Negative NAO coming?

[chionomaniac]

Some really good posts. Chionomaniac, I like your reasoning and think it does argue for the ao to average in the positive range through dec and into Jan. However, if the AK vortex gets displaced, there still can be transitory cold shots in an otherwise crappy pattern. I like the figure showing how snow cover might impact upon the nao.

Yes, we call them northerly topplers over here as the jet quickly reestablishes itself.

[uncle W]

I really like your posts I'd like to say first off, said posts are always informative in one form or another. This post gives me some hope for the upcoming winter. Is the first line of your data wrong? You list 1977 as a positive AO for winter following a negative in August. The 1977 line lists a negative winter low AO, the second most negative in your data set. Was 1977 really that volatile where it saw a -3 AO but also had an average of positive for the winter?

I was using the one month low AO index for the following winter...

this link has the monthly AO index...

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/monthly.ao.index.b50.current.ascii.table

[The_Global_Warmer]

The GFS long range every few days goes to a -NAO solution, but then loses it and goes back to a consistent positive NAO. In the long term.

[usedtobe]

As others have stated, the strength of the stratospheric vortex and the northern Annular mode right now are a big problem. That in my mind puts most of December in jeapardy for mid atlantic cold lovers. The polar night jet is strong, the temps near the poles in the stratosphere are quite a big colder than normal.

I guess it's no surprise that the AO shows no real signs of going negative for the forseeable future. I wouldn't trust models showing an a negative nao index especially a weak signal as I'd worry that such a forecast would be more of an artifact of the way the nao is calculated than a true measure of the blocking in the north atlantic and Greenland area.

Here's the ao forecasts. They are usually more robust than forecasts of the noa since it is calculated over a greater area.

The gfs and euro are really struggling in the 7 to 10 day plus periods . Yesterday's amplified euro in the middle of the country is not as impressive one last night's runs.

Anyway, given the robust polar night jet, lack of any high latitude blocking and MJO forcing. I still don't see a meaningful change for the mid atlantic except fro transient cold shots. Also Judah cohen put out his forecast for the winter based on the snow cover. He said the oct snow cover was about normal. If that means the AO ends up being around zero for the winter. This would be the la nina temp distribution (see middle panel below).

To really change I think we may need the mjo to get into the 8-2 range during the peak winter months and have a ssw event. We still have the atlantic ssta in a good configuration and have the AP index low, sso there certainly is hope. However, for the 1st couple of weeks of dec may be tough for snow lovers.

[Lee]

As others have stated, the strength of the stratospheric vortex and the northern Annular mode right now are a big problem. That in my mind puts most of December in jeapardy for mid atlantic cold lovers. The polar night jet is strong, the temps near the poles in the stratosphere are quite a big colder than normal.

I guess it's no surprise that the AO shows no real signs of going negative for the forseeable future. I wouldn't trust models showing an a negative nao index especially a weak signal as I'd worry that such a forecast would be more of an artifact of the way the nao is calculated than a true measure of the blocking in the north atlantic and Greenland area.

Here's the ao forecasts. They are usually more robust than forecasts of the noa since it is calculated over a greater area.

The gfs and euro are really struggling in the 7 to 10 day plus periods . Yesterday's amplified euro in the middle of the country is not as impressive one last night's runs.

Anyway, given the robust polar night jet, lack of any high latitude blocking and MJO forcing. I still don't see a meaningful change for the mid atlantic except fro transient cold shots. Also Judah cohen put out his forecast for the winter based on the snow cover. He said the oct snow cover was about normal. If that means the AO ends up being around zero for the winter. This would be the la nina temp distribution (see middle panel below).

To really change I think we may need the mjo to get into the 8-2 range during the peak winter months and have a ssw event. We still have the atlantic ssta in a good configuration and have the AP index low, sso there certainly is hope. However, for the 1st couple of weeks of dec may be tough for snow lovers.

A couple of things I'm wondering about and would like to know is if maybe you or HM, etc; would give an opinion on what may have a chance over riding/altering the current pattern drivers.. and that being what Robert (foothills) has been harping on; the abundant systems/lp's we continue to see and whether or not they may pop either a eastern canadian PV or a 50-50 that would pump up a Greenland block. The sst's are favorable in the N.Atlantic, so this would seem possible to me. Of course, I know there has to be the atmospheric connection, so is it that the cold strat. would not allow this? Appreciate the opinions and explanation.

[QVectorman]

As others have stated, the strength of the stratospheric vortex and the northern Annular mode right now are a big problem. That in my mind puts most of December in jeapardy for mid atlantic cold lovers. The polar night jet is strong, the temps near the poles in the stratosphere are quite a big colder than normal.

To really change I think we may need the mjo to get into the 8-2 range during the peak winter months and have a ssw event. We still have the atlantic ssta in a good configuration and have the AP index low, sso there certainly is hope. However, for the 1st couple of weeks of dec may be tough for snow lovers.

