Will there be a huge pattern change soon?

[Planetsnow]

From wxrisk

In looking at this overall pattern it is difficult to imagine a pattern with e such a severely negative NAO for such a prolonged period of time and yet not end up with a significant East Coast snowstorm. There is a considerable amount of research which shows that when the NAO is in a strongly negative phase... as it approaches zero or Neutral... the atmosphere appears to be favorably inclined for a significant low-pressure area to develop along the East Coast and if the conditions are right ...a major NE ( northeast) snowstorm can result.

However it may be the view of some that we may go to his entire negative NAO interval without seeing g a major snowstorm on East Coast and that could cause a lot of frustration whining and nashing of teeth. But first let me make the following argument before we go off the deep regarding how all these signs and synoptic indicators meteorologist use seemed to have failed again.

We just finish experiencing an extremely deep Noreaster which bought heavy snow high winds to far eastern New England and especially Maine and Nova Scotia with the MSLP dropping into the Upper 950s and L 960s. Of course it did not bring the major snowstorm to the I-95 cities or even to Boston for that matter... so it may appear to the casual observer that we are going through this prolonged interval of strongly negative NAO without saying any sort of snowstorm activity on the East Coast.

But that's not really the way the atmosphere works. In the overall large scale of things... looking from the Western Hemisphere for even perhaps North America scale ... the deep Low from a couple days ago does count as a severe noreaster which did form with this intense negative NAO in place along with a displaced Polar Vortex and a strong 50-50 low. The indicators DID VERIFY and in fact we have seen a major snowstorm --- the point is that just because it did not snow at your particular location does not mean there was NO massive Low . Such a perspective is really based on a MBY -- my back yead -- mentality.

Suppose the Low-pressure area from 2 days ago had developed just off the coast and we could have all watched this powerful system just missing the I-95 areas and bringing heavy snow high winds to say eastern Long Island and far southeastern Massachusetts / the Cape Cod area. Surely such an event would have counted as a severe noreaster that just missed the I-95 cities. This time around the event was further out into the Atlantic but it still counts towards verification of these synoptic level indicators.

Now however we have a different problem regarding this weekend. It appears again at all the pieces are in place for the development of a major snowstorm for the I-95 corridor-- from central Virginia to Boston Massachusetts. We have a severely negative NAO... A displaced PV... a 50-50 low... some phasing going on between the PJ (polar Jet) and STJ (subtropical jet) ... a trough axis which develops a severe negative tilt... and the cold air from 850 to the ground appears to be more than adequate to support and all snow precipitation type event.

what could possibly go wrong? Glad you asked that question. We have three problems with this weekend potential event.

First the velocities within the polar and subtropical Jet are very strong and the phasing event which occurs this weekend is likely to generate the surface low pressure as well as the 850 Low that is fairly far East of the position with relationship to the trough Axis. Of course the real forecast question is where does the trough Axis set up in relationship to the East Coast? If the trough Axis were to set up far enough to the West then a negatively tilted phase that occurred between the PJ and STJ would in fact develop the surface low close enough to the coast so large areas of them Atlantic would see a significant snowfall.

But most of the model data does not show that happening-- the trough Axis is a bit too far to the East when the phasing occurs. This results in the surface low pressure and 850 low developing fairly far to the East and not leaving a whole lot of room for a margin of error.

The next problem is that the 50/50 low is not really a in position and it begins to slide out to the East as this next system moves in over the weekend. This again supports an overall eastward surface and 850 low development... and there is a strong case the made that if we had a 50-50 low in the classic position we would see a major snowstorm on East Coast is the weekend.

The third problem is that their just too many darn short waves in the overall pattern as the polar and subtropical jets phase. A look at the 12z op ETA shows this problem nicely... and the 700 MB RH and Surface map reflects the numerous shortwave features quite nicely. There are simply too many surface low pressure areas along the middle Atlantic Coast this weekend to see a system consolidate... and by the time we do see a significant surface feature coalesce into 1 main Low the whole system is too far off the coast for a major or significant snowstorm.

I am hoping that this sort of set up for this weekend is going to be saved by some meteorologist and weather hobbyists as a classic example of the nuances one must focus on in forecasting the threat of significant East Coast snowstorms.

It appears that we had every possible feature in place and yet some other new wrinkle has developed which has to be taken into consideration with each new scenario. This is happen a lot this winter where we appear to be close to saying a major event across all regions and yet something always seems to come up. The fact of the matter is the last two or three winters have spoiled many of us into thinking that significant East Coast snowstorms are common occurrences. They are not and things always go wrong. Sometimes it's the location of the secondary redevelopment. Sometimes it's the low-level cold air. The point is that even when the overall Synoptic pattern is correct you can still have a lot of things go wrong and national lesson which has to learn from this weekend event.

The next question is what happens after this weekend event? There is no doubt that a new surge of very cold air for middle March come sweeping into the eastern half of the US this weekend and into next week. The noreaster which is going to develop a mess most of the Northeast this weekend will in fact become a huge low-pressure area over southeastern Canada near Newfoundland-- in essence a large-scale classic 50 / 50 Low. Again this seems to set up a spectacularly great pattern for the next event which comes out of the Western US next week...

The overall idea is that if we keep the block over northern Québec / Davis Straits and a huge 50/50 low the energy coming out of the Lower Rockies and Lower Plains would be forced to the south... The cold air would stay in place along the confluence zone on the US Canada border and air would be another significant winter storm threat March 17 --19. Indeed the GFS and euro ensembels strongly suport that idea as does the Op GFS.

But those ensembels also the primary Low gpoing up into the Great lakes and /or the Ohio valley as a signficant feature... and my concern is that for those snow bunnies in the I-95 cities the primary is too strong holds together for too long and makes it too far North so it is NOT a all snow event.

In fact if the 50/50 low is east or hgading east out to sea the March 18-19 event in the I-95 cities could be a primarily rain event but of course at this Point I dont yet.

and that is the CRUX of the problem for Next week with regard to the next signfiicant event for the Midwest and eas coast -- How long does the COUPLET of the 50 /50 Low and Queebc / Davis Straits hold? It is MY contention that these tweo features are DECOUPLING --- pulling aweay from each other.

You see the 50-50 low and the -NAO have a symbiotic relationship. These two features feed off of each other as it were. In the classic situation the large 500 MB Low over Newfoundland ( the 50/50 Low ) and the block over Greenland / Northern Quebebc anchor each other -- the fact is that the existence all of one of these features enhances and stabilizes the existence of the one.

However in the current situation by next week the blocking feature from Greenland will be located over northern Québec and the Davis Straits and it will continue to retrograde to the West. The large 50-50 low will be located directly south of the Block and we will have a True REX block situation. However the 50-50 low will continue to slide east as the block continues to retrograde to the West and this will bring about a decoupling between eastern features sometime after March 14 --15. Not only is this decoupling feature and timing very important with regard to the event for next week but also has implications as to how the second half of March is going to shape up across the entire North American continent.

If I am wrong and the decoupling does not occur between March 15 --20.. and the Rex block hold on to say March 23 then the latter half of March is going to be much colder over the eastern half of the US than what I am currently thinking