Expected Evolving Snow Cover Is The Cold Weather Key for December

Climate Impact Company Midday Update

Issued: Friday November 21, 2025

Highlight: The expected evolving snow cover is the cold weather key for December.

Fig. 1: The 12Z GFS day-13 snow depth forecast.

Fig. 2-3: The 12Z GFS U.S. medium range temperature anomaly forecast.

Discussion: The chart to remember, heading into the weekend, is the 12Z GFS snow depth forecast for day-13 (Dec 3^rd). Unlike the over-forecasting of snow tendency of the GFS (and ECM), snow depth forecasts are conservative and (more) reliable. On Dec. 3^rd the 12Z GFS projects substantial snow cover pushing southward through the Great Plains and across New England (Fig. 1). The snow cover biases the local climate cold and increases the risk of cold reaching Texas. The 12Z GFS develops the cold over the northwestern Great Plains accompanied by significant snow (Fig. 2). The snow extends farther south forcing very cold temperatures across the northern Great Plains and a sharp cold boundary reaching Northern Texas (Fig. 3). South of snow cover, particularly in the 11-15-day period, the Southeast is very warm.

Table 1: The midday 12Z GFS U.S. gas population weight HDD projections into early December.