AO Forecast to Plunge

[JoMo]

Where's my buddy gibbs?

Some place warm.

[donsutherland1]

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

I went as far back as 1950. Unfortunately, I'm not aware of any reconstructed AO Index data that goes back earlier than 1950. It would be great to take a closer look at some of those earlier winters you cited, given their widespread cold and generally large amounts of snow.

[tennvolfan]

I went as far back as 1950. Unfortunately, I'm not aware of any reconstructed AO Index data that goes back earlier than 1950. It would be great to take a closer look at some of those earlier winters you cited, given their widespread cold and generally large amounts of snow.

Looking at these years (and 1989-90) some January periods went on to deliver severe cold and snow in the Mid South (09-10, 16-17, 17-18) while others (55-56, 89-90) torched with little to no snowfall. It seems like a crapshoot. If we get a prolonged NAO and AO in this Nina, it appears that my area will more than likely torch. I just find it interesting that ENSO alone is a poor predictor overall.

[JBG]

Looking at these years (and 1989-90) some January periods went on to deliver severe cold and snow in the Mid South (09-10, 16-17, 17-18) while others (55-56, 89-90) torched with little to no snowfall. It seems like a crapshoot. If we get a prolonged NAO and AO in this Nina, it appears that my area will more than likely torch. I just find it interesting that ENSO alone is a poor predictor overall.

Do you mean "a prolonged positive NAO and positive AO in this Niña"?

[tennvolfan]

Do you mean "a prolonged positive NAO and positive AO in this Niña"?

Yup, sorry, most defintely positive ao/ nao. Didnt get to in depth, but in late Dec early Jan, NAO flipped from deep neagtive territory to positive on a dime. Feb and March '90 featured a severely positive NAO. We went from severe cold in mid Dec 89 to a torch for the rest of the winter. Dec was below normal snowfall-wise here, too (which is not saying alot in comparison to others' normals); it was a completely wasted pattern, not unlike what just happened.

[A-L-E-X]

Yup, sorry, most defintely positive ao/ nao. Didnt get to in depth, but in late Dec early Jan, NAO flipped from deep neagtive territory to positive on a dime. Feb and March '90 featured a severely positive NAO. We went from severe cold in mid Dec 89 to a torch for the rest of the winter. Dec was below normal snowfall-wise here, too (which is not saying alot in comparison to others' normals); it was a completely wasted pattern, not unlike what just happened.

I remember that well. The only snowstorm that winter here happened in November. December was one of the coldest on record (colder than most Januarys-- which is a big accomplishment, considering the mean temp difference is like 5 degrees for the month lol) we missed one storm to our south that was supposed to drop 8 inches, another one that was supposed to form a secondary offshore and also drop 8 inches, cut too close to the coast and it was mostly rain-- in between those storms it got down to 4 degrees! Around New Years we went to a very positive NAO and the avg temps of both January and February were like 10 degrees above normal (mean of around 40 both months-- unprecedented) and we were wearing Bermuda shorts in the middle of March for spring break in NYC with temps in the mid to upper 80s! Ive never seen it so warm so early here. Although last spring's 92 on April 7 gives it a run for its money lol.

[donsutherland1]

This morning, the AO stood at -4.076. It is forecast to bottom out over the next day or two. Already, this is the lowest AO reading in December during a La Niña with ENSO Region 3.4 anomalies of -1.00°C or colder.

The ensembles are now providing a firmer signal that the current AO- regime will likely come to an end during the first week in January. That would be consistent with the three past severe December blocking episodes during La Niña events (albeit weaker ones than the current La Niña). At the same time, the EPO is forecast to be climbing. Hence, the stage is being set for a pattern change after December that should see frequent troughing in the East give way to ridging and milder readings. Before then, one or two light to possibly moderate snowfall events remain possible for the big cities of the East. If some past La Niña episodes are relevant, 25%-30% of the season's snowfall could have fallen by the end of December (a bleak prospect given the snow dearth to date).

