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A Dual-Doppler Radar Study of an OK PRE-STORM Heat Burst Event

Ben C. BernsteinDepartment of Atmospheric Science, Colorado State University, Fort Collins, Colorado

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Richard H. JohnsonDepartment of Atmospheric Science, Colorado State University, Fort Collins, Colorado

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Abstract

Doppler and conventional radar, surface mesonetwork, and sounding data are used to investigate heat bursts that accompanied a mesoscale convective system (MCS) that traversed the OK PRE-STORM (Oklahoma–Kansas Preliminary Regional Experiment for STORM-Central) mesonetwork on 23–24 June 1985. The MCS formed along a dryline in western Kansas. As the system matured, an area of stratiform precipitation developed behind a line of convective towers that moved toward the southeast. Southwesterly flow at upper levels caused the stratiform precipitation to extend northeastward, allowing it to become isolated from the convective line. A broad surface mesohigh was observed beneath the core of the stratiform region. This feature was flanked by sharp pressure gradients and mesoscale low pressure areas to the northwest, north, and northeast. It was within these mesolows that the heat bursts occurred.

Time series of surface mesonetwork data show that heat bursts were characterized by sudden dramatic rises in temperature and falls in dewpoint. Strong, gusty winds and modest falls in θe also accompanied the bursts. Dual-Doppler radar data reveal an anvil-like structure in the precipitation field above a surface mesonet station that received heat bursts. Light stratiform precipitation was falling just to the west of the station, and a strong reflectivity gradient existed at the edge of the precipitation. Strong mesoscale inflow entered the anvil cloud region at midlevels, descended along the base of the anvil, and reached the surface in the area of the strong reflectivity gradient. Downdrafts exceeding 4 m s−1 were observed there. It is proposed that this lateral inflow jet warmed dry adiabatically as it descended, deformed a surface stable layer, and caused dramatic warming and drying at the surface.

Abstract

Doppler and conventional radar, surface mesonetwork, and sounding data are used to investigate heat bursts that accompanied a mesoscale convective system (MCS) that traversed the OK PRE-STORM (Oklahoma–Kansas Preliminary Regional Experiment for STORM-Central) mesonetwork on 23–24 June 1985. The MCS formed along a dryline in western Kansas. As the system matured, an area of stratiform precipitation developed behind a line of convective towers that moved toward the southeast. Southwesterly flow at upper levels caused the stratiform precipitation to extend northeastward, allowing it to become isolated from the convective line. A broad surface mesohigh was observed beneath the core of the stratiform region. This feature was flanked by sharp pressure gradients and mesoscale low pressure areas to the northwest, north, and northeast. It was within these mesolows that the heat bursts occurred.

Time series of surface mesonetwork data show that heat bursts were characterized by sudden dramatic rises in temperature and falls in dewpoint. Strong, gusty winds and modest falls in θe also accompanied the bursts. Dual-Doppler radar data reveal an anvil-like structure in the precipitation field above a surface mesonet station that received heat bursts. Light stratiform precipitation was falling just to the west of the station, and a strong reflectivity gradient existed at the edge of the precipitation. Strong mesoscale inflow entered the anvil cloud region at midlevels, descended along the base of the anvil, and reached the surface in the area of the strong reflectivity gradient. Downdrafts exceeding 4 m s−1 were observed there. It is proposed that this lateral inflow jet warmed dry adiabatically as it descended, deformed a surface stable layer, and caused dramatic warming and drying at the surface.

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