My latest CWG and at the end my Jan 8 pattern thoughts.

[ravensrule]

Great easy to read explanation, thanks again Wes.

[Ian]

Best line: the cheerleader thread.

Problem with some here is they gets attached to the idea it WILL snow near such and such period from weeks out that they sorta frame everything around hoping to fulfill those ideas.

Wes is a god among mets..

[usedtobe]

Best line: the cheerleader thread.

Problem with some here is they gets attached to the idea it WILL snow near such and such period from weeks out that they sorta frame everything around hoping to fulfill those ideas.

Wes is a god among mets..

Not a god, I''ve been wrong more than I like to admit. I do think it better to keep my thoughts in separate thread. I've though that for awhile and last night's comments got me to make the switch. Hope I have the self control to stay here in this thread and only post in the other when I see something really exciting.

[am19psu]

Awesome post

This really should be reproduced on the main board in the MR thread. This is the POTM, imo.

[Wonderdog]

Rather than clutter the Jan storm thread with my not always optimistic ideas about the pattern, I thought I'd start keeping them in their own thread.

We'll start with last night's 8-10 day comparison of the GSF and euro since the euro negative NAO look has some salivating. It could of course be correct but it has a tendency to overdo blocking so caveat emptor. The one nice thing about both models is they do have cross polar flow which should give us more chilly intrusions than we had in Dec but the lack of snow cover could make them less impressive than the initial forecasts of them.

The euro also allows some pacific flow into the u.s. because of the trough just off the Pac NW and with the negative nao look, the pattern would be one that would offer snow chances. It's a pretty good look, that's the good news. Now lets look at why there is reason to view it with skepticism. The Euro ensemble mean for 240 hours has a negative ao but the nao is pretty clearly positive. note the lower than normal heights over Iceland, Greenland and Baffin Bay. It too would suggest impulses would break through from the pacific but the positive NAO would make it harder to get the storms to track to our south with the negative PNA look to the pacific ridge, it's the old negative epo (good) but negative pna (bad). It's not a horrible look but we'd probably waffle between cool shots end end most storms as rain.

The gfs ensemble mean for 240 hours also has a positive nao

, it's not a warm look but also is not a frigid one and it has the nao even more positive than the euro ens mean.

What about the Stratospheric warming event. It certainly reversed the winds at 1 mb but has a ways to go before it reverses the winds at 30 mb. Plus if you look at the EP flux vectors, they start pointing more strongly towards the south (left) towards the end of the period just about the time that the 30 mb zonal wind decrease levels off. We have not had a wind reversal at 30 mb. The warming may have helped with the high heights over the north Pacific that have built locally but this still is not yet the big kahuna. It might end up being that but so far, it isn't.

Finally, lets look at the ens mean at the end of the period. No I'm not showing it because I think it is right, it won't be. I am showing it because it starts looking like it wants to take the ao back to positive. That may not happen but it probably does suggest that the AO may not spike high enough to guarantee that the NAO goes to negative and stays there. The change we'd like to see. is not being advertised.

Has the pattern changed yes, do we know the full ramifications of the change, no. We probalby will see more shots of cold than we have been seeing most of the winter and may see an overrunning event down the line though right now I don't really see it. I DO not think the Nao is going to go to a sustained negative period. Heck no, it is more likely to remain positive than negative for the forseeable future. Anyway those are my thoughts. I thought I'd keep them out of the cheerleader thread.

I don't know how to read these charts to say the AO and NAO are positive. Can anyone tell me how to do it?

[usedtobe]

I don't know how to read these charts to say the AO and NAO are positive. Can anyone tell me how to do it?

Here are the correlations with 500 h heights. Essentially when you have below normal heights over Greenland and iceland and above normal heights across the east coast to the azores you have a strongly positive NAO. Reverse that look and the nao is negative.

The AO looks more at the high latitudes around the northern Hemsiphere and is not limited to the north atlantic side.

[CoastalWx]

Those EP vectors and the temporary hault or steady trend in 30mb winds are a little discouraging. We should have another good warming coming up, but I hope we can try and change those features, otherwise it might not do much at all. Maybe this next one does, but who knows.

And I see no sign of any -NAO in the next 2-3 weeks anyways. I feel like people sometimes get too fixated on text data for indices, when you got to look at the 500mb pattern. Physically seeing the pattern gives you a much better understanding of what might happen.

