Some Weaker AO Parallels To This Time Last Year

[bluewave]

It's interesting how the AO pattern from this October on is showing some similarity to roughly the same time last year.

While the -AO was stronger last October,the height anomaly this October was near the same spot north of Alaska

as it was last October.The really big drop this year is being forecasted to begin earlier than last

year with impressive positive height anomalies over Greenland.

AO Last Year

AO This Year

OCT 09

OCT 10

[phil882]

It's interesting how the AO pattern from this October on is showing some similarity to roughly the same time last year.

While the -AO was stronger last October,the height anomaly this October was near the same spot north of Alaska

as it was last October.The really big drop this year is being forecasted to begin earlier than last

year with impressive positive height anomalies over Greenland.

AO Last Year

AO This Year

OCT 09

OCT 10

Note, however, the nearly polar opposite pattern in the Pacific, no doubt being driven by La Nina.

[GaWx]

Note, however, the nearly polar opposite pattern in the Pacific, no doubt being driven by La Nina.

Per the 11/21/10 0Z GFS ensemble mean fcast, the AO is forecasted to plunge to near -4. Only four other Nov's have had it that low on the dailies since 1950: 1998, 1985, 1968, and 1959 (lowest on record was -5.896 on 11/18/59).

AO dailes history since 1950:

ftp://ftp.cpc.ncep.n...1.current.ascii

[nzucker]

Per the 11/21/10 0Z GFS ensemble mean fcast, the AO is forecasted to plunge to near -4. Only four other Nov's have had it that low on the dailies since 1950: 1998, 1985, 1968, and 1959 (lowest on record was -5.896 on 11/18/59).

AO dailes history since 1950:

ftp://ftp.cpc.ncep.n...1.current.ascii

It's pretty crazy this is happening in a strong La Niña. I'm beginning to think the solar minimum is having some strange effects on our weather pattern since we've had seemingly non-stop blocking since Summer 2008, and it isn't quitting with a powerful cold event in the Pacific which usually strengthens the PV and mitigates these blocks. The AO forecast for the next week is starting to look eerily like Winter 09-10 at this point....although the strong Niña means the Pacific is going to dictate the pattern more with higher heights over the East and lower heights out west.

[nynjpaweather]

It's pretty crazy this is happening in a strong La Niña. I'm beginning to think the solar minimum is having some strange effects on our weather pattern since we've had seemingly non-stop blocking since Summer 2008, and it isn't quitting with a powerful cold event in the Pacific which usually strengthens the PV and mitigates these blocks. The AO forecast for the next week is starting to look eerily like Winter 09-10 at this point....although the strong Niña means the Pacific is going to dictate the pattern more with higher heights over the East and lower heights out west.

Gee, I know I've heard someone warn about this all Fall. Well, let's see how this all plays out. Should be an interesting winter to document.

[tombo82685]

Gee, I know I've heard someone warn about this all Fall. Well, let's see how this all plays out. Should be an interesting winter to document.

the only thing is, yea the nao and ao are both very negative, but the pacific is horrible. What looked to be a nice cold shot coming after tgiving, looks to be now transient one.

[nynjpaweather]

the only thing is, yea the nao and ao are both very negative, but the pacific is horrible. What looked to be a nice cold shot coming after tgiving, looks to be now transient one.

I take it you looked at the 12Z GFS. My advice is stop looking at the models beyond 180 hours and start looking at the forcing mechanisms influencing the developing 500 MB pattern. In other words, look at it this way. The models keep on going back and forth between a powerful negative NAO with a 50/50 low which keeps the northern half of the US cold or a moderating air mass with a rapidly weakening negative NAO. What we should be looking for is what mechanisms in the guidance created each forecast. What's driving the negative NAO in the first place to create such a forecast either way. You find that, then you don't care about run A or B.

[tombo82685]

I take it you looked at the 12Z GFS. My advice is stop looking at the models beyond 180 hours and start looking at the forcing mechanisms influencing the developing 500 MB pattern. In other words, look at it this way. The models keep on going back and forth between a powerful negative NAO with a 50/50 low which keeps the northern half of the US cold or a moderating air mass with a rapidly weakening negative NAO. What we should be looking for is what mechanisms in the guidance created each forecast. What's driving the negative NAO in the first place to create such a forecast either way. You find that, then you don't care about run A or B.

well not just the 12z gfs, but basically the last 5 runs of the euro. Except last night which showed the 50/50 low which kept the n mid atl and northeast cold.

[nynjpaweather]

well not just the 12z gfs, but basically the last 5 runs of the euro. Except last night which showed the 50/50 low which kept the n mid atl and northeast cold.

Those other 5 runs of the ECMWF operational had conflicting signals with some of the ECWMF ensemble guidance. The point is that the long range model guidance has become more bipolar than the US Congress.

[tombo82685]

Those other 5 runs of the ECMWF operational had conflicting signals with some of the ECWMF ensemble guidance. The point is that the long range model guidance has become more bipolar than the US Congress.

lol point taken. Its all going to come down to the thanksgiving day storm. We want that strong as possible and its needs to tranfer over to the coast ala last nights 0z gfs.

