On the evening of 29 October 2003, a light mist changed to light rain and snow. As temperatures fell, the moisture condensed, creating an icy wonderland.

Top photo: Joan Fisher, NCAR/SCD
Other photos: Brian Bevirt, NCAR/SCD

48 hours of fire and ice

Dry, high winds that fanned a 5,000-acre forest fire in the mountains northeast of Boulder (see last week's "Fire on the Mountain") were doused by a freezing rain that began the evening of 29 October 2003. Ice coated trees, grass, car windshields, and sidewalks, creating a beautifully hazardous situation that lasted through the next day.

Icing conditions can vary from a light accumulation of rime to a severe accumulation of clear ice made up of supercooled large drops.

Diagnosing and forecasting icing conditions remain a challenge as these are highly dependent upon mesoscale or cloud-scale processes that are often difficult to measure or predict by conventional observation tools. Subtle changes in these processes can significantly alter icing parameters such as cloud liquid water content, temperature, and droplet size which, in turn, can change the resulting icing conditions. Icing, of course, is a significant hazard to aviation

The Penn State/NCAR Mesoscale Model (MM5) and the Weather Research and Forecast Model (WRF) models, run by NCAR researchers on supercomputers supported by SCD, are being used to more accurately forecast cloud liquid, freezing drizzle and rain.

Photos, left: NCAR staff in Boulder regularly experience high winds, rain and show showers, rainbow and cloud formations — and this week, the remarkably complex and beautiful results of freezing rain. These images capture the diversity of ways in which physical structures of plants (needles, stalks, stems) interfaced with a slow moving, cold, damp air mass. The resulting interaction produced these spectacular ice and ice crystal formations.