Winter to return after Spring Break

While the CPC is showing mild weather across the U.S. through 3/22, I expect this to be changed radically in the coming days. Both the GFS ensembles and the ECMWF show the return of a wintry pattern to the Great Lakes and Northeast. As mentioned yesterday, some of the ensembles had been hinting at a cold clipper breaking down the flat ridge over the midsection of the country. Today, nearly all of the GFS ensembles and the European suggest that winter is not over yet.

There is very strong ensemble agreement for a clipper to cut across the Great Lakes in the Thursday/Friday time period of next week. This initial clipper will lead a series of cold highs across the same area through the early part of the third full week of March. What is remarkable is the similarity of the ensembles through 240 hours. I can’t ever remember seeing so little variability from this far out, which increases confidence in the pattern change.

Since the southern stream appears virtually shut-off during this time period due to strong ridging over the Southwest, any potential winter storm will develop as a Miller B storm where the energy will come from the northern stream in the form of a clipper that rounds the bottom of the trough. I think the most likely scenario for major winter storm development for the Northeast will be when the base of the trough swings through the Great Lakes sometime around the 3/20-3/24 time period. This will increase the amplitude of the wave-train and possibly allow one of the northern stream short waves to slow down and deepen. The key will be for one of these clippers to explosively deepen near Newfoundland and slow things down.

The Bottom Line:
The consistency of the ensembles breaks down past 240 hours (see the difference at 288 hrs), so there is the possibility of a “dry” cold outbreak similar to early February, but the consistency of the GFS and ensembles and the agreement with the ECMWF suggest winter is not yet over for the Midwest and Northeast.

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