Avoiding getting caught in squall lines while chasing

[Paul Schmit]

Hello everyone,
Well, with the "formal" chase season in my neck of the woods nearly over (and as a relatively new chaser), I'm hoping to use the ample interim time to keep learning as much as I can. A question I've thought about a lot since getting serious about chasing in the Plains is how best to plan ahead and execute strategy out in the field to avoid getting caught in front of an impenetrable line of storms and being forced to plow through it or drive an exceptionally long distance to get around. Although QLCS/MCS don't pose as much of a tornado threat as discrete supercells, the fierce wind, blinding rain, and large hail are still a force to contend with, potentially damaging your vehicle, impairing your ability to navigate and drive, impairing *other* drivers' ability to navigate and drive, and flooding road networks.

I realize avoiding heavy precipitation while storm chasing (setting aside the topic of core punching) is probably a fairly conservative strategy, but it's one that seems like a reasonable strategy for anyone fairly new to the Plains, or even anyone who seeks simply to mitigate risks posed by exacerbated driving hazards and potential damage to the chase vehicle. Several ideas come to mind:

1) Pick a target area near the expected point or line of initiation (perhaps ~20 minutes or less downstream) with the intention of intercepting when updrafts should be most discrete.
2) OR, pick a target area further downstream with sufficient road options to redirect toward the most isolated updraft or bail altogether if nothing discrete forms.
3) Avoid chasing in areas with significant component of mid/upper flow directed along primary surface boundaries, anticipating line formation will be the favorable storm mode.
4) Avoid chasing in the heart of weakly capped regions undergoing exceptionally strong, widespread vertical forcing.
5) Avoid chasing quickly propagating frontal boundaries.
6) Stick to the southern periphery of the favorable area for storm development before and during initiation (presuming primarily southerly or westerly storm motion, or rotating the entire scenario appropriately to accommodate other potential storm motion vectors).

Some of these strategies might be better than others, some may not be appropriate, and some may be overly conservative. A couple (1 and 2) are likely essential elements of any chase strategy, whether upscale growth and line formation are considered imminent or not. And there might be much better strategies out there used by people keen on preserving their windshields and avoiding the stress of driving through blinding precipitation. I'm very interested to hear everyone's thoughts on the subject.

Thanks!

Paul

 

[Jeff House]

Looks like a good list to me. For after the chase has started: I might add that when your beautiful classic supercell starts taking on HP characteristics, chase may be about over esp if you've seen 1-2 tornadoes. Even if not, if your gut does not feel right punt that HP. Also if a few cells in the immediate vicinity of each other are going HP, esp outflow dominant, a line may congeal soon. Cheers!

 

[Paul Schmit]

Thanks, Jeff. I suppose after the 5/31 event the notion of weak upper-level winds being correlated with HP modes should be cemented in everyone's minds. However, weak uppers aren't necessarily independently responsible for line formation, but your point about merging outflow boundaries seems especially relevant.

I'd be very curious to get a survey of chaser methodology regarding the choice of initial target area favoring either the anticipated area of initiation or the area further downstream closer to the axis where storms are anticipated to be more mature. (However, I realize the philosophies governing this choice go well beyond just the practical objective of avoiding being plowed over by a line.) The former choice seems to imply more work in keeping up with storm motion but perhaps more control in terms of getting into position before the storm reaches maturity, as well as more routing flexibility when deciding to bail, while the latter choice might require less movement to get into a good position but a more circuitous excursion in the event one misses the discrete phase.

 

[JamesCaruso]

I'd be very curious to get a survey of chaser methodology regarding the choice of initial target area favoring either the anticipated area of initiation or the area further downstream closer to the axis where storms are anticipated to be more mature. (However, I realize the philosophies governing this choice go well beyond just the practical objective of avoiding being plowed over by a line.) The former choice seems to imply more work in keeping up with storm motion but perhaps more control in terms of getting into position before the storm reaches maturity, as well as more routing flexibility when deciding to bail, while the latter choice might require less movement to get into a good position but a more circuitous excursion in the event one misses the discrete phase.

