AO Forecast to Plunge

[Harry]

Absolutely no way Nino 3.4 is weak now. It was -1.6 on the last weekly update. Such a rise would be beyond record setting. I think the MEI is the best measure of a Nina anyway. As for analogs 1950 is the only one that really fits at all.

Personally i would scratch every analog AFTER 1950.. 1950 may be a decent fit now ( Temps are a very good fit at THIS point ) but i highly suspect it wont remain that way. See solar as for why and that being a 2/3rd year nina event. That's me though.

As for the numbers that is what the daily stuff show. As for the weekly would you mind pointing me to the source of that as neither the aussies or CPC show such? Aussies showed -1.43 and cpc with -1.5! Keep in mind those numbers ( if i recall correctly ) are for the week before and thus last week which YES even the daily numbers showed. Keep in mind as you well know we have been seeing these ups and downs for most of this Nina across the whole basin. So it could be another case of that. Guess we will know in a few days or so.

[uncle W]

Truth be known, nobody can really say what this winter will do. It's too much of an oddball. Odd enough that they just had a serious tornado near Portland OR.

1962-63 was a cold winter just about everywhere. The entire northern US and western Europe both had a VERY cold January. The indices were all severely negative. The data back in 1903 isn't good enough to really know what happened there.

1962-63 was one of the coldest winters in my life time...From the 1964 NYC New York Daily news weather almanac...

[Harry]

Truth be known, nobody can really say what this winter will do. It's too much of an oddball. Odd enough that they just had a serious tornado near Portland OR.

1962-63 was a cold winter just about everywhere. The entire northern US and western Europe both had a VERY cold January. The indices were all severely negative. The data back in 1903 isn't good enough to really know what happened there.

1903-04 was a nina ( mod/strong Nina Following a mod/strong Nino as well ) and had a -PDO except in Jan which was slightly +. NAO though was on the +side all 3 months giving me the impression it may have been EPO/Pac driven plus the cold that winter was along the north into N.New England which does tend to go above normal with a -NAO if there is no help via cross polar flow/EPO. Thus my assumption. Someone feel free to correct me if i am wrong.

1962-63 was a very weak Nina. The blocking that winter was sick i do believe.

[uncle W]

1903-04 was a nina ( mod/strong Nina Following a mod/strong Nino as well ) and had a -PDO except in Jan which was slightly +. NAO though was on the +side all 3 months giving me the impression it may have been EPO/Pac driven plus the cold that winter was along the north into N.New England which does tend to go above normal with a -NAO if there is no help via cross polar flow/EPO. Thus my assumption. Someone feel free to correct me if i am wrong.

1962-63 was a very weak Nina. The blocking that winter was sick i do believe.

So far the ao hit -4 in late November...I wasn't checking the ao lately and I thank Don for waking me up...Most of the time it gets that low cold and or snow are in the headlines around NYC...

[tacoman25]

FYI.. BOTH Dec 1954 and 1988 had a +NAO for the month of December. Also the AO was pretty well into the positive side in Dec 1988 at +1.679. Sorry but they are non analogs at this point especially 1988-89. Not really sure what is good at this point as this is pretty remarkable what we have and look to have as far as the AO/NAO go and Nina? Lastly as well it is about certain now that per the Tri Monthly method this Nina will never reach strong and or end up as strong as either of those did. May have it with the MEI but that is about it. The whole basin has been slowly but surely warming the past week or so and really picked up with the warming yesterday and today. per the daily stuff we are now at a weak nina in 3, 3.4, and 4. Regions 3 and 3.4 are at about -0.8 or so and region 4 is at -0.7 or so.

This Nina surpassed 1954-55 in strength.

[tacoman25]

I have a question and maybe someone can help me out.

I was looking just at my area at La Nina winters since 1900, particularly those that had a cold December. Currently most of the OV is 6-10 degrees below normal, and the cold looks to stick around at least towards the end of the month. If we can maintain these kinds of negative departures, it would be only the 5th La Nina to have such a cold December for us. The others were 1903-04, 1950-51, 1962-63, and 2000-01. Not a single one of these winters featured a blowtorch January. January 1951 was above normal, but barely, and the only other month out of these winters that was above normal was February 2001.

Given the extreme blocking going on and that may end up repeating later on, why is this particular winter set to go against history and switch so dramatically to a warm pattern? I know it's a small sample of just 4 winters, but even when I looked at the entire set of 28 La Ninas since 1900, December was still the coldest month in just 4 of them. 14 others had January as the coldest, and February was the coldest in the final 10.

Also, what set apart 1903-04 and 1962-63 that featured all three months being severely cold? What was the blocking situation then?

1917 is a good year to look at right now as well. Very good pattern match to this December so far.