[usedtobe]

Per the 11/21/10 0Z GFS ensemble mean fcast, the AO is forecasted to plunge to near -4. Only four other Nov's have had it that low on the dailies since 1950: 1998, 1985, 1968, and 1959 (lowest on record was -5.896 on 11/18/59).

AO dailes history since 1950:

ftp://ftp.cpc.ncep.n...1.current.ascii

Larry, It's interesting that the strong nina year, 1998-1999 shows up. It ended up with each month Dec-March averaged having a positive nao and D-F having a positive ao with only March having a negative AO. The other years the ao was montly negative but 4 years hardly mean much.

[Lee]

Larry, It's interesting that the strong nina year, 1998-1999 shows up. It ended up with each month Dec-March averaged having a positive nao and D-F having a positive ao with only March having a negative AO. The other years the ao was montly negative but 4 years hardly mean much.

Yeah, hope that's not an omen and just a fluke coincidence,lol.

[GaWx]

Larry, It's interesting that the strong nina year, 1998-1999 shows up. It ended up with each month Dec-March averaged having a positive nao and D-F having a positive ao with only March having a negative AO. The other years the ao was montly negative but 4 years hardly mean much.

Yes, this is unlike last winter when the AO plunged to very low levels in Dec. during the El Nino and I got quite excited about the overall winter potential for the SE US. Since this is a moderate to strong La Nina and since this plunge is happening in late Nov. (i.e., very early), I'm not at this point getting excited about the upcoming winter as a whole temperaturewise for the SE US. However, despite mostly downplaying this year's S/IP potential in my area based on nonweak Nina climo, I'm now getting a little more interested in the potential for something good here in early Dec. based on history in and just after very strong blocks (NAO may get to near historic neg. levels of -3). All it takes is one well placed Miller A here. Atlanta did have three big snows in the late 1800's during moderate to strong La Nina's due to Miller A's, inlcuding one in early Dec.. Fwiw, three GFS runs over the last couple of days (including the last two) have had a well placed Miller A producing accumulating snow here. So, it is something to watch at least.

[Dr No]

It's pretty crazy this is happening in a strong La Niña. I'm beginning to think the solar minimum is having some strange effects on our weather pattern since we've had seemingly non-stop blocking since Summer 2008, and it isn't quitting with a powerful cold event in the Pacific which usually strengthens the PV and mitigates these blocks. The AO forecast for the next week is starting to look eerily like Winter 09-10 at this point....although the strong Niña means the Pacific is going to dictate the pattern more with higher heights over the East and lower heights out west.

I was just going to post how if the blocking persists well into this nina winter, then there is probably some other factor to the equation that is playing a much bigger role than previously thought. As you and many others have posted, the tropical forcing and GLAAM in a Nina year should correspond to a winter where the AO/NAO should be much less of a factor than last year. I guess, the weenie phrase applies here: only time will tell.

[Dr No]

Yes, this is unlike last winter when the AO plunged to very low levels in Dec. during the El Nino and I got quite excited about the overall winter potential for the SE US. Since this is a moderate to strong La Nina and since this plunge is happening in late Nov. (i.e., very early), I'm not at this point getting excited about the upcoming winter as a whole temperaturewise for the SE US. However, despite mostly downplaying this year's S/IP potential in my area based on nonweak Nina climo, I'm now getting a little more interested in the potential for something good here in early Dec. based on history in and just after very strong blocks (NAO may get to near historic neg. levels of -3). All it takes is one well placed Miller A here. Atlanta did have three big snows in the late 1800's during moderate to strong La Nina's due to Miller A's, inlcuding one in early Dec.. Fwiw, three GFS runs over the last couple of days (including the last two) have had a well placed Miller A producing accumulating snow here. So, it is something to watch at least.

While you are correct it's too early to tell, why is 10 days signifigant in respect to when the AO tanked last year?

[uncle W]

interesting how negative 1954-55 was...that's a boat load of info to digest...was there a daily max/min record made?...

[tacoman25]

Larry, It's interesting that the strong nina year, 1998-1999 shows up. It ended up with each month Dec-March averaged having a positive nao and D-F having a positive ao with only March having a negative AO. The other years the ao was montly negative but 4 years hardly mean much.

The pattern we are seeing is much more like 1950 and 1985 than 1998, though. We are seeing what will likely end up as the most severe November Arctic outbreak since 1985 for the PNW and Northern Rockies.

[RIC Airport]

Yes, this is unlike last winter when the AO plunged to very low levels in Dec. during the El Nino and I got quite excited about the overall winter potential for the SE US. Since this is a moderate to strong La Nina and since this plunge is happening in late Nov. (i.e., very early), I'm not at this point getting excited about the upcoming winter as a whole temperaturewise for the SE US. However, despite mostly downplaying this year's S/IP potential in my area based on nonweak Nina climo, I'm now getting a little more interested in the potential for something good here in early Dec. based on history in and just after very strong blocks (NAO may get to near historic neg. levels of -3). All it takes is one well placed Miller A here. Atlanta did have three big snows in the late 1800's during moderate to strong La Nina's due to Miller A's, inlcuding one in early Dec.. Fwiw, three GFS runs over the last couple of days (including the last two) have had a well placed Miller A producing accumulating snow here. So, it is something to watch at least.

1886-87, 1892-93?