AO Forecast to Plunge

[donsutherland1]

Several morning thoughts:

1. Previously, my thought had been that the AO could actually go positive during the first week in January +/- a few days. December superblock experience would suggest that the current blocking regime would persist perhaps into mid-to-late January or even longer with another round of extreme blocking before the blocking ends. Later, additional strong blocking would develop. It increasingly appears that December superblock experience is the way to go. At this time in January 1951, the strong but not extreme December block was nearing its demise. Ensemble guidance shows no such outcome for the current round of blocking. Hence, a dramatic 1950-51-style pattern flip appears unlikely.

2. The first point reinforces the idea that the area of warm anomalies for January will likely be more limited than usual for a moderate/strong La Niña.

3. With the EPO going negative, the burgeoning ridge over Alaska should allow for some of the hemisphere's most extreme cold to enter North America for the first time this winter. With perhaps another round of severe to extreme blocking likely, that ups the ante for the notable Arctic invasion, perhaps along the lines of those that occurred in Winters 1976-77 and 1984-85 during extreme January blocking. Although the cold might not be as extreme as during either of those cases, it could be more severe than the cold that has occurred over the last few winters. That outbreak might occur near mid-month +/- a few days on the Plains and just after mid-month in the East (probably a few days after the blocking bottoms out).

4. Before then, the Pacific Northwest could experience some severe cold, not to mention a possible long-duration snow event that might precede the worst of the cold. More immediately, some of the East Coast cities that were hammered by the recent blizzard could pick up a light or even moderate snowfall late this week and into the coming weekened. Consistent with La Niña events where phasing is critical, there remains a lot of uncertainty about that event. The GFS, GFS ensemble mean, and ECMWF ensemble mean are restrained. The operational ECMWF has a blockbuster event, possibly targeting interior areas, with some possible temporary p-type issues right on the coast i.e. NYC, Long Island, southern Connecticut, and the Jersey Shore. For now, I believe the reasonable continuity of the GFS and the GFS/Euro ensembles might be the better way to go until one has a better handle on the details that will prove critical to the outcome.

[PNW guy]

I live in Seattle and although I was really excited and in high anticipation of a blockbuster event beginning this weekend....in all honesty I don't think it is going to happen. As time progresses there is less and less influence of arctic air into western Washington in the models Ho hum westerly flow or a building ridge on or near the coast shunting the cold air into the midwest and east seems much more likely. I have not given up all hope but pretty much will believe it after it happens. With a positive PNA and a strong negative AO I don't think there is too much to get excited about.

To back up my point....here is the forecast for the Cascades for the weekend...which earlier showed -15 at 850mb on the maps just 4 days ago.

Doesn't look very cold to me...check out the snow level for Sat Sun.

Am I missing something??

WEST SLOPES NORTHERN CASCADES AND PASSES-

WEST SLOPES CENTRAL CASCADES AND PASSES-

INCLUDING THE CITIES OF...DARRINGTON...MARBLEMOUNT...CONCRETE...

INDEX...SNOQUALMIE PASS...RANDLE...PACKWOOD...ASHFORD...MORTON

400 AM PST MON JAN 3 2011

TODAY...SUNNY. FREEZING LEVEL 1500 FEET. AFTERNOON PASS TEMPERATURES NEAR 30. SOUTHEAST WIND IN THE PASSES NEAR 10 MPH THIS MORNING BECOMING LIGHT.

TONIGHT...PARTLY CLOUDY. FREEZING LEVEL 500 FEET. LIGHT WIND IN THE PASSES BECOMING WEST NEAR 10 MPH AFTER MIDNIGHT.

TUESDAY...PARTLY SUNNY. AFTERNOON PASS TEMPERATURES NEAR 30. WEST WIND IN THE PASSES NEAR 10 MPH.

TUESDAY NIGHT...CLOUDY WITH A CHANCE OF RAIN OR SNOW. SNOW LEVEL 1000 FEET. WEST WIND IN THE PASSES 5 TO 15 MPH.

