Can the pieces fall into place?

[earthlight]

I'm sure by now most of you have been watching the guidance very carefully over the past several weeks--and have seen the flip flopping which has evolved. There has been a great deal of uncertainty regarding the potential development of arctic cold which would bleed eastward from the Central United States towards the coast. The more broad problem has evolved from the interaction between the PNA and NAO phases--which haven't worked in tandem yet this cold season. That being said, we can now say with confidence that the NAO is, in fact, in a robust negative state. The latest CPC NAO values were well below -2 and dropping--forecast by most ensembles to approach -3 within the next few days and be well below -2 (and possibly below -2.5 as well) by December 1st. That being said, there is more to the NAO than the actual hard data and ensemble forecasts. One needs to dig deeper to see the exact developments aloft, especially at H5. It has been discussed several times here, but I figure it's worth beating a dead horse in this situation: An east-based NAO, especially in a generally -PNA pattern with northern stream dominance, will most likely not yield a favorable pattern for significant snowfalls.

Knowing all of this, we can say with confidence that we have seen some favorable trends amongst the guidance over the past several days, especially last nights 00z model suite. There has been much talk about the December 4-5 and 8-10 period for potential snowfall events--and fundamentally it all comes back to the NAO pattern aloft and the state of the pacific. On last night's 00z Canadian we can see the major features in place for the development of potential snow (albeit light with the first event). There is a strong 570dm NAO block extending towards Greenland, as well as a shortwave acting to reinforce this block over Northern New England. This shortwave and upper level confluence will serve to extend the block south--forcing the surface low pressure we see in this frame over Northern Illinois to redevelop southward over the Mid-Atlantic states. There is no way--in the pattern advertised--that that surface low gets any further north. The blocking and the confluence will not allow that to happen. This model does a good job in advertising the importance of this type of block to our pattern. A previously discussed east-based type NAO (with the block further to the east/northeast and the confluence subsequently not there) would not allow for this to occur.

We can also see the ensembles catching on to the idea of the more robust NAO block in the longer range on last nights 00z GFS Ensembles. Although the PNA may not be negative, there is a downstream ridge over the Western US (namely the Rockies), and the big NAO block allows for a cross-flow of very cold air and a large H5 mean trough over the Eastern United States. Also, we can see the ensembles for the next few days (shorter term) and we can clearly see the more east-based NAO ridge. Although the NAO is drastically negative, this type of pattern will not work. (The favorable long range NAO is the first image, the east based NAO is the second image).

All of this being said, where to do we go from here? Well we have a ton of energy in the pattern, that's one thing that we can say with confidence. We have seen a large amount of shortwaves coming out of the Pacific into the CONUS over the last several days. The guidance seems to finally be locking into the fact that the favorable NAO block will set up by next weekend. From there, our eyes should remain peeled. The shortwave forecast to develop December 4-5 does have some teeth to it, and I think there is the possibility that this could be a light snow producer. That being said--there is little room for large scale amplification of this feature and it should remain on the lower end of the potential. For me, the real questions begin to be raised by December 8-11th. Where has the NAO block gone by this point? At that point, we will be entering a favorable period where most guidance agrees heights will be significantly lowering over the west coast with a favorable shortwave set to eject northeast. Should the blocking set up as modeled, I think the first snowfall of significance (all the way to the coast) could occur during that time period. Guidance should be watched with the pattern in perspective at all times, and I think it's imperative that we keep that in mind over the coming week as we all watch with hope.

[jrodd321]

Excellent writeup, John. This period coming up really bears watching, and hopefully everything can fall into place for a nice snowstorm for us. Like you said, the players/potential is definitely there.

[Dsnowx53]

Great post!

I think it's great that this pattern got "delayed", since now it looks like the pattern will look its best during a more favorable period for snow.

[earthlight]

Great post!

I think it's great that this pattern got "delayed", since now it looks like the pattern will look its best during a more favorable period for snow.

Thanks dudes. The bolded part is certainly a possibility. Let's just hope it doesn't get delayed any further. All things considered, though, I think we are heading towards our first real potential winter weather threat(s) of the season the next week or two.

[Isotherm]

John, great write-up and you really hit on some key points regarding the importance of west vs east based -NAO blocks. IF we had a +PNA/-EPO coupling with the -NAO signal, the east based ridging wouldn't be as bad. In fact, we'd likely have a sustained cold pattern w/ plenty snow threats in the Northeast (lesser chances into the mid atlantic and SE with an east based NAO).

