Overview:
On November the 21st I mentioned in my post that I felt in the December 4-7 timeframe it would be possible to see a SECL (severe east coast low) with STJ interaction. This was over 15 days in advance of the system. Well as we have progressed in time closer to the aforementioned period I would like to update on the situation.

First off I am now thinking the SECL will come in the later part of my predicted timeframe. The main component however to the SECL will be the past. Yes I said the past because really in this setup what will determine the outcome of the SECL (future) will be the past and what specifically happens.

The main component to the SECL will be the setup in advance of it. There will be one major building block that is particularly important and that should receive the most attention. Literally the building block will be just that a "block." Can and will we establish a block?

A low in the December 4-5 timeframe will be important in accomplishing a block if one does occur. Models prog a low developing along the front or area of greatest contrast in temps the baroclinic zone. It is this impulse that will play a HUGE factor in our SECL. If this impulse is able to turn north and get caught by the Greenland ridging which I find likely to be in place (proged by many models i.e. 12z EMCWF) and form a cutoff 500mb low or our blocking 50/50. Yes it will block but in some aspects it might not be in the 50/50 position therefore we might not want to refer to it as a 50/50 low.

However if this impulse is say supressed and then is out to sea or creates a weak block that's progressive and quickly dissipates or departs it will not result in a block and not only is the SECL jeopardized but the effects if it were to occur are much different. We would stay zonal and progressive extremely faced paced with little in change.

So I keep mentioning this block but why is it so important and what are the effects? Simply put the block allows for troughiness and colder temps lower hgts in eastern US. In relation to our SECL however it allows for digging of the shortwave with STJ influence with GOM enhancement and PJ interaction possible also if suppressed under the block. The block would PREVENT an inland riding storm which equals warm air to its eastern flank with southerly winds and hgt increases which means rain for most to the east of it an only interior snowstorm. So the outcome of strong blocking is maybe snow and mix all the way to the coastal plain.

Let's break this down into some scenarios of what can play out and ultimately the effects so all of you readers can get a good feel and handle of the pattern.

Scenario 1: NO BLOCKING
This scenario features no blocking in turn there is absolutely no real source for cold, not sure if the vortex and pv would drop down, little if any insurance that the low won't travel inland infact with this scenario the low travels very far west and inland making it hard for even interior sections of the northeast to see snow. This favors a midwest snowstorm. The good news is no models really currently show this aspect however it was at one point an idea from many models.














Scenario 2: Weak Blocking Dissipates, Transient, Progressive, moves N and W
This scenario features some ridging with with weak blocking establishing and then most likely exiting. The PV is slightly further S and E and colder air is present over the entire northeast however suitable temps for snow will only be found inland so interior northeast sees a large snowstorm while the coastal plain sees rain. It is also possible with this scenario that behind the system colder air ushers in very quickly and with an extremely strong low pressure that gets wrapped up hgts fall very quickly and some snow manages to find its way even into the coastal plain although heavy snows are confined to inland or interior northeast. This favors a "coastal hugging" track.

































Scenario 3: STRONG BLOCKING LOW
This scenario features a strong well situated 500mb low cutoff and Greenland ridging to keep it in place as well as some PNA ridging into western Canada helping to block (H) it as well as the PV and Vortex coming very far S bring much colder temps to all of the northeast. A large STJ influenced low with the aid of the GOM moisture diggs deep and cuts into a large trough situated in the northeast and with blocking its option is to take a coastal track thats offshore in prime position for a SECS (severe east coast snowstorm) or MECS (major east coast snowstorm). Cold air in entrenced over the northeast and the low really blows up and goes through bombogenesis and pulls even colder air down and creates high winds (nor'easter).






























Remember there is always that idea the the shortwave doesn't dig rather very suppressed and heavily blocked pattern which would result in no SECL just another overrunning type event.

Things to Watch:

• Progressive pattern
• Shortwaves of kickers behind low
• Our first low and whether it becomes a significant blocking feature
• PNA western ridging
• Greenland ridging
• Strength and position of block
• Trends

Positives:

SO far this year the trend has been east (DT). Also models continue to develop the blocking with more ridging etc continue to watch the trends with this because this is the key in the track of the SECL and slowing down the strong PAC and progressive pattern. As the first event gets closer the models have yet to back off on blocking. We have seen blocking established before in this season so far but will or won't it be transient?

Conclusion:

The setup is dependent on several variables and even then there are several other aspects that add to the overall equation makeup and the final solution or result. As things continue to evolve I will make posts regarding key things I notice and hopefully will soon be able to determine the scenario which will occur.

Meteo 101 - Brian