Discrimination of Solid from Liquid Precipitation over Northern Eurasia Using Surface Atmospheric Conditions

Daily synoptic observations were examined to determine the critical air temperatures and dewpoints that separate solid versus liquid precipitation for the fall and spring seasons at 547 stations over northern Eurasia. The authors found that critical air temperatures are highly geographically dependent, ranging from -1.0 degrees to 2.5 degrees C, with the majority of stations over European Russia ranging from 0.5 degrees to 1.0 degrees C and those over south-central Siberia ranging from 1.5 degrees to 2.5 degrees C. The fall season has a 0.5 degrees-1.0 degrees C lower value than the spring season at 42% stations. Relative humidity, elevation, the station's air pressure, and climate regime were found to have varying degrees of influences on the distribution of critical air temperature, although the relationships are very complex and cannot be formulated into a simple rule that can be applied universally. Although the critical dewpoint temperatures have a spread of -1.5 degrees to 1.5 degrees C, 92% of stations have critical values of 0.5 degrees-1.0 degrees C. The critical dewpoint is less dependent on environmental factors and seasons. A combination of three critical dewpoints and three air temperatures is developed for each station for spring and fall separately that has improved snow event predictability when the dewpoint is in the range of -0.5 degrees-1.5 degrees C and has improved rainfall event predictability when the dewpoint is higher than or equal to 0 degrees C based on the statistics of all 537 stations. Results suggest that application of site-specific critical values of air temperature and dewpoint to discriminate between solid and liquid precipitation is needed to improve snow and hydrological modeling at local and regional scales.