When will the pattern change to cold occur?

[Isotherm]

Here's my latest thinking on my website: http://www.lightinthestorm.com/

Discussion/debate welcome. While there is a delay, I think in the end it works out in our favor...other thoughts welcome

Heading into mid November, we have a global pattern in place which argues for the maintenance of ridging into the Southeast/Eastern US, at least for the next couple weeks. The three "big ones" in terms of important teleconnections, the PNA, AO, and NAO, are all in an unfavorable phase for the time being, in terms of East Coast troughiness. Low height anomalies dominate the arctic, north atlantic, and Western US, lending support to the persistence of high heights (warmth) in the Eastern US. The question now becomes - when/will this pattern change? There have been some rumblings lately about December possibly being significantly more tame than expected a few weeks ago. While the timing may be slightly later than anticipated, my confidence remains high on the development of the much talked about negative NAO block. Thus, as the title says, I don't believe it's a matter of IF a pattern change will occur, it's WHEN. Let's dive into some of the specifics...

One of the primary foundations to my negative NAO forecast this winter is the maintenance of very low levels of geomagnetic activity, which, in my view, has the ability to significantly influence circulation patterns in the stratosphere and troposphere. Last winter lends evidence to the theory, given a negative NAO/Greenland blocking feature dominated the scene in the face of a poor Pacific (raging La Nina) and positive QBO (unfavorable stratospheric wind field).

While sunspot activity has picked up somewhat in the past couple years, note the low geomagnetic indicators. Recent days suggest barely detectable values for both the K index and Ap index.

K index - values 3 and under are low; values under 2 are very low.

A indices - values under 10 are low; values under 5 are very low.

Moving to tropical forcing, which I also utilized in my winter outlook, the MJO will be propagating through octants which are not conducive to the initiation of a -NAO block or sustained troughiness in the Eastern US, for 3 weeks at minimum. Most models are in consensus on a phase 1/2 approach by the end of November, and the Euro ensembles continue to push the MJO wave through phases 3-4 for the first 10 days of December. Phase 5 will likely by reached by about December 10th.

All of the above MJO phases mentioned, 2 through 6, but especially 3-5, are blowtorch city for much of the United States. Given the negative PNA/+EPO signal already in place (Gulf of Alaska/Pac NW US trough) coupled with the MJO signalling, the first 10 days of December could be warm to very warm across much of the country. This however is NOT to say the month will continue in this manner.

The MJO should continue to progress through octant 5-6, reaching a more favorable phase for Eastern troughiness by mid December. When we combine the future tropical forcing, state of geomagnetic activity, and second year Nina analogs for December, my confidence remains high that December will be a colder than normal month for the Great Lakes/Northeast. In fact, this delay in NAO block initiation may work out in our favor, considering December 1st-15th generally isn't a snow period anyway, as climatology is quite poor for the I-95 prior to December 15th in terms of large snowfalls. If the pattern change sets in as I expect it to by mid December, it will last longer into January than I originally thought, putting the thaw period later in January rather than taking up a large chunk of the month.

Bitterly cold air will undoubtedly build over the snow covered areas of Western Canada over the next 2 weeks; ensembles agree that Canada will turn colder than normal by week 2 - so it's not a matter of IF the cold air is avaiable. It's a matter of CAN we get the forcing mechanism to transport this cold air into the Lakes/Northeast in a sustained fashion.

The answer to that question should be yes, and it should occur approximately 4 weeks from now. We'll be in a largely back/forth cold/mild pattern until then - Pacific origin cool air swinging through the northern tier. If December starts off torching, don't fret, because that's not likely to be the case for the entire month.

[TheTrials]

great write up, what I wouldn't give for a re-curving typhoon right now.

[BxEngine]

Not a fan of cluttering up threads with stuff like this usually lol, but posts like this are great (and not just because we love snow lol), but because there is a learning experience involved. Many times these types have forced me to go to books and google to learn, and thats usually more important than the message itself. Easy to follow and well written. Nice job.

[SnowGoose69]

There is no question the last few runs of the GFS at least show the SE ridge going away after Day 10 but the Pacific just overwhelms the pattern with a zonal flow after that, of course with the -PNA there will be a continued threat for the SE ridge to form in a transient nature afterwards.

[NorEaster27]

The pacific looks pretty bad for the next 2+ weeks. Even if we get an -NAO and some blocking, if SE canda is void of cold air, its not going to help much. Also sunspot activity has picked up dramatically over the past 2 months. I wouldnt be using that as a solid reason why a -NAO or high latitude blocking would return.

