Negative NAO coming?

[chionomaniac]

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?

Strong mountain torque events can cause wave breaking from the troposphere into the stratosphere.

There are two types of wave breaking into the stratosphere. The first is 'remote' where the wave travels around the edge of the polar vortex before breaking in over the top. The second are local where the wave breaks centrally up through the vortex.

"Three-dimensional (3-D) simulations of a forced vortex show two classes of wave breaking: “remote” wave breaking where Rossby waves propagate up the vortex edge and break in upper levels (e.g., Figure 5c) and “local” breaking where the wave breaking occurs at lower levels of the vortex and inhibits further wave propagation into the upper levels [Dritschel and Saravanan, 1994; Waugh and Dritschel, 1999; Polvani and Saravanan, 2000]"

http://www.columbia.edu/%7elmp/paps/waugh+polvani-PlumbFestVolume-2010.pdf

I suspect that the last two winters that we have seen the latter type of wave breaking which even though it hasn't led to an early SSW, the winters have started with extensive northern blocking due to splits in the lower stratospheric vortex extending upwards. The early warmer stratospheric conditions have probably contributed to this.

c

[thunderbolt]

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...

uncle can you please give me the link for the ao index history. thanks thunderbolt

[brad1551]

I put money the NAO goes negative by the end of December or early January. Everyone needs to realize that the last couple of years we have been spoiled. Actually we are where were supposed to be. Patience everyone, patience. You will get snow this winter & you can bank on it. I do not need to say why. It will happen like every winter.

[usedtobe]

Looks like the models are evolving towards and positive PNA by 240 hours but they are still showing at pretty positive ao and nao.

For people who like cool weather in the east (mid atlantic PHl and south) , the ridgiing in the west is an improvement which probably will bring shots of seasonally cold air into the east. However, if you look closely, some of the memebers do show the troffing west of the mean which still might keep the coldest weather to our west. Notice all the blue shades across the high latitudes and iceland, that means the ao is still quite positive with no real blocking in sight.

The bad news is that there are signs on the GEFS ensembles that the pna ridge will be replaced by an rpna, the typical nina ridge position. During nina, there often are cold shots as amplification takes place and the ridge shifts eastward into AK and the west but the cold in the east is usually transitory as the tropical forcing associated with la nina tends to shift the ridge back west.

Note how the orange shades that were over the west coast have shifted back west. There is little skill in model forecasts so far in advance but such a shift would fit with nina climo. Also, the 384 hour still shows blues molsty blue shades at the higher latitudes. To me that's believable given the very cold stratosphere. We need upwelling events or Ozone to weaken that stratospheric polar vortex.

I'm not optimistic about our snow chances for the 1st several weeks of December but then some think I'm a pessimist.

[Ginx snewx]

Looks like the models are evolving towards and positive PNA by 240 hours but they are still showing at pretty positive ao and nao.

This is significant though.

[OSUmetstud]

This is significant though.

How is that significant? The ensemble mean at the end of the period is about +1.5 stdev...which is similar to what it is now. If you look at the day 14 graph..you can see a significant negative bias in the ensembles at that range. Maybe we get lucky and it gets to neutral but I wouldn't forecast it.

[usedtobe]

This is significant though.

Steve, look at the bottom panel of your map and how badly and too low the AO has been forecast. That's my point. If you look at the blue areas on the 06Z ensemble mean orecast, there still is not negative ao whether the product you are showing has one or not. I don't claim to have much skill at long range stuff but I'd bet you right no on the AO sign in two weeks.

[Snow_Miser]

This is significant though.

The AO Observations look seriously disjointed from the ENS Forecast...

[Ginx snewx]

Steve, look at the bottom panel of your map and how badly and too low the AO has been forecast. That's my point. If you look at the blue areas on the 06Z ensemble mean orecast, there still is not negative ao whether the product you are showing has one or not. I don't claim to have much skill at long range stuff but I'd bet you right no on the AO sign in two weeks.

Oh I agree , the fact that there was such a sharp drop off down to forecast level and the fact there seems to be a decline seems significant to me.

[uncle W]

uncle can you please give me the link for the ao index history. thanks thunderbolt

http://www.arctic.noaa.gov/detect/climate-ao.shtml

[usedtobe]

http://www.arctic.no...limate-ao.shtml

The articel/discussion by the University of Washington based on the work of Wallace is pretty interesting.

http://www.jisao.washington.edu/wallace/ncar_notes/#5Blocking

It pretty much says when the AO is strongly positive like it is right now, you don't get blocking in the north Atlantic but sometimes can in the AK. It also says that BWI is 3 times more likely to see snow with a negative ao versus positive ao. Even Mallow's old stomping ground is more likely to get snow with a negative ao.

[JBG]

NYC had an arctic outbreak in January 1972 between blow torches...It brought the coldest temperature of that winter of five degrees...A week before it was -60 in Alaska...November 1971 had a storm on Thanksgiving...Snow north of NYC...A brief cold shot then back to warmth...That's what I think will happen into early December...I think the ao/nao got negative late in the game that year...

Though the statististics show a respectable 22.9" that winter, the less said about that winter the better. That winter is indeed a case study in how sensible weather varies from statstics.