However, the PNA looks like it's in no rush to head positive, and it probably rarely will if at all this winter, considering the strong La Nina and strongly -PDO. Thus we need the north atlantic pattern to essentially be ideal for significant snow threats to come to fruition. Right now it still looks to me like the Dec 4th-5th short wave helps pump the Greenland block and set-up a 50/50 low just to our northeast. This in turn will aid in strong confluence across the US-Canadian border, forcing the next short wave to dive south. Truth be told, I'm more concerned about the following system (Dec 8th-11th) missing to the south or out to sea than cutting through the Great Lakes. With a severely negative AO and NAO, it simply isn't going to happen. We do have a bit of ridging poking up along the classic Boise ID axis in the Western US, which is a great position for an I-95 SECS.

All in all, the potential is probably as high as it can be in a strong La Nina for the Dec 7th-15th period. There's a chance the clipper on the 5th gives us some teaser snows, but I'm more interested in that setting the stage for what "could" be coming next. Emphasis on could, b/c I don't think we should get too excited just yet. It's quite possible we end up high and dry with nothing more than a 1-3" light snowfall in this cold period. Hopefully not, but we've got to think worst case scenarios atm.

[Dsnowx53]

Now it seems like we have to worry about the upper-level-low around Maine being too strong. Latest runs have shown that closing off and becoming an overly powerful feature, thus squashing any shortwave that tries to amplify.

Hopefully with the La Nina tendencies, we can perhaps move this upper-level-low a bit northward...

[earthlight]

Now it seems like we have to worry about the upper-level-low around Maine being too strong. Latest runs have shown that closing off and becoming an overly powerful feature, thus squashing any shortwave that tries to amplify.

Hopefully with the La Nina tendencies, we can perhaps move this upper-level-low a bit northward...

If you look at the images I posted from the modeling a few days ago, the changes are rather drastic and not too positive. The ULL and confluence trended way stronger, and more importantly, the shortwave trended way weaker. We could live with the confluence if the shortwave were to be strong enough--but it doesn't look that way as of now.

The setup aloft, generally, still offers a ton of potential..so it is certainly way too early to give up on anything. But we now know the changes we need in order to get back into a more solidified threat.

[Dsnowx53]

If you look at the images I posted from the modeling a few days ago, the changes are rather drastic and not too positive. The ULL and confluence trended way stronger, and more importantly, the shortwave trended way weaker. We could live with the confluence if the shortwave were to be strong enough--but it doesn't look that way as of now.

The setup aloft, generally, still offers a ton of potential..so it is certainly way too early to give up on anything. But we now know the changes we need in order to get back into a more solidified threat.

Yeah, we definitely do need a stronger shortwave, because although we do have a very nice block, it seems to be a bit of a SE-based -NAO...the highest heights are to the SE of Greenland, which forces the upper-level-low to retrograde well to the south and east of what would leave more room for amplification. We need the upper-level-low to somehow be forced a bit more to the west...that way, we can leave more room for amplification in the east. If we have that huge area of confluence too far east, then it leaves very little room for a shortwave to turn the corner. Also, with a further west upper-level-low, that combined with increased amplification would increase the chances of a major phase, which would easily yield a MECS...that's what the Canadian is showing.

[nzucker]

Yeah, we definitely do need a stronger shortwave, because although we do have a very nice block, it seems to be a bit of a SE-based -NAO...the highest heights are to the SE of Greenland, which forces the upper-level-low to retrograde well to the south and east of what would leave more room for amplification. We need the upper-level-low to somehow be forced a bit more to the west...that way, we can leave more room for amplification in the east. If we have that huge area of confluence too far east, then it leaves very little room for a shortwave to turn the corner. Also, with a further west upper-level-low, that combined with increased amplification would increase the chances of a major phase, which would easily yield a MECS...that's what the Canadian is showing.

Quite ironic that everyone was worried about the blocking breaking down in a strong La Niña year, and now the confluence is killing us again just as it did in the 2/5/10 storm last winter.

[Voyager]

Quite ironic that everyone was worried about the blocking breaking down in a strong La Niña year, and now the confluence is killing us again just as it did in the 2/5/10 storm last winter.

A repeat of that storm would literally push some folks here off the proverbial cliff.

[ptb127]

Indeed.

[Alpha5]

A repeat of that storm would literally push some folks here off the proverbial cliff.

