act of cutting through the hook/RFD from the west...

Rob, I'm confused. If the hook slice technique is to drive west-east (to the) north of the tornado, then how can it be that "You follow in the debris path meaning that your roads may be blocked, and you're much more likely to come across injuries and deaths", and "The tornado is moving away from you"?

I think the debris is more likely to be from the RFD as you are cutting through in a hook slice, correct?

 

[Dan Robinson]

I suppose a hook slice could refer to going west-east *south* of the meso, though that region of precip/RFD is relatively small compared to the region to the north. Come to think of it, "hook slice" might not always be the right word - I think sometimes "hook slice" is applied to someone riding the notch eastward. You could hook slice to get to that position, but it doesn't always mean a chaser did. You could just as easily come from the east, south or north to get into the notch - which is probably the "danger zone" one should be more concerned with. That is, you can get into the same trouble in that spot no matter which way you approached to get there. For example, with El Reno, many of us were never really in the hook prior to the incidents - we were north of the tornado in the inflow notch, but not in the RFD (to the south) or hook precip (to the west). To get to that spot, all I did was wait for the storm to approach from the west, never having to cross the hook precip. The meso rapidly developed to the south, and I stayed directly north of it as the event progressed. Technically I was never in the hook, just in the notch the whole time.

 

[Rob H]

You could just as easily come from the east, south or north to get into the notch - which is probably the "danger zone" one should be more concerned with. That is, you can get into the same trouble in that spot no matter which way you approached to get there.

What Dan said is pretty much correct: the hook is the RFD appendage, slicing means going through it, and the only way that really makes sense in the context of seeing the tornado is going from behind the storm, through the hook, into the cage/notch. This usually means you are driving west to west, and south of the meso because of E/NE storm motion. Technically you could slice a hook to escape, but is this a forum about storm escaping or storm chasing?

The ultimate goal of the hook slice is always to end up in the cage/notch otherwise you can't really see anything. So any discussion about the dangers of the cage/notch are applicable to hook slicing. The actual act of slicing the hook isn't very dangerous, unless you have strong RFD knocking down lines/trees (which can happen). I like the distinction because it's more of an active strategy as opposed to sitting in the path and passively letting the bearcage envelop you.

I think the debris is more likely to be from the RFD as you are cutting through in a hook slice, correct?

I deleted my earlier post on this because I didn't feel comfortable encouraging people to try it, but I'll try to rephrase some of it.

Once you hook slice, you don't really want to leave the bearcage, you want to stay in there with the tornado. So you have precip behind you to your west, the tornado is somewhere off to your south/east, and the hail core is to your north. On the best of situations with a fairly classic supercell and a large tornado shunting away hydrometeors, you maybe have 2-3km to play with. You really, really don't want to consider east as an option because that's directly in the path of a tornado that you are very close to. So you're going to be stair-stepping, moving north, east, north, east with the motion of the storm, at the mercy of the road network, staying north/west of the tornado, ie. behind it. You really don't want to go on dirt roads in case something goes wrong, and eventually your road network will cut you off and you'll need to let the tornado pass in front of you. This is the point when you drive over chunks of barns with nails sticking out, tree limbs, or come across a town that's been hit.

And since you're within 1km or so of the tornado as it passes through the town, guess who the first person on the scene is? Trust me, I don't want to see the damage, but if I'm following the tornado directly into town I consider it a responsibility to do whatever I can to help because I can guarantee I'll be there before any emergency vehicles or before people have even climbed out of their demolished houses.

 

[JamesCaruso]

IF one is going to hook slice a storm that is more along the continuum toward HP, how do you really know if you are transecting the hook north of the meso, south of the meso, or even directly west of the meso (and therefore emerging under it)? Assuming a very wet RFD/hook, there is no visibility on the approach, so how do you really know where you are relative to the meso? I would think the ONLY way to know is via radar (base velocity), but as we all know that is never going to be real time. If radar/GPS shows you are on a latitude that is south of the meso, and the storm is moving NE, then at least you know that if there is a radar delay the meso is, if anything, getting even further away than it appears on radar. But if you are on a latitude that is north of the meso, then the opposite is true; you may think you are north of it but meanwhile you are actually due west of it. Aren't you really just rolling the dice on where you emerge? And aren't you relying on having that small precip free zone around the tornado to see where you are before you drive right into it? Wasn't the lesson of El Reno that you might not have such a precip free zone, in a situation where the entire meso is practically on the ground, and the wrapping RFD is nearly indistinguishable from the tornado?