In February we started off with a wonderful (for that year) 3-4" that got rained on later that week, with a nasty cutter. Then a few light events and a slopfest around February 19-20 (though a record storm inland). Record highs in a Leap Day torch. A few cold days in March, then a cold and drizzly April, and a miserable June. The winter after, 2.9" for the whole winter. A weather period that was definitely underwhelming.

[uncle W]

Though the statististics show a respectable 22.9" that winter, the less said about that winter the better. That winter is indeed a case study in how sensible weather varies from statstics.

In February we started off with a wonderful (for that year) 3-4" that got rained on later that week, with a nasty cutter. Then a few light events and a slopfest around February 19-20 (though a record storm inland). Record highs in a Leap Day torch. A few cold days in March, then a cold and drizzly April, and a miserable June. The winter after, 2.9" for the whole winter. A weather period that was definitely underwhelming.

you forgot the 5" of snow we got on 2/26 that wasn't forecast...The KU storm on 2/19/1972 didn't have enough cold air plus the storm hugged the coast...The early 70's is a text book on how hard it is to get a good snowstorm in NYC...The AO was positive thru January 72 but fell slightly negative for February and March...

[SnowGoose69]

The SST anomalies are now miserable in the NATL, I had not liked the anomalies from roughly the NC/VA/SC-PEI/Newfoundland corridor since September and that was why I had forecast predominatly a +NAO for this winter, the Greenland region anomalies had been fine until recently, but now they are getting worse, likely because the continuous run of deep lows going across the North Atlantic, we now see numerous areas of below normal SSTs near Greenaland. At this point we need the AO and or EPO to save us as they did in 1993-94 because I still anticipate we'll spend at least 60-65 of the 90 days from Dec 1 -Mar 1 with a +NAO this year.

[Rainshadow]

Though the statististics show a respectable 22.9" that winter, the less said about that winter the better. That winter is indeed a case study in how sensible weather varies from statstics.

In February we started off with a wonderful (for that year) 3-4" that got rained on later that week, with a nasty cutter. Then a few light events and a slopfest around February 19-20 (though a record storm inland). Record highs in a Leap Day torch. A few cold days in March, then a cold and drizzly April, and a miserable June. The winter after, 2.9" for the whole winter. A weather period that was definitely underwhelming.

That June was even miserable before Agnes.

[CoastalWx]

Wow, what a horrible forecast from the models.

[usedtobe]

Wow, what a horrible forecast from the models.

If that wasn't bad enough, after our flirt with the positive pna coming up and lasting thru day 10, by the end of the period, the ridge starts retrogressing on the ens means from the 00Z and 06Z runs. I looked at the atlantic ssta pattern and to me it looked pretty neutral, not as bad as implied by snowgoose. That said, the mjo only gets to phase 4 by dec 11on the gfs and euro ens which is not conducive to cold across the conus with the euro suggesting it might enter the circle of death. MJO forecasts aren't that good but if they were to verify with the ridge retrogression taking place, it would be hard to see any snow hopes thru most of dec for the dc to phl crowd. a negative ao gies bwi about 3 times the snow that they get with a strongly positive ao. The strongly positive one make it real hard to get snow. If you compare the day 10 areas of red on the maps to this one which is at the end of the period, you can see the retrogression. Taht would fit with nina climo and with the forecast progression of the mjo. December is starting to shape up as a ji suicide watch type month.

[okie333]

Wow, what a horrible forecast from the models.

Something's been wacky with their site since yesterday... I wouldn't think too much of it.

[usedtobe]

Something's been wacky with their site since yesterday... I wouldn't think too much of it.

But if you look at the forecast of the height field hat I posted, the map has a very positive nao and ao and both are very positive now so I don't think the forecast is that goofy.

[Rainshadow]

But if you look at the forecast of the height field hat I posted, the map has a very positive nao and ao and both are very positive now so I don't think the forecast is that goofy.

Wes,

The current +NAO train wreck aside, the GFS MJO progs are pretty robust through the warm phases, like you said more so than the Euro. But when we were on the flip side earlier this month, the GFS MJO outlooks were too robust with the cold phases. The Indian ssta are still warm, so this might add some corroboration to the GFS MJO outlook on this side, but gosh darn if this is more than a WAG statement by me.

[CoastalWx]

Wes,

The current +NAO train wreck aside, the GFS MJO progs are pretty robust through the warm phases, like you said more so than the Euro. But when we were on the flip side earlier this month, the GFS MJO outlooks were too robust with the cold phases. The Indian ssta are still warm, so this might add some corroboration to the GFS MJO outlook on this side, but gosh darn if this is more than a WAG statement by me.

I commented yesterday in the SNE thread about how the NCEP models were going nuts with it. It looks like no other model is even close.

[usedtobe]

Wes,

The current +NAO train wreck aside, the GFS MJO progs are pretty robust through the warm phases, like you said more so than the Euro. But when we were on the flip side earlier this month, the GFS MJO outlooks were too robust with the cold phases. The Indian ssta are still warm, so this might add some corroboration to the GFS MJO outlook on this side, but gosh darn if this is more than a WAG statement by me.

