Winter 2013-14 medium range discussion

[easternsnowman]

It looks like there remains a lot of uncertainty with the upcoming weather. I still feel the pattern is looking like a 2007-8 repeat which also had an above normal October.

[donsutherland1]

Some quick thoughts...

 

1. The MJO remains in Phase 4 today. It has been locked in the low-amplitude circle for almost all of the last 40 days. At present, there's little evidence that it will gain higher amplitude over at least the next week or two.

 

2. The November 22-30 period looks to be colder than normal in the eastern third of the U.S., consistent with the ideas discussed earlier in this thread (#40). The first week of December will probably wind up colder than normal in that region, though there is still some degree of uncertainty.

 

3. There remains a risk that the AO will turn positive to strongly positive by or during the first week in December, potentially leading to a lifting of the cold anomalies northward into Canada and the development of a more zonal flow. The EPO still looks to remain predominantly negative entering December and perhaps beyond.

 

What happens when the AO and EPO are not in agreement?

 

When wavelengths are shorter, the kind of outcome that is playing out across North America and is expected over the next two weeks is not uncommon. However, for the winter as a whole, during which wavelengths are longer, there is a bias toward warmth in the East, cold in the West. That outcome has occurred, in general, when the EPO was predominantly negative and AO predominantly positive/strongly positive, AO was predominantly negative and the EPO was predominantly positive/strongly positive. Examples of the former situation included winters 1990-91 and 1992-93. Examples of the latter situation included winters 1952-53 and 2012-13.

[Isotherm]

I know a lot of the discussion has been regarding the signs pointing towards +AO, especially the first half of the winter, but what are people seeing in regards to the EPO. The AO and EPO certainly don't always go hand in hand, and it seems like some of the prominent analogs to this year had significant -EPO periods....especially from late December to early February.

 

 

Strongly agree and this is what I talked about in my winter outlook thread. +AO/-EPO patterns have shown since 1950 to be quite cold for the northern tier. Even a winter like 1992-93 which was one of my analogs, had a +1.7 AO for DJF yet temps for DJF finished normal to slightly below in NYC due to the EPO.

 

http://www.americanwx.com/bb/index.php/topic/41743-my-winter-outlook-2013-14/

[donsutherland1]

December 1-7, 2013 Thoughts...

 

The generally cold pattern now underway and likely to be reinforced from time to time with fresh shots of unseasonably cold air is likely to continue during the first week in December. Both the ENSO-teleconnection cases and objective analogs from the GFS ensembles centered around 12/1 are in good agreement that the eastern third to half of the U.S. and a large part of Canada will be colder than normal.

 

 

It remains plausible that at least one of the cold shots during that timeframe, perhaps much like the upcoming one Sunday-Tuesday of next week could feature low temperatures 1-2 standard deviations below normal. That would potentially bring readings into the teens or low 20s for at least some of the big cities from Philadelphia to Boston. Cold shots that have produced teens or colder during the first week of December in that region have often signaled a cold month, as the cold anomalies have proved to great to overcome once the pattern shifted.

 

One would look for indications of perhaps a cold December on the partial teleconnection cases. For nearly two weeks, they have been very consistent with the idea of a transition to a milder pattern and overall warm anomalies in a large part of CONUS, and cold anomalies across much of Canada. However, the latest data has produced the first colder solution in a while. It remains to be seen whether that is a temporary departure or perhaps an indication that December could be cold. For now, uncertainty about December has increased. My December thoughts will likely be posted early next week, just prior to the Thanksgiving Day holiday. The winter thoughts will be posted around or perhaps just after Thanksgiving Day.

 

Finally, looking ahead to the winter as a whole, the ensembles have backed off the prospect of a sustained period of blocking in the extended range. Instead, after a brief period, the AO is forecast to revert back to positive or strongly positive values. This outcome is perhaps another signal that the winter will likely feature a predominant AO+ regime. Having said that, there is some possibility that as the QBO approaches 0, possibly in February or March, blocking could become somewhat more frequent.  

 

Some discussion has focused on the idea that the EPO could bail out the CONUS from a warm outcome were the AO to become predominantly positive. However, it should be noted that when the AO is strongly positive, the EPO typically is positive and almost always not strongly negative. For example, for the December 1981-2010 base period, the EPO was positive in 57% of the cases when the AO was +0.5 or above. During those AO cases, the EPO was above -1.0 82% of the time. Hence, while the EPO has frequently gone strongly negative (about 40% of the past 30 days have seen the EPO at or below -1.0), the EPO could be more neutral to weakly negative than strongly negative in December.

 

For now, the cold close to November in parts of the CONUS will likely extend into at least the first week in December.

[griteater]

Enjoy reading your thoughts in here Don, and appreciate the effort.

 

Pretty good signal for a -EPO pattern on the 18z GEFS throughout the first week of Dec.

 

 

[Isotherm]

 

Some discussion has focused on the idea that the EPO could bail out the CONUS from a warm outcome were the AO to become predominantly positive. However, it should be noted that when the AO is strongly positive, the EPO typically is positive and almost always not strongly negative. For example, for the December 1981-2010 base period, the EPO was positive in 57% of the cases when the AO was +0.5 or above. During those AO cases, the EPO was above -1.0 82% of the time. Hence, while the EPO has frequently gone strongly negative (about 40% of the past 30 days have seen the EPO at or below -1.0), the EPO could be more neutral to weakly negative than strongly negative in December.

 

For now, the cold close to November in parts of the CONUS will likely extend into at least the first week in December.