At least we got some good storms last year, SNE got screwed every time

[earthlight]

Just a brief update this afternoon and evening. The important features are all here on the GFS this afternoon and just a quick glance at the model shows the problems with this setup at our latitude. We can learn alot from watching the guidance and this piece of guidance is telling us something as they all are. The image below shows the 18z GFS at 54 hours and I have marked the important features. First of all, we can see our shortwave of interest (which is probably the most important feature). This feature has trended stronger over the past few days as it has moved into better data assimilation areas in the Pacific. Secondly, we can see the upper level low and vortex over the Northeast United States. Not only is this feature large, but it has a ton of confluence associated with it and a northwest flow aloft. You can view the northwest winds aloft at most levels by looking at the NCEP or PSU Ewall maps which show the wind barbs and direction. Third, we see the ridge axis which has built in between the two features discussed (not bad wavelength separation here, if you live in the Mid-Atlantic). This ridge axis was not here last night on the 00z guidance suite of the GFS, as it was weaker with the shortwave initially and did not allow the feature to dig. Finally, we can see the ridge building out west, moreso than last nights guidance as well, which could help the feature to ampify. That being said, this feature has very little space to amplify, and really has nowhere to go in the pattern. The northwest flow aloft means this feature is going to dive southeast. The trend towards a stronger shortwave is good for the Mid Atlantic as it could allow for more ridging ahead of the feature, and slightly more amplification and a more developed precipitation shield which would otherwise be mundane. Still, the ULL is just way too close for us to expect anything of significant in our area. Even if the ECMWF from last night 00z was correct, the phase would occur as the ULL dropped into the system, which means the system would swing off the coast, with the confluence backing into our area once again as the system deepened, and then the surface low would be tugged towards the ULL towards the Gulf of Maine with a cold conveyor belt developing off the shores of New England. Basically, this synoptic setup as advertised is not favorable for frozen precipitation in our area at all--so I suggest that if we don't see any significant changes we begin to turn our attention to the not so distant future setups and potential.

[earthlight]

Also, you can see how much the potential set up has evolved since the initial post. The GGEM image I posted at the top of the thread had a much, much better synoptic setup with a well placed confluent upper level low and strong shortwave over the midwest. So overall, the trends have definitely not been in the right direction since then.

[Allsnow]

Im really starting to think we end up cold and dry the next week or so.......Blocking is not changing in the models......which is just going to crush everything. You want snow go to the lake regions. Upsetting it might end up like this, but perhaps as the blocking relaxes we get something.

[Dsnowx53]

Great post, John, and I entirely agree. The NW flow aloft, combined with the stubborn ULL give this system very little room to amplify.

Of course, the shortwave continues to trend stronger, and the ULL has trended weaker, but we pretty much need the shortwave to keep trending at this rate for every new set of model runs, along with the ULL being as progressive as it was on the Canadian to have a chance at significant snows. Is that a possibility? A slight one...you cannot rule anything out. But I think we need to keep our expectations low.

Despite the good recent trends, we are still pretty far behind that CMC map. There is still some time, but most likely not enough time to get the features to change into ones that support a significant snow event.

[Dsnowx53]

Something to add...as long as the s/w trends stronger, that would have to mean at least a little bit of weakening and flattening of the ULL. Look how on the Canadian, the ULL is very flat, because it's wedged between the big shortwave and the block. If we can continue to increase the strength of the shortwave, it really forces the ULL to become wedged, and thus get a bit flattened.

Obviously, that's much easier said than done. But if the s/w continues to get stronger, it pumps out some sort of riding out ahead of it, which forces the ULL to either move a bit north, or flatten a bit...in this case, it would probably just flatten more than anything because there's the block to its north that prevents large scale movements.

That's really our only hope.

[Kaner587]

Something to add...as long as the s/w trends stronger, that would have to mean at least a little bit of weakening and flattening of the ULL. Look how on the Canadian, the ULL is very flat, because it's wedged between the big shortwave and the block. If we can continue to increase the strength of the shortwave, it really forces the ULL to become wedged, and thus get a bit flattened.

Obviously, that's much easier said than done. But if the s/w continues to get stronger, it pumps out some sort of riding out ahead of it, which forces the ULL to either move a bit north, or flatten a bit...in this case, it would probably just flatten more than anything because there's the block to its north that prevents large scale movements.

That's really our only hope.

I hate to use this as a last bit of hope because we've been burned too many times in the last couple winters, but up until I believe 72 hours out, and for some of the models even 48 and 36 hours out, Dec. 19th looked to be a mid-atlantic special with no precip in our vicinity. Also, in this time period before the storm last yr, initial storm track was for a lower mid atlantic special, and we obv know how it turned out. Granted it's a much different pattern in a different yr, but it definitely goes to show that over-modeled confluence, even by a little, has huge implications since a deviation of only 200 miles or so North or NW puts us in line for at least some impact from this system. I agree we need to watch the trends with the s/w which has obviously trended much stronger and hope that the confluence is over modeled, as it sometimes is in this time period. Just some food for thought

[Absolute Humidity]

