Fig. 1: 12Z ECM 240-hr SLPA forecast reveals a southward plunging arctic front into the North-central U.S.
Discussion: The 12Z ECM indicates a large area of stratospheric warming shifts from Eurasia/Siberia across Alaska and into the U.S. late in the 10-day forecast. ECM is the first model to identify and deliver an arctic air mass to the North-central U.S. on day-10 (Fig. 1). The air mass is cross-polar but from an area in north/northwest Eurasia which is not unusually cold. Nevertheless, 12Z ECM projects temperatures 20-30F below normal into North Dakota in 10 days. The air mass trajectory is south0-southeastward. U.S. snow cover ahead of this event indicates 2-6 in. of snow across the Dakotas eastward to New England but not the southern Great Lakes or Ohio Valley (Fig. 2). The air mass is likely to have the greatest chance of southward penetration without moderation in the Great Plains toward Texas.
Fig. 2: 12Z ECM 240-hr snow cover forecast.