WEDNESDAY...RAIN OR SNOW. SNOW LEVEL 2500 FEET. AFTERNOON PASS TEMPERATURES NEAR 30. SOUTHWEST WIND IN THE PASSES 10 TO 15 MPH.

WEDNESDAY NIGHT...RAIN AND SNOW. SNOW LEVEL 3500 FEET.

THURSDAY...RAIN AND SNOW LIKELY. SNOW LEVEL 3500 FEET.

THURSDAY NIGHT AND FRIDAY...RAIN AND SNOW LIKELY. SNOW LEVEL 3000 FEET.

FRIDAY NIGHT AND SATURDAY...SHOWERS LIKELY. SNOW LEVEL 1500 FEET.

SATURDAY NIGHT AND SUNDAY...SHOWERS LIKELY. SNOW LEVEL 1500 FEET.

TEMPERATURE / PRECIPITATION MOUNT BAKER 34 21 30 / 0 10 10 SNOQUALMIE PASS 29 18 30 / 0 10 10 STEVENS PASS 30 15 29 / 0 10 10

[donsutherland1]

I live in Seattle and although I was really excited and in high anticipation of a blockbuster event beginning this weekend....in all honesty I don't think it is going to happen. As time progresses there is less and less influence of arctic air into western Washington in the models Ho hum westerly flow or a building ridge on or near the coast shunting the cold air into the midwest and east seems much more likely. I have not given up all hope but pretty much will believe it after it happens. With a positive PNA and a strong negative AO I don't think there is too much to get excited about.

To back up my point....here is the forecast for the Cascades for the weekend...which earlier showed -15 at 850mb on the maps just 4 days ago.

Doesn't look very cold to me...check out the snow level for Sat Sun.

Am I missing something??

The models had been showing that the current period of cold would come to an end with a milder interval. The severe cold and prospect of a long-duration snow event, possibly starting with rain, was progged to occur after the mild interval. Most of the ensemble members take the PNA negative during or just after the 1/8-10 timeframe. That's when the risk of severe cold increases.

The 6z GFS is still showing the potential for severe cold beginning after 1/10. Right now, one shouldn't focus on the exact details, but the general picture that is being provided, which would be consistent with EPO-/PNA-/AO- situations. The lowest 2 meter readings shown on the 6z GFS are:

1/10: -6.6°C (20°F)

1/11: -8.1°C (17°F)

1/12: -10.4°C (13°F)

1/13: -12.7°C (9°F)

1/14: -13.9°C (7°F)

1/15: -14.2°C (6°F)

1/16: -13.3°C (8°F)

1/17: -11.3°C (12°F)

IMO, while one cannot yet be sure that the historic-type cold depicted will verify as set forth on that model run, I do believe that there will likely be one or more days with low temperatures at least in the teens. Moreover, given the Pacific Northwest's climatology, there is bound to be moisture around for at least some of that timeframe. Hence, even as the GFS leads to the pattern with some snowfall and has a fantasy snowstorm at the end of its range, the general idea that there should be snowfall opportunities is not unreasonable. But before then, the current cold spell, which is merely a shot across the bow that winter is not likely to be relatively uneventful, will give way to a milder interval (modeled consistently). It's afterward that much colder air entering North America courtesy of the EPO- will be available to be tapped.

In the end, I'll be surprised if the Pacific Northwest is spared. I suspect that before January ends, Seattle will have several days with low temperatures at least in the teens, at least one of which could be below 15°F. Moreover, I expect that Seattle will have picked up at least 3"-6" monthly snowfall.

[Srain]

Don, I wanted to include some other La Nina Winters that offers examples for Arctic Intrusions in our part of the world for the record and hopefully some thoughts as well.

