As I mentioned earlier this week, the pattern for the past week here in New York City had been such that the prevailing storm track had been to the south of the area. The city was on the northern fringe of last Saturday's storm that produced significant snow across southern NJ, southeast PA, DC, VA, MD and DE. A weaker storm Tuesday night into Wednesday produced 1" to 3" in NYC with again more snow to the south of the area. The more southern storm track was in response to a blocking cutoff low that was circulating across eastern Canada. The models indicated that for this storm, the cutoff low or cyclonic vortex would actually move slightly south and west or retrograde keeping the entire Northeast in a dry, northwest flow of air. The maps above indicate the cutoff low and how it deflected the storm out the east instead of allowing it to track the coast closer to NYC (and the 40/70 benchmark) keeping the snow away from the NYC metro area. When comparing the jetstream pattern to some of the other storms that did produce significant snow in the NYC region (such as the early March 2009 storm), there was no cutoff low to the north that kept the Northeast in a dry northwest flow of air and the long wave trough that formed in the east generated a more classic coastal N'oreaster-type storm. A strong west to east or northwest to southeast upper air flow can and will cut off precipitation and keep it from moving north if the flow is strong enough, the air is dry and if the cutoff low is forecast to remain nearly stationary, moves south or retrogrades. A deep low over eastern Canada will push the storm track to the south. This happened a year or so ago in January of 2009 and I remember a similar scenario occurring in 2006. A strong west to east jet can deflect hurricanes approaching the Northeast and it certainly can push Nor'easters off the coast and easterward out to sea. The amazing aspect of this storm is of course the huge snowfall totals that were not seen for decades in DC. The intense rising motion in response to divergence aloft, the huge amount of moisture that was drawn in from the Pacific, the cold high to the north set the stage for this epic snow event. The same area as well as the Northeast has another chance for snow this upcoming Wednesday, more on that in later posts.
George Wright is a Certified Consulting Meteorologist with Wright Weather Consulting, Inc. Our website is WrightWeather.com.
George Wright is a Certified Consulting Meteorologist with Wright Weather Consulting, Inc. Our website is WrightWeather.com.