[Nikolai]

the Pacific is just terrible for next 2 weeks +

early December could bring change but I would agree that mid December is more likely

enjoy the Indian summer... first legitimate Indian Summer I've ever seen I think, given we had the snowstorm... ridiculous!

[earthlight]

Very nice post and I agree with everything outlined here.

The Pacific pattern and the mean trough on the West Coast of the United States has been in retrograde for a week or two now. Over the next few weeks, we will begin to see some of the first signs of the pattern transition. Tom, you and I have both been pretty vocal on the fact that we expect it to occur in the middle of December. I think think are right on schedule right now.

As it is, the pattern is favorable for a anomalous southeast ridge to pump as the -PNA pattern takes hold. The weak blocking in the Atlantic doesn't even have a chance as it is now. However, notice towards 96 hours as the blocking builds towards Western Greenland and even leaks into the Davis Straight. The Pacific is also in transition by this time, and we're able to get some lower heights into our area. I guess we can call this the first good sign.

The ridge in the N Pacific building towards Western Alaska forces another large trough over the Northwest US and West Coast through Day 7. Making matters worse, the NAO relaxes on almost all global guidance---meaning the mid level heights are going to rise dramatically over the East.

However, it's after this time that the changes begin to occur. By Thanksgiving global ensembles are hinting at the mean trough retrograding to the Gulf of Alaska. It's going to take some time for the NAO to respond. The MJO will be in an unfavorable state for a week or two thereafter--but it's better than it could have been. A few days ago the GEFS means were taking the MJO into a moderate Phase 1. We're beginning to see more of a transitional MJO on most global guidance now...into a weak 1 and then the COD..followed by a week 2-3.

Drawing on your post, it's going to take a good 3-4 weeks to get this pattern re-aligned. But once it does so, I think we'll land around the middle of December...and we'll be ready to get going at a fairly normal climatological time. It's going to take patience.

[Isotherm]

The pacific looks pretty bad for the next 2+ weeks. Even if we get an -NAO and some blocking, if SE canda is void of cold air, its not going to help much. Also sunspot activity has picked up dramatically over the past 2 months. I wouldnt be using that as a solid reason why a -NAO or high latitude blocking would return.

Sunspot activity can bounce around and do whatever it wants; that isn't and never has been the basis for my NAO forecasts. As long as geomagnetic activity stays very low (like it has been for the past 2 years - that aspect hasn't changed), the tendency for enhanced high latitude blocking will exist.

SE Canada actually is not warm at all in the next couple weeks. If you note the Canadian ensemble map I posted, SE Canada is near normal through D 10. Near normal air in SE Canada would be below average for the Northeast US. Lack of cold air to our north is not the problem, it's getting the mechanism to pull it southward. And through week 3 essentially, there isn't much forcing conducive for Eastern troughiness.

[Isotherm]

Very nice post and I agree with everything outlined here.

The Pacific pattern and the mean trough on the West Coast of the United States has been in retrograde for a week or two now. Over the next few weeks, we will begin to see some of the first signs of the pattern transition. Tom, you and I have both been pretty vocal on the fact that we expect it to occur in the middle of December. I think think are right on schedule right now.

As it is, the pattern is favorable for a anomalous southeast ridge to pump as the -PNA pattern takes hold. The weak blocking in the Atlantic doesn't even have a chance as it is now. However, notice towards 96 hours as the blocking builds towards Western Greenland and even leaks into the Davis Straight. The Pacific is also in transition by this time, and we're able to get some lower heights into our area. I guess we can call this the first good sign.

The ridge in the N Pacific building towards Western Alaska forces another large trough over the Northwest US and West Coast through Day 7. Making matters worse, the NAO relaxes on almost all global guidance---meaning the mid level heights are going to rise dramatically over the East.

However, it's after this time that the changes begin to occur. By Thanksgiving global ensembles are hinting at the mean trough retrograding to the Gulf of Alaska. It's going to take some time for the NAO to respond. The MJO will be in an unfavorable state for a week or two thereafter--but it's better than it could have been. A few days ago the GEFS means were taking the MJO into a moderate Phase 1. We're beginning to see more of a transitional MJO on most global guidance now...into a weak 1 and then the COD..followed by a week 2-3.

Drawing on your post, it's going to take a good 3-4 weeks to get this pattern re-aligned. But once it does so, I think we'll land around the middle of December...and we'll be ready to get going at a fairly normal climatological time. It's going to take patience.

