When will the pattern change to cold occur?

[Weathergun]

I don’t necessarily see much of December, being all out blowtorch, either. But being just unfavorable for any significant snowstorms or sustained cold.

On the Euro ensembles, the PNA never really gets to or east of the Rockies, before retreating back west towards the Aleutians. Nor does build very much into Alaska or NW Canada. I think most of cold air dumps into Western or Central US. While we see more modified or transient cold shots here trough about 10th. Then we see at least weak or modest SE ridge return after the 12/10. The Euro ensembles have the MJO moving slow but pretty weak in phases 4/5 next month. So that I might mean we don’t see strong SE ridge that could torch us more. I don't see this changing before the 12/20. And Euro ensembles have been pretty consistent in not getting the MJO in the favorable phases around Christmas or so.

For storm threats, I think mostly SW flow events, that are probably more rain than snow for NYC south. If there is going to be a bigger storm it's probably not till after Christmas.

I also wonder why really we don’t see stronger SE ridge on the GEFS, since it has the MJO much stronger in phases 4/5, than the Euro Ensembles. It been inconsistent with the MJO and I don’t trust what’s it’s showing at all.

[SnowGoose69]

I don’t necessarily see much of December, being all out blowtorch, either. But being just unfavorable for any significant snowstorms or sustained cold.

On the Euro ensembles, the PNA never really gets to or east of the Rockies, before retreating back west towards the Aleutians. Nor does build very much into Alaska or NW Canada. I think most of cold air dumps into Western or Central US. While we see more modified or transient cold shots here trough about 10th. Then we see at least weak or modest SE ridge return after the 12/10. The Euro ensembles have the MJO moving slow but pretty weak in phases 4/5 next month. So that I might mean we don’t see strong SE ridge that could torch us more. I don't see this changing before the 12/20. And Euro ensembles have been pretty consistent in not getting the MJO in the favorable phases around Christmas or so.

For storm threats, I think mostly SW flow events, that are probably more rain than snow for NYC south. If there is going to be a bigger storm it's probably not till after Christmas.

I also wonder why really we don’t see stronger SE ridge on the GEFS, since it has the MJO much stronger in phases 4/5, than the Euro Ensembles. It been inconsistent with the MJO and I don’t trust what’s it’s showing at all.

Its tough to get a big snow event whenever the NAO is positive, but that does not mean it can't snow, that +PNA is a huge factor and always gives you a chance since that western ridge is so important when it comes to getting an East Coast snow event, 1/22/87 is a great event of a major event that occurred with a massive Yukon/BC/AK ridge but +NAO. The key when the NAO is positive is timing, you want some sort of disturbance to be coming ashore on the West Coast so that ridge can start ejecting eastward, that way when the trough goes negative you don't get a Lakes event, however; if that disturbance comes ashore too early the trough axis is too far east and the storm misses. 2/23/89 is a good example of a +NAO/+PNA snow event that narrowly missed with the exact setup I mention above because that ridge was ever so slightly too far east as well as the trough.

[Sundog]

Its tough to get a big snow event whenever the NAO is positive, but that does not mean it can't snow, that +PNA is a huge factor and always gives you a chance since that western ridge is so important when it comes to getting an East Coast snow event, 1/22/87 is a great event of a major event that occurred with a massive Yukon/BC/AK ridge but +NAO. The key when the NAO is positive is timing, you want some sort of disturbance to be coming ashore on the West Coast so that ridge can start ejecting eastward, that way when the trough goes negative you don't get a Lakes event, however; if that disturbance comes ashore too early the trough axis is too far east and the storm misses. 2/23/89 is a good example of a +NAO/+PNA snow event that narrowly missed with the exact setup I mention above because that ridge was ever so slightly too far east as well as the trough.

So it's basically a thread the needle setup like feb 2006? I know there was a beautiful PNA ridge with that one but can't remember if the NAO was cooperative.

[TheTrials]

So it's basically a thread the needle setup like feb 2006? I know there was a beautiful PNA ridge with that one but can't remember if the NAO was cooperative.

it went slightly negative right before the event and had a 50/50. It wasn't as thread the needle as people make it out to be.

March 2009 was a totally PNA driven storm as were most of the events in 93-94

[SnowGoose69]

it went slightly negative right before the event and had a 50/50. It wasn't as thread the needle as people make it out to be.

March 2009 was a totally PNA driven storm as were most of the events in 93-94

March 2009 was a successful version of 2/23/89, the setup was virtually identical at 500mb, except that in 09 the system was better captured and pulled more up the coast. 1993-94 the PNA was mainly negative outside of December and during the January arctic outbreak to most people's surprise, it was actually negative for both the 2/8 and 2/11 events, however the -EPO resulted in a very suppressed gradient setup and there was consistently a split flow pattern going as well, often times a split flow pattern can mask the effects of a +NAO. We saw that in December 2007 early on.

