Storm Observing: Choosing a Target Area
(reposted from Weather or Not [Roger’s weblog])
My target area is where I expect to begin the active intercept, plain and simple.
THE IDEAL: Forecast location of initiation of storms most likely to become photogenic and/or tornadic supercells.
THE REALITY (situationally dependent):
Situation: The above, if I can leave early enough and storms aren’t going to be racing along at Warp Six.
* Example: This strategy worked absolutely perfectly for Rich and me on the Stockton KS day (15 May 99). We made a fantastic storm initiation forecast that morning in GLD, saw no more data the rest of the day, ate a leisurely late (all you can eat!) lunch in Colby, then sat on a hilltop NW of Hays for an hour or so watching Tcu in the narrow corridor between advancing dryline and retreating outflow boundary. The eventual Stockton supercell went up just to our NW, with roads favorably aligned/positioned for observing, and intercept and viewing of the tornadic phase was ridiculously simple. This is extraordinarily rare, the ultimate dream of every chaser, and for that, the #1 ranked chase day of my ~20 years doing it.
* Situation: If storms will be fast moving and/or there are unfavorable geographic barriers like a river valley or lack of roads, the target is about an hour downshear from where we expect CI, based on forecast storm speed and direction.
Example: This strategy worked reasonably well for us 19 Apr 96 in IL. No data seen after initial forecast that morning in KC. We targeted the area E of the dryline bulge in west-central IL. Initiation was expected in MO, but we wanted to be E of the MS River in order that our options would not be limited by the river itself, and that a fast moving storm would have room to mature into early tornadic potential before it got to us and active intercept would begin. We were within about 400 yards of the start of the first tornado near Winchester IL. Only unfavorable roads, and a long train of cars behind a puttering yokel who drove 25 mph in a 55 mph zone for 12 miles, kept us from being in optimal position for the next couple of tornadoes we saw.
* Situation: If initiation will occur before we can get there, or has already happened, the target is just downshear and slightly to the right (usually E) of where I expect a photogenic and/or tornadic supercell to be by the time we can reach the area of interest.
Example: This strategy worked fairly well on 10 Jun 4, where Elke and I headed W from LBF immediately upon noting initiation in VIS imagery near Julesburg, with the storm headed toward a narrow but intensely favorable area of combined buoyancy and shear. Secondary target was easily attainable farther SE once we would be done with this area. We knew the storm would head into the Sandhills, and that we had to zip there fast on favorably positioned I-80. The result: 38 minute tornado observed. Then we let the storm go off into the almost roadless Sandhills, still marginally tornadic but a messy HP that we didn’t mind leaving at that point. The secondary target (dryline bulge into SW Nebraska and NW Kansas) gave us two more supercells but nothing tornadic.
* Situation: First storm craps out, doesn’t develop, or becomes very difficult to intercept because of roads and terrain. Reposition to a preconceived secondary target.
Example: 10 Jun 4, as above. Also was 25 May 97, when Steve Corfidi and I were time constrained by being on a day shift at work. No data was seen while in the field on either day. The major area of potential S of ICT was unreachable…too far! Our initial target, therefore, was the supercell SW of Norman near Middleburg, which was ongoing by the time we could leave. Secondary target was the “tail end” area farther SW around Duncan or Elmore City, in case our storm went bad. We simply could not get there in time for the tornado on old Highway 9, and instead saw the storm wrap up into a horrendous HP bears cage — tornadic but terrible for observing. We briefly watched two more rotating storms in close proximity to the SW — one near Lindsay that was scrawny and didn’t look to have much future, the other near Purdy that had a rotating wall cloud and brief stubby funnels but was headed into unfavorable road network. On supercell number four, we found the treasure — friendly Okie farmers who gave us cold Pepsis in their west-facing garage as we casually chatted and watched the Duncan tornado in the distant WSW. It was an ad-hoc, rural Oklahoma, tornado-watching party. Quote of the day: “Yeah, we see them twisters all the time. There was one a few years ago over yonder across them fields, tore them fences all to hell.” We later observed the infamous “UFO funnel” near Loco. Photos and summary here.
* Situation: Multiple potential targets, pick the best for viewing based on meteorology, roads and terrain.
Example: 16 May 91, Haysville/Andover II storm. Another day with no data seen after making the forecast. I analyzed maps at DDC and picked a target area along the KS border N of END, near the forecast location of the dryline/outflow triple point. [Rich, who wasn’t with me that day, was even more precise on the phone: Anthony KS, earning him the temporary title of “Supercell Prophet.”] After a brief survey of damage in Laverne from the previous day’s event (which I missed!), headed E to END. All along the way I could scan for robust CI from within the crystal clear dry slot, while watching a magnificent arc of Cu and Tcu located W-N-SE. Saw the well positioned storm go up to our NNW while near Medford, intercepted it near Conway Springs, and observed five tornadoes along with 5 inch diameter hail. Other possibilities were farther E along the outflow boundary near TUL (distance, trees) and along the bent back occluded front ENE of DDC (closest target but concerns about both weak instability and too many storms). Tornadic storms did fire in both alternate areas, but we hit the jackpot that day.
Those are examples of how it can and should work. Other situations dictate different target determinations; but for me those have been the most common modes of targeting. Naturally, there have been many, many more days where it didn’t work out as well as hoped, including most chase days last year. The days I didn’t get on the “best” storm were those where the ideal target was too far away given personal circumstances, or where I didn’t make the best target choice (i.e., 11 Jun 4 in IA, too far E along the warm front). Such is life. Live and learn!
Thanks to Bob Henson for generating discussion offline about this topic.
Roger Edwards