Based on theMicap s charts, the EC objective analysis field and the T213 physical quantity field, the strong cold wave weather p rocess occurred in Aletai area from February 11 to 13, 2009 was analyzed and focused on causes of strong temperature dropp ing and rainfall during thisweather p rocess. The results indicated that the strong cold air coming from Nova Island and Taymyr accumulated over the west Siberia along the northeast and the north wind zone before the UralMountain ridge. Due to the cold air from northwest of UralMountain ridge attacking, the ridge went southeast and impeled the Siberia cold air going south on a large scale, which resulted in this strong cold wave over the area. Northern cold air and the warm and moist air from south branch trough converged over this area caused the strong rainfallwith the dynamic condition and the water vapor condition.

Based on the mean monthly, maximum and minimum temperature series, the temperature changing characteristics in
Urumqi airport in recent 50 years were analyzed in this paper. The results show that the mean annual temperature trends was 0.033
℃/a, and there were obvious warming trends in spring, autumn and winter, the temperature tendency rate was 0.0949℃/a in
winter, which was the largest. But the temperature in summer was dropping by the rate of 0.028℃/a. In recent 50 years, there
were cold- warm- cold- warm evolution processes in Urumqi airport. A long cold period was in 1950s which was obvious in four
seasons, a warm period was from 1961 to 1975, the second cold period was from 1976 to 1988, another warm period was from 1989
to 2000. 70% of anomalous cold years (seasons) were in 1950s and 41% anomalous warm years (seasons) were in 1990s. The mean
annual maximum and minimum temperatures presented obviously increasing trend, and the latter was much steadier. From the results
it is known that the minimum temperature would be more sensitive to monitor the intensity of greenhouse.From 1989 to 2000,abrupt
warming occurred mainly in nighttime.These facts would contribute to study the temperature change in Urumqi airport.