That's when the freezing level is far enough down in altitude where we can get so much snow.
当冰点高度足够低时,就会产生降雪。
BBC 听力 2016年4月合集
The major gathering of oil exporting nations has failed to secure an agreement on freezing production levels to drive up prices.
为助推油价回升,主要石油输出国举行会议,但最终未能就冻产达成协议。
英语百科
Freezing level
The freezing level, or 0°C (zero-degree) isotherm, represents the altitude in which the temperature is at 0°C (the freezing point of water) in a free atmosphere (i.e. allowing reflection of the sun by snow, etc.). Any given measure is valid for only a short period of time, often less than a day.