In a classic supercell there is likely enough visibility to know where you are (I recall doing this myself in Missouri in 2009 - knew where the meso was at all times, but it was also the first and only time I got into some big hail and cracked a windshield as we emerged into the vault region; the notch is adjacent to the largest hail northeast of the updraft, and it takes a lot of luck for the available roads to enable you to thread the needle). In a highly volatile El Reno type environment you probably don't try this at all. But this question is about a more typical HP or hybrid classic/HP scenario.

I imagine the answer is going to be, you DON'T know for sure where you're going to emerge, that's the whole point, that's why it's so dangerous and shouldn't really be attempted! But just wondering if there really is some way to gain some confidence in where you are going to come out relative to the meso, and at least lessen the risk and do a smarter (or at least less stupid) hook slice.

 

[Rob H]

As a tl;dr answer: yes, you don't know where you'll emerge, especially on storms like El Reno. Hook slicing can be dangerous, and if EHI is pegged, I would call people foolish to even try it.

(Again, this is all assuming northern hemisphere, right moving, E/NE storm motion supercells and needs to be adjusted for anything besides that.)

You watch the winds/rain at whatever levels you have visible and feel the way the wind is pushing on the car. If you're close to a big tornado either on the ground, or forming, there will be substantial "pulling" into that area. As long as the surface flow doesn't have a westerly component, the tornado is moving away from you. What if there's a meso handoff? That's a very real possibility, and I'm not sure what that would feel like. I'm guessing if you're further out the surface flow might be divergent and slow down a little where it's splitting. If you're closer, whatever meso is more powerful at the time would dominate the surface flow, and you might have some back-and-forth gusts between the two areas.

One really important thing to note: tornadoes don't behave the same. You might be saying "well duh", but they can really surprise you! After being within 1/4 mile of a few tornadoes I expected strong inflow pointing into the tornado as I got closer. When I approached the Rozel EF-4, inflow wasn't very strong and all of a sudden I got blasted by cyclonic winds that actually pushed the car a few inches on the gravel road. Was Rozel weakening? Was it ramping up? I have no idea what was going on with the wind fields but it acted radically different than what I expected.

This is only conjecture, but from looking at TWISTEX's position, reading the audio transcript, etc. I wonder if surface flow was a large component of their confusion in the final minute or two. They would have been in broad tornadic flow that masked smaller influences until they were too close to react to. They may have felt strong gusts every so often pulling in what seemed to be almost random directions. They probably felt strong surface flow off to the east, and then extremely strong flow to their south seconds before being impacted. If you ever lose that situational awareness and say "that's weird" about something, you really should let the storm go and immediately use your escape plan. Not a criticism of Tim at all, but a good lesson.

Storms are always unpredictable, but my personal experience is that anytime you get above 3000-3500 MLCAPE storms can do some crazy things with multiple tornadoes/vortices. Playing in the bearcage when crazy things can happen takes an already bad idea and makes it substantially worse.

 

[Paul Knightley]

FWIW, personally I think the procedure is only really *reasonably* safe when classic-ish supercells are present; typically a classic supercell will move at a reasonable pace, with fairly balanced inflow/updraught, with a tornado which *should* behave in a reasonably predictable way. I would suggest this is because outflow/inflow are fairly balanced too, as as the low-level circulation motion is likely determined primarily by interacting downdraughts, it shouldn't do anything too weird.

When you get into the HP end of the spectrum, downdraughts are clearly playing a greater role in the evolution of low-level features such as the low-level mesocyclone, and the tornado. With El Reno, the very powerful RFD/occlusion downdraught, and ingestion of flow from the forward flank core (perhaps?) caused a powerful N-S (or NW - SE) low-level flow, which the tornado seemed to develop at the 'end' of (for want of a better term!). These powerful downdraughts then aided in the motion which we all have looked at (SE then E and then NE), as well as the tornado rotating around the parent mesocyclone - also, remember HP supercell mesocyclones tend to migrate towards the 'front' of the cell too, with the FFD and RFD effectively merging. All of a sudden you reach a part of the spectrum where a 'hook' doesn't really exist as a radar feature.

As has been mentioned, large CAPE values amidst modest shear and plentiful low-level moisture should be key indicators that HP mode is favoured, and deviant motion might be more likely (pre-existing boundaries aside, which can also bring 'surprising' motions). Hopefully most (and it should be all!) chasers will know what mode of convection is favoured, and thus plan their strategy accordingly, but be prepared to amend when environmental conditions in the field evolve.

 

[Rob H]

I'm going to single out two chasers here. Daniel/Greg if you're reading this, I apologize, but your experience was very well documented and is a useful learning tool. I love your videos, and am glad you made it out relatively unscathed.

