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Characteristics of East-Central Florida Tornado Environments

Bartlett C. HagemeyerNational Weather Service Office, Melbourne, Florida

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Gary K. SchmockerNational Weather Service Office, Melbourne, Florida

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Abstract

Climatological analyses indicate that strong morning tornadoes in the dry season, and weak afternoon tornadoes in the wet season, are significant forecast problems in east-central Florida. To address this issue, an analysis of upper-air soundings for Tampa Bay, West Palm Beach, and Cape Canaveral, Florida, released within ±2 hours of tornado touchdowns in the County Warning Area (CWA) of future National Weather Service (NWS) Weather Forecast Office (WFO), Melbourne, Florida, was completed. Mean dry- and wet-season tornado-proximity soundings to 200 mb were produced, and selected mean diagnostic parameters and variance statistics computed.

Both dry- and wet-season tornado environments were associated with deep moist layers overlain by dry air, but no capping inversions. Dry-season cases were characterized by lower-tropospheric ow values well above normal, very low Convective Available Potential Energy (CAPE) and Bulk Richardson Number (BRN), strong speed and directional shear at low levels, a strong midlevel dry intrusion, and a maximum wind at 200 mb. The thermodynamic environment of the wet-season cases under westerly flow was close to mean seasonal values, but U increased steadily above 650 mb to a mean westerly maximum wind at 275 mb. These middle and upper-level winds, greatly exceeding mean seasonal values, allow thunderstorms developing along low-level convergent boundaries to be organized and sustained by the production of strong, persistent, tilted updrafts and continued low-level inflow of high ow air.

Abstract

Climatological analyses indicate that strong morning tornadoes in the dry season, and weak afternoon tornadoes in the wet season, are significant forecast problems in east-central Florida. To address this issue, an analysis of upper-air soundings for Tampa Bay, West Palm Beach, and Cape Canaveral, Florida, released within ±2 hours of tornado touchdowns in the County Warning Area (CWA) of future National Weather Service (NWS) Weather Forecast Office (WFO), Melbourne, Florida, was completed. Mean dry- and wet-season tornado-proximity soundings to 200 mb were produced, and selected mean diagnostic parameters and variance statistics computed.

Both dry- and wet-season tornado environments were associated with deep moist layers overlain by dry air, but no capping inversions. Dry-season cases were characterized by lower-tropospheric ow values well above normal, very low Convective Available Potential Energy (CAPE) and Bulk Richardson Number (BRN), strong speed and directional shear at low levels, a strong midlevel dry intrusion, and a maximum wind at 200 mb. The thermodynamic environment of the wet-season cases under westerly flow was close to mean seasonal values, but U increased steadily above 650 mb to a mean westerly maximum wind at 275 mb. These middle and upper-level winds, greatly exceeding mean seasonal values, allow thunderstorms developing along low-level convergent boundaries to be organized and sustained by the production of strong, persistent, tilted updrafts and continued low-level inflow of high ow air.

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