Thursday, February 25, 2016

What the heck happened this winter?

Will there be a snowstorm or two in the Mid Atlantic or Northeast in March? I think there's a decent chance. But even if there is, and someplace gets quite a few inches of snow....most will think it adds insult to injury....too little too late. But I definitely understand the motivation to throw hands,  Anyone who loves Northeast winters, surely didn't love the winter of 2015-2016.

For those who haven't given up on snowstorms; the mean trough looks best in the March 4-10 time period...but will we get a storm, and even more than that does anyone really care?  As I sit here and look at the calendar; I can see meteorological winter will be over in 5 days. But to be fair, the winter of 2015-2016 was a non-winter, but it was still interesting and had it's moments.  

Moments like the Mid Atlantic Blizzard that brought many record amounts of snow. New York City going below zero for the first time in 22 years. In fact for a few days the air overhead, was the coldest Northeast air mass in 60 years. But to be realistic, winter is rapidly running down, and is out of time..... In hindsight, I guess Punxsutawney Phil was a better meteorologist than I thought....Maybe I shouldn't have laughed at him.  

So what happened?

When I made my final 2015-2016 winter outlook.. I showed the factors that would lead to ridging on the East Coast for November and December....and then troughing for January, February, into March. Here are charts I snagged from Weatherbell...  looking back at the 500mb pattern you can see that is exactly what happened.

                                                                        Nov -Dec
                                                                      Jan, Feb into Mar

The Positive PNA without doubt made the West Coast ridge. But that ridge was just a little too far west. So we didn't get the proper phasing.

  EPO worked better for us last year-there was a lot more cold in that pattern.  If you look back at the winters of 2013-2014 and 2014-2015  the EPO was negative. Here is a chart that goes back to mid December that shows the EPO has been much more positive than negative this winter.  

The long wave flow has been stretched to the breaking point. We saw that with the last was going to hit the Northeast...but then physics took over and corrected the storm well to the west. We could have overcome the ridge too far west, if we would have had blocking high take position in eastern Canada. It's still hard for me to get my head around the idea that timing wouldn't even allow one Canadian high to setup in the proper positioning.  With no blocking no snowstorms of consequence.  The trough goes as far east as it can....but physics has to move it north at some point ...this has been the story all winter.

In-spite of it being a strong El Nino, we never really saw a intense Subtropical Jet that could sustain itself... tie this in with a messed up long wave pattern and we get short waves that work their way past the ridging in the west....As these are working their way east, they end up moving more north than east. The track heads for the eastern Great Lakes, were it encounters and merges with a piece of the displaced polar vortex..this makes it deepen a lot more.  This forces a kind of chain reaction.....where the next shortwave comes down the stream, it gets damped out, before we get the cold air in place....Then 5 days later we repeat the entire process.  So we end up with cutters. In-spite of all the cold air to our north, we get just enough cold air repression., that results in either a weak storm or no storm.

But in-spite of all of this, we could have had a very decent season, if the North Atlantic had cooperated. The real culprit for the way winter 2015-2016 turned out was the North Atlantic Oscillation (NAO).  Basically NAO is about the degree of blocking of the jet stream over the North Atlantic.  When it's in a negative phase we see high pressure setup around the vicinity of Greenland.  This slows down and blocks the west to east jet stream flow. This in turn buckles the jet over the eastern CONUS, which allows cold air to invade the Northeast and Mid Atlantic.  The majority of this winter has seen the NAO in a positive phase. The only time the NAO really turned negative was in Mid January. The month of February saw three events fall victim to the lack of a negative NAO.   If we had seen even a moderate amount of blocking during the December into March timeframe, this winter would have ended up much different.