The conditions:
4000+ MLCAPE - http://www.spc.noaa.gov/exper/ma_archive/images_s4/20130531/23_mlcp.gif
45kt SR 9-11km Anvil Winds - http://www.spc.noaa.gov/exper/ma_archive/images_s4/20130531/23_ulsr.gif
1.7 pwat - http://www.spc.noaa.gov/exper/ma_archive/images_s4/20130531/23_pwtr.gif

SR anvil winds of 45kt and 1.7 pwats suggested that the El Reno environment was likely to be more on the HP side of things. 4000+ MLCAPE says two things to me: that updrafts won't have a problem being weighed down by water, and that crazy things can happen.

Warning sign #1 - before initiation I would probably be having the discussion with my chase partner about how we're giving storms a wider berth and trying to stay out of the bearcage because the name of the game this day is "violent tornado potential, unpredictability, and lots of precip".

https://www.youtube.com/watch?v=2SbQ1hbrLLA#t=2698
They are behind the tornado to the west. Note the wind/rain flowing into the tornado, "pointing" at it. They make a decision to stay off dirt roads, which is wise in this scenario. But they're starting to be in precip so they've fallen behind. The stated goal is to hook slice/drive through the rear precipitation area, and come out ahead of the tornado.
Warning sign #2 - trying to get ahead of any tornado west->east through precip is usually a really bad idea.

Warning sign #3 - "I didn't notice I40 has changed direction slightly to the southeast, placing us closer to the tornado"
"Slightly" is an understatement - it's a 2 mile drop to the south. Losing that situational awareness that you are now 2 miles closer to the tornado is a bad thing. Core punching is different in that you can have a very wide margin of error. When hook slicing/coming from the rear, you have a much smaller window. If you're not in the hail core, that means you're between the hail core and the tornado usually. A two mile error in this zone is a pretty big deal.

Note the wind/rain patterns. They're pointing to the SW, they're ahead of it for now, but it's heading in their direction.
https://www.youtube.com/watch?v=2SbQ1hbrLLA#t=2914

Warning sign #4 - 30 seconds later, surface flow is pointing to the S. They're no longer gaining ground on the tornado, and you can hear Daniel say that he has to slow down because of hydroplaning. At this point there are signs that your plan to beat the storm will not work, and then you have to slow down even more. Alarm bells should be going off, because you've realistically lost your chance to get ahead of it. I never try to get ahead of a tornado when doing this, so when surface flow points to the south, I stop and let the tornado get ahead of me. You know the condition of the road to your west since you just drove on it, and you know the tornado isn't likely to swing around or form upstream, so west is a very good escape route when hook slicing. You give up on the storm and let it safely pass in front of you, while staying away from power lines/trees that could come down in the RFD.
https://www.youtube.com/watch?v=2SbQ1hbrLLA#t=2948

Warning sign #5 - One minute later, surface flow is notably stronger meaning that the tornado is either intensifying or you are getting closer to it (or both). They note that they're paying attention to traffic in the opposite direction which makes them think the road ahead is clear. The road ahead *is* clear at the moment, but it won't be for long, so that's a false assumption. Also, don't rely on the public to lead you to safety because they'll drive right into a tornado without knowing it. Don't trust other chasers for that matter.
https://www.youtube.com/watch?v=2SbQ1hbrLLA#t=2969

Surface flow gets even stronger, and it's still pointing S of them. They're not gaining ground on the tornado, and it's getting closer.
https://www.youtube.com/watch?v=2SbQ1hbrLLA#t=3016

Surface flow is pointing to the SE, which means its ahead of them. But there seems to be some cyclonic curvature to it, which strongly implies you're in the outer winds. This is likely a big tornado. At this point the ham transmission goes out asking for a visual confirmation on the location of the tornado.
Warning sign #6 - ALARM BELLS! If you are asking other people to help you locate the tornado, this is a sign that you have lost situational awareness and quickly need to abort whatever it is you're doing!
https://www.youtube.com/watch?v=2SbQ1hbrLLA#t=3088

Hit by the semi. Listening to any of these warnings and stopping, or going west, in a three minute window would have resulted in a different outcome.
https://www.youtube.com/watch?v=2SbQ1hbrLLA#t=3214

I can't state how critical warnings like #4 and #6 are. If anyone takes away anything from this thread it should be that you need to continually re-asses your plan vs. how things are playing out, and that you can never, ever lose situational awareness. Either one of those should cause you to bail, abort, quit, escape, run away.

 

[JamesCaruso]

Rob, thanks for that in-depth analysis. I have not looked at the videos yet but will do so when I have a more reliable wi-fi connection than I do at the moment. I also have a question about storm mode but I think it would be OT to post here so I am starting a new thread.

Jim