AO Forecast to Plunge

[JoMo]

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.

I think the 'damage' has already been done.

[Whacker77]

Just to be clear, when I mentioned warming I meant it wasn't as cold as it had been.

[tacoman25]

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.

Not always, especially for your area. 2008-09...

[tennvolfan]

Just looking at a couple of analogs (FWIW) :

1916-17, and 1917-18 actually had cold and periods of snow in my area (Mid South).

- Jan 17 torched for awhile, but sharply colder mid-late month with a major snowstorm and severe cold. Feb and March '17 torched.

- Jan '18 started to torch but sharply tuned colder for one of the snowiest months on record. Feb started to torch mid month and winter was pretty much over.

1955-56 After a relatively cold Dec, the rest of the winter had a few bouts of cold weather with very little winter weather.

Granted, being much further away from the east coast and relatively close to the plains could make a subtle difference in the pattern in this area.

[pcbjr]

Out of curiosity, what is to kep the current neg AO/NAO from bouncing up to near 0 or into the positive range, and then bouncing down again in 2 - 3 weeks? Looking at the ensemble means, it seems that's been the general pattern (trend) the past few months.

Any explanation appreciated!

[donsutherland1]

Earlier today, I noted that the ensembles are 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). Most of the ensembles suggest that the AO will probably come out somewhere above -2 and below +1 to begin January. The AO will probably become positive sometime during the first week in January.

The idea is that milder conditions will likely begin to take hold in the East.

The following is the composite temperature anomaly for January cases when the AO ranged from -1.99 to 0 when the ENSO Region 3.4 anomaly was between -1.75 and -1.25:

The following is the composite temperature anomaly for January cases when the AO ranged from 0 to +1.99 when the ENSO Region 3.4 anomaly was between -1.75 and -1.25:

Although the operational GFS and GFS ensembles are not yet showing a pattern consistent with the above composites, the 12/17/2010 0z Reforecast ensembles are hinting at such a change in late December. I believe the Reforecast ensembles may be a little premature in ending the cold, but I believe that their signal is the first hint of the pattern evolution I expect to unfold as the AO rebounds and then moves positive, probably sometime during the first week in January. Before then, I do believe that the snow-starved big cities of the East will see some accumulations of snow. The weekend system is likely a miss for everywhere except perhaps parts of Long Island and extreme eastern New England where some light snows or flurries could fall. The system shown for around 12/25-26 should be more potent, possibly bringing a moderate snowfall to parts of the East, but odds are against a blockbuster snowstorm.

[Carvers Gap]

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.

Don, if I've missed this in a previous part of the thred...just disregard. How many moderate to strong La Nina's happened during a -PDO? Would a -PDO soften the impact of a strong to moderate La Nina? Seems like our winters here in TN have cooled since the PDO went negative, whether Nina, Nino, or Nada. Thanks for your earlier post today.

[donsutherland1]

Some quick thoughts on the 12/18 0z run of the GFS:

1. I like the idea of the possibility of a moderate snowstorm (3"-6"/4"-8" type) before the blocking regime ends. I don't believe we'll see a KU storm, but suspect that the GFS is fairly reasonable in advertising one or two threats.

2. The GFS has swung in the extended range toward a solution that would be consistent with the breaking down of the current AO- regime (something I expect to occur in the first week in January +/- a few days).

Composite temperature anomalies:

GFS 384-hour forecast (1/3/2011 0z):

Note: Aside from the general idea of a SE ridge popping and milder regime developing in the East, one should not latch onto the exact details. What is important is that the model might be providing its first hint of what likely lies ahead as the block dissipates.

[A-L-E-X]

Question for you Don, I know you favor moderate snow over KU 10"+ events, but do you think it likely we could get multiple moderate snowfall events rather than just one before the blocking ends?

[donsutherland1]

Don, if I've missed this in a previous part of the thred...just disregard. How many moderate to strong La Nina's happened during a -PDO? Would a -PDO soften the impact of a strong to moderate La Nina? Seems like our winters here in TN have cooled since the PDO went negative, whether Nina, Nino, or Nada. Thanks for your earlier post today.

I'll have to take a closer look. I believe a cyclical cold PDO is helpful, but a PDO- combined with a La Niña doesn't assure a cold winter e.g., 1949-50 had a strongly negative PDO and moderate La Niña, but was exceptionally warm in the eastern third of the nation, including Tennessee.

