T639模式对新疆北部暖区强降雪过程的预报效果检验

Validations of T639 model forecast skill for severe snowfall events in the warm sector in northern Xinjiang

利用T639模式降水产品资料,对2009—2014年11月至次年3月新疆北部阿勒泰地区15次暖区强降雪过程中的预报效果进行了分析与检验。结果表明:T639模式对阿勒泰地区暴雪的预报性能好于大雪,其中12—24 h预报准确率最高,而60 h预报准确率随时效延长而降低,漏报率随时效延长无明显的变化规律,空报率在60 h时效内随时效延长而明显升高,且明显高于漏报率;相对于暖区强降雪发生频率较低的站,暖区强降雪发生频率较高的站其大(暴)雪预报准确率较高;T639模式在暖区强降雪预报中存在明显的系统性偏大,48 h预报时效内T639模式降水预报产品在该区暖区强降雪中具有一定的参考价值;T639模式降水产品对短波低槽型暖区强降雪的预报能力较差,而对低涡型暖区强降雪的预报能力较好;造成该模式降水产品在阿勒泰地区预报效果不同的重要原因是其对水汽通量散度和垂直速度的预报存在误差。

Using the precipitation products from T639 model, we have conducted an analysis and validation on the forecast skill for 15 se- vere snowfall events in the warm sector in the Altai region of northern Xinjiang between November the current year and March next year from 2009 to 2014. The results indicate that the prediction performance of T639 model to snowstorm events in Altai region is better than that to heavy snow. The forecast accuracy is the highest within forecast time length of 12-24 hours. For 60h forecast, the forecast accuracy reduce, the missing alarm does not present an obvious change, and the false alarm increases obviously with the extension of time length. Furthermore, the false alarm is obviously higher than the missing alarm. The forecast accuracy of heavy snow （snowstorm） at the automatic weather stations （AWSs） with large frequency of heavy snowfall in the warm sector is higher than that of at the AWSs with low frequency of heavy snowfall. The forecast of T639 model to severe snowfall in the warm sector presents significantly a large systematic bias. The precipitation forecast products from T639 model have a certain reference value on the severe snowfall in the warm sector in the Altai region within the time length of 48 hours. The precipitation products from T639 model can seldom forecast the shortwave low trough type severe snowfall in the warm sector, while they can often forecast the low vortex center type. Owing to a forecast error in water vapor flux divergence and vertical velocity, the pre- cipitation products from T639 model present a different forecast skill in the Altai region.