The relationship of cool season significant tornado events and buoy data in the western Gulf of Mexico

Although significant tornadoes (F2 or greater) across the Gulf Coast States are not uncommon during the cool season (October-February), forecasting these events can be quite challenging as the region is often affected by strong, fast moving baroclinic weather systems which fail to produce severe thunderstorms, including tornadoes. Most often, the primary ingredient differentiating the more active severe thunderstorm producing systems is the presence of rich Gulf moisture (i.e. surface dew points at or above 60 F). Though the Gulf of Mexico is in close proximity to the region, prior frontal passages and/or extended periods of offshore low level flow across the Gulf coast may impede the return of moisture ahead of some cool season weather systems. However, when Gulf moisture is able to move inland into the area from east Texas across the lower Mississippi Valley, the severe weather potential generally increases.

Currently, forecasters at the Storm Prediction Center and local NWS forecast offices are tasked with forecasting the possibility of severe thunderstorms out to 8 days in advance. This is complicated by the frequency of strong, progressive weather systems during the cool season, and the limited ability of numerical models to accurately forecast the return of higher Gulf moisture, especially beyond 2 days.

Since accurate forecasts of low level moisture are among the most difficult challenges associated with cool season severe thunderstorm forecasts, it is hoped a thorough examination of buoy data from the western Gulf of Mexico will aid in recognizing potential moisture increases ahead of these systems. This study will investigate relationships between significant tornado events and the existence of richer moisture over the western Gulf of Mexico during the cool season from 1993-2004. Hourly data from Gulf buoy 42002 (located at 25.17 N, 94.42 W) are examined, with an emphasis on surface dew point trends in the days prior to significant tornado occurrences. Gulf buoy 42002 was chosen for this study due to its location away from the shallower shelf waters, and because it is within common return flow patterns over the western Gulf of Mexico. Forty-five significant tornadoes (30 tornado days) over eastern Texas, Arkansas, Louisiana and Mississippi were gathered from October 1993 through February 2004 for use in this study.