The averages do not pick up the extremes that have occurred since the Fall of 1949 and Winter of 1950. For South Central Texas, although on average moderate to strong La Nina conditions favor increasing probabilities of warmer and drier periods from the Fall through the Winter, there have been a few exceptions in the sub tropical climate over South Central Texas. Even though the active wintertime jet stream is displaced north of South Central Texas, there have been cases since the Fall of 1949 and Winter of 1950 where sub tropical weather patterns linked with features over the Tropics and Mid Latitudes to bring occasional cold outbreaks and periods of heavy rain and precipitation to South Central Texas. A few significant Arctic Outbreaks have come during La Nina Events, including December 1950; late January to February 1951; January and February 1985; February 1989; and January and February of 1996. Another feature that shows up with La Nina winters is more extremes between warm and cold, especially with the dry winters. February of 1996 was an extreme example where it was very cold at the beginning of the month, then set all time February Highs on February 21st, followed by very cold conditions at the end of February 1996. The February monthly record high at Del Rio of 99 on February 21, 1996 was later tied, when the high was 99 on February 25, 2008. The high on February 21, 1996 at Austin Mueller Airport was 99, at Austin Bergstrom 101, and at San Antonio 100 on February 21, 1996. The Winter of 1964/1965 had rainfall wetter than usual for Austin and San Antonio. The winter of 1967/1968 was wetter than usual at Austin, Del Rio, and San Antonio. In January 1968, a slow moving cutoff low came across the area from the west and caused a January flood, similar to the December 1991 floods. The January 1968 case occurred during a weak La Nina period, while the December of 1991 case occurred during a moderate to strong El Nino. January 1968 was the wettest January at San Antonio and the 4th wettest January at Austin Mabry. In November of 1974, during a La Nina period, a heavy rain event came to Austin, and caused flooding. From the Fall of 1984 through the Winter of 1985, during a La Nina period, wetter than usual conditions came most of the time, as relief from the dry period in 1984 came in the Fall of 1984. There were also a number of cold outbreaks in January and February of 1985. This included the heavy snow event that came in January 1985, a record for San Antonio and Del Rio and the 7th heaviest snow for Austin. In January 1985 the first snow event came January 2nd followed by a 2nd snow event from January 11th to 13th, 1985. January 1985 holds the record for the most snow in a month at San Antonio, 15.9 inches of snow, and at Del Rio, with 9.8 inches of snow. For snowfall at Austin January 1985 comes in 2nd place with 7.5 inches of snow, after the record of 9.7 inches of snow in January 1937. Floods from a heavy rain event in October 1998 during La Nina were followed by very dry conditions from December 1998 through the Winter of 1999. In the La Nina period from the Fall of 2000 through the Spring of 2001, wetter than usual conditions came, accompanied by occasional cold outbreaks.

http://www.srh.noaa.gov/images/ewx/wxevent/laninascntrltx.pdf

[donsutherland1]

Don, I wanted to include some other La Nina Winters that offers examples for Arctic Intrusions in our part of the world for the record and hopefully some thoughts as well.

http://www.srh.noaa....inascntrltx.pdf

A wonderful write-up. Many thanks for posting it. I do believe that there is an above normal risk (for a moderate/strong La Niña event) for an Arctic shot that would impact Texas, even as I still suspect that the month as a whole could wind up milder than normal. The monthly outcome will depend largley on how strong and persistent the January blocking is, and a colder outcome is not completely off the table.

[tacoman25]

Still early to see how it all plays out, but it's correct to say this pattern has the potential to be absolutely nuts with cold for almost all of the nation. A sick ridge over AK is THE signal you want to see to build up the strongest cold air masses in North America, and the fact that the NAO relaxes as this AK ridge gets cranked up actually helps build the cold. You would not want the NAO tanked too because if the Greenland ridge was too strong, it would actually connect to the AK ridge and effectively shut off cross polar flow. In the upcoming pattern, it looks like we keep that pathway open for awhile. Maybe the AO / NAO will tank anew after mid month, but by then the strong cold will be in place.

Can you say Jan 1985 meets Dec 1983?

[wxmx]

Can you say Jan 1985 meets Dec 1983?

Ridiculous block in the 12z Euro...1069mb! When was the last time there was a 1060+mb in the CONUS...Dec '89? 1060mb in the Euro this run

[beavis1729]

Ridiculous block in the 12z Euro...1069mb! When was the last time there was a 1060+mb in the CONUS...Dec '89? 1060mb in the Euro this run

I believe you're right.

