Cold air funnels are favored near the center of cold-core closed midlevel lows.  This upper air map from May 18, 2006 shows an environment which led to this cold air funnel.  Notice the closed isoheights (black solid lines) over the lower great lakes, and the closed rotation in this area.  Also, the coldest temperatures (-28 degrees C, in dashed red) are co-located with the upper low.  The cold air funnels developed in the immediate vicinity of this core of cold air aloft.