Sounds like we're pretty much in agreement here. Yeah it will certainly take some patience; I know many will be antsy to get the cold pattern rolling by early December, but that probably won't happen. However, I think week 3-4 is a good time frame to get things looking better globally. As you correctly explained, the retrograde of the trough into the GOA is step 1, followed by the break down of the arctic low height anomaly, the development of blocking near greenland, and finally the resultant trough in the East, which will liekly take all of 4 weeks to accomplish. MJO won't be favorable until mid dec.

[CooL]

Great stuff. I love how i dont have to skim because something is pointless or i dont understand it. Very good writeup.

What is the difference between a east based NAO and a west based NAO and why is a west based nao notorious for being good for east coast snow?

thanks, and those MJO maps are cool btw

[Isotherm]

Very nice post and I agree with everything outlined here.

The Pacific pattern and the mean trough on the West Coast of the United States has been in retrograde for a week or two now. Over the next few weeks, we will begin to see some of the first signs of the pattern transition. Tom, you and I have both been pretty vocal on the fact that we expect it to occur in the middle of December. I think think are right on schedule right now.

As it is, the pattern is favorable for a anomalous southeast ridge to pump as the -PNA pattern takes hold. The weak blocking in the Atlantic doesn't even have a chance as it is now. However, notice towards 96 hours as the blocking builds towards Western Greenland and even leaks into the Davis Straight. The Pacific is also in transition by this time, and we're able to get some lower heights into our area. I guess we can call this the first good sign.

The ridge in the N Pacific building towards Western Alaska forces another large trough over the Northwest US and West Coast through Day 7. Making matters worse, the NAO relaxes on almost all global guidance---meaning the mid level heights are going to rise dramatically over the East.

However, it's after this time that the changes begin to occur. By Thanksgiving global ensembles are hinting at the mean trough retrograding to the Gulf of Alaska. It's going to take some time for the NAO to respond. The MJO will be in an unfavorable state for a week or two thereafter--but it's better than it could have been. A few days ago the GEFS means were taking the MJO into a moderate Phase 1. We're beginning to see more of a transitional MJO on most global guidance now...into a weak 1 and then the COD..followed by a week 2-3.

Drawing on your post, it's going to take a good 3-4 weeks to get this pattern re-aligned. But once it does so, I think we'll land around the middle of December...and we'll be ready to get going at a fairly normal climatological time. It's going to take patience.

Also good point re the PNA regime. The worst looks to occur D 5-7 with the tanking of the PNA and strong troughing in the Western US (better now than 1 month from now!). But GFS ensembles do actually relax the PNA to the point of neutrality by D 15+ or so, by which time we should see the western GOA trough settling into place, and the CONUS ridge retrograding westward as well.

[Isotherm]

Here's the worst of it at D 8-10 as John and I were just discussing. Pretty disgusting picture overall...the unholy trifecta of -PNA/+AO/+NAO...

[NYCSuburbs]

Nice post! It's informative and nicely written, and I agree with your points as well. I have one question though, what is the accuracy of the MJO forecasts going out to a month? The MJO image you posted shows it gradually moving through phases 1-4, but is there also a possibility that the MJO ends up in the COD? If it does so, would that be supportive or not supportive of getting a pattern change by mid December?

[Sundog]

Great stuff. I love how i dont have to skim because something is pointless or i dont understand it. Very good writeup.

What is the difference between a east based NAO and a west based NAO and why is a west based nao notorious for being good for east coast snow?

thanks, and those MJO maps are cool btw

West based NAOs produce a more favorable trough orientation that is conducive to bringing storms up the coast.

[Isotherm]

Great stuff. I love how i dont have to skim because something is pointless or i dont understand it. Very good writeup.

What is the difference between a east based NAO and a west based NAO and why is a west based nao notorious for being good for east coast snow?

thanks, and those MJO maps are cool btw

Thanks, here's a cool illustration of east vs west based NAO. The former features the core of the pos heights over Iceland/Western Europe while the latter has the pos heigh anomalies centered over Greenland/Hudson Bay region (ala the past 2 winters). Since the negative height field will occur directly south of these anomalies, we want the block to orient itself over greenland.

[Snowstorms]

Sunspot activity can bounce around and do whatever it wants; that isn't and never has been the basis for my NAO forecasts. As long as geomagnetic activity stays very low (like it has been for the past 2 years - that aspect hasn't changed), the tendency for enhanced high latitude blocking will exist.

