The strongest cold wave weather occurred on Ap ril 19 to 20 of 2008 in Hexi Corridorwhich influenced by the strong cold air
moving southeastward from West Siberia. The circulation situation evolvement characteristc of thisweather eventwas analysed based on
Micap s data, six hours reanalysis data ( horizontal resolution 2. 5°×2. 5°) from NCEP /NCAR. The 300 hPa high - level jet stream,
500 hPa vorticity, temperature advection and vertical velocity, 700 hPa water vapor flux divergence from 08: 00 Ap ril 15 to 08: 00 Ap ril
20 (60 - 105°E, 35 - 60°N) were caculated. The results show that the onset of the cold wave was related to high - level jet moving
southeastward and strengthening gradually, and the positive vorticity area at 500 hPa was in accord with the frontal zone in front of
trough, which was benefit to the strongest cold airmoving southeastward. The low - levelwater vapor flux divergence distribution influenced precipitation obviously under the cold wave weather condition, rainfall occurred in the area of the minimum value ofwater vapor
flux divergence, and no rainfall but dustweather occurred in the area of the maximum value.