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November Tornado Tendencies for the Continental United States


Last month I addressed the spatial probabilities for tornado formation for the month of October. Since November is only a few days away I have decided to show you some data I am playing with for November, as I continue to work on other projects and future articles.

Note: To fully appreciate the contents of this article, please review the following articles that are related either directly or tangentially to the subject matter:

One of the great things about using multiple workstations and monitors (utilizing the fantastic application Input Director devloped by Shane Richards) is the ability to display varying data types on separate monitors while writing an article! For example, I am currently glancing at tabular data for the month of November and notice that from the time frame the data is available (1950-2006), no F5 (ignoring the abhorrent EF scale) tornadoes were reported, however eighteen (18) F4 tornadoes occurred during the same time frame (with many coming from a single outbreak noted below). As an FYI the last tornado officially ranked as an F5 was the Elie, Manitoba tornado of June 22, 2007, with the last prior event occurring during the Oklahoma Tornado Outbreak beginning on May 3, 1999.

For fun I have plotted a spatial probability distribution of only F4 tornadoes for our time frame, and not surprisingly, the pattern falls strongly along the southeastern United States bordering the Gulf of Mexico. Previous research has shown me an oscillatory pattern of medium to strong tornado formation based upon seasonal migratory transitions associated with the availability of thermal and dynamic atmospheric processes (note graphic below), not to mention the integration and collaboration with teleconnective tendencies.

November F4 Tornado Distribution 1950-2006

A quick examination of the spatial probability of all tornado events for the same time frame exhibits a similar, yet slightly altered pattern of distribution (see graphic below).

November Tornado Distribution 1950-2006

Does a similar pattern to what i discussed here come to mind? I shall leave that to your investigative abilities.

November has historically proven to be a bull or bear market for tornado formation. I have been fortunate enough to enjoy very fruitful observation of “off-season” events over the years. Let’s begin by examining an overall frequency chart, and reviewing some things I have mentioned before.

November Tornado Frequency 1950-2006

As i have previously discussed, a brief examination shows an increasing frequency of events as the years progress. Historically this has been attributed to an increased “awareness” of severe weather potential, increased saturation of media coverage, and quite importantly the integration of the WSR-88D radar network utilized by the National Weather Service that replaced the aging WSR-74 and archaic WSR-54 systems.

According to this wikipedia entry “the first installation of a WSR-88D for use in everyday forecasts was in Sterling, Virginia on June 12, 1992. The last system was installed in North Webster, Indiana on August 30, 1997.” Glancing again at our November frequency chart above, one could glean a possible reason for the increase in events reported was due to the implementation of those systems. Similar to my previous discussions covering snowfall and tropical activity, our level of technologies for the detection and observation of any weather event are not nearly what is necessary for complete confidence in the analysis of historic tendencies. However, our country is certainly coming closer to a reasonable level of comfort, and is leading the way worldwide.

However there does appear to be a somewhat stronger emphasis for the month of November in intensity oscillations of overall occurrences does there not? Over the years I have attributed this apparent cycle to seasonal changes with the introduction of strong meridional flow and the production of intense waves of mid-latitude cyclones and the appearance of early season strong winter storms. However, many other factors do enter into the equation especially since I have noticed changes in seasonal transition over the last few years.

For grins and giggles, below are a few general statistics on November Tornadoes

  • Average F Scale rating: 1.09
  • Median F Scale rating: 1.00
  • Highest Fatalities
    • 1. Evansville, Indiana Tornado of November 6, 2005. 24 deaths, 238 injuries (F3)

          – NWS Preliminary Assessment with photos is available here
          – Wikipedia entry is available here

      2. Huntsville, Alabama Tornado of November 15, 1989. 21 deaths, 463 injuries (F4)

          – NWS synopsis of event is available here
          – Wikipedia entry is available here

      3. November 22, 1992 Tornado Outbreak. Multiple Events = 17+ deaths, 208+ injuries

          – Wikipedia entry of outbreak available here
         

I do not see the opportunity for tornado formation in our immediate future, however something does seem to be stirring down the line.

As always stay tuned to your favorite weather outlet, stay informed, and stay safe!

cheers,

–patrick

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