After having looked back at pre-1950 data for a larger sample of La Niña events, a grim statistic stands out: No KU-type storm has occurred with a La Niña as strong as the current one (R3.4 anomaly currently at -1.5°C). The clipper that exploded into a paralyzing Mid-Atlantic blizzard in December 1909 occurred when the R3.4 anomalies were around -1.00°C. No events occured with a La Niña anywhere close to as strong as the present one. All the other KU-type events going back to 1871 occurred with R3.4 anomalies that were milder than the December 1909 figure (-0.50°C to -0.85°C accounts for most of the La Niña KU-type events). Significant Midwest/Great Lakes (U.S. into Ontario/Quebec) have, on occasion, occurred with R3.4 anomalies < -1.00°C. Given the expansive sample, barring consistent and strong support from multiple models and ensemble systems, any model or ensemble system that shows a KU-type snowstorm when the La Niña is as strong as it currently is (even the Euro or Euro ensembles) is very likely a suspect run(s).

[usedtobe]

This morning, the AO stood at -4.076. It is forecast to bottom out over the next day or two. Already, this is the lowest AO reading in December during a La Niña with ENSO Region 3.4 anomalies of -1.00°C or colder.

The ensembles are now providing a firmer signal that the current AO- regime will likely come to an end during the first week in January. That would be consistent with the three past severe December blocking episodes during La Niña events (albeit weaker ones than the current La Niña). At the same time, the EPO is forecast to be climbing. Hence, the stage is being set for a pattern change after December that should see frequent troughing in the East give way to ridging and milder readings. Before then, one or two light to possibly moderate snowfall events remain possible for the big cities of the East. If some past La Niña episodes are relevant, 25%-30% of the season's snowfall could have fallen by the end of December (a bleak prospect given the snow dearth to date).

After having looked back at pre-1950 data for a larger sample of La Niña events, a grim statistic stands out: No KU-type storm has occurred with a La Niña as strong as the current one (R3.4 anomaly currently at -1.5°C). The clipper that exploded into a paralyzing Mid-Atlantic blizzard in December 1909 occurred when the R3.4 anomalies were around -1.00°C. No events occured with a La Niña anywhere close to as strong as the present one. All the other KU-type events going back to 1871 occurred with R3.4 anomalies that were milder than the December 1909 figure (-0.50°C to -0.85°C accounts for most of the La Niña KU-type events). Significant Midwest/Great Lakes (U.S. into Ontario/Quebec) have, on occasion, occurred with R3.4 anomalies < -1.00°C. Given the expansive sample, barring consistent and strong support from multiple models and ensemble systems, any model or ensemble system that shows a KU-type snowstorm when the La Niña is as strong as it currently is (even the Euro or Euro ensembles) is very likely a suspect run(s).

Don, Great research that is much appreciated.

Wes

[donsutherland1]

Thank you, Wes.

[easternsnowman]

If the pattern changes do we go to a 89-90 type, or does the blocking comeback? I still say our best chances for snow are from mid-Feb to mid March.

[snowlurker]

This morning, the AO stood at -4.076. It is forecast to bottom out over the next day or two. Already, this is the lowest AO reading in December during a La Niña with ENSO Region 3.4 anomalies of -1.00°C or colder....

As the name indicates, I usually just lurk here but wanted to express my appreciation for your research and analysis. It really is powerful stuff.

[donsutherland1]

If the pattern changes do we go to a 89-90 type, or does the blocking comeback? I still say our best chances for snow are from mid-Feb to mid March.

Easternsnowman,

I'm not sure if the pattern change will be as dramatic or long-lived as occurred in 1989-90. Moreover, winters that had extreme blocking events in December often had another strong blocking episode at some point later on. If things play out as I suspect, January will liekly turn warmer. The second half of January will probably be quite mild (with cold and snow in the Pacific Northwest). February will probably be the warmest month (overall anomalies) but late February/early March could turn colder. A cold March is plausible in the East, but only if strong blocking redevelops. A lot will depend on how fast the La Niña weakens and whether strong blocking redevelops. If the Region 3.4 anomaly is warmer than -0.80°C, odds would probably favor a colder March. If not, odds would probably favor a warmer March, but there are exceptions e.g. Winter 1970-71. The latest ensemble guidance points to the latter ENSO Region 3.4 conditions. Hence, the redevelopment of strong blocking would be crucial for the endgame to Winter 2010-11.