[donsutherland1]

Question for you Don, I know you favor moderate snow over KU 10"+ events, but do you think it likely we could get multiple moderate snowfall events rather than just one before the blocking ends?

I believe we'll see one or perhaps two such events. I'd be surprised if there were more than two moderate events before the block ends (and the end of the block is something I'm not looking forward to).

[A-L-E-X]

I believe we'll see one or perhaps two such events. I'd be surprised if there were more than two moderate events before the block ends (and the end of the block is something I'm not looking forward to).

Me neither Don-- but I remember someone posted info that if we do torch, such a torch period in the middle of winter usually doesnt last more than six weeks at the most. I'll use the same formula as what happened in 2005-06 and hope that sometime later in Feb or March as the nina wanes we have another period of strong blocking and a perhaps a larger event, something like March 1956 perhaps.

[Yes_Probably_Maybe_No]

I'm learning this stratosphere stuff, but if I remember correctly. some of the warming in Oct/Nov that propagated out of Asia into the Poles has accounted for the -AO. The difference being this time the MT torque isn't favorable to propagate this up.

Anyways, Asia has been cooking.

10 hPa anomalies

Perhaps some good news for second half of Jan-Feb?

NCEP Stratosphere-Troposphere monitoring also indicates some warming going on near 1 hPa.

OT a bit, I stumbled upon the wave breaking thread and I saw the graphics for it, but I was wondering if someone could hop in there and explain them a bit. Thanks ahead of time.

[jbcmh81]

Not always, especially for your area. 2008-09...

January was the only decent month. There was less than 2.5" of snow in December, February and March combined (total seasonal snowfall was well below normal), and none of those months were cold either. December was normal and February-March were above. It was not a good winter.

[Snow Wizard]

Although the operational GFS and GFS ensembles are not yet showing a pattern consistent with the above composites, the 12/17/2010 0z Reforecast ensembles are hinting at such a change in late December. I believe the Reforecast ensembles may be a little premature in ending the cold, but I believe that their signal is the first hint of the pattern evolution I expect to unfold as the AO rebounds and then moves positive, probably sometime during the first week in January. Before then, I do believe that the snow-starved big cities of the East will see some accumulations of snow. The weekend system is likely a miss for everywhere except perhaps parts of Long Island and extreme eastern New England where some light snows or flurries could fall. The system shown for around 12/25-26 should be more potent, possibly bringing a moderate snowfall to parts of the East, but odds are against a blockbuster snowstorm.

Are the reforecast ensembles something different than the regular ensemble?

[donsutherland1]

Are the reforecast ensembles something different than the regular ensemble?

Yes, they incorporate MOS-based forecasting.

[uncle W]

AO is below -4 again...

[Whacker77]

If I'm reading the chart right, has the AO been positive just 34 days since the first of September? This is the 109th day since then so the negative persistance of the blocking has been high. The AO's been positive about 31% of the time.

[donsutherland1]

Today, the AO stood at -5.172. That is only the ninth time on record that the AO has fallen to -5 or below in December. It is also the 8th lowest December figure on record and the first -5 or below reading when the ENSO Region 3.4 anomaly was negative.

Today's reading shattered the daily record of -4.238 set last year.

[pcbjr]

Today, the AO stood at -5.172. That is only the ninth time on record that the AO has fallen to -5 or below in December. It is also the 8th lowest December figure on record and the first -5 or below reading when the ENSO Region 3.4 anomaly was negative.

Today's reading shattered the daily record of -4.238 set last year.

Don,

What implications do you see to the "first -5 or below reading {with} the ENSO Region 3.4 anomaly {being} negative"? Since this set-up/configuration apparently is a "new kid on the block" (pun intended), there's probably not much to gauge it against (or is there?); do you foresee this seemingly unique situation impacting us in so far as temps are concerned as we move forward, and if so, how (and if I may be so bold, why)?

Thanks!

[donsutherland1]

Don,

What implications do you see to the "first -5 or below reading {with} the ENSO Region 3.4 anomaly {being} negative"? Since this set-up/configuration apparently is a "new kid on the block" (pun intended), there's probably not much to gauge it against (or is there?); do you foresee this seemingly unique situation impacting us in so far as temps are concerned as we move forward, and if so, how (and if I may be so bold, why)?

Thanks!

