December 2012 Pattern Analysis

[tmagan]

KNYC has seen about three-quarters of an inch of rain since the Nor'Easter.

[bluewave]

It still looks like most of the cold air will be locked up near Alaska around the day 10

time frame. Any frontal wave development should favor interior Northeast spots for at

least the chance of frozen precip on the front end before WAA takes over.

[Sundog]

Bluewave it looks like 2 or maybe 3 members are skewing this warmer than it would look. The majority of the members are neutral to cold.

[bluewave]

Bluewave it looks like 2 or maybe 3 members are skewing this warmer than it would look. The majority of the members are neutral to cold.

In any event, there wont be enough cold air around for anything colder than normal to a few degrees

below normal around behind any cold front.

Euro ensembles

[BxEngine]

Had a round of freezing drizzle this morning, some roads were pretty slick.

[jm1220]

I'd much rather see the NAO block retrograde west some so that it's not centered over eastern Greenland. There has to be more resistance to a storm cutting north and more confluence for me to be confident of wintry wx near the coast. New England is obviously a different story and gradient/SWFE patterns are awesome for most of them. But here, we really need more blocking or the SE ridge will run the show and most of us just get rain.

[friedmators]

Had a round of freezing drizzle this morning, some roads were pretty slick.

Was 29 degrees with light rain on my way into work.. Did not find anything frozen on metal signs or surfaces though.

[snywx]

Freezing rain up here all morning.. Temp just rose above freezing. 33F now w/ Lgt rain.

[MJO812]

The GFS was stormy. It is still hinting at a storm in the 15-20th timeframe.

[CooL]

After the 15th, the GFS goes to town with the pattern and storms. One that will bring this place back from the dead

[MJO812]

After the 15th, the GFS goes to town with the pattern and storms. One that will bring this place back from the dead

-West based NAO and a neutral PNA

[forkyfork]

you all pay attention to the day 10 gfs when it shows snow but ignore it all other times

[CooL]

you all pay attention to the day 10 gfs when it shows snow but ignore it all other times

People will jump on you if you post anything negative about the day 10 gfs

Ignoring a bad gfs run is the best thing to do to avoid a weenie breakdown

[earthlight]

you all pay attention to the day 10 gfs when it shows snow but ignore it all other times

To be fair the majority of us are highlighting a broad period of potential based on things other than the GFS OP.

[MJO812]

Euro is impressive mid month. A nice NAO develops.

[Weathergun]

The 12z GEFS today supports storm threat 18-19th. Besides the big -NAO, there is also small progressive ridge moving over the Rockies and Central Plains. This is the one to watch for us, IMO.

[Snowshack]

Nice to see this creeping closer instead of being delayed.

[Snow_Miser]

The 12z ECMWF now also has this storm system that many people have been disucssing about on this thread on the 16th.

A bit too warm for coastal locations, but this can easily change. It has a 990 mb low near the BM.

[Isotherm]

The 12z GEFS today supports storm threat 18-19th. Besides the big -NAO, there is also small progressive ridge moving over the Rockies and Central Plains. This is the one to watch for us, IMO.

Agree. This is the time frame I'm watching as well for our first real snow threat, 18th-21st. Block retrograding west as short wave energy cuts underneath toward the mid atlantic coast. Threats prior to that will likely be New England-favored w/ too much SE ridging still in the picture.

[earthlight]

Agree. This is the time frame I'm watching as well for our first real snow threat, 18th-21st. Block retrograding west as short wave energy cuts underneath toward the mid atlantic coast. Threats prior to that will likely be New England-favored w/ too much SE ridging still in the picture.

Doug and I were talking about this last night -- I haven't seen anything yet to change the thoughts. Glad we're in relative agreement. I think there could be two threats -- one a few days earlier on the 15th-16th and then the second one is the one that we would be more interested in at least in this forum. The mean trough over the Southwest US has a very nice look to it, but we'll have to see what the individual perturbations and nuances do and we won't know those details for several days at the earliest.