[Kevin Druff]

The ensembles are now providing a firmer signal in the East... ridging and milder readings... If some past La Niña episodes are relevant, 25%-30% of the season's snowfall could have fallen by the end of December (a bleak prospect given the snow dearth to date).

What's that sound I hear? Oh, yes. It's the boo birds coming out for Don's forecast.

Guess it's a good thing my wife is due in January and I'll have something to distract me for the end of winter.

[tacoman25]

After having looked back at pre-1950 data for a larger sample of La Niña events, a grim statistic stands out: No KU-type storm has occurred with a La Niña as strong as the current one (R3.4 anomaly currently at -1.5°C). The clipper that exploded into a paralyzing Mid-Atlantic blizzard in December 1909 occurred when the R3.4 anomalies were around -1.00°C. No events occured with a La Niña anywhere close to as strong as the present one. All the other KU-type events going back to 1871 occurred with R3.4 anomalies that were milder than the December 1909 figure (-0.50°C to -0.85°C accounts for most of the La Niña KU-type events). Significant Midwest/Great Lakes (U.S. into Ontario/Quebec) have, on occasion, occurred with R3.4 anomalies < -1.00°C. Given the expansive sample, barring consistent and strong support from multiple models and ensemble systems, any model or ensemble system that shows a KU-type snowstorm when the La Niña is as strong as it currently is (even the Euro or Euro ensembles) is very likely a suspect run(s).

Good analysis, but again remember, we are also dealing with a more severe -AO than has ever been seen with a Nina this strong before...

[uncle W]

Good analysis, but again remember, we are also dealing with a more severe -AO than has ever been seen with a Nina this strong before...

1964-65 had a negative ao on average and 1970-71 also I think...This year we already seen a lower -oa than both of those years...

[donsutherland1]

Good analysis, but again remember, we are also dealing with a more severe -AO than has ever been seen with a Nina this strong before...

My guess is that the current severe blocking and possibility for another episode later in the winter will probably have a larger impact on temperatures e.g., one won't see the near coast-to-coast blowtorch of Winter 1998-99, than blockbuster East Coast snowstorms. Unlike last winter's often very active El Niño-driven subtropical jet, this winter one will have to look more to the polar jet and/or phasing to produce larger storms. While a phased December 1909 solution might be a possibility, everything has to come just right for such a bomb to impact the big cities of the East. Should severe blockiness persist for much of the winter (something I don't expect), frequent smaller events could certainly add up. I'm just not keen on a KU-type storm and believe odds are against any such storms this winter. Of course, I could be wrong.

[tacoman25]

My guess is that the current severe blocking and possibility for another episode later in the winter will probably have a larger impact on temperatures e.g., one won't see the near coast-to-coast blowtorch of Winter 1998-99, than blockbuster East Coast snowstorms. Unlike last winter's often very active El Niño-driven subtropical jet, this winter one will have to look more to the polar jet and/or phasing to produce larger storms. While a phased December 1909 solution might be a possibility, everything has to come just right for such a bomb to impact the big cities of the East. Should severe blockiness persist for much of the winter (something I don't expect), frequent smaller events could certainly add up. I'm just not keen on a KU-type storm and believe odds are against any such storms this winter. Of course, I could be wrong.

Yes, I agree that cold temperatures are much more likely than huge snowstorms for the East with this level of blocking and a La Nina. Still, my point is that past Nina examples are only so good when we are seeing such unprecedented blocking.

It's definitely clear that this winter is not turning out at all like the late 1990s Ninas. I just didn't understand how in the discussions this summer/fall, some people still didn't want to believe we have entered a different climate regime than we were in back then. The global evidence for this the past few years is overwhelming.

[Harry]

Yes, I agree that cold temperatures are much more likely than huge snowstorms for the East with this level of blocking and a La Nina. Still, my point is that past Nina examples are only so good when we are seeing such unprecedented blocking.