Personally, I prefer to be in the anticipated area of initiation. I find it very fulfilling to do a forecast that successfully puts me on a storm from its very birth. I also want to be there for the storm's most discrete phase, which can be fleeting. Being early on a storm also helps allow for better positioning, without having to join a caravan of chasers jockeying for position.

Of course, there are disadvantages to this approach; in addition to what you noted, there is the difficulty of not knowing which storm to commit to or when. I do like to hang back a little further east of the initiation area on an outbreak day, to allow some time for one storm to organize and become dominant. But on a "regular" day, you don't know what you might miss by waiting until storms move a particular distance.

 

[Joshua Nall]

Most just go where ever the greatest risk of discrete storms with tornadoes will be, which is probably why there won't be many replies. If a line does develop, right in front is where the best photo opportunities are and the traffic behind you is held up by the line. It's a cool place to be. The thing to do would be to stay out in front and duck into some sort of shelter and let it pass over.

As to whether you want to be near the point of initiation or downstream a ways to see a tornado is totally dependent in the expected evolution and storm speed.

 

[Mike Johnston]

Sooner or later, you're going to get caught in a squall line whether you are chasing or not. Sure, there's always a threat of severe, but I wouldn't base my initial targeting decision on the risk of a squall line. If it is apparent you will over overtaken by a squall line, I would say just stop somewhere like a coffee house, sit down and let the storm pass you by.

 

[Joey Krastel]

That's what I did yesterday in Russell, KS. Storms initiated VERY quickly and went totally linear in a matter of an hour. I like to position myself a little east of the initiation area for days when squalls are more than likely. Try to stay ahead by a few miles for best photo opportunities, and good lighting is enhanced here. It started to look messy so we pulled into a Dairy Queen and let it pass. The thing with squall lines, is 90% of the time, things seem sub-severe and the worst conditions only last a few minutes. Lightning shots from behind the line are nice when precip stops.

 

[Paul Schmit]

Yeah, I'd have to say that I've seen quite a few amazing shelf cloud/gust front shots taken near the leading edge of massive squall lines that would suggest they can be just as photogenic as a pancake stack meso. Having not been through many Plains squalls in the spring (but lots of low-topped, front- and/or trough-driven squalls on the east coast), I'm not sure how fleeting the large hail threat can be once storms congeal and go linear. On the highest probability severe days with tons of ambient SRH, I've definitely noticed there can be plenty of localized areas of intense rotation (and likely some big hail), but on days with mostly speed shear, perhaps the hail threat (or, at least the large hail threat) abates early on and it mostly becomes a wind and rain event. Once you get a massive cold pool behind a good squall, there's always something a little peaceful about the trailing rain after the leading gust front passes.

I'll definitely keep the DQ/coffee strategy in mind.

Thanks as well for the comments on pre-initiation positioning. I was right on the dryline (or maybe even a couple miles west) on the May 19 OKC event, dropping south from Enid, and was pretty much pinned on the backside of the supercells going through town for the rest of the day...the storms were just too close together and it was extremely tough to visually confirm what was going on underneath. In hindsight, being a little further east and not having to deal with the horrible contrast of the sun practically overhead rendering everything under the base impossible to make out would probably have simplified the chase more. Will have to iterate some more and keep working on a good strategy. (First lesson learned: stay the hell out of metro areas.)

 

[chrisbray]

Since I usually only chase Illinois, getting caught by a squall line is about all I have the option of doing

 

[David Mikulec]

Did someone say "squall line"? April 24, 2010...

 

[Jake Orosi]

Sooner or later, you're going to get caught in a squall line whether you are chasing or not. Sure, there's always a threat of severe, but I wouldn't base my initial targeting decision on the risk of a squall line. If it is apparent you will over overtaken by a squall line, I would say just stop somewhere like a coffee house, sit down and let the storm pass you by.