I believe we're seeing the implications with the persistent cold in the East, especially the Southeast. As long as the block lasts, any qpf will provide snowfall opportunities for many areas. Unfortunately, things would have to come together just right for a blockbuster snow event. Moderate events are more likely, and I suspect that the system modeled for around 12/25 has a decent chance to bring a moderate snowfall (3"-6"/4"-8" maybe a few locally higher amounts). If one adjusts the track somewhat farther south (due to stronger blocking) for the 12/18-20/1995 event, one can probably have a reasonable guess as to area that would probably see accumulating snow (not necessarily amounts).

Ray's (famartin) outstanding website should be referenced for that event: http://www.njfreeways.com/weather/1996/19-Dec-95.html

Extreme cold has not occurred, as the coldest air is not located on our side of the globe.

[pcbjr]

I believe we're seeing the implications with the persistent cold in the East, especially the Southeast. As long as the block lasts, any qpf will provide snowfall opportunities for many areas. Unfortunately, things would have to come together just right for a blockbuster snow event. Moderate events are more likely, and I suspect that the system modeled for around 12/25 has a decent chance to bring a moderate snowfall (3"-6"/4"-8" maybe a few locally higher amounts). If one adjusts the track somewhat farther south (due to stronger blocking) for the 12/18-20/1995 event, one can probably have a reasonable guess as to area that would probably see accumulating snow (not necessarily amounts).

Ray's (famartin) outstanding website should be referenced for that event: http://www.njfreeway.../19-Dec-95.html

Extreme cold has not occurred, as the coldest air is not located on our side of the globe.

Thanks Don! Very informative (as always).

You raise another question (maybe a 2 parter) in my mind: What do you think this means after about the 1st (as it seems to me the AO/NAO may/will go slightly positive, but it doesn't look like a canon shot way upward into positive territory - after all it has to climb a lot just to get to neutral), and does the "first -5 or below reading {with} the ENSO Region 3.4 anomaly {being} negative" keep the cold on the other side of the globe?

[Ottawa Blizzard]

I believe we're seeing the implications with the persistent cold in the East, especially the Southeast. As long as the block lasts, any qpf will provide snowfall opportunities for many areas. Unfortunately, things would have to come together just right for a blockbuster snow event. Moderate events are more likely, and I suspect that the system modeled for around 12/25 has a decent chance to bring a moderate snowfall (3"-6"/4"-8" maybe a few locally higher amounts). If one adjusts the track somewhat farther south (due to stronger blocking) for the 12/18-20/1995 event, one can probably have a reasonable guess as to area that would probably see accumulating snow (not necessarily amounts).

Ray's (famartin) outstanding website should be referenced for that event: http://www.njfreeway.../19-Dec-95.html

Extreme cold has not occurred, as the coldest air is not located on our side of the globe.

Don, do you see the coldest air making it over to our side of the globe at any time this winter in January and February?

[donsutherland1]

Thanks Don! Very informative (as always).

You raise another question (maybe a 2 parter) in my mind: What do you think this means after about the 1st (as it seems to me the AO/NAO may/will go slightly positive, but it doesn't look like a canon shot way upward into positive territory - after all it has to climb a lot just to get to neutral), and does the "first -5 or below reading {with} the ENSO Region 3.4 anomaly {being} negative" keep the cold on the other side of the globe?

Pcbjr,

Once the AO goes positive, a milder regime will take hold in the East. Now, multiple runs of the GFS (and also reforecast ensembles) have hinted at just such a development. Also, the extreme block has forced the cold air farther south. Hence, Europe is shivering under some extreme cold.

[donsutherland1]

Don, do you see the coldest air making it over to our side of the globe at any time this winter in January and February?

I believe that will happen. Whether the pattern will cause the cold to dump into eastern North America or western North America will be the issue. Odds might favor the latter, as 30-45 days from now, the trough will likely be locked in the West if things unfold as I suspect they will.

[donsutherland1]

To put the current extreme blocking event into perspective, I took a look at all Decembers when the ENSO Region 3.4 anomaly was -1.00°C or colder (1950-2009). Those Decembers were 1955, 1964, 1970, 1973, 1975, 1984, 1988, 1998, 1999, and 2007.

The following are some statistics from those cases:

Average AO: +0.517

AO+: 68.7% days

AO-: 31.3% days

Lowest AO: -2.792, December 19, 1973 (nearly 2.4 standard deviations from the mean)

Lowest monthly average: -0.444, 1955

The following are statistics to date for December 2010:

Average AO: -1.713 (nearly 1.6 standard deviations below the mean)

AO+: 11.1% days

AO-: 88.9% days

Lowest AO: -5.172, December 18 (>4 standard deviations from the mean)

[uncle W]

To put the current extreme blocking event into perspective, I took a look at all Decembers when the ENSO Region 3.4 anomaly was -1.00°C or colder (1950-2009). Those Decembers were 1955, 1964, 1970, 1973, 1975, 1984, 1988, 1998, 1999, and 2007.

