2018 severe wx/chase season discussion

[Jeff Duda]

The moisture problem stems from the fact that we haven't really had a trough take a southerly-enough track since the beginning of the month to induce deep, strong onshore flow from the Gulf, and thus the metaphorical "firehose" of moisture from the Gulf has been more like a trickle or has been shut off. The decent moisture that is in place currently is the result of 10+ days of no cold fronts to clear out the moisture + ET + what little trickle of moisture is actually coming in off the Gulf.

As long as we continue to be locked into this split-flow pattern where the main polar jet is along or north of the Canadian border and all we get are these measly cutoffs oozing into the Rockies before stalling and filling, there will be insufficient widespread flow for supercells and also generally no synoptic scale moisture return off the Gulf. Can't say return flow off the western Atlantic is out of the question, but the trajectories needed for such moisture to reach the Plains are less than probable. It also doesn't help that the subtropical jet is a bit far south and for some reason is failing to generate the troughs we would need to see good Plains setups.

I think I mentioned this before, but this kind of seasonal evolution is why I hate seeing really active troughing patterns in March-early April. I know this isn't entirely scientific to say, but it does seem like that type of pattern (frequent high-amplitude troughs crossing the CONUS) exhausts itself after a few weeks or up to a month or two, and then it seems like it has to reload. So when that pattern sets up too early, you get this death ridge/split flow/zonal flow lameass crap during the climatological peak of the season. What I like to see is the active troughing pattern set up starting mid-late April so that synoptic-scale cyclogenesis episodes coincide with the stronger diabatic heating and better moisture return of mid-late spring rather than early spring when CP air masses still pervade the eastern 2/3rds of the US and moisture is always questionable. In the former cases you're much more likely to have the ingredients in place for a prolonged period of more significant severe events, at least a few of which are bound to promote satisfying chase setups and/or tornado outbreaks.

 

[JamesCaruso]

...

I think I mentioned this before, but this kind of seasonal evolution is why I hate seeing really active troughing patterns in March-early April. I know this isn't entirely scientific to say, but it does seem like that type of pattern (frequent high-amplitude troughs crossing the CONUS) exhausts itself after a few weeks or up to a month or two, and then it seems like it has to reload. So when that pattern sets up too early, you get this death ridge/split flow/zonal flow lameass crap during the climatological peak of the season. What I like to see is the active troughing pattern set up starting mid-late April so that synoptic-scale cyclogenesis episodes coincide with the stronger diabatic heating and better moisture return of mid-late spring rather than early spring when CP air masses still pervade the eastern 2/3rds of the US and moisture is always questionable. In the former cases you're much more likely to have the ingredients in place for a prolonged period of more significant severe events, at least a few of which are bound to promote satisfying chase setups and/or tornado outbreaks.

Jeff, this is an interesting observation. You gave the caveat that it “isn’t entirely scientific,” but as a non-meteorologist that is limited to anecdotal observations and pattern recognition, I would similarly always get uneasy about what would be “left” during peak chasing season if there had already been a lot of early activity.

This year, however, there hasn’t been much activity, so I am surprised at how poorly things are turning out. I wasn’t really following Plains weather much back in March/April, except to be generally aware from this forum that things were off to a slow start. So I am surprised to see your observation that it was actually *too active*, *too early*. In retrospect, having been focused more on the unusual frequency/severity of winter storms for that time of year here in Philadelphia, I guess there were a relatively high number of troughs crossing the country back then (at least in March; I don’t remember much about April, but if anything wasn’t there a persistent trough in the east and ridging in the west?)

So then how does all this (frequent early season troughs) reconcile with such a slow severe weather season in the Plains? Why weren’t those troughs producing at the time? Was it the path they took, i.e. not digging into the Plains? You mention the lack of moisture at that time of year, but wouldn’t the troughs, if present, facilitate moisture return at any time of year? I guess you are saying it’s not that a favorable pattern per se has exhausted itself, it’s more just the absolute number of troughs that we’ve pretty much “used up” so to speak, is that a fair characterization? Still, hasn’t the atmosphere had sufficient time to “reload” by now? Are you thinking that it “reloads” by June or are we pretty much done in your estimation?