That sounds about right to me. Squall line time is Denny's time. A lot of chain restaurants have free wifi these days, so it's a good opportunity to relax, have a bite, and do some up/downloading.

It may be my inexperience showing, but I tend to think that once you've got a heavy squall line passing you, that more often than not means your chase day is over - although naturally there are exceptions.

 

[cdcollura]

Good day all,

Simply be there for initiation ... This is where the forecasting skills pay out.

Also, avoid any "linear" forced areas (such as May 21, 2013 in Texas or April 9, 2013 in OK) where initiation will be an immediate squall line.

 

[Windshear Kear]

Yeah, I'd rather be there for initiation. May 31st was pretty amazing to watch the cap break. At the flip of a switch it went from a few cumulous clouds..to towering cumulous rocketing to 50K feet!! That never gets old!!

 

[Tim Vasquez]

Part of the difficulty with squall lines is that several different storm modes can come into play. A lot of NWS forecast discussions don't distinguish between these. SPC outlooks usually do, but only in a general sense, sometimes ambiguous ("storms should do X but may do Y"), and with a limited amount of refinement as the day goes on. The distinction, however, is very, very important from a chase targeting standpoint.

For instance consider storm-relative helicity and LM/RM motion. Not just from the 12Z sounding or the SPC fields, but actually worked up manually starting with the 12Z radiosonde and adjusted using sources like WSR-88D VAD/VWP and profiler data, and evaluated subjectively in the 0-1, 0-2, and 0-3 km layer. If the RM motion is well to the right of the environmental winds and the LM is on the wind plot itself (or close to it), there is a better likelihood that the squall line will break up into discrete supercells. This is especially true if there is good instability, and less so if there is a strong thermal gradient along the boundary and linear convergence. If this is the case, I'd say target the best theta-e 1-2 hours downstream from expected initiation. If the LM and RM are pretty much on both sides of the line, then the line will likely fill in and you're probably better off at tail end charlie. Forcing near and upstream of initiation needs be monitored closely (observed pressure falls, model pressure falls and 500 mb vorticity, etc) to see if there might be a game changer on the linear vs. point convergence spectrum. This is something that can also cause a response in the surface wind field and change the SRH on small time/space scales, as a result, the convective mode changes.

If SRH isn't that much of a factor, I'd next start looking at the possibility of bow echoes and derechos. A lot of what's in the literature is pattern based and doesn't discriminate between other storm types. However it does appear that strong bulk shears in the 0-1, 0-2, 0-3, and 0-6 km layers in combination with moderate to high CAPEs are important. I've seen less on anticipating serial type systems (smaller-scale) vs. progressive (large bowed MCS) except for whether the bulk shear vectors are parallel to a boundary (progressive) or perpendicular (serial). The chase targets here are very different of course and I've rarely seen tail end charlie produce anything interesting. With the progressive systems you have prominent bookend vortices (e.g. SGF on 5/8/2009). A north bookend can be roughly targeted perhaps 1-2 h in advance, and I can name at least 1 rain-wrapped tornado here caught by a chaser. Leading edge vortices are also a possibility. With serial systems I can't really think of any good chase strategy except luck.

Overall squall lines are a mess, but with the mobile devices we have now, they're no longer the rainy monsoon trainwrecks that spelled the end of the chase day. Also the trailing stratiform region of an MCS can have some absolutely amazing lightning displays, yielding not just the familiar anvil crawlers but constant cloud-to-cloud lightning on a massive scale. The problems here are often rainy trailing stratiform areas and broken/overcast stratus filling in behind the storm and obscuring the view, so quite often we never get a look at any of this. For this I would consider the storm-relative anvil level wind component perpendicular to the MCS axis. If this is fairly high (25+ kt) the extensive, rainy trailing stratiform regions should be less of a problem. I'd also make sure there's not very cold air coming in behind the MCS, since that would likely result in overcast stratus.

Hope that gives some additional info to consider.

Tim

 

[chrisbray]

Wow Tim, that was quite a lot of info. Myabe within the next year I can hope to completely digest everything you said