Cause Analysis and Prediction of Abnormal First Snow Date in Hubei
Based on the first snow date (FSD) data of Hubei from 1961/1962 to 2012/2013, we reveal the atmospheric circulation features in abnormal early/late FSD. For the late FSD years in Hubei Province, the circulation distribution of the sea surface temperature anomaly (SSTA), the height anomaly and low level wind field from November to February that year can be illustrated as follow: SSTA in Northwest Pacific and in the Southern Pacific Ocean to the east of New Zealand is abnormally higher, which is good for the weakening of Ural Mountains Ridge, and the weakening of Lake Baikal low pressure and Aleutian low. Meanwhile, East Asian trough is strengthened and Bengal Bay trough is weakened. The corresponding 500 hPa height field shows a “- + -” wave train distribution from north to south in Eurasia. In mainland China, the low level wind field is controlled by abnormal north winds. Otherwise, the FSD comes early. Typical circulation distribution in 2013/2014 agrees with the late FSD in Hubei. In addition, prediction model for FSD is established by using SSTA in the key areas, which accurately predicts the late FSD in 2013/2014 and gives a good reforecasting test with the accuracy getting to 75%. So, this is a new method for the prediction of FSD in Hubei.