Thanks for helping me better understand this and put some context around my disappointment.

 

[Paul Knightley]

This season has been dominated by a blocky pattern in the jet, largely as a hangover from the major sudden stratospheric warming event we had in late winter. This really disrupted the polar vortex and since then we've seen rather anemic flow around the N Hem. Tropical forcing seems to be fairly non-existent, and no doubt sea temps in the N Pacific will have had some effect on the way the jet behaves. Interestingly, 2006 has come up numerous times this year so far as an analogue (although 2013 is one too) based on various teleconnection indices, and 2006 was a poor year, overall, for chasing.

 

[Andy Wehrle]

Strange thing is though, I remember May 2006 being very cool with hardly any storms, just stratiform showers when we got rain. This May we've had plenty of summerlike days and no shortage of thunderstorms (in fact already the 4th wettest May on record for Madison), just nothing to get them to severe levels on an organized scale.

 

[Royce Sheibal]

@Jeff Duda I think you're being more scientific than you realize. We had a very strongly swinging MJO from Feb-April, which tends to encourage your massive troughs. Now that the MJO has finally settled down in magnitude (as would be expected after a several month up period) we're stuck in the MJO doldrums, which are not great for troughs. Some amplification would be nice, sadly it doesn't look too promising right now.

 

[Brett Nickeson]

I wasn’t really following Plains weather much back in March/April, except to be generally aware from this forum that things were off to a slow start. So I am surprised to see your observation that it was actually *too active*, *too early*. In retrospect, having been focused more on the unusual frequency/severity of winter storms for that time of year here in Philadelphia, I guess there were a relatively high number of troughs crossing the country back then (at least in March; I don’t remember much about April, but if anything wasn’t there a persistent trough in the east and ridging in the west?)

So then how does all this (frequent early season troughs) reconcile with such a slow severe weather season in the Plains? Why weren’t those troughs producing at the time? Was it the path they took, i.e. not digging into the Plains? You mention the lack of moisture at that time of year, but wouldn’t the troughs, if present, facilitate moisture return at any time of year?

The folks above have more scientific explanations of why this occurred, but in general the answer is that it was still basically winter when the jet was active. It's hard to get moisture and adequate instability when you're at 45 degrees for a high and it's snowing once a week up through early April. We went straight from a winter pattern and 25 degrees below normal to a late June pattern and 15 degrees above normal within about a two week period.

Just a miserable, miserable year.

 

[Eric Bucsela]

That's the problem with these "ripples in the flow" setups without a robust warm sector. They have very little tolerance for things going wrong and no spatial coverage for the targets to shift before things are hopelessly out of alignment. Friday's setup seems to be hanging on a thread with no room for anything at the surface or aloft to shift even 50 miles in any direction. Saturday's NAM has the better overlap of decent flow and moisture, but surface flow is weak (and in Iowa of course).

Thanks for your comments Dan but I’m still not clear why Friday looks so marginal, esp in SW KS. To my non-professional eye, both NAM and GFS show decent wind fields, CAPE approaching 3000 and a breakable cap. At least one NAM run has a cell pop in that area by 0-3z. DPs are already in mid- to upper 50s and a little advection could help that. DDC is somewhat optimistic but SPC is obviously not too jazzed. Guess I still have a lot to learn!

 

[Jeff Duda]

This year, however, there hasn’t been much activity, so I am surprised at how poorly things are turning out. I wasn’t really following Plains weather much back in March/April, except to be generally aware from this forum that things were off to a slow start. So I am surprised to see your observation that it was actually *too active*, *too early*. In retrospect, having been focused more on the unusual frequency/severity of winter storms for that time of year here in Philadelphia, I guess there were a relatively high number of troughs crossing the country back then (at least in March; I don’t remember much about April, but if anything wasn’t there a persistent trough in the east and ridging in the west?)

As far as "active" goes, I was referring to the frequent troughing, not to severe weather report numbers.

