Mobile Sounding Observations of Lake-Effect Snowbands in Western and Central New York

Abstract

Measurements of the thermodynamic environments in the vicinity of lake-effect snowbands were obtained during the winter of 1987/88, using portable radiosonde equipment. During the experimental period, a total of 17 soundings were launched on ten field days. These soundings covered both single- and multiple-band events under a variety of conditions, including heavy snowfall rates of up to 13 cm h?1. As expected, the soundings showed moist-adiabatic conditions within the cloud layer with a stable layer at cloud-top level. In an intense single-band case, soundings showed a parcel buoyancy of 2.5°C within the hand at 2 km above ground level (AGL). Furthermore, the base of the inversion within the band was displaced some 0.6 km above that of the surrounding environment. Sensible heating of the low-level air as it flowed over the warm lake is postulated to be the primary source of this temperature surplus. Strong surface convergence and parcel buoyancy within the band apparently combined to produce the overshooting cloud top and the observed heavy snowfall rate. Multiple- band soundings showed little difference between the thermodynamic environments within and adjacent to the bands. Analysis of the soundings indicates that the depth of the mixed layer may be of greater importance than the strength of instability in determining the intensity of lake-effect precipitation.