Wintertime Characteristics of Supercooled Liquid Water over the Grand Mesa of Western Colorado

Abstract

Wintertime supercooled liquid water (SLW) observations have been made over the Grand Mesa of Colorado from early 1983 through March 1985. Measurements were made with aircraft, microwave radiometers, and tower-mounted icing meters. Results of analyses of this large data set are summarized. It was found that SLW was produced largely when 70 kPa winds measured by Grand Junction rawinsondes were southwesterly and in excess of 10 m s^-1, and when the air approaching the Mesa at the same level was near saturation. Aircraft measurements indicated that SLW was primarily limited to above, and just upwind of the Mesa, except during some periods of prolonged synoptic-scale cloudiness. Highest SLW contents were generally recorded at the lowest levels sanpled. Over a five month period, micrcowave radiometers recorded SLW over the Mesa 29% of the time, in a total of 115 episodes. Hourly averages of vertically integrated SLW were as high as 1.07 mm, but the median was 0.08 mm. Half of all episodes lasted less than 3 h, while 12% lasted longer than 12 h. Eighty percent of the hours with positive average SLW were contained within episodes of 5 h duration or longer. The SLW flux, if converted to snowfall over a 10 km distance, would be approximately half the natural precipitation.