is DT SECSY? (sexy)
It's 1:00 AM on Saturday November 17 .... and I am functioning on 6 hours of sleep. But instead of waiting until Saturday morning here I am posting comments and analysis of the 312 hour GFS ensemble. That is because right now DT is sexy.
And even beyond NOV 30 there is ANOTHER potential significant East coast winter storm threat December 5-7 with a very similar pattern. But before we get into this ... let me present again my winter storm terminology which is something I have been using for a couple of decades. Some of you may already be familiar with these acronyms
These acronyms refer to different types of winter storms based on the geographical impact. Most of these terms are pretty much self explanatory. Assuming that the 0z Saturday November 17 run of the GFS ensemble (GEFS) is correct- and given its close proximity to the European ensemble runs I believe it is---then the event that we are looking at on or around the 30th of NOV is likely to be a SECS event ( pronounced sex).
Hence the hashtag #isDTsecsy? (does DT/ wxrisk see a significant East Coast snowstorm threat in the near future?)
The term THE BIG DOG refers to a euphemism used by me and some other meteorologists that focus on significant snow storms over the eastern CONUS. (the term " WOOF" refers to models that seem to be saying possible SECS MECS HECS . To the best of my knowledge I started using the term first back in the early 1990s and now many meteorologists and weather hobbyists use or at least know of the term.
There are several features to look at here on this impressive looking 500mb map valid 11/30/18. First let's take a look at the Pacific Ocean. Notice there is a distinct in he Jet stream as it approaches West coast of North America. This is called a ' SPLIT FLOW PATTERN" . By that I mean to say that the jet stream to split into two distinct branches. The POLAR JET (PJ) which I have highlighted in blue and the SUBTROPICAL JET (STJ) t which I have highlighted in red.
The development of a split flow pattern is significant in tracking the possible development of an East coast winter storm. When the jet stream splits over the eastern Pacific... it becomes easier for them to merge or phase over the eastern CONUS. Of course there is no guarantee that the jet streams will merge or phase over the eastern conus. But if they don't split coming into the West Coast then the 2 jet streams cannot merge/ phase later on over the eastern conus. .
Looking in the southern jet stream (STJ) over the the Louisiana Arkansas Delta ...the thick black line represents a significant piece of energy in the southern jet stream known as a " shortwave". This shortwave obviously is going to generate a significant area of LOW pressure over the Gulf coast states on November 29 and 30th. (This is assuming again that the GEFS is accurate in its depiction of the pattern on November 30). Obviously having a significant area of LOW pressure in the southern jet stream is a major piece of the puzzle when it comes to getting the East Coast snowstorm.
Remember to get an East Coast snowstorm you have to have 1) a significant moisture source which is usually LOW pressure in the southern jet stream and 2) you have to have cold air coming in from the northern jet stream into the northeastern U.S..
If we take a look of southeastern Canada you will notice the thick black circle represents a "50/50 LOW" --- which is sometimes called a "Newfoundland LOW" . The 50/ 50 Low is Low pressure that often is quite large and intense at the surface and the Upper levels of the atmosphere at or near 50 degrees North latitude and 50 degrees West Longitude. In this case the GEFS shows a fairly pronounced 50/50 Low. Usually the GEFS does not show the 50/ 50 LOW in significant detail. So the fact that the model is depicting it at this point in time is fairly significant.
The depiction of this 50/50 LOW is critical for several reasons. First it is possible that even though you have LOW pressure in the southern jet stream ....that system might track up the spine of the Appalachian Mts or even into the Great Lakes. Obviously if you are snowstorm lover on the East Coast this is very bad and it would mean rain. So having a large ocean Low over southeastern Canada keeps the southern LOW staying to the south.
In addition the strong 50/50 LOW also keeps the cold HIGH pressure over eastern Canada locked in place. This means the cold air stays in place longer and you get better snow totals --or at least you don't change over to rain.
If we take a look at northeastern Canada the red circle shows a very strong blocking pattern over Greenland which is known in the weather business as the negative phase of the NAO (-NAO). This feature is currently a massive blocking pattern over Scandinavia and Iceland and it has been around for several months.
What is happening is that this feature is retrograding or moving backwards into Greenland. In doing so it is setting up the pattern the favors East coast winter storm development at the last few days of November time and into the first half of December 2018.
In addition the AO /arctic oscillation is also turning negative although these maps do not show that .
In summary based upon everything I am seeing on the 312 hour GFS ensemble ... there is no reason to think there' is not going be a significant East coast winter storm on or about November 30. I have placed the Telecnnections or the key jet stream pattern configuration markers on both the GFS ensemble and the European ensemble for November 30. And as I stated in the videos on the wxrisk/ youtube page ... this is an ideal textbook set a for an East coast snowstorm. All five Teleconnections are present on both of these models.
All that being said it is important that we do not get caught up in circular reasoning. By that I mean to say that we cannot assume that November 30 is a likely to to happen based upon the model depiction that we are seeing here. Be cause we do not know if the model depiction of the upper air pattern is going to be accurate. We still have a long way to go and it's possible that something may change between now and let's say November 28.
That being said ..IF after thanksgiving the upper air map is looking like this on the models then we really do have something to watch and enjoy if you like snowstorms on the East Coast.