All my long range statements are wags as I think most are from others. We still don't know enough about the various forcing to really know for sure what is going to happen past day 5. However, this pattern blows and until we see signs of high latitude blocking your and my neck of the woods aren't going to see much snow. For new england, the pattern is not that bad. They can survive, ji can't without a negative ao.

[NorEaster17]

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.

Not sure what your original totals were (havent seen the forecast) but the only thing I'm holding onto is the fact that NYC metro has been getting 9 inches of snow on average in Decembers for the past 11 years. So Im always thinking they'll see none this year; but based on this fact, they could get 6", they could get a foot..

Also something to remember as many use the NAO religiously,.... it snows with a positive NAO in NYC/I-95 areas. Timing and atmospheric temps are key. There doesnt have to be blocking or persistant cold in place (even though that helps the chances).

[Huffwx]

Not sure what your original totals were (havent seen the forecast) but the only thing I'm holding onto is the fact that NYC metro has been getting 9 inches of snow on average in Decembers for the past 11 years. So Im always thinking they'll see none this year; but based on this fact, they could get 6", they could get a foot..

Also something to remember as many use the NAO religiously,.... it snows with a positive NAO in NYC/I-95 areas. Timing and atmospheric temps are key. There doesnt have to be blocking or persistant cold in place (even though that helps the chances).

Past results doesn't predict future earnings. Just saying-- December looks bleak, no matter how you slice it. I'd hedge zilch before I said 9 inches in NYC in December.

[Mitchel Volk]

As it looks to me the I-95 snowfall for December is going to be well below normal. As earlier stated the pattern could not be any worst for snowfall for the coastal Northeast. AFter that itis too early to tell how January and February looks like, I do remember that December 1989 was -10 below normal and January 1990 was +10 above normal so things can reverse. However, I did cut my NYC winter snowfall forecast from 40" to 20". So December will feature above normal temperatures with below normal snowfall. +NAO and -PNA is not a good pattern for the I-95 snowfall. MJO is more useful for tropical weather prediction, if there a study for mid latitude snowfall and MJO please post the links.

[CoastalWx]

As it looks to me the I-95 snowfall for December is going to be well below normal. As earlier stated the pattern could not be any worst for snowfall for the coastal Northeast. AFter that itis too early to tell how January and February looks like, I do remember that December 1989 was -10 below normal and January 1990 was +10 above normal so things can reverse. However, I did cut my NYC winter snowfall forecast from 40" to 20". So December will feature above normal temperatures with below normal snowfall. +NAO and -PNA is not a good pattern for the I-95 snowfall. MJO is more useful for tropical weather prediction, if there a study for mid latitude snowfall and MJO please post the links.

Tropical forcing defintely plays a role in the winter, especially in the heart of winter when wavelengths have adjusted and stabilized. Favorable MJO phases can really bring up +PNA ridging.

You think it's early to cut the snowfall so drastically? Although, I suppose 40" is already above normal by a good amount.

[usedtobe]

As it looks to me the I-95 snowfall for December is going to be well below normal. As earlier stated the pattern could not be any worst for snowfall for the coastal Northeast. AFter that itis too early to tell how January and February looks like, I do remember that December 1989 was -10 below normal and January 1990 was +10 above normal so things can reverse. However, I did cut my NYC winter snowfall forecast from 40" to 20". So December will feature above normal temperatures with below normal snowfall. +NAO and -PNA is not a good pattern for the I-95 snowfall. MJO is more useful for tropical weather prediction, if there a study for mid latitude snowfall and MJO please post the links.

I don't know of any research about snow and the mjo, however, there are certain phases that favor cold in the east versus warmer than normal.

http://www.cpc.ncep....bined_image.png

There is also at least one article that suggests the mjo may play a role in the modulating the nao.

http://www.nature.co...ature07286.html

Though there is another article that suggests the nao strength plays a role in the strength of mjo

Another that says the mjo can affect the nao and the nao can affect the mjo in the atlantic.

http://journals.amet.../2008JCLI2515.1

http://www.agu.org/p...0GL046131.shtml

This is a slide taken from Lin, one of the authors of one of the articles listed above.

[Ginx snewx]

As it looks to me the I-95 snowfall for December is going to be well below normal. As earlier stated the pattern could not be any worst for snowfall for the coastal Northeast. AFter that itis too early to tell how January and February looks like, I do remember that December 1989 was -10 below normal and January 1990 was +10 above normal so things can reverse. However, I did cut my NYC winter snowfall forecast from 40" to 20". So December will feature above normal temperatures with below normal snowfall. +NAO and -PNA is not a good pattern for the I-95 snowfall. MJO is more useful for tropical weather prediction, if there a study for mid latitude snowfall and MJO please post the links.

Wow, based on Dec?

[Amped]

This is updating.

[JBG]

you forgot the 5" of snow we got on 2/26 that wasn't forecast...The KU storm on 2/19/1972 didn't have enough cold air plus the storm hugged the coast...The early 70's is a text book on how hard it is to get a good snowstorm in NYC...The AO was positive thru January 72 but fell slightly negative for February and March...

5" on 2/26/1972?