Backing Winds: Really Necessary for Tornadoes?

That’s right, fellow storm chasers, you read my headline right. I’m about to raise a few eyebrows by tossing out the possibility that backing winds–or, more precisely, what we normally consider to be backing winds as depicted on forecast maps–aren’t always vital to tornadic storms.* This isn’t speculation as much as it is observation. Over the years I’ve seen a number of tornadic events develop in the midst of southwest surface flow, enough to think that the absence of southeasterly winds on the forecast map isn’t always a deal breaker.

What is indispensable are the conditions that southeasterly boundary layer winds tend to create. I’m thinking of ample deep-layer moisture and sufficient low-level storm-relative helicity. Those are what count. If they are present, it doesn’t much matter which way the wind blows from our perspective. The atmosphere sees things differently and doesn’t care what we think. It just does what it does.

Let me quickly say, I’m a huge fan of southeasterly surface winds. I love to see them on forecast maps. And I’m aware that winds can back locally in ways that the maps don’t portray. What I’m really talking about here is forecasting using the tools we have to work with, which continue to improve. Until last year, for instance, I’d never heard of the HRRR. It’s a marvel. But generally speaking, in contemplating the prospects for a chase day we’re still dealing with pretty broad brush strokes, and the farther we live from Tornado Alley, the better we need to be at determining how those strokes will play out.

A Regional Thing?

In writing about forecasting matters, I still feel very much like a neophyte who may be getting into matters that are over my head. I’m no Jon Davies or Chuck Doswell. I’m not even a meteorology student. But you know the old saying about fools, angels, and where they tread.

My sense of things is that as we move east of the Mississippi, southeasterly surface winds become less important for moisture fetch–and, I might add, southwesterly 850s aren’t such a terrible thing. Why? For one thing, moisture sources in the Gulf of Mexico no longer lie to the southeast, but to the south, and even to the southwest in eastern parts of the CONUS. Also important, the desert southwest isn’t nearly so proximate an influence. Thus, H85 winds that would kill a setup with dry air advection in Oklahoma can carry moisture up into Illinois and Indiana. Moreover, that moisture is apt to follow a curvy path–one that can, for instance, take it first northwest from the Gulf, then north, then northeast up into the Great Lakes.

All that to say that the trajectory of moisture transport can look different in different parts of the country.

As for helicity, does it really matter whether you’ve got southeasterly, or even southerly, surface winds as long as 0-1km SRH is in the neighborhood of 150 or greater? Years of reading convective outlooks leads me to believe that the SPC doesn’t think so.  What I’m saying here is no doubt old hat to them. But it may seem a bit out of the box to at least some storm chasers, particularly those whose thinking has been conditioned by setups in the southern and central Great Plains. The whole concept of storm-relative helicity suggests that the term backing is, well, relative, a matter of how winds relate to a storm as it moves, not to the compass. That’s why right-turners produce. A few days ago in Pennsylvania, overall storm motion was consistent with unidirectional winds from the west; yet a rogue supercell deviated to the right and spun up a tornado near Greensburg.

A Few Examples

Seeing is believing. Here are a few maps that show surface conditions around the time of tornado incidents east of the Mississippi.

july-13-2004-roanoke-ilThe July 12, 2004, Roanoke, Illinois, tornado is an example of a classic northwest flow event. Rated F4, the tornado was large, long-lived, and not the first violent tornado to occur in northwest flow during the warm season in Illinois. Four years earlier, the disastrous 1990 Plainfield F5 was fueled by massive CAPE amid northwest flow.

june-5-2010-elmwood-iljune-5-ilx-pm-soundingThe June 5, 2010, central Illinois outbreak was a sort of quasi northwest flow situation. Mid-level winds were predominantly westerly with just a slight northerly component to them. The surface and 850 winds were unquestionably veered. Besides the surface map, I’ve also included the ILX 00z sounding, which preceded tornadogenesis by roughly an hour.

august-24-2007-pottervillepotterville-500mb-12zFinally, the Potterville, Michigan, tornado practically dropped in my lap, but I ignored what the radar was showing me because I was too dumb to believe my eyes even when the dynamics were plainly visible in the clouds right over my head. This was not a northwest flow event; in fact, as you can see by comparing the surface and 500mb maps, it looked to be unidirectional from the southwest, with directional shear increasing as the trough moved east and mid-level winds became more westerly.

You can find plenty more examples besides these, I’m sure. My point is simply this: Don’t be too quick to write off a synoptic setup because of veered surface winds in the forecast, particularly east of the Mississippi. If moisture is in place and there’s reason to hope for adequate SRH, then it can pay to take a deeper look. Things could pop. They’ve done so before and they’ll do so again.

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* ADDENDUM, March 3, 2013: The term “backing” has a couple of different applications. I used it a bit naively in the title and copy to mean southeasterly surface winds, which is the meaning by which I first came to understand the word. That becomes apparent quickly  in the article, but it bears explaining. If I were writing this  post today, I’d simply say “southeasterly” and erase any uncertainty of what I meant.

Highlights from the 2009 COD Severe Weather Conference

Paul Sirvatka of COD, conference organizer

Paul Sirvatka of COD, conference organizer

The 2009 College of DuPage Severe Weather Symposium is now behind me, and in the light of it, it seems a bit weird to think that the day after, I headed over to my buddy Bill’s to watch the next episode of the Storm Chasers series on Discovery Channel. It feels like two different worlds, like boarding a bus in Grand Rapids and getting off on Mars. But the difference is superficial, a matter of editorial slant; the raw material remains the same, and however it gets spun on television, it’s nevertheless the stuff of research. In reality, people really, truly are going out there and surrounding supercells with an armada of mobile radars and other devices, including manned probe vehicles, all in the interest of collecting data that can increase our understanding of, in a nutshell, what makes tornadoes happen.