It does seem the models do try and retrograde everything nw. So the ridging near NW AK goes into Siberia, and the PV north of Hudson Bay moves west and heights lower in the GOA. Not the best scenario for the east. I don't know if they are rushing this retrograde too quickly, but it's on the table in some shape or form right now. After day 16...I have no idea what might happen. I guess it depends on what happens in our favorite layer of the atmosphere.

[WinterWxLuvr]

Here are the correlations with 500 h heights. Essentially when you have below normal heights over Greenland and iceland and above normal heights across the east coast to the azores you have a strongly positive NAO. Reverse that look and the nao is negative.

The AO looks more at the high latitudes around the northern Hemsiphere and is not limited to the north atlantic side.

Thanks for posting that Wes. I knew what a neg AO looked like than I did a neg NAO.

The amazing thing about the three stat charts at the bottom is that a neg AO, by stats, is 1.5 times more likely than a pos AO, and when combined with a neutral AO, together they are nearly 3 to 1 as likely as a pos AO yet, here we are, at about day 130 of an almost unbroken pos AO.

[usedtobe]

Those EP vectors and the temporary hault or steady trend in 30mb winds are a little discouraging. We should have another good warming coming up, but I hope we can try and change those features, otherwise it might not do much at all. Maybe this next one does, but who knows.

And I see no sign of any -NAO in the next 2-3 weeks anyways. I feel like people sometimes get too fixated on text data for indices, when you got to look at the 500mb pattern. Physically seeing the pattern gives you a much better understanding of what might happen.

It does seem the models do try and retrograde everything nw. So the ridging near NW AK goes into Siberia, and the PV north of Hudson Bay moves west and heights lower in the GOA. Not the best scenario for the east. I don't know if they are rushing this retrograde too quickly, but it's on the table in some shape or form right now. After day 16...I have no idea what might happen. I guess it depends on what happens in our favorite layer of the atmosphere.

I think down the line the mjo will again emerge as a factor, right now the GWo is probably helping the pattern as its in phase 7 or 8 but that is not likely to last. I saw the same retrogression and see that the OP GFS looks to be shifting the vortex back north. That would not be good for the east but who knows. Like you I don't see a negative nao.

[usedtobe]

Thanks for posting that Wes. I knew what a neg AO looked like than I did a neg NAO.

The amazing thing about the three stat charts at the bottom is that a neg AO, by stats, is 1.5 times more likely than a pos AO, and when combined with a neutral AO, together they are nearly 3 to 1 as likely as a pos AO yet, here we are, at about day 130 of an almost unbroken pos AO.

And the average length of a strong vortex event is 2 months. The nao has also been positive for about the same length of time and has been more positive than the AO. YOU can also see from the charts that when the AO is as high as it was, the nao pretty much has to be the same sign.

[Ian]

Thanks for posting that Wes. I knew what a neg AO looked like than I did a neg NAO.

The amazing thing about the three stat charts at the bottom is that a neg AO, by stats, is 1.5 times more likely than a pos AO, and when combined with a neutral AO, together they are nearly 3 to 1 as likely as a pos AO yet, here we are, at about day 130 of an almost unbroken pos AO.

is that their likelihood or the sample size? n/m i guess the former..

[WinterWxLuvr]

is that their likelihood or the sample size? n/m i guess the former..

Ian, I guess, to me, it means that if you had predicted what Jan 8th's AO reading would have been back in Oct. you could have said that the odds would have been 3 to 1 against it being positive.

[usedtobe]

is that their likelihood or the sample size? n/m i guess the former..

That's a good question. I think if you look historically back in the past the negative AO occurred more often but that has not been the case in the last couple of decades. I think someone from the University of Washington published a paper on the trend. I don't remember where I saw it.

[WinterWxLuvr]

That's a good question. I think if you look historically back in the past the negative AO occurred more often but that has not been the case in the last couple of decades. I think someone from the University of Washington published a paper on the trend. I don't remember where I saw it.

And the odds that I posted are statistical odds only. They wouldn't take into account any of the variability from year to year, nor the conditions of the atmosphere at the time. And for that reason, wouldn't be very useful except in the sense that one might say that what we are experiencing right now has been, statistically rare.

[usedtobe]

This website shows how the AO tendency has changed. I think the last couple of years made us think that the negative cycle was back. This year, is a cautionary note.

http://www.appinsys.com/globalwarming/AO_NAO.htm

[Bob Chill]

ens forcast for the AO now shows little confidence in either direction. A couple days ago showed a half decent consensus of it dipping into neg territory but that has changed to just about 50/50 in any direction.