[wxmx]

1903-04 was a nina ( mod/strong Nina Following a mod/strong Nino as well ) and had a -PDO except in Jan which was slightly +. NAO though was on the +side all 3 months giving me the impression it may have been EPO/Pac driven plus the cold that winter was along the north into N.New England which does tend to go above normal with a -NAO if there is no help via cross polar flow/EPO. Thus my assumption. Someone feel free to correct me if i am wrong.

1962-63 was a very weak Nina. The blocking that winter was sick i do believe.

Dec/Jan cold, Feb/Mar not so much...pretty good pattern switch

[Snow Wizard]

Personally i would scratch every analog AFTER 1950.. 1950 may be a decent fit now ( Temps are a very good fit at THIS point ) but i highly suspect it wont remain that way. See solar as for why and that being a 2/3rd year nina event. That's me though.

As for the numbers that is what the daily stuff show. As for the weekly would you mind pointing me to the source of that as neither the aussies or CPC show such? Aussies showed -1.43 and cpc with -1.5! Keep in mind those numbers ( if i recall correctly ) are for the week before and thus last week which YES even the daily numbers showed. Keep in mind as you well know we have been seeing these ups and downs for most of this Nina across the whole basin. So it could be another case of that. Guess we will know in a few days or so.

What is your opinion on how the NW will fare this winter? I see a lot of speculation on here it's going to be an all east winter. I'm sure there is some bias there though.

BTW I looked again and it was -1.5 on the last update.

[Snow Wizard]

1917 is a good year to look at right now as well. Very good pattern match to this December so far.

Ugh.

Thank goodness that November didn't match at all in the NW. The nina was actually pretty weak also. If 1903 and 1917 are the best analogs somebody should just shoot me now.

[Harry]

This Nina surpassed 1954-55 in strength.

My bad.

Had my years mixed up.. Was thinking 55-56. Still a poor NAO/AO match though.

[Harry]

What is your opinion on how the NW will fare this winter? I see a lot of speculation on here it's going to be an all east winter. I'm sure there is some bias there though.

BTW I looked again and it was -1.5 on the last update.

I went slight below normal temps/above normal precip and above normal snowfall and still like those ideas despite my confidence taking a bit of a hit with this unexpected -AO/-NAO which is a bit more extreme then i had counted on. I do believe the cold will return to the PAC NW. Say January? Despite what some say you still can get cold in the PAC NW with a -NAO as well. That's me though..

[jbcmh81]

1917 is a good year to look at right now as well. Very good pattern match to this December so far.

Before looking into things today, I had thought also that 1917-18 was a Nina, but the links I found did not list it that way, but rather simply cold neutral, so I didn't include it in the list. But if it's to be included, that would actually make 5 La Nina winters that saw a very cold December that stayed cold during the DJF period or even got colder during the January period. January 1918 was extremely cold here in the OV and featured a blizzard similar to January 1978.

[jbcmh81]

Dec/Jan cold, Feb/Mar not so much...pretty good pattern switch

Actually February 1904 was extremely cold in the Northern Plains, Great Lakes and OV, and the Northeast down through the Mid-Atlantic. March was near normal to slighly below in those same areas, despite what that map is showing. That entire winter was brutal.

[Ottawa Blizzard]

1917 is a good year to look at right now as well. Very good pattern match to this December so far.

December 1917 was much colder up in Ontario and Quebec than this December is turning out to be. I just don't see the match. 1916-17 would seem to be a better match.

[tacoman25]

December 1917 was much colder up in Ontario and Quebec than this December is turning out to be. I just don't see the match. 1916-17 would seem to be a better match.

When you look at the big picture, Dec 1917 is a much better match so far.

[Harry]

When you look at the big picture, Dec 1917 is a much better match so far.

Both of them did atleast have a -AO/-NAO. But yeah 1917 is a better match overall.

[pcbjr]

If i may ...

Where does all of this take us regionally?

[Snow Wizard]

When you look at the big picture, Dec 1917 is a much better match so far.

That is one month. November was a horrible match at least in the West and the Nina was much weaker. I bet my next paycheck this winter will not look like 1917-18.

[JBG]

1917 is a good year to look at right now as well. Very good pattern match to this December so far.

The New Years cold wave that winter was rather powerful. I think the second lowest temperatures in NYC's records. Can we top (or go below) that?

[donsutherland1]

With the AO still forecast to plunge to extremely low levels, the following are Northern Hemisphere and North America 500 mb anomalies for all cases during which the AO fell to -4 or below in December:

Northern Hemisphere:

North America:

Two quick points:

1. Usually for at least two to sometimes three weeks after the AO had first fallen to such levels, troughing was fairly frequent in the East.

2. Often a few days after the AO first fell to -4, there was a major amplificatiion near or along the mid-Atlantic/north Atlantic coasts.