The conference featured some of the most knowledgeable and revered names in severe weather research, operational forecasting, and storm chasing: Eric Rasmussen. Chuck Doswell. Roger Edwards. Roger Wakimoto. Josh Wurman. The list goes on, but the point is, a lot of very knowledgeable heads were present in the Double Tree Hotel’s conference room this past week, and some of the insights they shared were fascinating.

Taylor and Carlsen of Environment Canada

Taylor and Carlsen of Environment Canada

Some of the coolest stuff didn’t even come out of the United States. Neil Taylor and Dave Carlsen of Environment Canada shared a photogrammetric analysis of the Elie, Manitoba, F5 tornado, and preliminary findings from the 2008 UNSTABLE team’s exploration of a well-known but hitherto unresearched dryline phenomenon in Alberta. The latter featured EC’s own mobile mesonet, complete with a Doppler-equipped airlplane.

Here are just a few, representative snapshots of the many other topical materials covered:

* Adam Houston talked about the effects of entrainment on unstable parcels, and suggested that the important issue for storm formation isn’t whether a parcel is merely unstable, but whether it is “supercritical”–i.e., possesses enough CAPE to overcome the effect of entrainment.

Eric Rasmussen

Eric Rasmussen

* Eric Rasmussen shared some of the prelimary findings of VORTEX2, describing the interaction of the RFD with horizontal vortex rings in tornadogenesis.

* Roger Edwards discussed the forecast funnel and the pros and cons of numerical models in operational forecasting.

* Al Pietrycha offered an operational forecasting perspective on non-mesocyclone tornadoes, and more specifically, on landspouts.

* For his dinner presentation Saturday night, Chuck Doswell gave an overview of the history of severe weather forecasting and research, and shared his outlook on things to come.

The shape of the future was in fact a topic of concern for a number of the speakers, notably Doswell and Edwards. Amid the influx of information from the research community on misocyclones, vorticity arches, moisture

Roger Edwards

Roger Edwards

convergence, and so on, those on the operational side focused on a more pragmatic matter: the widespread over-reliance on numerical models versus hand analysis.

Will forecast models replace human forecasters? According to Doswell and Edwards, yes, at least for most forecasting scenarios. Edwards emphasized that when it comes to severe weather events–the most difficult to forecast, and the costliest in terms of lives and property–humans will still play an important role. But both men deplored the degree to which forecasters have abdicated hand analysis to the models, which continue to make advances in accuracy at the expense of human development. In a word, the attention and the money are being invested in building better technology, not better forecasters.

Doswell’s message to meteorology students was blunt: either soak in as much information as possible, and commit to becoming experts at hand analysis and motivated self-educators, or else find a different career. Chuck, who is not known for being shy about sharing his viewpoints, wasn’t being nasty, just extremely forthright.

Chuck Doswell speaks

Chuck Doswell speaks

The mets from Environment Canada, Carlsen and Taylor, were clearly shocked to learn how dependent United States WFOs have become on forecast models. The Canadian meteorologists take hand analysis as a given part of their jobs, and couldn’t imagine not rolling up their sleeves and interacting with the surface and upper-level charts firsthand.

If there was a primary take-away value for me from this conference, I guess that’s it: the importance of getting my arms around hand analysis. Practically speaking, while I found the other material fascinating and enriching, much of it was not particularly applicable to my needs as a storm chaser. The first priority is to get to the right storms. Everything else falls into place from there.

COD Severe Weather Symposium: Are You Going?

It’s drawing closer, and I’m getting excited. I’m talking about the College of DuPage’s upcoming Severe Weather Symposium, which will be held November 5-7. With a lineup of presenters that features some of the foremost luminaries in severe thunderstorm research, the event promises to be stellar.

I’m surprised I haven’t seen more talk about it on Stormtrack, but maybe that’s because the symposium is being held in Chicago rather than out in the Great Plains. Or perhaps it’s because the midweek timing puts a crimp on people who have to work.

But while proximity may be an issue for some and scheduling for others, the content is compelling enough that if you’re anywhere within a couple hundred miles, it will truly be your loss if you don’t make time for this event. Looking over the agenda, here’s what I see:

* All of Thursday afternoon is devoted to various aspects of convective initiation. If you want to improve your targeting skills with the latest information, this day alone ought to be worth its weight in gold.

* Day two focuses largely on tornadogenesis, but includes other topics such as a photogrammetric analysis of the Elie, Manitoba, F5 tornado, and issues in severe weather warnings. The latter presentation will no doubt address the hotly contended use of the enhanced “tornado emergency” wording.

* Day three will…well, look, here’s the complete agenda. You can read it for yourself, and conclude, as I did, that this is going to be a standout event for storm chasers.

I’ve been waiting for a long time for another severe weather conference courtesy of Paul Sirvatka and the College of DuPage. I attended two of their symposiums some years ago, back when my storm chasing skills were still very formative, and each one was time well spent. This one looks to be the best yet. Poised between the end of a stormless autumn and the long, desperate, SDS-riddled winter months, it will provide a welcome immersion into the world of tornado research and operational forecasting that ought to bear dividends when the Gulf reopens for business again next spring.