So then how does all this (frequent early season troughs) reconcile with such a slow severe weather season in the Plains? Why weren’t those troughs producing at the time? Was it the path they took, i.e. not digging into the Plains? You mention the lack of moisture at that time of year, but wouldn’t the troughs, if present, facilitate moisture return at any time of year? I guess you are saying it’s not that a favorable pattern per se has exhausted itself, it’s more just the absolute number of troughs that we’ve pretty much “used up” so to speak, is that a fair characterization? Still, hasn’t the atmosphere had sufficient time to “reload” by now? Are you thinking that it “reloads” by June or are we pretty much done in your estimation?

Troughing does not guarantee sufficient moisture return in the early season. If a major cold front swept out the entire CONUS east of the Rockies and the Gulf itself of moisture, all the 50 kt surface southerlies off the Gulf wouldn't do a damn thing to restore moisture over land. With less direct heating in the early season, it takes longer for evaporation of surface water off the gulf to "recharge" the atmosphere with moisture also. Furthermore, while this is less common of a failure mechanism, if you're coming off a major drought (such as was the case in the south-central/southwest US this past winter) in a source region for good lapse rates, that can promote early EMLs and capping. March sun isn't all that strong just yet, so diurnal destabilization is also not guaranteed to break early season caps if they're strong enough.

So there can remain multiple failure modes in the presence of even a strong trough in the early season.

Regarding your last set of questions - as I mentioned, my interpretation was not entirely scientific, meaning I can't identify a single set of physical processes that mystically govern the total number of troughs that will cross any given longitude in a year, although I do suspect there are underlying larger-scale physics processes that may indeed explain this phenomenon. [ADD: As Royce mentioned, I should probably be looking at MJO indices. Unfortunately my knowledge of larger-scale processes is pretty lacking, as I never studied those in school. Seems like others in this thread have a better handle on it, though.] So I would be hesitant to use the phrase "used up our number of troughs for the season", although that is kind of what I'm hinting at. I have no idea how much time it would take for a more active pattern to reappear, so I cannot say with any certainty whether we may be done for the season as far as large-scale troughs go. Typically June is ruled by mesoscale setups anyway, as moisture and heating are generally always there; you generally only need some sheared flow somewhere to get a big event, and you don't necessarily need a big trough to get sheared flow.

 

[Jeff House]

Friday trouble is dewpoints/LCLs. Moisture will try to recover but 850/925 mb was scoured by the Tenn. Valley trough. Forecast soundings revert to inverted V by late afternoon Friday lowest levels - allows evaporative cooling gust out. Even at the ground South Texas dews are below 70 - awful. ARW version of the WRF really does not get target area dews to even 60 deg. Touches it and mixes out. NAM version of the WRF, usually pretty bullish, barely touches 65 before mixing out. Both CAMs low level wind fields and reflectivity look like gust outs early. Might get a quick landspout, but I can't see a path to a good multi-cycle show.

Saturday CAMs don't look a whole lot better but I think dews will be higher. Goal is to avoid a mess of clusters. CAMs might improve. Fundamentals are not bad. Models show a slightly veered LLJ, but not a problem considering westerlies farther up. Plenty of outflow boundaries. Maybe just too much convection too early?

Here is my take on this weekend vs a Major or mid-major family event (FE). It is understood that minor FEs are blown off for chasing. Mid-major FEs might get skipped for an excellent chase set-up. I would not skip a Major FE for any chase set-up. @JamesCaruso I really wanted to PM but ST setting(s) will not permit. If the play is a mid-major FE I see a 50/50 choice. If the play is a Major FE, I would personally not chase. However each individual is different, with unique risk tolerances and relationships. Stormtrack is a like Planet Fitness, a judgement free zone. I might chase 50/50 a great/excellent set-up (this is not) if the play/sports game was regular season (mid-major FE). A first ever play, or sports post-season feels more like a Major FE. Lurkers, I cannot stress enough these are personal choices.

