1.  Longitude vs. Month

One can see that during the warm season there is not much longitudinal variation in when tornadoes occur.  On the whole there tends to be more tornadoes in the western half of the domain (i.e., from Mississippi westward).

2.  Longitude vs. Hour

                                                    WHOLE YEAR                                                                                    COOL SEASON (NOV-MAR)

Note that when all >=F2 tornadoes are plotted, there is a strong diurnal signal, with a sharp increase in the number of tornadoes reported between 1800 and 0600 UTC.  If only cool season tornadoes are examined, the diurnal signal is damped, especially in the eastern half of the domain (i.e., east of 85W, or the longitude bands which include the florida panhandle.  There is a signal of enhanced nocturnal tornado occurrence in the latitude band from approximately 86-90W, or roughly in Alabama and Mississippi.

3.  Longitude vs. Hour- Percentage

These plots illustrate the percentage of tornado reports which occurred in each hour interval for each longitude band (e.g., 0.3=30% means that 30% of the tornado reports in that 1-degree longitude band occurred at that time).

During the warm season, there is a sharp gradient between 1500 and 1800 UTC where there is a rapid increase in the percentage of tornado reports.  This is especially true in the eastern half of the domain, where 30% of warm season tornado reports occur between 2100 and 0000 UTC.  During the cool season, the diurnal signal is much more damped, and the gradient is much weaker.  The diurnal signal is strongest in the extreme western part of the domain, which encompasses Arkansas and Louisiana.  There is a shift in the peak time of occurrence from 0000 UTC (in the western part of the domain) to 1800 UTC (in the eastern half of the domain).  There is a nocturnal secondary peak between 0900 and 1200 UTC (e.g., early morning before sunrise) east of roughly 83W, or from the Florida peninsula eastward.  There is also a weak maximum in this range between 0300 and 0600 UTC (after sunset until midnight).

3.  Longitude vs. Hour - Ratio
 

These plots show the ratio of cool/warm season tornadoes to the total number of tornadoes which occurred, for each time interval in each longitude band.  For example, 0.7 means that 70% of the tornado reports in that 1-deg longitude band in that 3-h time interval occurred during the cool season.

Broadly speaking, cool-season tornado occurrence dominates the 0300-1800 UTC time frame, where upwards of 50% of all reports occur during the cool season, regardless of longitude.  However, within this preferred overnight-early morning time frame, there are longitudinal variations.  For example, in the eastern part of the domain, the strongest cool-season dominance signal is between 0300 and 0600 UTC, and this signal shifts later and later as one moves westward towards 86W (~ eastern Alabama), where the strongest cool-season preference is between1500 and 1800 UTC (early morning hours towards noontime).  Moving farther west, there is a broad strip between 87W and 89W (~western Alabama into Mississippi) where there is a strong preference for cool season tornadoes to occur, but there is not a diurnal preference.  That is, over 60% of all tornado reports (>=F2) between 0000 and 1800 UTC occur during the cool season.