A composite synoptic climatology of Florida peninsular tornado outbreaks

Abstract Previous work by Hagemeyer and Matney (1994) identified Florida tornado outbreaks from 1950 through 1993. This work uses reanalysis data (NMC Gridpoint cd-rom Version, 1995) to create a synoptic climatology of 30 defined tornado outbreaks with an F2 or greater tornado. A superpose epoch analysis, similar to Businger (1985), of sea level pressure, height, wind and temperature at 850 mb, 700 mb, 500 mb, and 250 mb was constructed. These fields were produced in one day increments from three days before to the initial time of the outbreak (day -3 to day 0). Two additional fields for each of these composites were created: 1) monthly climatological anomalies of the specified parameter and 2) the application of a two sided Student's t-test to determine if the anomalies are significant at the 95 percent confidence level. When compared with independent analysis fields, a consistent pattern is evident during these tornado outbreaks.

Results at day -3 show a split flow along the Western U.S. coastline with a strong southern jet stream. The corresponding shortwave trough exists between California and Texas over the inter-mountain west. Farther west, a statistically significant wind maximum is located over the North Pacific close to 130 W and 40 N and slowly moves to the east in a zonal flow. By day -2, the area of enhanced wind moves through California into the west side of the mid and upper trough over the inter-mountain west. At day -1, the area of enhanced wind moves over the Rockies resulting in a significant increase in the statistically significant height anomalies over southwestern U.S. The area of significant wind anomalies increases in areal extent and covers the southern U.S. and central Gulf of Mexico. The mid and upper trough over the inter-mountain west deepens rapidly and becomes slightly negatively tilted as it continues moving east. A moist, southerly 850 mb flow develops and pools moisture over Florida. Patterns associated near tornado outbreak times on day 0 are characterized by a rapidly evolving surface low pressure area over the southeast Gulf coastal region corresponding to an intensifying low latitude trough over Louisiana and strong jet streak. Areas of statistically significant height and wind anomalies cover the eastern U.S., and a trailing area of moisture between 1000 and 666 mb, likely associated with a squall line, is located in the region of maximum positive vorticity advection. Interestingly, this scenario varies little in most F2 or greater Florida tornado outbreak cases, and this procedure may be helpful in studying tornado outbreak commonalities in other locations.