The following may be as scientifically awful as predicting EF levels, but I want to quantify this weekend. Friday and Saturday both probably have about a 40% chance of producing more than a landspout. Add other factors like cell selection, roads, whatever, and probably go 20% chance of success each day - likely generous. 80% chance of failure, but 64% of failing both days, so 36% chance of intercepting at least one day. However the chance of something memorable is probably 10% or less. I prefer 33% or better odds.

And that 33% is with nothing on the family calendar. This weekend I have nothing, but I am still not chasing. Maybe I'm too pessimistic. We were packing our bags, and punted the plan around 00Z yesterday. I may miss the next Rozel, but I doubt it. Those chasing, I do wish you good luck!

 

[Dan Robinson]

Thanks for your comments Dan but I’m still not clear why Friday looks so marginal, esp in SW KS. To my non-professional eye, both NAM and GFS show decent wind fields, CAPE approaching 3000 and a breakable cap. At least one NAM run has a cell pop in that area by 0-3z. DPs are already in mid- to upper 50s and a little advection could help that. DDC is somewhat optimistic but SPC is obviously not too jazzed. Guess I still have a lot to learn!

In a "good" season, you have abundant moisture and broad areas of upper level flow that overlap in large areas, maximizing the potential for healthy supercells and for one or more of them to benefit from a small-scale feature like a dryline bulge, warm front or outflow boundary. In seasons like this, deep moisture and upper support are occurring in only very small areas (if at all), meaning the chances for them to overlap at the right time are very low, much less be coincident with an OFB or some other mesoscale feature that could enhance tornado potential. It's just harder in our current setup to get everything you need to line up correctly because the basic ingredients are in short supply.

 

[JeremyS]

It may only be one run, but the long range 12Z GFS at least shows some hints of the pattern changing a bit, i.e. the jet stream not up near the North Pole and it actually makes an appearance in the lower 48 and sticks around starting Memorial Day weekend. Also several days of increased 500mb flow aoa 30 kts, which as we know is kind of the baseline for all you need when you have good instability in May/June.

 

[JamesCaruso]

@JeffHouse - thank you so much for your advice. I suspect I am quite a few years older than you, but you have wisdom beyond your years and from your posts in the “family guilt” thread I know we share similar values. Even at my age, it was difficult to decide between chasing and my daughters’ play. I was truly torn. So your advice was more helpful than you can imagine. Actually putting a calculus to it was a great way to objectively assess the probabilities underlying the situation (especially for an accountant like me). I appreciate that you took the time to help, and were able to evaluate my situation in such a way; so many are so hardcore to the point where chasing trumps all else and would not have the ability to weigh the situation as you did. Also a nice subtle distinction you picked up on, how my girls’ first play qualifies as a more significant “family event” than if it was not their first one. So again, thank you. I almost needed “permission” from a fellow chaser to blow off this weekend.

Which is exactly what I decided to do. If it was a clear cut classic setup, I would chase no matter what. If it was dead, I would stay home no matter what. It’s the “iffy”, marginal, conditional, setups like this that are difficult. If I had nothing going on, I would easily choose to chase. But with a family event, it becomes an agonizing decision: is it “good enough” on the Plains to justify missing the play? I weighed the probabilities and decided the answer to that is no. The fact is that even in the best setups, more can go wrong than can go right - one little ingredient out of balance, one little mistake on forecast, storm selection, or road option - as you noted and quantified.

Friday could be pretty good, I had a flight to ICT for my target somewhere east of DDC that I selected yesterday morning. But then it gets progressively less favorable after that. Imagine I go out there, have *possibly* one or two good days on Fri/Sat, then Sun and beyond I’m sitting out there not even chasing and maybe even coming home early - I would feel terrible to miss the play for no good reason and to maybe not even be chasing on the actual day of the play (Sunday).

Sure, I might miss something out there over the next couple of days. But unless I can spend the whole season out there, I will always miss stuff. Worst case scenario, this weekend ends up being the only good activity of the whole next two weeks and I miss it. Well if that’s the case, screw it, it wouldn’t be worth going out there for such little activity anyway.