That being said the GFS ensemble members are all over both of these threats with almost every member showing two potential events with shortwaves ejecting northeast out of that aforementioned Southwest US troughing. Where the baroclinic zone sets up on the periphery of the Southeast Ridge will be a huge factor in whether or not these are wintry threats for our area. If the blocking doesn't develop like it is modeled to, the surface low could get very far north and we'll be WAA'd. Hopefully the more blocky models are correct...because then we could be looking at some really nice potential events.

Although its hard to say whether or not the blocking will develop it is very encouraging to see the wave pattern in the high latitude blocking developing on the GEFS H5 height anomalies map. If you loop through it you can track anomalous ridge features developing at 0-24 hrs initially over Russia...which build off each other to the west every few days and eventually end up over Greenland by Day 7. Pretty cool to see.

[Dsnowx53]

Doug and I were talking about this last night -- I haven't seen anything yet to change the thoughts. Glad we're in relative agreement. I think there could be two threats -- one a few days earlier on the 15th-16th and then the second one is the one that we would be more interested in at least in this forum. The mean trough over the Southwest US has a very nice look to it, but we'll have to see what the individual perturbations and nuances do and we won't know those details for several days at the earliest.

That being said the GFS ensemble members are all over both of these threats with almost every member showing two potential events with shortwaves ejecting northeast out of that aforementioned Southwest US troughing. Where the baroclinic zone sets up on the periphery of the Southeast Ridge will be a huge factor in whether or not these are wintry threats for our area. If the blocking doesn't develop like it is modeled to, the surface low could get very far north and we'll be WAA'd. Hopefully the more blocky models are correct...because then we could be looking at some really nice potential events.

Although its hard to say whether or not the blocking will develop it is very encouraging to see the wave pattern in the high latitude blocking developing on the GEFS H5 height anomalies map. If you loop through it you can track anomalous ridge features developing at 0-24 hrs initially over Russia...which build off each other to the west every few days and eventually end up over Greenland by Day 7. Pretty cool to see.

It might turn out that the 15-16th event could be the one that finally sinks the gradient far south enough to benefit our area for the later wave. Also, if the 15-16th event is strong enough, it could provide a nice 50/50. And that wouldn't necessarily be a transient 50/50 low either, because of the NAO block that we'd have downstream of that. Could really make things interesting for Dec 18-20.

And yeah, I wonder if there is a physical mechanism that explains the gradual westward building of each highly anomalous ridge. Following that progression would lead to a west-based block of some sort, though we're not really in a stratospheric state where the block would last for that long. This could mean a holiday/post holiday torch.

[Isotherm]

Doug and I were talking about this last night -- I haven't seen anything yet to change the thoughts. Glad we're in relative agreement. I think there could be two threats -- one a few days earlier on the 15th-16th and then the second one is the one that we would be more interested in at least in this forum. The mean trough over the Southwest US has a very nice look to it, but we'll have to see what the individual perturbations and nuances do and we won't know those details for several days at the earliest.

That being said the GFS ensemble members are all over both of these threats with almost every member showing two potential events with shortwaves ejecting northeast out of that aforementioned Southwest US troughing. Where the baroclinic zone sets up on the periphery of the Southeast Ridge will be a huge factor in whether or not these are wintry threats for our area. If the blocking doesn't develop like it is modeled to, the surface low could get very far north and we'll be WAA'd. Hopefully the more blocky models are correct...because then we could be looking at some really nice potential events.

Although its hard to say whether or not the blocking will develop it is very encouraging to see the wave pattern in the high latitude blocking developing on the GEFS H5 height anomalies map. If you loop through it you can track anomalous ridge features developing at 0-24 hrs initially over Russia...which build off each other to the west every few days and eventually end up over Greenland by Day 7. Pretty cool to see.

It might turn out that the 15-16th event could be the one that finally sinks the gradient far south enough to benefit our area for the later wave. Also, if the 15-16th event is strong enough, it could provide a nice 50/50. And that wouldn't necessarily be a transient 50/50 low either, because of the NAO block that we'd have downstream of that. Could really make things interesting for Dec 18-20.