It's definitely clear that this winter is not turning out at all like the late 1990s Ninas. I just didn't understand how in the discussions this summer/fall, some people still didn't want to believe we have entered a different climate regime than we were in back then. The global evidence for this the past few years is overwhelming.

Notice how they have all gone silent as well. Almost certain we will go through it again next winter etc etc.

[jbcmh81]

Yes, I agree that cold temperatures are much more likely than huge snowstorms for the East with this level of blocking and a La Nina. Still, my point is that past Nina examples are only so good when we are seeing such unprecedented blocking.

It's definitely clear that this winter is not turning out at all like the late 1990s Ninas. I just didn't understand how in the discussions this summer/fall, some people still didn't want to believe we have entered a different climate regime than we were in back then. The global evidence for this the past few years is overwhelming.

All of which makes me question the idea that many seem to have of a basic end to winter after very early January. I could see January or February being warm, but not both.

[snowstormcanuck]

The ensembles are now providing a firmer signal that the current AO- regime will likely come to an end during the first week in January. That would be consistent with the three past severe December blocking episodes during La Niña events (albeit weaker ones than the current La Niña). At the same time, the EPO is forecast to be climbing. Hence, the stage is being set for a pattern change after December that should see frequent troughing in the East give way to ridging and milder readings. Before then, one or two light to possibly moderate snowfall events remain possible for the big cities of the East. If some past La Niña episodes are relevant, 25%-30% of the season's snowfall could have fallen by the end of December (a bleak prospect given the snow dearth to date).

This is some of the best news I've heard in a while Don. Despite the shift in ENSO, the -AO/-NAO regime, just like last winter, has been an unmitigated disaster for everybody N of 42 and E of about 80. If it wasn't for Lake Huron bailing me out, I'd be sitting at 1.0" for the season on December 17th.

I know a more progressive pattern puts me at risk for running into a torch, but after experiencing this extreme blocking for a winter and a 1/4, I think almost any alternative pattern is better than this one.

[tacoman25]

All of which makes me question the idea that many seem to have of a basic end to winter after very early January. I could see January or February being warm, but not both.

I think the Jan 10 - Feb 10 period will likely be warm overall for most the East. But I would not be surprised to see a cold second half of February - March (going by other years that had a similar progression, as Don alluded to).

However, given the tendencies of this year (and last) towards extreme blocking - anything is possible. The least likely scenario, I think, is Jan-Mar blowtorch for the East, ie 1990.

[jbcmh81]

I think the Jan 10 - Feb 10 period will likely be warm overall for most the East. But I would not be surprised to see a cold second half of February - March (going by other years that had a similar progression, as Don alluded to).

However, given the tendencies of this year (and last) towards extreme blocking - anything is possible. The least likely scenario, I think, is Jan-Mar blowtorch for the East, ie 1990.

I don't even know why 1989-90 keeps getting brought up. That was a neutral after Nina winter, which tend to always be awful. 1985-86, 1989-90, 1996-97, 2001-02... yeah I'm not seeing the resemblance so far other than that a few of them had colder Decembers. I have no problem with the idea that we have a warmer month than this December, which for many particularly farther away from the East Coast, should come in at least top 20 coldest. I could actually see something similar to last winter, where we see two or three weeks of warmth before back to cold again.

[JoMo]

I think the Jan 10 - Feb 10 period will likely be warm overall for most the East. But I would not be surprised to see a cold second half of February - March (going by other years that had a similar progression, as Don alluded to).

However, given the tendencies of this year (and last) towards extreme blocking - anything is possible. The least likely scenario, I think, is Jan-Mar blowtorch for the East, ie 1990.

Ok, Gibbs

[tennvolfan]

I don't even know why 1989-90 keeps getting brought up. That was a neutral after Nina winter, which tend to always be awful. 1985-86, 1989-90, 1996-97, 2001-02... yeah I'm not seeing the resemblance so far other than that a few of them had colder Decembers. I have no problem with the idea that we have a warmer month than this December, which for many particularly farther away from the East Coast, should come in at least top 20 coldest. I could actually see something similar to last winter, where we see two or three weeks of warmth before back to cold again.