[TheTrials]

March 2009 was a successful version of 2/23/89, the setup was virtually identical at 500mb, except that in 09 the system was better captured and pulled more up the coast. 1993-94 the PNA was mainly negative outside of December and during the January arctic outbreak to most people's surprise, it was actually negative for both the 2/8 and 2/11 events, however the -EPO resulted in a very suppressed gradient setup and there was consistently a split flow pattern going as well, often times a split flow pattern can mask the effects of a +NAO. We saw that in December 2007 early on.

yeah, i just re-looked at those, abosolutely a -PNA. It was all EPO

[MJO812]

Man, the 6z GFS is cold in the long range.

[NYCSuburbs]

Man, the 6z GFS is cold in the long range.

It's still not making up its mind... after a somewhat warmer 0z run which attempted to build another eastern ridge, the 6z run locks the arctic air in with no Alaskan PV, but there's still no blocking with a +NAO/AO. The start of December does have a colder look to it, with less ridging and some more cold, probably bringing slightly below average temperatures, but especially when considering that no -NAO/-AO develop yet, I'm thinking that we'd probably have to wait until late December or January for better chances of more sustained cold and snow, with transient cold and some snow before then but mixed with warm spells as well.

[MJO812]

It's still not making up its mind... after a somewhat warmer 0z run which attempted to build another eastern ridge, the 6z run locks the arctic air in with no Alaskan PV, but there's still no blocking with a +NAO/AO. The start of December does have a colder look to it, with less ridging and some more cold, probably bringing slightly below average temperatures, but especially when considering that no -NAO/-AO develop yet, I'm thinking that we'd probably have to wait until late December or January for better chances of more sustained cold and snow, with transient cold and some snow before then but mixed with warm spells as well.

Yep, the models are all over the place. One run has sustained cold and then the next run is warm. At least the ensembles have been consistent with the cold in the long range ( helped out by the + PNA.) The ensembles also show a + NAO in the long range.

[NYCSuburbs]

Yep, the models are all over the place. One run has sustained cold and then the next run is warm. At least the ensembles have been consistent with the cold in the long range ( helped out by the + PNA.) The ensembles also show a + NAO in the long range.

The -EPO also looks nicer for this time frame, but the NAO/AO aren't cooperating. As the ensembles show, it can be cold without a -NAO/-AO, but the cold won't be sustained and most of the snow events would likely stay inland/well inland. At this rate, it seems that the main issue for December would be for the NAO and AO to become negative while the EPO/PNA are still supportive. December probably shouldn't be as bad as this month was, but I'm placing my hopes for a better pattern in January.

[Isotherm]

Major to historic snow events generally do not occur without some type of negative AO or NAO, but we've seen numerous instances of moderate or significant snowfalls under +NAO/+AO/+PNA regimes.

A good example is January 1984. New Brunswick NJ recorded 15-16" of snow that month, nearly 40" for the winter actually (in a mainly +NAO season).

Jan 1984 featured a +AO, +NAO, yet the PNA ridge was impressive particularly in the mid month time frame, allowing for storminess along the EC.

http://www.meteo.psu.edu/~gadomski/NARR/1984/us0119.php

Scroll through Jan '84 to see the progression on the PSU site.

The trough axis was positioned in the Mid-west/central US, and the +PNA ridge along/just west of CA/OR/WA, very similar to what's progged in the current pattern.

Note mid Jan 1984:

Now note the D 8-10 period. Similar ridging offshore of the West Coast, PV over Hudson Bay, trough in Mid west, height rise along the East coast. Not a bad match.

I wouldn't rule out moderate type snowfall i nthe Dec 5th-10th period.

[earthlight]

Just added a footnote in the thread title--lets try to keep this the general discussion thread on anything not related to current obs for the upcoming storm/rain/torch/etc.

[earthlight]

Major to historic snow events generally do not occur without some type of negative AO or NAO, but we've seen numerous instances of moderate or significant snowfalls under +NAO/+AO/+PNA regimes.

A good example is January 1984. New Brunswick NJ recorded 15-16" of snow that month, nearly 40" for the winter actually (in a mainly +NAO season).

Jan 1984 featured a +AO, +NAO, yet the PNA ridge was impressive particularly in the mid month time frame, allowing for storminess along the EC.

I wouldn't rule out moderate type snowfall in the Dec 5th-10th period.

I was thinking that this was a possibility for a while, but as it seems now the timing of any shortwave worth noting and the appreciable cold air is just atrocious. The models have a pretty significant trough on the west coast now--so I guess you can't rule anything out with the shortwaves diving south on the east side of that ridge axis from Central Canada into the Plains.

If you loop the GFS, it's actually really threatening for a few frames around 156-180 hours. Watch the shortwave race southward and almost hook up with the southern stream vorticity over Oklahoma. Rings a bell, doesn't it? The problem is, there's very little working to slow the pattern down enough to allow this thing to get going.

http://www.meteo.psu.edu/~gadomski/AVN_0z/avnloopnew.html

[tmagan]

One word best describes this upcoming pattern -- ephemeral.

