Cut-off

As we head thru April, we continue to see the lower latitudes of the southern United States warm much faster than the higher latitudes of Canada. This disparity has noticeable effects on the jetstream. We start to see periods of increased wave number (an increase in troughs and ridges in the jetstream) and high-amplitude waves that lead to cut-off lows (large, cold vortices in the atmosphere that dive south, then persist over a given region for days).

See the above graphic, which shows the jetstream over North America. The jetstream transitions from semi-zonal (near west to east) with a split over the western Atlantic, to a larger-wave-number, high-amplitude, cut-off flow five days later.

These high-amplitude and cut-off storm systems are notorious for producing cold rain, with snow over the higher elevations. [UPDATE] WITH ENOUGH COLD AIR PRESENT, MAJOR APRIL SNOWSTORMS CAN OCCUR. THIS LOOKS TO BE THE CASE FOR THE NORTHEAST APRIL 15TH THRU APRIL 17TH.