The nao on the other is pretty much unanimously forcast to remain positive for the foreseeable future. Then, of course, the 12z gfs builds a 1055hp over greenland starting around the 19th or so and keeps the ridge in place through the end of the run. Pretty skeptical for sure but hey, not going to argue with a model showing the nao going negative and holding for 4+ days. It looks like the big cutter helps build the ridge so I guess if the storm doesn't happen or is weak then no -nao.

[usedtobe]

ens forcast for the AO now shows little confidence in either direction. A couple days ago showed a half decent consensus of it dipping into neg territory but that has changed to just about 50/50 in any direction.

The nao on the other is pretty much unanimously forcast to remain positive for the foreseeable future. Then, of course, the 12z gfs builds a 1055hp over greenland starting around the 19th or so and keeps the ridge in place through the end of the run. Pretty skeptical for sure but hey, not going to argue with a model showing the nao going negative and holding for 4+ days. It looks like the big cutter helps build the ridge so I guess if the storm doesn't happen or is weak then no -nao.

What's interesting is even with its negative AO the pattern still is lousy for us on the run. I'm skeptical about the evolution. It could happen but I'll wait until I see more of a consensus among the ens mean forecasts. Operational model seem to like to build blocks.

[Wonderdog]

Here are the correlations with 500 h heights. Essentially when you have below normal heights over Greenland and iceland and above normal heights across the east coast to the azores you have a strongly positive NAO. Reverse that look and the nao is negative.

The AO looks more at the high latitudes around the northern Hemsiphere and is not limited to the north atlantic side.

Thanks Wes. Very helpful.

[Bob Chill]

Operational model seem to like to build blocks.

Heh, the op and my 7 year old son have something in common.

There's been plenty of "ok" nhem 500 patterns modeled for the last week or so. Nothing great but nothing ghastly either. Considering we're in primetime MA snow climo, you would have to think the odds of some accum snow are tipped in our favor right. Probably going to be a sneakly little overrunning event or clipper that gets picked up inside of 5 days. I'm cool with that.

[ThreeRedheads]

Here are the correlations with 500 h heights. Essentially when you have below normal heights over Greenland and iceland and above normal heights across the east coast to the azores you have a strongly positive NAO. Reverse that look and the nao is negative.

The AO looks more at the high latitudes around the northern Hemsiphere and is not limited to the north atlantic side.

Very helpful post, Wes!

If I understand it correctly, this euro map shows a negative NAO? Just want to make sure I understand your explanation.

[winterymix]

I DO not think the Nao is going to go to a sustained negative period. Heck no, it is more likely to remain positive than negative for the forseeable future. Anyway those are my thoughts. I thought I'd keep them out of the cheerleader thread.

Thanks for keeping the articles coming, Wes. In order to denjoy the science and not be disappointed by snow drought, I think it helps being middle-aged.

I tried to find correlations between Baltimore winters with ten inches or less of snow since 1950, AO index, Oceanic La Nina, El Nino index, AO on exactly February 1

of each of those low-snow seasons as well as the average NOA index for January/February of those seasons. Using my amateur knowledge, it seems interesting

to take those select data points and look for correlations or even inverse correlations. Below, please note the data table and somewhat useless chart.

If it is going to be a crummy snow season, I'd like to know why, as well as how often this has happend previously. Most of the weak snow seasons around Baltimore

seemed to have had neutral to postive NAO states on average for January/February. My take is that

ENSO state defines the season and that NAO seems to hold the greatest local influence here in the Mid-Atlantic. It seems that a negative AO is icing on the cake,

it can make for a great snow season but is a secondary influence. A negative AO with lack of blocking may be "wasted cold". Wes, I think you have said all of the

above, many times and more elegantly.

[usedtobe]

In my new effort not to be debbie downer, I'll post the 240 hr euro from 12Z this morning. It does still show a weak negative nao but has low heights remaining over Greenland. It also has the ao being quite negative. the troffiness/low off the pac nw?western Canada keeps a stream of flow coming in for the pacific at the same time that arctic air settle southward so maybe beyond day 10 things might get interesting those I could see the ens mean being more conservative about the NAO.

I'm still not impressed with tomorrows event and think it either is light rain or nothing. Probably the former. Very marginal 850 temps and surface temps in the upper 30s seem a little warm to get excited about.

Winterymix, nice post. Work by Wallace suggests that 2 inch or greater event are almost 3 times as likely with a negative AO.