And yeah, I wonder if there is a physical mechanism that explains the gradual westward building of each highly anomalous ridge. Following that progression would lead to a west-based block of some sort, though we're not really in a stratospheric state where the block would last for that long. This could mean a holiday/post holiday torch.

Pretty much sums it up. I agree that our threat in the 18th-21st period basically hinges on getting the east based nao to retrograde at least to Greenland, preferrably the Davis Straits. That's a monster -PNA signal progged on modelling so we're going to need all the help we can get from the north atlantic to suppress the SE ridge. I think 15th-16th is probably too early for us but as you both noted, it could possibly send the baroclinic zone southward for the next short wave to zip east to the VA capes.

Post Christmas, the weakening -QBO combined with strong blocking from both the NAO and AO in December means, in most cases, that both indices remain negative for the better part of January. I think we're looking at least a 40 day block period here which could take us to early/mid Jan, before a breakdown occurs.

[earthlight]

Pretty much sums it up. I agree that our threat in the 18th-21st period basically hinges on getting the east based nao to retrograde at least to Greenland, preferrably the Davis Straits. That's a monster -PNA signal progged on modelling so we're going to need all the help we can get from the north atlantic to suppress the SE ridge. I think 15th-16th is probably too early for us but as you both noted, it could possibly send the baroclinic zone southward for the next short wave to zip east to the VA capes.

Post Christmas, the weakening -QBO combined with strong blocking from both the NAO and AO in December means, in most cases, that both indices remain negative for the better part of January. I think we're looking at least a 40 day block period here which could take us to early/mid Jan, before a breakdown occurs.

Coincidentally we had a similar (in length) blocking episode back in 2010 which began around the same time that this one is forecast to. Not making any other comparisons in regards to strength or positioning...but that one also was touched off by an Aleutian Ridge which eventually made its way around the high latitudes into Greenland and the Davis Straight.

I also recall people calling for a breakdown after Christmas..which was delayed 10-15 days until the middle of January.

[rcad1]

this might be a very dumd question but when you guys reefer to the block breaking down in mid Jan that would mean a pattern change from cold and stormy to warm and less stormy or maybe not warm but normal im I correct or im I reading your statements wrong??? Also what do you guys think happens after that do you think the Cold air reloads and we get another change to colder weather for Feb I know this is a very long time from know and many things can and prob will change was just wondering your opion or best educated guess...

[MJO812]

MJO looks nice

[Isotherm]

this might be a very dumd question but when you guys reefer to the block breaking down in mid Jan that would mean a pattern change from cold and stormy to warm and less stormy or maybe not warm but normal im I correct or im I reading your statements wrong??? Also what do you guys think happens after that do you think the Cold air reloads and we get another change to colder weather for Feb I know this is a very long time from know and many things can and prob will change was just wondering your opion or best educated guess...

Good question and it's a very difficult one to answer with high confidence at this point. My thoughts on the progression of this winter haven't changed much from when I put out my winter forecast (and that's a good sign b/c last year at this time I was biting my nails off, as were many of us).

The NAO is turning negative now and the AO has already been negative for 7-10 days. Both indices will reach very low values by mid December and one can see this with the 500mb height anomalies on model data suggesting blocking across the Arctic and North Atlantic. Assuming this goes as planned, negative NAO/AO blocking episodes usually run in periods of about 30-50 days on average. After they break down, sometimes that's it for the winter, while other times, yet another 30-50 day blocking episode develops. The winter of 2009-10 was so historic for snowfall due exactly to this -- the first severe blocking period from early December to early January, a brief pattern relaxation, then another more severe -NAO/AO episode from early Feb through mid March.

