Thursday, December 18, 2014

Where We Have Been and Where We Are Going

     So, lets cut right to the chase shall we. The question that is on many minds, where is the snow? Well, its in Maine, head north !  Before I can get into that lets discuss how we have gotten to where we are now this season. First there was a drought, but we have certainly have taken care of that for the most part during the past 60 days or so with well above normal precipitation observed for most locations in Southern New England. In the temperature department , November featured below average temperatures for most the area, now into December we are seeing slightly above avg temps. I thought it would be a bit cooler, but it has not. The Climate Prediction Center has been right on though for the most part. We will see how the rest of the month shapes up, but I can tell you there are very good signals of cooler air heading into January. It has been a fairly "normal" period of weather in recent months, no real extremes occurred other than some daily precipitation records. The map below shows the daily high and low temps for Hartford CT since October. Nothing really jumps out in either direction and only one extreme was reached, and that was a record high of 67° on November 12. 

Click on images for larger views

November did feature a few snow "events" though. Four for some communities ! That is quite rare, and actually many folks across SNE saw more snow in November than what they have received thus far in December. Thankfully no snow was observed in October this season which is a good thing as many of you know I have a strong belief that seeing snow during October is a  curse for snowfall ahead. So as we sit here today on December 18, just a week away from Christmas and most SNE locations are right around either side of avg snowfall to date thus far, though I feel we need to get a decent storm in here before the month comes to a close if you really want that "big" winter. Why? A look back in time to past seasons shows that this month is critical towards the big one. Using Boston for December, the years between 1996 and 2003 there was not one December that featured more than a total of 10" for the month. Only ONE of those seasons finished above normal. 1981-1992, same thing , not one December even hit 10" of snow and only 2 of those seasons even finished above avg which is around 42" . History says we really need to get one before December wraps up. 

So that's a little write up on where we have been and now to touch on where we may be heading. We know for the past two months it has been quite active but we have lacked cold high pressure along the Canada/New England border that is necessary to lock in cold air as storms approach. You see, when coastal storms approach, they come with mild air from the tropics or sub tropics and from the moist Atlantic Ocean, its what feeds storms into cyclogenesis and when you lack a dome of *established* cold air, it is very hard to get a true SNE Snowstorm in the month of December. There is another wildcard this season so far too and that is well above avg SST's (sea surface temperatures) off the Mid-Atlantic coast right up into the Gulf of Maine. What this means is any onshore wind flow (which usually occurs as a storm is approaching and during it for a time till winds shift) brings milder air into coastal locations. Inland areas are less effected but still to an extent depending on the intensity of the winds and direction. We really need to get these ocean temps down before we can get too excited along the coast for "snowstorms" .
Here is a map showing those current SST anomalies. You can clearly see they are running well above avg.

The Pattern ahead looks to remain very active, but as discussed previously , its been mild for December for many so far, how do we change that and where do forecasters look for that big "pattern change" ? Well, there are a few places, 1st off models, but most of all teleconnections and more specifically The Arctic Oscillation (AO) and the North American Oscillation (NAO) . What you look for in a big pattern change is sharp changes in these phases, the graphs below show that we are heading in that direction and in a favorable direction with AO projected to head down as well as the NAO which will provide for some much needed Greenland Blocking . 

There is the hope for the snowlovers right there as we move into January, so lets see how this pans outs. Models are suggesting a huge dip in the jet stream in the days ahead but they are not in total agreement as to where the eastern edge of the dip/trough sets up and its eventual tilt which is very important along the East Coast. The Image below is a projection from the GFS model showing the 500mb height anomalies for Christmas Eve time frame. Notice the big ridging off to the northeast producing a high block, keeping storminess over the Northeast US. It's tilt is not quite ideal but could do the trick. Think of the red, yellow & orange (& green here) as a brick wall. We just have to watch trends, it already has shifted a bit in recent days. 

There are the signals that should bring us into a more conducive Winter pattern. Very anomalous. Often anomalous projections lead to anomalous results ! 
The forecast ahead is difficult past some ocean effect moisture on Sat & Sunday but we will likely track a wave of low pressure up the coast Saturday into Tuesday that looks to bring some rain and snow/mix for favored locations to some areas most likely Tuesday before the potential of a very large storm system that likely will move off to our west keeping us in the warm sector and mostly rain and wind on Christmas Eve into early Christmas morning as Santa is making his deliveries which the big fella will have a hard time doing over the Northeast, but something tells me he will get er done. Is there a chance the storm trends colder? Outside shot, yes. We would need to redevelop a new coastal low for that to occur, while that may happen, the negative tilt to the jet would still bring in marine air in regardless. This storm does bring BIG changes in its wake though and don't be surprised to see a few festive snow flakes flying around on Christmas Day ! Now that would be nice. Maps below are for Christmas Eve. Someone is going to have to get Santa a windbreaker for his flight into the Northeast   

A reminder: The first official full day of Winter occurs on Monday December 22 and will end on Thursday March 19th. The Southern New England Weather forecast remains calling for below normal temperatures and snowfall near either side of average. Thank you for reading.   ~Anthony