December 2012 Pattern Analysis

[MJO812]

EURO looks terrible though.

Yep. The -PNA is killing the pattern.

[CooL]

EURO looks terrible though.

Because It's supposed to. Don't expect any major changes in the pattern until after the 15th. Possibly after a few lake cutters

[PB GFI]

That ridge off the west coast ( too far west ) is driving this pattern . We dont change , until " IT " changes . There is a bit of a silver lining .You are seeing a little of the southern jet breaking through so this pattern is great from the Rockies into the upper midwest through the Canadian praries . So when the pattern does break down ( i hope ) , you will have laid down some good snow cover out in front of any highs that get discharged our way , so air masses wil not modify as much as they would have otherwise . The key is going to be , when that trough fianlly comes east , will it still have enough blocking to caught under ? or will be progressive and then we start the whole thing again . Curious to see if the Euro weeklies still show a change week 4 .

[MJO812]

I can't wait to see the euro weeklies because it had a nice west based -NAO on them. Hope they still show it.

[bluewave]

This month in some respects is starting look like December 1978. By just

looking at the NAO and AO, you would automatically think cold and snowy.

But the big problem that month was also the Pacific which allowed just enough

of a SE Ridge for above normal temperatures here.If the AO does tank to

-4, then this will be the first drop below that level with a mild December

pattern since 1978. All the other -4 drops since then have been colder

or snowier than this year including 2010, 2009, 2000, and 1995. This is the

kind or rarity that most folks around here would rather not see.

[earthlight]

Hopefully some of the long range guidance has a clue. The GFS and Euro ensembles both are keying in on the restructuring of the pattern beginning with the Polar Vortex which re-orients itself as the Pacific pattern reshuffles a bit as well. Around the same time a block retrogrades all the way from North of Iceland, through Greenland, and into a very favorable west-based position. This type of pattern has correlated to some very snowy periods from NYC into New England, historically...especially the tandem of the ridge into the Bering Sea and the ridge over Greenland and the Davis Straight.

[MJO812]

Euro also develops a 2nd wave that rides the coast. Snow inland and rain on the coast.

[denvillenj]

when is the euro showing that Snow88?

[MJO812]

when is the euro showing that Snow88?

At 132 hours. The Nogaps and the GFS/GEFS also show the same situation.

[Chaser25973]

I think it's amazing that no matter how good teleconnections A, B, C and D are, if teleconnection E isn't up to par, we don't get snow and cold. Just goes to show you how complex weather is as a science and how many causes there are for our weather.

[MJO812]

12z Euro is way different than the 0z run. It's laughable. It stays cold in the east after the storm next week.

[MJO812]

The vortex breaks up on the GFS by mid month .

[Snow_Miser]

The 18z GFS is not a very warm run by any means. One of the main reasons for it being pretty cold is that it establishes a solid -NAO with higher than normal 500 mb heights in the west based NAO regions:

[earthlight]

I don't understand why people keep paying so much attention to the Operational models when it's been well documented that they aren't very useful at this range...but yeah that would be a historically good pattern if the 18z OP GFS is right.

If you're going to watch models..I really urge people to pay more attention to ensemble means in the long range...the trends on them...and take a look at the Euro weeklies every once and a while as well.

[MJO812]

18z gefs has the 2nd wave for next week . Interesting since the op didn't show anything.

[MJO812]

No west based NAO on the weeklies. Looks like a SWFE pattern.

[Snow_Miser]

No west based NAO on the weeklies. Looks like a SWFE pattern.

Not a terrible pattern. Certainly not as good as they were before, though they consistently change with their long range depictions, which is to be expected, and almost certainly will look different in their next update.

The 18z GEFS is also pretty sweet day 9-10 and beyond.

[MJO812]

Not a terrible pattern. Certainly not as good as they were before, though they consistently change with their long range depictions, which is to be expected, and almost certainly will look different in their next update.

The 18z GEFS is also pretty sweet day 9-10 and beyond.

GEFS has a great pattern . Weeklies aren't bad . South west flow events usually favor SNE northward.

[TWCCraig]

Incredible night for radiational cooling, especially out east. Down to 20F already at Westhampton! 26F at Montauk Point (surprising since it's right near the water), Martha's Vineyard at 19F! Just imagine what it will be like later.

[tmagan]

01Z Temperatures

[Cfa]

Did LGA have its first freeze this morning?

[Guest Pamela]

Did LGA have its first freeze this morning?

Yes...it was strange, since I thought they had a frost free climate.

[tmagan]

Yes...it was strange, since I thought they had a frost free climate.

I was there last Saturday, and it felt very cold.

[snywx]

21.7/18 up this way

[earthlight]

Without getting into too much detail, I think we could be looking at our first responsive storm threat, owing to the changing pattern being advertised on model guidance, in about 10 days time...between Dec 16 and 19 if it all shakes down as expected. With the -PNA regime settling in and most global ensembles now indicative of a positive height anomaly both over the Bering Sea and one retrograding from Iceland over Greenland and towards the Davis Straight -- the general pattern will be at least moderately favorable (way more favorable farther north over New England) at the time.

It's important to remember that this is very far out in time..so obviously things can change fairly dramatically as we approach this period. But it seems to me like there will be at least a window of opportunity in this period as guidance brings a mean trough out of the southwest US and moves it eastward into a pattern that seems relatively controlled by a weak/slight southeast ridge and baroclinic zone with the block to the north -- without knowing any potential nuances or shortwaves that could exist within this mean trough over the southwest US.