I hate to use this as a last bit of hope because we've been burned too many times in the last couple winters, but up until I believe 72 hours out, and for some of the models even 48 and 36 hours out, Dec. 19th looked to be a mid-atlantic special with no precip in our vicinity. Also, in this time period before the storm last yr, initial storm track was for a lower mid atlantic special, and we obv know how it turned out. Granted it's a much different pattern in a different yr, but it definitely goes to show that over-modeled confluence, even by a little, has huge implications since a deviation of only 200 miles or so North or NW puts us in line for at least some impact from this system. I agree we need to watch the trends with the s/w which has obviously trended much stronger and hope that the confluence is over modeled, as it sometimes is in this time period. Just some food for thought

True but last years 84hr NAM was the first model to peg that one and it held it pretty much right up until the storm. That being said, climo says always remember, it likes to snow near the 5th of December

[NorEaster27]

I hate to use this as a last bit of hope because we've been burned too many times in the last couple winters, but up until I believe 72 hours out, and for some of the models even 48 and 36 hours out, Dec. 19th looked to be a mid-atlantic special with no precip in our vicinity. Also, in this time period before the storm last yr, initial storm track was for a lower mid atlantic special, and we obv know how it turned out. Granted it's a much different pattern in a different yr, but it definitely goes to show that over-modeled confluence, even by a little, has huge implications since a deviation of only 200 miles or so North or NW puts us in line for at least some impact from this system. I agree we need to watch the trends with the s/w which has obviously trended much stronger and hope that the confluence is over modeled, as it sometimes is in this time period. Just some food for thought

Good post, I suspect the upper level low over new england dosent drop as far south as the 12z gfs was showing it. It also probably ends up weaker, however its going to be tough to get some good ridging ahead of this shortwave. Many variables are still in play as you state and the timing will also be huge of both the sw and the ul low, both of which are still up in the air. Way too early to write this off or get excitied. Whatever happens its good to have a potential storm to track.

[Kaner587]

Good post, I suspect the upper level low over new england dosent drop as far south as the 12z gfs was showing it. It also probably ends up weaker, however its going to be tough to get some good ridging ahead of this shortwave. Many variables are still in play as you state and the timing will also be huge of both the sw and the ul low, both of which are still up in the air. Way too early to write this off or get excitied. Whatever happens its good to have a potential storm to track.

I love the optomism noreaster. But in all seriousness it is nice to have something to track again, its amazing how fast winters come and go. Truth is I don't feel like this will actually have much of an impact for our area but we will see. Also gotta give credit to the GFS pegging Dec 5th as a threat 2+ wks out...

[NorEaster27]

I love the optomism noreaster. But in all seriousness it is nice to have something to track again, its amazing how fast winters come and go. Truth is I don't feel like this will actually have much of an impact for our area but we will see. Also gotta give credit to the GFS pegging Dec 5th as a threat 2+ wks out...

Lol, reading between the lines my early call would be little to no impact on our area. I'm sure most ppl here were expecting that from me anyway hahaha. However, I'm not going to slam the door this early in the game lol. Like I said its just too early with too many variables. Maybe ill go more optimistic this year

[Kaner587]

Lol, reading between the lines my early call would be little to no impact on our area. I'm sure most ppl here were expecting that from me anyway hahaha. However, I'm not going to slam the door this early in the game lol. Like I said its just too early with too many variables. Maybe ill go more optimistic this year

Well we wouldn't want that! look what you pessimism did for us last yr!! In two diff locations (central westchester and south shore of LI) I saw 1 1ft storm and 2 18in+ storms..please let that happen again haha.

[green tube]

what the hell is that orange and blue thing with a face?

[NorEaster27]

what the hell is that orange and blue thing with a face?

Otto the Orange

[green tube]

Otto the Orange

ahh. thanks.

[Kaner587]

ahh. thanks.

Gotta represent the CUSE...I graduated from syracuse in 2009

[NorEaster27]

Gotta represent the CUSE...I graduated from syracuse in 2009

My brother is a sophomore at cuse, went from 63 degrees this morning...to 35 and sleet...to 32 and snow.

[NYCSuburbs]

I'm catching up on the models as I didn't have internet access most of today, but it looks like the snow from the Sunday clipper stays south of NYC, right? The NAM looks like it's close but still too far south for NYC to get snow, with the best chance of accumulating snow towards northern VA-southern PA.

[NEG NAO]

I'm catching up on the models as I didn't have internet access most of today, but it looks like the snow from the Sunday clipper stays south of NYC, right? The NAM looks like it's close but still too far south for NYC to get snow, with the best chance of accumulating snow towards northern VA-southern PA.

North trend starts within 48 hours on the models - no way is VA and DC going to have a snowstorm from a clipper in early december - more like DC north to NYC... the first system of the year is always the toughest for the models to get right this far out and for us to forecast.....