This winter, my thinking is we'll have one severe blocking episode, over the course of the next month, though I don't expect the AO or NAO to be consistently/strongly positive at any point this entire winter. With that being said, the Pacific pattern will probably be unfavorable w/ the cold PDO correlated to a -PNA and troughiness leaning toward the West. John noted 2010-11 as potentially similar - We may see a sensible weather pattern evolve somewhat similarly to that year. I think February will be our warmest month relative to normal this winter (but just slightly so). If my thoughts are correct, the NAO/AO will approach more neutral values by mid January - and although that's not bad - I think the poor Pacific will cause the SE ridge to dominate from later Jan into Feb. If a 2010-11 scenario occurs, the blocking breaks down early Jan but then the Pacific steps in to help us for a few weeks. Then the Pacific went to crap, and our winter did shortly thereafter in February 2011. MJO forcing suggests we may get some Pacific help later this month (dec) but I'm not confident the Pacific will be on our side very long this winter.

A lot of "IFs" in this reply, but those are my thoughts at this point for the winter. Here's my winter forecast if you want to read the reasoning behind my expectations:

http://www.lightinthestorm.com/

[Isotherm]

Coincidentally we had a similar (in length) blocking episode back in 2010 which began around the same time that this one is forecast to. Not making any other comparisons in regards to strength or positioning...but that one also was touched off by an Aleutian Ridge which eventually made its way around the high latitudes into Greenland and the Davis Straight.

I also recall people calling for a breakdown after Christmas..which was delayed 10-15 days until the middle of January.

Yeah I think there are definitely similarities to 2010 - pretty analogous PDO/PNA/blocking wise. ENSO was weak and this year ENSO is not much of a factor for us.

The thing I'm conflicted about is will we see an impressive PNA surge like 2010-11 had. MJO suggests maybe, if we can get phase 1-2 to do its magic later this month. I doubt it'll be able to sustain itself though into January, which is why I think if/when the blocking breaks down, we could be mild for awhile post mid jan. This will be an interesting winter to follow with the first yr in awhile of neutral ENSO...

[earthlight]

Yeah I think there are definitely similarities to 2010 - pretty analogous PDO/PNA/blocking wise. ENSO was weak and this year ENSO is not much of a factor for us.

The thing I'm conflicted about is will we see an impressive PNA surge like 2010-11 had. MJO suggests maybe, if we can get phase 1-2 to do its magic later this month. I doubt it'll be able to sustain itself though into January, which is why I think if/when the blocking breaks down, we could be mild for awhile post mid jan. This will be an interesting winter to follow with the first yr in awhile of neutral ENSO...

I'm really, really iffy on the MJO in specific as this pattern develops especially since the last forecast MJO impulse not only faded but the forecast totally crapped the bed. But the forecast NAO blocking is very impressive.

I wonder if, if the pattern develops as modeled, and the PV is elongated westward a bit...we could see a PNA spike at the tail end of the blocking pattern similar to 2010 as well.

[earthlight]

Good question and it's a very difficult one to answer with high confidence at this point. My thoughts on the progression of this winter haven't changed much from when I put out my winter forecast (and that's a good sign b/c last year at this time I was biting my nails off, as were many of us).

Don't remind me...last winter was one of my worst forecasting busts ever. I remember both of us were hammering the fact that Dec was pretty much shot and that things would change after 12/25 and New Years. I was convinced the SSW event would bring the cold air to this part of the globe -- and although the SSW occurred (which many still don't understand...it actually did happen)...it happened on the wrong side of the pole for our area to benefit.

[Isotherm]

Don't remind me...last winter was one of my worst forecasting busts ever. I remember both of us were hammering the fact that Dec was pretty much shot and that things would change after 12/25 and New Years. I was convinced the SSW event would bring the cold air to this part of the globe -- and although the SSW occurred (which many still don't understand...it actually did happen)...it happened on the wrong side of the pole for our area to benefit.

Tell me about it...my worst winter forecast ever as well by far....looking back I think the signals were fairly clear by early/mid Dec that the winter was going to suck, or in the best case scenario, pull a 2006-07 type deal with the feb reversal.

Agree about the SSW, plenty of misinformation still going around regarding last winter's bust. Many think the SSW was fake and just "made up", but it certainly was real for 70% of the rest of the northern hemisphere - Europe, Asia, etc. England's on one helluva run - this is their 4th winter in a row that's probably colder/snowier than normal.