SE Canada actually is not warm at all in the next couple weeks. If you note the Canadian ensemble map I posted, SE Canada is near normal through D 10. Near normal air in SE Canada would be below average for the Northeast US. Lack of cold air to our north is not the problem, it's getting the mechanism to pull it southward. And through week 3 essentially, there isn't much forcing conducive for Eastern troughiness.

Amazing post Isotherm! Seems very reasonable.

Once that -PNA/+EPO regime finally breaks down the Pacific will finally become favorable but despite that we would need the Atlantic to be favorable as well. Models develop and sustain a -NAO thru this week but then develop a +NAO regime there after thru atleast the 25th. With the EPO/NAO being favorable around Nov 16th-19th we could see a quick cool shot across the East but a torch there after sadly enough. SE Ridge anomaly stays consistent as the Pacific is pumping it up across the East.

And the AP index has remained very low. In fact it took a big drop in October, now down to values around Jan 2011. I expect another drop in November if Geomagnetic Activity doesnt pick up.

And I live in SE Canada and based on what I've seen, many regions should be warmer than normal come D9 and D10 after a nice cool down mid week.

I certainly think this Winter will not be a dud and in fact if we look at Dec 1993 we saw such a similar occurrence and perhaps Dec 2008 can be plausible. The first 15 days or so were quite warm across the East but the second half turned much cooler and snowier so it all depends when and where it all happens but I foresee a cold and snowy December at this point.

[Alpha5]

Here's the worst of it at D 8-10 as John and I were just discussing. Pretty disgusting picture overall...the unholy trifecta of -PNA/+AO/+NAO...

Also pretty important is the +EPO thats helping to create some solid zonal flow over the pacific which is a no go if you want any vorts to develop or amplify

[earthlight]

What is the difference between a east based NAO and a west based NAO and why is a west based nao notorious for being good for east coast snow?

The west and east based NAO are terms that define where the -NAO ridge axis is located, or where the higher heights near the -NAO region are. An east based NAO generally features higher heights/positive height anomalies over eastern Greenland while a west based NAO features higher heights back over Central Greenland/Western Greenland towards the Davis Straight and sometimes (like last December) even extending back over North-Central Canada.

The difference in the two can be quite dramatic. An east based NAO in a bad pattern (or even a good one at times) can sometimes be a disappointment. Although the NAO will register negative, the effects on our pattern can be negligable at times especially if the Pacific pattern isn't cooperating. We can see an example of an east based type -NAO (may be more towards neutral technically but who's counting) over the next few days, coincidentally, as the source of the mid level ridge building towards Greenland is actually to the east/northeast of there. There are better examples for sure, but we'll use this for comparisons sake.

http://i.imgur.com/Y2W3p.png

Here's an example of a west based NAO from last winter. This is an extreme example, with historic height anomalies over Central Canada the Davis Straight, and Western Greenland. Still, the point is made when you look at the overall height field. The pattern literally forces a mean trough underneath into the Northeast United States while maintaining a good cold air source.

http://i.imgur.com/XfrtJ.png

Generally, west based NAO blocks have a tendency to produce..at least in my experience.. more often that the east based blocks. But fundamentally, the difference lies in the placement and intensity of the blocking and the effects on the pattern at our latitude.

[earthlight]

A nice sign on the GEFS means around November 28th, so give or take two weeks from today. You'd have to roll this pattern forward about a week thereafter, too, which would take us to around Dec 5. There has been a rather recurrent theme of inconsistency around this range (what a surprise) over the past several on-hour ensemble cycles...but this is definitely one of the better looking maps I have seen in the past week or so. Comparatively, look earlier in the thread to see the H5 maps from around this next week. The mean trough/negative height anomalies have retrograded to the Gulf of Alaska, and with the help of some higher heights conveniently placed near the Davis Straight..we start to get some cold air.

[Neblizzard]

I agree John that map show lowering of the wavelengths over the east, definitely an improvement. The pacific while not great by any means also looks slightly better. Babysteps,,,,

[earthlight]

GEFS still insistent on the MJO impulse ejecting into Phases 2 & 3 instead of the COD. Phases 2 & 3 historically still favor impulses of a big southeast ridge over the Eastern 1/3 of the US and the continuation of lower heights near the NW US and Pacific.

Hopefully we can speed through here and get towards the more favorable phases as we get to the middle of December, where the effects of even phases 2 & 3 historically become less in regards to the SE Ridge.