FYI - all-time highest pressure in U.S. appears to be 1064 mb on 12/24/1983 in Miles City, MT.

[Whacker77]

So in this scenario of potentially historic cold, is it possible 49 of 50 states could end up with snow on the ground? I would guess Florida would be the odd man out, but didn't it snow in Miami in 1977? Heck I wasn't born until that March.

[tacoman25]

So in this scenario of potentially historic cold, is it possible 49 of 50 states could end up with snow on the ground? I would guess Florida would be the odd man out, but didn't it snow in Miami in 1977? Heck I wasn't born until that March.

I believe that happened last winter.

[pcbjr]

So in this scenario of potentially historic cold, is it possible 49 of 50 states could end up with snow on the ground? I would guess Florida would be the odd man out, but didn't it snow in Miami in 1977? Heck I wasn't born until that March.

NOPE - we're in it this time around (or nobody is!!!).

[Rainshadow]

Don,

Apologies if I started this conversation in another thread, but below is one of the reasons I was surprised (and wrong heading into this winter) at the resiliency of the -nao, in past previous winters with a strong -nao, the ensuing winter as posted previously by another met (I forget who, sorry) reached close to neutrality, if not positive looks like 70-80% of the time.

[nzucker]

Don,

Apologies if I started this conversation in another thread, but below is one of the reasons I was surprised at the resiliency of the -nao, in past previous winters with a strong -nao, the ensuing winter almost always reached close to neutrality, if not positive.

This is seemingly the first time we've had a continuous block for multiple years in a row. The -NAO started in Summer 2008 and has kept up.

[donsutherland1]

Don,

Apologies if I started this conversation in another thread, but below is one of the reasons I was surprised (and wrong heading into this winter) at the resiliency of the -nao, in past previous winters with a strong -nao, the ensuing winter as posted previously by another met (I forget who, sorry) reached close to neutrality, if not positive looks like 70-80% of the time.

Tony,

Like you, I didn't expect to see blocking to the magnitude that we've had thus far, particularly with a moderate/strong La Niña. It will be interesting to see how the blocking situation evolves over the remainder of the winter. To date, it has been relentlessly persistent.

[OhioValleyWx]

I am on board that I did not expect this much blocking but it is truly amazing. I was telling a few people that if the storm that bashed the east coast did not cut, the pattern would reload. With it being a strong La Nina I, too, believed blocking would fizzle but it did not and I did a complete 180 for January. This is hard to fathom but when I sit back and look at everything I have not seen elements aligned like this in any year. I am sure there are some close years that many have thrown up and listed and that helps but I truly feel that with all the signals the way they are shaped now, no analog or package would be able to be found. Again, maybe a few had a general theme but finding a direct correlation for the 2009-2010 H5 schemes might go unknown, thus all the nuances and quarks that are changing how we view La Nina's with a very cold PDO and a subtly cooling AMO.

Josh

[NaoPos]

This is seemingly the first time we've had a continuous block for multiple years in a row. The -NAO started in Summer 2008 and has kept up.

Looks as if the 70's had a few years grouped together.

[MN Transplant]

Way off the track here, but I found an interesting stat that I didn't quite know where to put. With the release of the RSS satellite data for December and all of the talk yesterday about the possible Arctic outbreak, I wanted to check to see if there was any relationship between extratropical N. Hemisphere temps and Arctic outbreaks in the US. Probably few realize that December 2010 was the 4th warmest for 20-82.5°N in the satellite record. I didn't see any interesting connections in the data, other than a general warmer N. Hemisphere = warmer continental US. But it isn't a perfect match, and even then we can see cold outbreaks, such as Jan '09 after a warm Dec '08.

So, that aside, the correlation that I did find interesting was between December 20-82.5° temps and March continental US temps. The three warmest extra-N Hem Decembers ('03, '06, '99) matched up with the three warmest US Marches per RSS ('04, '00, '07). Most likely irrelevant in this new era of Superblocking, but just a fun correlation that I found.

[A-L-E-X]

This is seemingly the first time we've had a continuous block for multiple years in a row. The -NAO started in Summer 2008 and has kept up.

