SHOCK TO THE SYSTEM: WINTER WEATHER TO RETURN THIS WEEK AND IN THE WEEKS TO COME

…WINTER TO RETURN FULL THROTTLE WITH BELOW AVERAGE TO AVERAGE JANUARY TEMPERATURES OVER THE NEXT SEVERAL WEEKS…
…Several CHANCES of Significant East Coast Snowstorms are upcoming, first in the Jan 16-18 timeframe as discussed in the previous post…
After a very warm and rainy day today by January standards, a cold front will cross the area from west to east this evening and it will turn SHARPLY colder. Expect highs only in the mid 20’s to 30’s, and lows in the teens to 20’s across most of the northern mid-Atlantic from northern VA into northern PA, and east to the coast for the remainder of the week, quite a change given how warm it’s been in these parts over the past 6-8 weeks. You can see the Arctic air invading the plains and mid west this morning. Although it won’t be as harsh, that air is headed toward us tonight (map courtesy of weather.com).
TempTWC.png
There will be a chance of light snow and snow showers coming Tuesday into Wednesday, with a clipper low which scoot to our north and redevelops east of Long Island and in the Gulf of Maine, which can bring a coating to an inch or two to selected locales. Those along the NE NJ coast into Long Island may see a bit more depending on how quickly that development to our northeast takes place (map below courtesy of Levi Cowan, Tropicaltidbits.com).
GFSclipper
That low which will then move to a position in the region of eastern most Canada, just southeast of the Davis strait. This low position will be of PARAMOUNT importance with regards to the Martin Luther King weekend storm possibilities.  This 50/50 low (named for its position around 50N latitude and 50W longitude), in conjunction with the strong Greenland block (aka the -NAO), will be the catalyst in slowing down the upper level flow upstream over the remainder of North America.
Euroens2.png
On the map above from the overnight European ensemble mean (courtesy of Ryan Maue at Weatherbell, LLC), which is for next Saturday evening, you can see the large area of low pressure in question south of Greenland, with blocking high pressure just to it’s north. These two features allow for greater chances of interaction of energy from the northern (or polar) and southern (or subtropical) branches of the jet stream. The setup shown above is a classic one for a major east coast snowstorms, as illustrated in the book Northeast Snowstorms by Kocin and Uccellini (and as an aside, anyone with an interest in big east coast snowstorms, I highly recommend reading through it). Namely, those features include, a +PNA or western ridge centered in the vicinity of Idaho/western Montana, an eastern trough centered over the Mississippi valley, a strong -NAO in the form of blocking high pressure stretching from Greenland to the west shore of Hudson bay, and the aforementioned 50/50 low. All of the ensemble means from the various model suites have these features, some stronger than others, but all in general agreement for this upcoming holiday weekend.
0z Canadian ensemble mean:
canens1
0z GEFS mean:
gfsens1
Now, the presence of these features INCREASES THE LIKELIHOOD of a major east coast winter storm during this time period, BUT IT IS NOT A GUARANTEE. Why? Because at a week out, the individual energies (or shortwaves) in the northern and southern jet stream cannot be accurately modeled on a consistent basis. As I always like to say, the kitchen is open and the menu is set, but what comes to the table is far from decided at this point in time.
shortwaves.png
You can see from the map above at 500mb (or upper atmosphere, about 5600m above sea level, courtesy of stormvistawxmodels.com) taken a few days before the holiday weekend,  there are at least 6 or 7 shortwaves that are seen scattered around the southern and western areas of North America, all of which could possibly contribute to storm formation a few days down the road. There is NO WAY that the models can figure out which ones will interact (or not interact) to produce (or not produce) a storm at this time interval – they are just not that good. They each have their own biases/issues; however, as we get closer in time, within 4-5 days, things will become more clear.
So, what can be said this far out is that there are increased chances of something big happening around the Martin Luther King holiday weekend, and confidence regarding the details of what will or will not happen will increase as we move forward. For those insistent on following each model run with bated breath, I suggest you compare the runs at 500mb first before looking at any surface maps, if at all, until at least Tuesday or Wednesday.
One thing I will say regarding the operational models – the European parallel, which will replace the operational model in the coming months, has been the most consistent in the last few days in showing a major east coast snowstorm. I’m watching this rather closely because the European guidance is far from perfect, but the best we have, and it’s operational model has been very inconsistent from run to run. One of the chief biases of the model in general is to hold back too much southern stream energy in the southwest US, which has huge implications given the strength of the southern/subtropical jet stream this year. I’m curious as to see if perhaps this bias has been diminished with the newer parallel, given this is a known problem. This storm (or lack thereof) should be a good test.
And one other thing – this is far from the last opportunity of significant snow along the eastern seaboard. Given the very active subtropical jet stream and the blocking and available cold over the next few weeks, there should be multiple chances, some of which will come to fruition, while others do not.
More as we get closer.
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