The implications for such developments would be that December will likely remain generally colder than normal in the eastern third to half of the U.S. through the rest of the month. There could be a few days of milder weather. More immediately, even as the GFS has now joined the Euro with respect to the possible weekend event, the possibility that the storm could come close enough to bring a few inches of snow from Richmond to Boston cannot be altogether dismissed.

Finally, when it comes to January, during cases in which the ENSO Region 3.4 anomaly was -1.00 or below, the La Niña pattern typically predominates unless the AO is severely negative. The noted January 1985 Arctic outbreak occurred when the AO was below -3.000. The mean high and low temperatures for select cities illustrates the above noted case:

AO: -3.000 or below:

Boston: 30.8°-18.5°

New York: 34.8°-23.6°

Philadelphia: 36.4°-22.4°

Washington, DC: 41.2°-25.5°

AO: -2.999 to -1.000:

Boston: 36.0°-23.1°

New York: 38.7°-25.9°

Philadelphia: 39.8°-25.5°

Washington, DC: 43.5°-28.9°

AO: -0.999 to 0.000:

Boston: 37.9°-22.2°

New York: 39.3°-27.1°

Philadelphia: 41.6°-26.2°

Washington, DC: 45.2°-30.0°

The implication of this data is that as the AO- regime fades and breaks, probably during the first week in January or a few days afterward if the December 1950, 1995, and 2000 cases are representative, a milder regime should evolve for the East. Farther West, the suddenly winter-starved Pacific Northwest might be looking forward to a culmination of winter weather (both cold and snowfall opportunities) from near mid-January through the rest of January if some past cases are representative.

[wxmx]

Actually February 1904 was extremely cold in the Northern Plains, Great Lakes and OV, and the Northeast down through the Mid-Atlantic. March was near normal to slighly below in those same areas, despite what that map is showing. That entire winter was brutal.

Yes, there's a disconnect of the 500mb and near surface temps in the areas you mention. But, overall, it was a pretty good pattern switch for the rest of the CONUS. This is reanalysis stuff, so data is not as trustworthy as 1950+ data.

[donsutherland1]

Today's AO was -2.300. It continues to be projected to fall to somewhere between -5 and -4 over the coming days.

Three quick thoughts:

1. I like the idea of a swath of 3"-6" locally 4"-8" snows across parts of Virginia for tomorrow and tomorrow night. I do have some concerns about mixing/changeover in SE VA, including Norfolk.

2. The 12/15 12z run of the GFS is more aggressive than I think will play out for most of the major cities with respect to the weekend event, but I believe some event is more likely than no event (12z ECMWF). A several inch snowfall is still possible for the big cities.

3. Building on the January data posted earlier today, it should be noted that GWO Phases 2 and 3 have typically been the coldest, on average, during moderate or strong La Niña events (ENSO Region 3.4 anomalies of -1.00 or lower), both when the AO was positive and negative. The great January 1985 Arctic outbreak occurred during GWO Phase 2. Phase 5 has sometimes witnessed strong shots of cold when the AO has been negative. Phase 4 was the warmest, in general. Phase 1 came out even warmer, especially when the AO was positive, but data is insufficient and could be skewed by an anomalous event.

[NinjaWarrior2]

The pattern right now is perfect/near perfect for very cold air, -PNA which allows Canadian/Western Canadian cold to come into the country, combined with a -NAO/AO allowing cold to get to the east, I think once the NAO/AO block weakens, we warm up some and a more casual La Nina pattern will show up.

[pcbjr]

The pattern right now is perfect/near perfect for very cold air, -PNA which allows Canadian/Western Canadian cold to come into the country, combined with a -NAO/AO allowing cold to get to the east, I think once the NAO/AO block weakens, we warm up some and a more casual La Nina pattern will show up.

The question is (in all seriousness since I do not have the expertise to suggest an answer) - when does the NAO/AO block weaken, and for how long?

[donsutherland1]

The pattern right now is perfect/near perfect for very cold air, -PNA which allows Canadian/Western Canadian cold to come into the country, combined with a -NAO/AO allowing cold to get to the east, I think once the NAO/AO block weakens, we warm up some and a more casual La Nina pattern will show up.

NinjaWarrior2,

The opposite is true with respect to the PNA when it comes to severe Arctic outbreaks in the eastern U.S. Since 1950, in 68% of the December cases in which the temperature fell below 10°F (-12.2°C) in Philadelphia, the PNA was positive. In 32% of such cases, it was negative. Moreover, in 27% cases, the PNA was +1 or higher. In just 9% of cases, the PNA was -1 or lower. Severe arctic outbreaks in 1950, 1960, 1963, 1976, 1980, and 1989 saw a positive PNA. Severe arctic outbreaks in 1951, 1955, 1962, and 1983 saw a negative PNA. The composite 500 mb anomaly shows a ridge in the west and deep trough in the east.

[tacoman25]

Where's my buddy gibbs?