[Dark Energy]

I'm liking the cool down late week, finally back to normal. But the cold snap about 10 days away seems to be delayed with each model run. SHOCKER!!

[SnowGoose69]

Major to historic snow events generally do not occur without some type of negative AO or NAO, but we've seen numerous instances of moderate or significant snowfalls under +NAO/+AO/+PNA regimes.

A good example is January 1984. New Brunswick NJ recorded 15-16" of snow that month, nearly 40" for the winter actually (in a mainly +NAO season).

Jan 1984 featured a +AO, +NAO, yet the PNA ridge was impressive particularly in the mid month time frame, allowing for storminess along the EC.

The worst setup I have ever seen with a relatively significant snow event in the last 25 years was probably 12/28/90, a pure overrunning event, the AO and NAO were positive and the PNA was raging negative. I don't know what the EPO was but given that massive high over SE Canada and the cold air supply in the northern Rockies and west Canada its highly possible the EPO was negative. Many places saw 5-7 inches of snow across the region.

http://www.meteo.psu...1990/us1228.php

[TheTrials]

cmc says all the mid-month pattern change forecasts are going to bust. The cmc ensembles have been much less aggressive that the gfs with any projected cooldown for a good week now. they have not waivered.

[bluewave]

It looks like NYC has a shot at its first freezing or below morning in the 7-10 day as we are getting a sustained drop in the EPO for a change.

[KEITH L.I]

The worst setup I have ever seen with a relatively significant snow event in the last 25 years was probably 12/28/90, a pure overrunning event, the AO and NAO were positive and the PNA was raging negative. I don't know what the EPO was but given that massive high over SE Canada and the cold air supply in the northern Rockies and west Canada its highly possible the EPO was negative. Many places saw 5-7 inches of snow across the region.

http://www.meteo.psu...1990/us1228.php

wow..shows you during the winter some horrible setups can lead to a snowstorm..hideous pattern

[Stormlover74]

That morning it was only supposed to be 1-3 but they upped it to 3-6...I ended up with close to 8 with a coating of ice on top..less than 72hours later it was completely gone

The worst setup I have ever seen with a relatively significant snow event in the last 25 years was probably 12/28/90, a pure overrunning event, the AO and NAO were positive and the PNA was raging negative. I don't know what the EPO was but given that massive high over SE Canada and the cold air supply in the northern Rockies and west Canada its highly possible the EPO was negative. Many places saw 5-7 inches of snow across the region.

http://www.meteo.psu...1990/us1228.php

[uncle W]

late December 1984 there was a snowstorm between torches...3-5" fell...It melted in 70 degree temperatures a few days later...

http://climate.usurf.usu.edu/products/output.php

[tacoman25]

wow..shows you during the winter some horrible setups can lead to a snowstorm..hideous pattern

There was a ton of Arctic air that had been dumped into the CONUS leading up to this, which made the resulting observed weather even in the East colder than this pattern would indicate.

[TheTrials]

-20 850's on the euro getting into the CONUS at 180 hours. Euro may be trying to bring a wave up the front as well that the GFS brings through and then pushes the trough east.

[TheTrials]

foot race between the cold air and the precip on the euro at 192

[TheTrials]

HM says the 12/15 predictions are in trouble

http://www.americanwx.com/bb/index.php/topic/30013-something-for-the-nerds/page__view__findpost__p__1149317

[KEITH L.I]

HM says the 12/15 predictions are in trouble

http://www.americanw...ost__p__1149317

I'm getting to the point where I'm not expecting much this winter..and that's ok..we have had some blockbusters the last 10 years!..For this winter I'm in the whatever you can get mode right now

[NYCSuburbs]

HM says the 12/15 predictions are in trouble

http://www.americanw...ost__p__1149317

Seems reasonable with the way how the pattern is behaving. There's some medium range improvements, but instead of becoming sustained, they appear to fade away towards the long range, with the -EPO slowly moderating towards neutral with a dropping PNA while the MJO goes into the COD and the NAO/AO stay positive. I would also think that another warm up may be possible around or after the middle of December, and although transient troughs like we've seen this month should probably continue, at this rate I'm thinking we'll probably have to wait until January before we get any real chance of a sustained wintry pattern.

[uncle W]

I'm getting to the point where I'm not expecting much this winter..and that's ok..we have had some blockbusters the last 10 years!..For this winter I'm in the whatever you can get mode right now

I still think we will see at least two good weeks or more of cold and snow...It will probably come in late January or February...I expect at least one storm 6" or more...I still think the AO/NAO will finally go negative in late January or February...

[KEITH L.I]

I still think we will see at least two good weeks or more of cold and snow...It will probably come in late January or February...I expect at least one storm 6" or more...I still think the AO/NAO will finally go negative in late January or February...

sort of like 71-72 or 73-74..remember Dec 73 was very mild but we squeezed in that ice storm

[NorEaster27]

late january