STORM TRACK: January 31, 1983 (Volume 6 Issue 2)

Many ST readers are familiar with the fact that I am frequently trying to improve forecasting techniques by applying what we learn chasing storms. Recently, I have acquired the capability to use an interactive computer to develop forecasting tools. One of these is the wind hodograph (this shows how the wind speed and direction varies up through the atmosphere), which is computed and plotted on a screen. It appears that the morning wind structure in the lowest 6,000 to 9,000 feet, combined with the "buoyant energy" available to a growing storm, may largely determine the type of storm that could occur on any given day.

To facilitate this research, it is necessary to classify storms, based largely upon the observation of chasers, according to a few easily observable qualities. This is the latest version of the classification scheme:

I. Outflow Dominates (Chasers curse and swear)

A. One rather short-lived storm, no regeneration along the gust front. Example- "air mass" storms of the SE U.S. in the summer.

B. Regeneration along the gust front well away from the original storm.

II. Rough Balance Between Inflow and Outflow (Multicell storms) Most type II storms are maintained by incorporating discrete updrafts from the flank or stone periphery.

A. Multicells undercut by outflow. Often have repeated generation of mesocyclones with wall clouds frequently undermined by outflow; not "cyclic." Gust fronts stay close to updrafts.

B. Steady squall line.

C. "Steady hook mode." Does this multicell storm even exist? This would have a persistent wall cloud or tornado, yet be a multicell.

D. Cyclic tornadogenesis. New wall clouds/tornadoes form rapidly as the gust front surges around and ahead of an ongoing tornado. Examples: May 28, 1980 Tulia, TX storm; May 17, 1981 Tecumseh, OK storm, and May 19, 1982 Pampa, TX storm. Perhaps a fairly common storm type.

III. Inflow Dominates (True supercells, chasers in ecstacy) These are maintained by continuous propagation of one strongly dominant, steady updraft. Little or (typically) no flanking line.

A. Weak rear flank downdraft, little or no gust front. Can produce tornadoes but does so with apparent difficulty. Example: Borger storm photographed by Al Moller, ST, Nov 82.

B. No discernible rear flank downdraft. Possibly can't produce tornadoes. Bluesteins "bell-shaped" storms probably fit here.

It must be pointed out that storms can and do evolve from one form to another. For example, the Pampa storm appeared to evolve from type II-D to III-A. I have been classifying storms mainly according to that character which is exhibited through most of the storm's life.

I have some guesses as to what combinations of wind structure and instability produce which type of storms. Oddly enough, type II-B (squall lines) can occur with just about any combination, so evidently some other factors must be involved. Since squall lines are very common over some parts of the country, it will be important to determine what additional factors play strong roles in determining their structure.

With the addition of more "cases," I hope to be able to tell if storm types truly are easily predictable, and I'll share the results with ST readers when they are available. Until then, I would appreciate input from the readers about the classification scheme and ways to improve it without complicating it.