[donsutherland1]

Today, the AO stood at -3.370. It could reach -4 or below either tomorrow or Saturday.

The point made yesterday that often a few days after the AO first fell to -4 in December, there was a major amplificatiion near or along the mid-Atlantic/north Atlantic coasts remains relevant. Some of the models have trended in that direction. Certainly, I believe the probability of at least a few inches of snow in the big cities of the East has increased. In the meantime, Virginia is presently enjoying some welcome accumulating snow.

Continuing the theme of looking farther ahead, using the La Niña-Severe December Blocking analogs, January would likely see milder anomalies overspread the eastern half of the U.S., with the month winding up warmer than normal. The best timing for the start of that trend would be during the first week of January +/- a few days. Before then, troughing should remain frequent in the East.

February could wind up becoming the warmest month relative to normal, but blockiness and cold could return late in the month, especially if a new severe blocking regime develops as happened in Winter 2000-01. In fact, the monthly AO figure for the 1950-51, 1995-96, and 2000-01 winters was below -1.4 in all of those cases. Hence, March would likely wind up on the cold side of normal. The Pac NW would probably see its most notable winter weather during the second half of January perhaps into the start of February.

The usual caveat is the tiny sample size. Unfortunately, severe AO blocking in December during moderate/strong La Niñas has been rare.

[Carvers Gap]

Today, the AO stood at -3.370. It could reach -4 or below either tomorrow or Saturday.

The point made yesterday that often a few days after the AO first fell to -4 in December, there was a major amplificatiion near or along the mid-Atlantic/north Atlantic coasts remains relevant. Some of the models have trended in that direction. Certainly, I believe the probability of at least a few inches of snow in the big cities of the East has increased. In the meantime, Virginia is presently enjoying some welcome accumulating snow.

Continuing the theme of looking farther ahead, using the La Niña-Severe December Blocking analogs, January would likely see milder anomalies overspread the eastern half of the U.S., with the month winding up warmer than normal. The best timing for the start of that trend would be during the first week of January +/- a few days. Before then, troughing should remain frequent in the East.

February could wind up becoming the warmest month relative to normal, but blockiness and cold could return late in the month, especially if a new severe blocking regime develops as happened in Winter 2000-01. In fact, the monthly AO figure for the 1950-51, 1995-96, and 2000-01 winters was below -1.4 in all of those cases. Hence, March would likely wind up on the cold side of normal. The Pac NW would probably see its most notable winter weather during the second half of January perhaps into the start of February.

The usual caveat is the tiny sample size. Unfortunately, severe AO blocking in December during moderate/strong La Niñas has been rare.

I read much of what you write and find it very informative. Today, the CPC released their January outlook and JFM outlook. I'd be interested on your take of what they had to say, especially your interpretation of their -AO comments. I do want to stress that I'm not asking for a full blown critique of their work. I actually felt their discussion viewed January from a different and beneficial angle. Their forecast appeared cooler than what I've seen posted by many here on American.

http://www.cpc.ncep....nge/fxus07.html

[A-L-E-X]

Today, the AO stood at -3.370. It could reach -4 or below either tomorrow or Saturday.

The point made yesterday that often a few days after the AO first fell to -4 in December, there was a major amplificatiion near or along the mid-Atlantic/north Atlantic coasts remains relevant. Some of the models have trended in that direction. Certainly, I believe the probability of at least a few inches of snow in the big cities of the East has increased. In the meantime, Virginia is presently enjoying some welcome accumulating snow.

Continuing the theme of looking farther ahead, using the La Niña-Severe December Blocking analogs, January would likely see milder anomalies overspread the eastern half of the U.S., with the month winding up warmer than normal. The best timing for the start of that trend would be during the first week of January +/- a few days. Before then, troughing should remain frequent in the East.

February could wind up becoming the warmest month relative to normal, but blockiness and cold could return late in the month, especially if a new severe blocking regime develops as happened in Winter 2000-01. In fact, the monthly AO figure for the 1950-51, 1995-96, and 2000-01 winters was below -1.4 in all of those cases. Hence, March would likely wind up on the cold side of normal. The Pac NW would probably see its most notable winter weather during the second half of January perhaps into the start of February.

The usual caveat is the tiny sample size. Unfortunately, severe AO blocking in December during moderate/strong La Niñas has been rare.

Don, you might have to look back at years like 1909-10, 1916-17, 1917-18 and 1955-56.

[A-L-E-X]

The 60's are probably the best snow years around here in history and the entire decade was mostly -PDO/la nina. ENSO is important, but this year should prove it's only one factor. NAO is just as important and seems to operate as a separate entity.

Also, we have had some good moderate to strong ninas, but they were back in the early part of the 20th century (the years I referenced above.)  Small sample size might be the reason why we've pidgeon holed specific mod and strong ninas as being very bad for snow here.