[Isotherm]

GEFS still insistent on the MJO impulse ejecting into Phases 2 & 3 instead of the COD. Phases 2 & 3 historically still favor impulses of a big southeast ridge over the Eastern 1/3 of the US and the continuation of lower heights near the NW US and Pacific.

Hopefully we can speed through here and get towards the more favorable phases as we get to the middle of December, where the effects of even phases 2 & 3 historically become less in regards to the SE Ridge.

John, have you seen the ECMWF MJO forecast? It pushes MJO well into phase 3 by the end of November, at a faster pace than GFS guidance. At the Euro's pace, we'd easily be into more favorable octants by mid December.

[earthlight]

John, have you seen the ECMWF MJO forecast? It pushes MJO well into phase 3 by the end of November, at a faster pace than GFS guidance. At the Euro's pace, we'd easily be into more favorable octants by mid December.

That would certainly be better. I think what's really being insinuated by most models is that this is going to be a process. We are going to be climbing out of this unfavorable pattern for a few weeks.

Its interesting also to see the different historical effects that these MJO phases have in December as compared to November. We could see some different results as time goes on.

All of this seems to be lining up fairly well with the flipping major indexes in mid December. Only speculation at this point but I like where we are at. The EPO, AO, etc will be more favorable by then.

It's going to take some patience but we will get there.

[famartin]

Meanwhile, the meteorologist formerly known as SouthlandWx posted this on FB today. Not sure his reasoning and have no idea if he's correct or not... I thought it was funny, but the rest of you may not...

[earthlight]

We're beginning to see the first signs of some blocking towards the Davis Straight by the end of the month (post-thanksgiving). With the retrograding trough over the West Coast moving into the Gulf of Alaska, the pattern would undoubtedly begin to transition if this GEFS height anomaly map were correct. Notice the good source of cold air and the presence of fairly aggressive positive height anomalies near Western Greenland and the DS into Central Canada.

http://www.meteo.psu.edu/~gadomski/ENSHGTAVGNH_18z/f324.gif

[Isotherm]

We're beginning to see the first signs of some blocking towards the Davis Straight by the end of the month (post-thanksgiving). With the retrograding trough over the West Coast moving into the Gulf of Alaska, the pattern would undoubtedly begin to transition if this GEFS height anomaly map were correct. Notice the good source of cold air and the presence of fairly aggressive positive height anomalies near Western Greenland and the DS into Central Canada.

http://www.meteo.psu...NH_18z/f324.gif

Man, that's some gorgeous signalling over Greenland. Definitely some improvement further out on ensembles.

[Isotherm]

Just for shiggles, here's a temp composite map of all Novembers preceding 40"+ winters in NYC since 1960.

Of the 12 years, 10 were warm. Only 1995 and 2002 had cold Novembers. So don't worry, a Nov torch in itself means little.

[earthlight]

Just for shiggles, here'a temp composite map of all Novembers preceding 40"+ winters in NYC since 1960

Of the 12 years, 10 were warm. Only 1995 and 2002 had cold Novembers. So don't worry, a Nov torch in itself means little.

You likely saved 5 cliff jumpers on this board with this post. Humanitarian, you are.

[bluewave]

Just for shiggles, here's a temp composite map of all Novembers preceding 40"+ winters in NYC since 1960.

Of the 12 years, 10 were warm. Only 1995 and 2002 had cold Novembers. So don't worry, a Nov torch in itself means little.

Yeah, It's really difficult to tell one way or another what the winter is going to be like just from November temperatures around here.

One example when November gave us a good signal for the historic winter cold to follow was 1976. Novembers have been

really getting warmer especially recently. It gives you a good idea why there were more bigger November snows a long

time ago. Notice how October has held relatively steady over the years.

http://www.erh.noaa....iestmonths.html

NYC November temperatures

NYC October temperatures

[uncle W]

Just for shiggles, here's a temp composite map of all Novembers preceding 40"+ winters in NYC since 1960.

Of the 12 years, 10 were warm. Only 1995 and 2002 had cold Novembers. So don't worry, a Nov torch in itself means little.

today was the fifth warmest November 14th on record...69 degrees today knocks 1955 from the top five with 68 on this date...The others...

1993 72 great winter

1973 71 Great December ice storm...

1980 71 below zero Christmas day...

1989 70 White Thanksgiving and very cold December...

2011 69 ???

1955 68 snow on the 19th...Very cold December...Big March snows...