This had me wondering for a long time if +NAO was the "natural state"-- because we have seen multiple years of +NAO many times, but this is the first time since the 70s that we've seen a multiple year -NAO

[donsutherland1]

Some quick AO stats:

December 2010: -2.631 (lowest December figure for any La Niña event)

2010 Average: -1.043 (lowest annual average since regular recordkeeping began in 1950)

2010: 11 months < 0

February 2010: -4.266 average (lowest monthly figure since regular recordkeeping began in 1950)

[A-L-E-X]

Hey Don-- how often do multiple year neg AO/NAO happen and are they really less frequent than multiple year pos AO/NAO ?

[donsutherland1]

Hey Don-- how often do multiple year neg AO/NAO happen and are they really less frequent than multiple year pos AO/NAO ?

Alex,

I'll have to check that out when I get home. I don't have the data with me.

[donsutherland1]

Hey Don-- how often do multiple year neg AO/NAO happen and are they really less frequent than multiple year pos AO/NAO ?

There are longer-term AO cycles. On an annual basis, the AO averaged < 0 from 1950-1963. It has been predominantly positive from 1982 through 2008, but now appears to be heading back to a predominant negative state. Multiple years of positive or negative AO are not uncommon. Since 1950, there have been 9 occasions during which the AO averaged < 0 for two or more consecutive years. There have also been 5 occasions on which it averaged > 0 for two or more consecutive years.

[A-L-E-X]

There are longer-term AO cycles. On an annual basis, the AO averaged < 0 from 1950-1963. It has been predominantly positive from 1982 through 2008, but now appears to be heading back to a predominant negative state. Multiple years of positive or negative AO are not uncommon. Since 1950, there have been 9 occasions during which the AO averaged < 0 for two or more consecutive years. There have also been 5 occasions on which it averaged > 0 for two or more consecutive years.

Thanks Don! Seems like the AO cycles last approx 15 years or so.

[VAwxman]

Don,

Apologies if I started this conversation in another thread, but below is one of the reasons I was surprised (and wrong heading into this winter) at the resiliency of the -nao, in past previous winters with a strong -nao, the ensuing winter as posted previously by another met (I forget who, sorry) reached close to neutrality, if not positive looks like 70-80% of the time.

I assume that is for DJFM?

I looked at DJF and found that many times a strong negative NAO for one met winter (DJF) was followed by a negative NAO the next met winter too. Funny how just adding in March make such a big difference if that's the case (or maybe yours is JFM).

[Rainshadow]

I assume that is for DJFM?

I looked at DJF and found that many times a strong negative NAO for one met winter (DJF) was followed by a negative NAO the next met winter too. Funny how just adding in March make such a big difference if that's the case (or maybe yours is JFM).

Brian,

To be honest I don't know. I found the graph in a fall Eastern thread and used it in our winter workshop, the only reason I still had it. I can't go back and see it. Strange how if true one month could change so much. There were other factors though (QBO switch, Al's pacific pressure correlation and Jack's NF pool) that were pointing to a neutralish nao for this winter, all looking wrong.

[vortmax]

Thanks Don! Seems like the AO cycles last approx 15 years or so.

I think we'd be jumping the gun to presume the AO has long term cycles with only 2 said cycles occurring. We've been tracking the '11-year cycles' of the sun for much longer and this one has everyone pretty much stumped.

[donsutherland1]

I think we'd be jumping the gun to presume the AO has long term cycles with only 2 said cycles occurring. We've been tracking the '11-year cycles' of the sun for much longer and this one has everyone pretty much stumped.

Three quick points:

1) There is some literature on longer-term AO cycles and longer-term NAO ones.

2) The duration is longer than 15 years (possibly somewhere in the vicinity of 30 +/- some years, and "possibly" is a key disclaimer. Sample size issues leave a lot of uncertainty as to the duration and nature of such cycles).

3) A lot about what drives the AO cycles, what leads to extreme events is still subject to further research. There are both top-down (e.g., major stratospheric warming events, but sometimes major stratospheric warming events are a response to strong blocking, not the trigger for it) and bottom up (SSTAs, etc.) responses, not to mention feedbacks.