The following are some statistics from those cases:

Average AO: +0.517

AO+: 68.7% days

AO-: 31.3% days

Lowest AO: -2.792, December 19, 1973 (nearly 2.4 standard deviations from the mean)

Lowest monthly average: -0.444, 1955

The following are statistics to date for December 2010:

Average AO: -1.713 (nearly 1.6 standard deviations below the mean)

AO+: 11.1% days

AO-: 88.9% days

Lowest AO: -5.172, December 18 (>4 standard deviations from the mean)

if you used the Dec/Jan mei Dec. 26th 1961 comes close...

[pcbjr]

Don,

Thanks!

I appreciate the input, greatly.

I look at the ensembles back to September (up and down) and I keep scratching my head; maybe you can ease my "confusication" (as my youngest puts it) - it seems the AO/NAO may/will go slightly positive in a week or two (as that appears to be the cycle), but it doesn't look like a Roman Candle upward into positive territory - after all it has to climb a lot just to get to neutral (????), and none of the recent "ups" have been dramatic ones (???).

[okie333]

I believe that will happen. Whether the pattern will cause the cold to dump into eastern North America or western North America will be the issue. Odds might favor the latter, as 30-45 days from now, the trough will likely be locked in the West if things unfold as I suspect they will.

How about Central North America?

[uncle W]

lowest daily winter ao value since 1950...I hope I didn't miss a date...

season.......value.....date.....

1949-50......-2.854.....3/15/50

1950-51......-4.353.....12/27/50

1951-52......-3.805.....3/4/1952

1952-53......-3.766.....12/27/52

1953-54......-3.495.....1/30/54

1954-55......-3.064.....1/4/55

1955-56......-4.564.....2/15/56

1956-57......-4.473.....2/21/57

1957-58......-4.030.....3/11/58

1958-59......-4.026.....1/7/59

1959-60......-4.108.....1/28/60

1960-61......-2.719.....1/10/61

1961-62......-4.417.....3/4/62

1962-63......-5.010.....1/21/63

1963-64......-4.470.....12/20/63

1964-65......-3.973.....1/26/65

1965-66......-5.130.....1/28/66

1966-67......-4.147.....12/13/66

1967-68......-3.490.....2/7/68

1968-69......-5.282.....2/13/69

1969-70......-6.365.....3/5/70

1970-71......-2.821.....2/6/71

1971-72......-3.100.....2/5/72

1972-73......-2.044.....12/17/72

1973-74......-2.792.....12/19/73

1974-75......-1.695.....12/18/74

1975-76......-3.262.....1/24/76

1976-77......-7.433.....1/15/77

1977-78......-5.291.....2/5/78

1978-79......-4.387.....1/25/79

1979-80......-3.705.....1/24/80

1980-81......-4.318.....3/4/81

1981-82......-3.804.....12/30/81

1982-83......-3.410.....2/6/83

1983-84......-3.706.....3/13/84

1984-85......-6.226.....1/19/85

1985-86......-3.894......2/6/86

1986-87......-3.507.....3/9/87

1987-88......-2.314.....2/28/88

1988-89......-0.318.....3/4/89

1989-90......-3.482.....12/10/89

1990-91......-3.381.....3/9/91

1991-92......-2.597.....12/4/91

1992-93......-2.228.....3/2/93

1993-94......-3.503.....2/24/94

1994-95......-3.116.....3/9/95

1995-96......-4.353.....12/19/95

1996-97......-3.377.....12/30/96

1997-98......-4.269.....1/10/98

1998-99......-3.856.....3/10/99

1999-00......-2.118.....2/18/00

2000-01......-4.854.....2/25/01

2001-02......-3.293.....12/28/01

2002-03......-3.575.....1/22/03

2003-04......-4.387.....1/17/04

2004-05......-4.337.....2/26/05

2005-06......-3.569.....12/5/05

2006-07......-2.184.....2/4/07

2007-08......-2.468.....1/2/08

2008-09......-3.178.....2/3/09

2009-10......-5.821.....12/21/09

2010-11......-5.172.....12/18/10 as of 12/18