Blowing off the weekend, and departing for the Plains potentially on Monday instead, I still have two full weeks to look forward to out there. If next week doesn’t shape up too well, I may be able to shift my whole trip a bit - run it from Memorial Day weekend until around June 7. I hope that doesn’t happen, I would rather stay with the original schedule and get out there for next week and the week after, returning June 3. But we’ll see what happens.

Fortunately, my chase partner was very understanding and supportive, absolutely zero vibe that I was introducing a new variable at the last minute with the play and making him miss a couple of days of chasing.

You know I will be eyeing things up closely tomorrow and ready to go berserk if there’s a significant tornado out in my target area [emoji51]

Hope this wasn’t too OT but Jeff House deserves a public thank you and anyway isn’t this thread partly about making these difficult decisions relative to the overall pattern???

 

[Dan Robinson]

James, I think you made the right call. Friday just looks abysmal right now. I have the next three days free to chase, and even I'm sitting here at my desk ready to just go to bed instead of starting the usual drive to Salina. Take a look at the dewpoint charts on all of the short term models. Moisture just craters through midday thanks to mixing (a big problem we saw in 2006). The HRRR has Dodge City mixing to 49F by 19z, and everywhere west of I-35 falling below 60. That coupled with the consistent linear signals on the CAMs (too much lift coming in) means Friday will likely turn out similar to today.

Saturday looks slightly better, but a one-day affair in more difficult chase terrain. As we all know, the atmosphere could surprise us, but I'd be OK with missing this entire system, and I live a day's drive away.

 

[Quincy Vagell]

Agreed that favoring family/loved ones over a messy severe weather setup is the right decision.

The only reason I'm chasing on Friday is that it's my last off day for a bit and I was already out chasing today. Saturday could be a bit better, but has been the case with almost every setup this month, there are red flags there as well. Even before this week, I already committed to not chasing Saturday. I could have changed that if it looked like there was going to be a major event, but that's clearly not going to be the case. After the past few days, a break will be welcomed to reload and prepare for late May.

My advice is that anyone who's on the fence about chasing marginal setups coming up, you might want to heavily consider the pros and cons. See if you can hold resources/PTO/etc. until later in the season. While there will be chases to be had (probably at least 75% of the remaining days in May), expect most of them to be challenging, localized and/or conditional. As boundary layer moisture has been a concern for a while, the biggest red flag overall is a lack of more substantial upper level flow. Without that, aside from mesoscale accidents, don't expect much in the way of long-lived supercell activity in the Plains, at least over the next week or so.

If you're out chasing, good luck. There will be storms and hopefully you can find them, just be patient and keep expectations in check.

 

[JamesCaruso]

My advice is that anyone who's on the fence about chasing marginal setups coming up, you might want to heavily consider the pros and cons. See if you can hold resources/PTO/etc. until later in the season. While there will be chases to be had (probably at least 75% of the remaining days in May), expect most of them to be challenging, localized and/or conditional. As boundary layer moisture has been a concern for a while, the biggest red flag overall is a lack of more substantial upper level flow. Without that, aside from mesoscale accidents, don't expect much in the way of long-lived supercell activity in the Plains, at least over the next week or so.
.

Agreed, and I would add that even when on a chase vacation and having every day available to chase, it is simply not much fun to drive all over the place knowing that the chances of success are slim to none, so one needs to decide if they are willing to put in that much effort on marginal setups. There is a cost/benefit equation on each individual day, even on a chase vacation. I don’t necessarily mean cost in terms of money once you are already out there and already paying for food, hotels, etc.; I mean more of a cost in terms of the stress and frustration, and the time and effort of driving vast distances, which is less appealing to me the older I get. Drive six or eight hours for a great setup, sure, but not for a marginal one, chase vacation or not.

Having said all that, I would still advise getting out there at some point no matter what, and that’s what I plan to do, although now I am trying to shift from Memorial Day weekend to around 6/7 when I absolutely must be back home. But I can’t imagine blowing it off completely and having to wait another whole year. I would go out there just for the experience and the vacation, although I wouldn’t stay a full two weeks if nothing was going on.