Finally, as for solar cycles, there is still much to be learned about the sun. It wasn't too long ago that NASA proclaimed a new model could accurately predict a renewed active sun based on a conveyor belt of sorts beneath the suns's surface. That model's veracity was shattered in the face ot the sun's failure to emerge decisively from its still relatively quiet state over the past two years. The reality is that there is still no reasonably accurate way to make short-term solar forecasts (level of activity over the next several months). Based on the relatively consistent 11-year cycles, the sun should become more active down the road. But how active remains the big question for which there really is no good answer.

[vortmax]

Three quick points:

1) There is some literature on longer-term AO cycles and longer-term NAO ones.

2) The duration is longer than 15 years (possibly somewhere in the vicinity of 30 +/- some years, and "possibly" is a key disclaimer. Sample size issues leave a lot of uncertainty as to the duration and nature of such cycles).

3) A lot about what drives the AO cycles, what leads to extreme events is still subject to further research. There are both top-down (e.g., major stratospheric warming events, but sometimes major stratospheric warming events are a response to strong blocking, not the trigger for it) and bottom up (SSTAs, etc.) responses, not to mention feedbacks.

Finally, as for solar cycles, there is still much to be learned about the sun. It wasn't too long ago that NASA proclaimed a new model could accurately predict a renewed active sun based on a conveyor belt of sorts beneath the suns's surface. That model's veracity was shattered in the face ot the sun's failure to emerge decisively from its still relatively quiet state over the past two years. The reality is that there is still no reasonably accurate way to make short-term solar forecasts (level of activity over the next several months). Based on the relatively consistent 11-year cycles, the sun should become more active down the road. But how active remains the big question for which there really is no good answer.

I understand completely...just wanted to be sure that numbers like 15 weren't thrown around as the new norm. Hard numbers seem to stick in people's minds...

[A-L-E-X]

Three quick points:

1) There is some literature on longer-term AO cycles and longer-term NAO ones.

2) The duration is longer than 15 years (possibly somewhere in the vicinity of 30 +/- some years, and "possibly" is a key disclaimer. Sample size issues leave a lot of uncertainty as to the duration and nature of such cycles).

3) A lot about what drives the AO cycles, what leads to extreme events is still subject to further research. There are both top-down (e.g., major stratospheric warming events, but sometimes major stratospheric warming events are a response to strong blocking, not the trigger for it) and bottom up (SSTAs, etc.) responses, not to mention feedbacks.

Finally, as for solar cycles, there is still much to be learned about the sun. It wasn't too long ago that NASA proclaimed a new model could accurately predict a renewed active sun based on a conveyor belt of sorts beneath the suns's surface. That model's veracity was shattered in the face ot the sun's failure to emerge decisively from its still relatively quiet state over the past two years. The reality is that there is still no reasonably accurate way to make short-term solar forecasts (level of activity over the next several months). Based on the relatively consistent 11-year cycles, the sun should become more active down the road. But how active remains the big question for which there really is no good answer.

Don, I think that 11 year cycle that people reference is only one of several solar cycles nested one within the other. I actually think the solar influences the AO cycle which then influences the NAO. It makes a great deal of sense, when you consider the fact that for various reasons the arctic regions are more susceptible to solar changes than other areas.

[A-L-E-X]

I understand completely...just wanted to be sure that numbers like 15 weren't thrown around as the new norm. Hard numbers seem to stick in people's minds...

Not really-- it was just based on the length of the last two. There is no reason to think that cycles cant vary in length and anyone who thinks otherwise would naturally be stumped. Stellar cycles dont always follow hard and fast rules for various reasons (mostly because of the nature of the nuclear reactions going on inside.) Anyone who thinks cycles cant change in length and periodicity is in for a rude awakening-- or, more likely, already has had one lol.

When it comes to stuff like this, you quickly learn that there are no such things as "hard numbers." This is high end cutting edge physics we're talking about here-- and some of it even involves quantum mechanics (if it were up to classical physics, energy from the interior of the sun or any star wouldnt make it to the surface like it does.)