32nd Conference on Broadcast Meteorology/31st Conference on Radar Meteorology/Fifth Conference on Coastal Atmospheric and Oceanic Prediction and Processes

Monday, 11 August 2003
Radar Observations of a Freezing Drizzle Case in Colorado
Kyoko Ikeda, NCAR, Boulder, CO; and R. M. Rasmussen
Poster PDF (682.5 kB)
On 4 March 2003 a strong synoptic low pressure system over southeastern Colorado and a southward-advancing Arctic cold front created a favorable condition for freezing drizzle over central Colorado. A warm, moist, southerly flow overran cold air associated with the Arctic front, leading to freezing drizzle by a collision-coalescence process with no evidence of melting snow. The precipitation associated with the system changed abruptly from freezing drizzle to snow as the cold air advanced. Measurements from a Doppler radar will be used in conjunction with the surface and upper-air measurements to document the freezing drizzle event. Radar reflectivity was weak (less than 0 dBZ) and uniform over central Colorado while the surface observations reported freezing drizzle. Upper-air soundings showed a classical vertical thermal structure confirming the observations. Cloud top temperatures from infrared satellite images also suggest the presence of freezing drizzle. As the cold front moved southeastward, the freezing drizzle signatures dissipated and the reflectivity structure became non-uniform with reflectivity values up to 30 dBZ.

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