A lot of great info as usual!

[Lee]

Just looked @ the Goofus and it actually shows a scenario similar to what I was noting/questioning as a pattern altering possibility, so much so, that it looks as if I had already looked @ it .

I know the outcome , in light of it not only being the GFS but in respect to what others have presented in aquiring a pattern change, is not very likely.

[usedtobe]

Just looked @ the Goofus and it actually shows a scenario similar to what I was noting/questioning as a pattern altering possibility, so much so, that it looks as if I had already looked @ it .

I know the outcome , in light of it not only being the GFS but in respect to what others have presented in aquiring a pattern change, is not very likely.

I've be a little suspicious of any model that pops a negative nao in hte next couple of weeks. The noa ensembles have shown a bias of forecasting the noa to be too low.

Note the low correlation between the 14 day forecast and reality. Below o.50 is way too low to have much faith in it. Could the great lakes low showing up on the guidance pop a temporary ridge over southern greenland, sure though I suspect it would be short lived. Also, look at the ensemble members for that time range. They are all over the place.

[NJwinter23]

Pretty clear that any cold period we get in the coming weeks will have to be +pna driven, starting with the first few days in early December...the extent of the cold I do not know, and will likely deal a lot with how the models handle that mess of a cut off next week. No hope for the NAO in plain site, and i definitely agree the time to watch will be later in December.

[tombo82685]

Pretty clear that any cold period we get in the coming weeks will have to be +pna driven, starting with the first few days in early December...the extent of the cold I do not know, and will likely deal a lot with how the models handle that mess of a cut off next week. No hope for the NAO in plain site, and i definitely agree the time to watch will be later in December.

if we get that big cutoff, you think we could maybe pump a short lived ridge into greenland, maybe timed correctly with a storm we could have some blocking.

[skierinvermont]

weekly update for stratospheric temps shows they have continued to plunge.

[Alpha5]

weekly update for stratospheric temps shows they have continued to plunge.

What drives stratospheric temps? I understand the connection between the stratosphere and AO, but what causes stratospheric temp anomalies? The sun?

[HM]

What drives stratospheric temps? I understand the connection between the stratosphere and AO, but what causes stratospheric temp anomalies? The sun?

Stratospheric temperatures are driven by ozone. Higher the ozone=higher the temperatures. The sun is a major driver in ozone formation and destruction:

http://www.atmosphere.mpg.de/enid/m2.html

[HM]

Here is some good news: It appears the "active region count" has begun to make the turn downward.

The TSI has recently had a spike but this should be the relative max if we begin to turn downward:

Kinda cool that the TSI looks a little like how the AO has been trending too:

But that's just eyeballing it. I haven't actually done anything statistical here but the two graphs have some similarity. It could be noise for all I know.

[Srain]

There are starting to be some trends in the ensembles that may suggest a bit of a change is ahead regarding the NAO. While it may be transient, the switch to a +PNA/-NAO regime could give some hope for the cold weather lovers.

[usedtobe]

There are starting to be some trends in the ensembles that may suggest a bit of a change is ahead regarding the NAO. While it may be transient, the switch to a +PNA/-NAO regime could give some hope for the cold weather lovers.

Steve,

I have little faith in the nao forecasts. Look at the bottom panel. The forecast nao was way higher than the observed. That seems to be a bias so far this winter. Eventually, that may switch but not yet. Also when the correlation is below .40 that means that the forecast nao is explaining less than 16% of the variance of the NAO. Essentially the model is sucking at forecasting the nao at that time range. That's way too low to use in a forecast setting. More importantly to me is that the AO is still forecast to be positive at that time range. It's forecast should be a little more robust than forecasts for the nao. Plus the stratospeheric vortex is colder and stronger than normal.

I think the pna change is more likely but may not initially have enough amplitude to the ridge to matter too much. The 240 hour Eruo shows how the pattern might start pulling down cold air and my guess is that it is right that any arctic shot will first come to the west and plains before getting east. However, the models beyond day 4 or 5 have been pretty bad lately so I wouldn't give any run too much credence.

[Rainshadow]

Steve,

I have little faith in the nao forecasts. Look at the bottom panel. The forecast nao was way higher than the observed. That seems to be a bias so far this winter. Eventually, that may switch but not yet. Also when the correlation is below .40 that means that the forecast nao is explaining less than 16% of the variance of the NAO. Essentially the model is sucking at forecasting the nao at that time range. That's way too low to use in a forecast setting. More importantly to me is that the AO is still forecast to be positive at that time range. It's forecast should be a little more robust than forecasts for the nao. Plus the stratospeheric vortex is colder and stronger than normal.

I think the pna change is more likely but may not initially have enough amplitude to the ridge to matter too much. The 240 hour Eruo shows how the pattern might start pulling down cold air and my guess is that it is right that any arctic shot will first come to the west and plains before getting east. However, the models beyond day 4 or 5 have been pretty bad lately so I wouldn't give any run too much credence.