[Dsnowx53]

Without getting into too much detail, I think we could be looking at our first responsive storm threat, owing to the changing pattern being advertised on model guidance, in about 10 days time...between Dec 16 and 19 if it all shakes down as expected. With the -PNA regime settling in and most global ensembles now indicative of a positive height anomaly both over the Bering Sea and one retrograding from Iceland over Greenland and towards the Davis Straight -- the general pattern will be at least moderately favorable (way more favorable farther north over New England) at the time.

It's important to remember that this is very far out in time..so obviously things can change fairly dramatically as we approach this period. But it seems to me like there will be at least a window of opportunity in this period as guidance brings a mean trough out of the southwest US and moves it eastward into a pattern that seems relatively controlled by a weak/slight southeast ridge and baroclinic zone with the block to the north -- without knowing any potential nuances or shortwaves that could exist within this mean trough over the southwest US.

Totally agreed here. Although we want a +PNA, if we can get the block to retrograde west a bit - or at least enough of a block to provide a good, sustained confluence zone in SE Canada, we can flatten out the height field in the Atlantic. That way, when a huge low closes off in the southwest states in a -PNA regime, it'll be an overrunning and coastal threat as opposed to something that cuts into the lakes. The storm would run into a brick wall in that scenario.

Not to forget that we might finally be building a decent cold air source and snow pack to our north. Anything to help shift the gradient south is a plus.

[MJO812]

0z GGEM for Dec 16

http://meteocentre.c...PN_228_0000.gif

[earthlight]

Totally agreed here. Although we want a +PNA, if we can get the block to retrograde west a bit - or at least enough of a block to provide a good, sustained confluence zone in SE Canada, we can flatten out the height field in the Atlantic. That way, when a huge low closes off in the southwest states in a -PNA regime, it'll be an overrunning and coastal threat as opposed to something that cuts into the lakes. The storm would run into a brick wall in that scenario.

Not to forget that we might finally be building a decent cold air source and snow pack to our north. Anything to help shift the gradient south is a plus.

The interesting thing is that although our first threat for wintry weather might not occur until 10-12 days from now, we are seeing this move up in time rather rapidly which is a great sign for those who are concerned about the "Always 10 days away" fallacy. The GFS has arctic cold dumping into the Western US from Alaska in response to a re-oriented Polar Vortex by 144 hours. There is a massive ridge into the Bering Sea and a tremendously anomalous block over Greenland, albeit centered on the Eastern shore.

This type of pattern screams for the development of some kind of gradient down the road once we start to get pertubations into that west coast mean trough that eventually are forced northeast along the baroclinic zone. The question then becomes -- where is the blocking, how strong is it, and where does this gradient really develop? One can hope that this anomalous block at 144 hrs can retrograde with some strength to a position farther south and west. Either way, the odds favor New England entering a very snowy period if this guidance is correct...and I wouldn't count out our area from getting involved as well. (Seriously, check out the image below, it's pretty close to a classic composite for a developing gradient pattern which is favorable for many in the Northeast).

http://www.meteo.psu.edu/~fxg1/ENSHGTAVGNH_18z/f144.gif

[Dsnowx53]

The interesting thing is that although our first threat for wintry weather might not occur until 10-12 days from now, we are seeing this move up in time rather rapidly which is a great sign for those who are concerned about the "Always 10 days away" fallacy. The GFS has arctic cold dumping into the Western US from Alaska in response to a re-oriented Polar Vortex by 144 hours. There is a massive ridge into the Bering Sea and a tremendously anomalous block over Greenland, albeit centered on the Eastern shore.

This type of pattern screams for the development of some kind of gradient down the road once we start to get pertubations into that west coast mean trough that eventually are forced northeast along the baroclinic zone. The question then becomes -- where is the blocking, how strong is it, and where does this gradient really develop? One can hope that this anomalous block at 144 hrs can retrograde with some strength to a position farther south and west. Either way, the odds favor New England entering a very snowy period if this guidance is correct...and I wouldn't count out our area from getting involved as well. (Seriously, check out the image below, it's pretty close to a classic composite for a developing gradient pattern which is favorable for many in the Northeast).

http://www.meteo.psu...NH_18z/f144.gif

Yeah, the aspect of there being some sort of threat definitely keeps moving up. Getting energy to dive down the downstream side of the Pacific Ridge actually starts at around day 5.

The one thing that might get "pushed back", or should I say "muted" with time is how far west the block retrogrades. And perhaps how amplified we can get the Pacific ridge...the MJO phase 1 forcing is still up in the air a bit. We need that ridge to be amplified enough to keep the flow cross polar as opposed to Pacific oriented. But the fact that we're going to have a block just east of Greenland seems to be set in stone, too. But an east based

-NAO will not be enough for our area in this setup for an all snow event.

But having a cold air source so near-by will certainly help things. Even in a not all snow event, there should be enough of a baroclinic zone to ignite lots of precip to break out well ahead of a disturbance, before WAA would kill us. All hypothetical, of course, but lots of options are on the table with a NAO block, a strong disturbance in the SW, and a strong baroclinic zone.

[Weathergun]

I've been looking at this period 15-20th for some event, for a while now. But I'm concerned about the strength of confluence zone, underneath any -NAO ridge. The GEFS keeps waffling on the amount of heights that builds into Alaska/Bering Sea.