Cloud-Top Temperatures for Precipitating Winter Clouds

A study of precipitating clouds using remotely sensed brightness temperatures from the Geostationary Operational Environmental Satellite (GOES) 8/12 Imager was conducted during the second half of the winter of 2003 (February through March) and during the winter of 2004 (December through March). Data were collected using an acquisition algorithm to retrieve cloud-top temperatures above every surface station reporting precipitation throughout the contiguous United States (CONUS). Cloud top temperatures were determined using a 2 x 2 pixel box surrounding the station with pixel resolution at satellite subpoint of 2.3 km x 4.0 km. This method was chosen to alleviate parallax and navigational errors in satellite data. Data were included in the sample if the standard deviation of the surrounding 4 pixels were less than or equal to 1°C. The data were then separated into four categories based on the surface precipitation type (rain, snow, freezing rain, and snow) and graphed in a frequency distribution as a function of cloud-top temperature. Results of the study indicate that liquid precipitation exhibits a bimodal distribution with modes near -45°C and -14°C. Similar frequency distributions between the rain and freezing-rain graphs suggest that the only difference between these processes is the near-surface temperature profile. Snowfall reports tend to exhibit a Gaussian distribution that is skewed heavily towards higher temperatures with a pronounced mode at -16°C. A very sharp drop in the frequency distribution warmer than -12°C is indicative of the depletion of ice nuclei with progressively higher temperatures. Sleet reports were too few to draw any significant conclusions.