I think it was more of the fact that December 89 was cold with a severely neg AO/NAO followed by a sharp rise in both to severely positive with a torched winter. More of a representation of AO/NAO than ENSO.

[A-L-E-X]

This morning, the AO stood at -4.076. It is forecast to bottom out over the next day or two. Already, this is the lowest AO reading in December during a La Niña with ENSO Region 3.4 anomalies of -1.00°C or colder.

The ensembles are now providing a firmer signal that the current AO- regime will likely come to an end during the first week in January. That would be consistent with the three past severe December blocking episodes during La Niña events (albeit weaker ones than the current La Niña). At the same time, the EPO is forecast to be climbing. Hence, the stage is being set for a pattern change after December that should see frequent troughing in the East give way to ridging and milder readings. Before then, one or two light to possibly moderate snowfall events remain possible for the big cities of the East. If some past La Niña episodes are relevant, 25%-30% of the season's snowfall could have fallen by the end of December (a bleak prospect given the snow dearth to date).

After having looked back at pre-1950 data for a larger sample of La Niña events, a grim statistic stands out: No KU-type storm has occurred with a La Niña as strong as the current one (R3.4 anomaly currently at -1.5°C). The clipper that exploded into a paralyzing Mid-Atlantic blizzard in December 1909 occurred when the R3.4 anomalies were around -1.00°C. No events occured with a La Niña anywhere close to as strong as the present one. All the other KU-type events going back to 1871 occurred with R3.4 anomalies that were milder than the December 1909 figure (-0.50°C to -0.85°C accounts for most of the La Niña KU-type events). Significant Midwest/Great Lakes (U.S. into Ontario/Quebec) have, on occasion, occurred with R3.4 anomalies < -1.00°C. Given the expansive sample, barring consistent and strong support from multiple models and ensemble systems, any model or ensemble system that shows a KU-type snowstorm when the La Niña is as strong as it currently is (even the Euro or Euro ensembles) is very likely a suspect run(s).

Thanks, Don. Im thinking that the winter of 1916-17, which was also a strong nina and featured the first of back to back 50 inch plus snowfall seasons in NYC featured a bunch of lesser snowfalls rather than a KU event?

The other possible winter analog would be 1955-56 which featured a KU event in March-- by which time the nina had weakened. Is your thinking that the nina will weaken enough by February or March to allow something like that to happen?

[A-L-E-X]

Remember folks, KU event = 10 inches or more. A 6" significant snowfall event is still entirely within the realm of possibilities.

[A-L-E-X]

I don't even know why 1989-90 keeps getting brought up. That was a neutral after Nina winter, which tend to always be awful. 1985-86, 1989-90, 1996-97, 2001-02... yeah I'm not seeing the resemblance so far other than that a few of them had colder Decembers. I have no problem with the idea that we have a warmer month than this December, which for many particularly farther away from the East Coast, should come in at least top 20 coldest. I could actually see something similar to last winter, where we see two or three weeks of warmth before back to cold again.

So if next year is neutral we might be in trouble lol. But that was also when the nao was in its positive phase, so the other end of the cycle might make a difference even for neutrals after ninas.

[uncle W]

from Christmas 1989 to May 19th 1990 the AO was way positive and only four days in that span were slightly negative...

[Harry]

I think it was more of the fact that December 89 was cold with a severely neg AO/NAO followed by a sharp rise in both to severely positive with a torched winter. More of a representation of AO/NAO than ENSO.

And there is plenty of things that explain WHY that happened as it did in 2005-06 as well. As mentioned i still think Jan offers the best potential for some torching east of the MS river.

[Whacker77]

About ten days ago, DT posted a map showing the sub surface temperatures in the Pacific were warming. He wasn't sure if it was an aberration though. I hope I'm not misrepresenting what he wrote. Having said that, I also thought I had also seen some data which showed warming in the 3.4 and 4 regions of the Pacific. Assuming that data remains operative, how does that affect any outlook for January? Is the blowtorch there, but just not as warm? If a dumb question, just ignore.