Wes,

At least the day 7 NAO correlation has been better; hopefully it holds in a forecasting sense that if a change becomes apparent and it carries into that forecast time frame, we'll have better confidence of a pattern change. The PNA may fall off the bus first, but until the pv moves away from the pole we'd likely need a pretty large amplitude ridge to get any really relative to normal colder air in our neck of the woods and would suspect it'd be transitory at this juncture.

Have a Happy Thanksgiving! It felt strange hanging outdoor Christmas lights in short sleeves this morning.

[usedtobe]

Wes,

At least the day 7 NAO correlation has been better; hopefully it holds in a forecasting sense that if a change becomes apparent and it carries into that forecast time frame, we'll have better confidence of a pattern change. The PNA may fall off the bus first, but until the pv moves away from the pole we'd likely need a pretty large amplitude ridge to get any really relative to normal colder air in our neck of the woods and would suspect it'd be transitory at this juncture.

Have a Happy Thanksgiving! It felt strange hanging outdoor Christmas lights in short sleeves this morning.

BY day 7, the forecasts are not bad. The correlations are high enough to have some faith in the models so we probably won't be caught completely unawares. I'm liking this weather. Tomorrow I'm going out golfing again.

[winterymix]

Steve,

I have little faith in the nao forecasts. Look at the bottom panel. The forecast nao was way higher than the observed. That seems to be a bias so far this winter. Eventually, that may switch but not yet. Also when the correlation is below .40 that means that the forecast nao is explaining less than 16% of the variance of the NAO.

Can the scientists responsible for the model bias determine the cause and fix it

early enough in the winter season to help forecasters?

Either that, or can they use some statistical masking technique to put out a forecast that

is adjusted to remove the bias?

[usedtobe]

Can the scientists responsible for the model bias determine the cause and fix it

early enough in the winter season to help forecasters?

Either that, or can they use some statistical masking technique to put out a forecast that

is adjusted to remove the bias?

I think it is the nature of the models to try and build the blocking too quickly in some patterns but once established to sometimes break it down too quickly. If you go back to August, there was a period when the models were not negative enough. I'm not sure you can do an easy bias correction when the bias may shift when the pattern shifts. That said. You certainly can look at the verification and see that the ensembles have generally been too low with their forecasts of the index.

[skierinvermont]

What drives stratospheric temps? I understand the connection between the stratosphere and AO, but what causes stratospheric temp anomalies? The sun?

Short term there's variations in ozone and also upward propagation from the troposphere via snowcover. I bet other things besides snowcover can cause tropospheric waves to propagate upwards but I don't really know. Also I think volcanic aerosols may have an effect?

[Mitchel Volk]

The 30 day ECMWF forecast shows that the NAO will mainly remain positive. I all ready reduced my snowfall totals for NYC due to this pattern. The Rossby wave pattern look dreadful for I-95 Snow.

[stormman]

The 30 day ECMWF forecast shows that the NAO will mainly remain positive. I all ready reduced my snowfall totals for NYC due to this pattern. The Rossby wave pattern look dreadful for I-95 Snow.

Isnt it a bit premature, I mean yes it looks to remain mostly positive for the month of december, but what if it were to flip after that and all of jan and feb were to be mostly neg?

[easternsnowman]

The 30 day ECMWF forecast shows that the NAO will mainly remain positive. I all ready reduced my snowfall totals for NYC due to this pattern. The Rossby wave pattern look dreadful for I-95 Snow.

30 day euros are so reliable as of late

[easternsnowman]

Alot of forecasts see december somewhat above or near normal and then january and maybe feb cold.

[MJO812]

The 30 day ECMWF forecast shows that the NAO will mainly remain positive. I all ready reduced my snowfall totals for NYC due to this pattern. The Rossby wave pattern look dreadful for I-95 Snow.

Just because of the Euro forecast? I don't get it. We all know how reliable the models are in the long range.

[lbchandler]

Alot of forecasts see december somewhat above or near normal and then january and maybe feb cold.

Same forecasters who one month ag saw Dec as cold and snowy and Jan turning milder into Feb.

[OSUmetstud]

I'm pretty sure there is more than just the euro weeklies signaling blocking being tough to come by in December....but weenies will be weenies.

[BethesdaWX]

We've been spoiled the last few winters with the persistent troughing, not upset to go through a ridgy stretch, not in the least. Going into denial over it and whining is typical.

Still sticking to my late December idea, I think we'll see changes in the AO showing up at least on the modeling by then, if not beginning to occur.

[uncle W]

what a difference a year makes...I don't have todays AO index number but I think it's over +3.000...Last year the AO dipped to -4.058 on 11/26...Then fell to -5.265 0n 12/18...The next dip was -2.411 0n 1/22...It rose to +3.914 on 2/4 and the winter pattern changed...