 

 

If this month is any clue for the upcoming winter, there might be a large separation / disagreement between the EPO and AO state. Around November 10th, AO values were 3 to 4 standard deviations above normal, while simultaneously the EPO fell to 4 to 5 standard deviations below normal. That's a difference of around 8 standard deviations. Also it's unlikely that the AO would remain above +2 for long durations.

 

The 500mb pattern is important as well. A weakly negative EPO could be effective or ineffective depending upon the placement of the positive height anomaly (similar to the NAO). A positive height anomaly centered around AK would be a more effective -EPO than that same positive height anomaly near British Columbia's west coast.

[tacoman25]

 

Some discussion has focused on the idea that the EPO could bail out the CONUS from a warm outcome were the AO to become predominantly positive. However, it should be noted that when the AO is strongly positive, the EPO typically is positive and almost always not strongly negative. For example, for the December 1981-2010 base period, the EPO was positive in 57% of the cases when the AO was +0.5 or above. During those AO cases, the EPO was above -1.0 82% of the time. Hence, while the EPO has frequently gone strongly negative (about 40% of the past 30 days have seen the EPO at or below -1.0), the EPO could be more neutral to weakly negative than strongly negative in December.

 

For now, the cold close to November in parts of the CONUS will likely extend into at least the first week in December.

 

Good points.

 

However, I think it's worth noting that if you look at neutral ENSO +AO/-EPO Novembers, you have 1966, 1978, 1990, 1993, 1996, and 2003. Here is the composite for the winters that followed:

 

 

 

Now, 1978-79 was a historically cold winter and obviously skews the composite cold. But even if we remove that winter, we are still left with far from a blowtorch signal.

 

 

 

 

Perhaps even more intriguing, half of these years are good QBO analogs: 1966, 1978, and 1990. All had episodes of extreme/historic cold in the CONUS.

[donsutherland1]

 

Enjoy reading your thoughts in here Don, and appreciate the effort.

 

Pretty good signal for a -EPO pattern on the 18z GEFS throughout the first week of Dec.

 

 

 

Thanks Griteater.

 

It will be interesting to see what today's data shows. Yesterday's data produced the first colder solution in a while on the partial teleconnections cases I use for trends, but it could well have been a temporary departure. Given the earlier consistency, I still lean toward a warmer outcome being more likely than a colder one, but the probability of that scenario has fallen.

 

The EPO continues to look negative for the foreseeable future. However, the large difference between the EPO- and AO+ typically has not been long-lived. How things evolve will be interesting to say the least.

[donsutherland1]

If this month is any clue for the upcoming winter, there might be a large separation / disagreement between the EPO and AO state. Around November 10th, AO values were 3 to 4 standard deviations above normal, while simultaneously the EPO fell to 4 to 5 standard deviations below normal. That's a difference of around 8 standard deviations. Also it's unlikely that the AO would remain above +2 for long durations.

 

The 500mb pattern is important as well. A weakly negative EPO could be effective or ineffective depending upon the placement of the positive height anomaly (similar to the NAO). A positive height anomaly centered around AK would be a more effective -EPO than that same positive height anomaly near British Columbia's west coast.

The kind of extreme separation that has occurred recently has typically not been long-lived. It has produced sometimes memorable outcomes e.g., the Arctic outbreak in late December 1983.

 

I fully agree about the 500 mb pattern.

[donsutherland1]

Good points.

 

However, I think it's worth noting that if you look at neutral ENSO +AO/-EPO Novembers, you have 1966, 1978, 1990, 1993, 1996, and 2003. Here is the composite for the winters that followed:

 

DJF-EPO+AO.png

 

 

Now, 1978-79 was a historically cold winter and obviously skews the composite cold. But even if we remove that winter, we are still left with far from a blowtorch signal.

 

 

DJF-EPO-no1978.png

 

 

Perhaps even more intriguing, half of these years are good QBO analogs: 1966, 1978, and 1990. All had episodes of extreme/historic cold in the CONUS.

A number of those winters have featured notable cold as you mentioned. Even if the winter winds up milder than normal, I don't think a 2011-12-style "torch" for the winter as a whole is very likely and I also suspect that there will be at least some cold shots that will likely exceed what took place during the last few winters.

[Bob Chill]

Don, I don't post on the main forum often but I always stop by to read your posts. You are a great asset here. 

 

Nov has been a conflicting month to say the least making Dec a difficult month to get a handle on. Historically, when the AO is  +1sd or higher in Dec it's a harbinger of a warm month (or vice versa) in most of the US. Particularly the east. One thing that was made starkly obvious last year is that a big -AO can be rendered useless with cold delivery when the PAC puts up a good fight. It's intriguing that we are seeing the exact opposite right now. 

 

Of course the million dollar question is can it continue this year. Tuesday's globals and ensembles definitely threw some caution in there. Some of the sign of things going awry for the cold pattern showed up and i pretty much expected the bad trend to continue. But they didn't. At least not yet. 

 

The lack of favorable blocking in the nao domain is definitely a problem for sustained cold in the east (stating the obvious). But the progressive flow seems to want to go a good job sending some unusually cold air masses into the US. They may only hang around for 2-3 days before quickly moderating but it's hard to complain either way. 

 

One thing that's recently showed up is a nino type flow with energy undercutting the ridge in the west. Also, the are hints of the pv getting displaced into Canada. The op gfs yesterday showed it moving all the way to se Canada but it was in lala range and certainly not something to expect. However, a placement near Hudson is a typical winter look and the GEFS has shown the possibility of that happening for a couple runs in a row. 

 

This is the end of the 6z GEFS from this morning:

 

 

 

A similar look was there yesterday too. I find it at least slightly encouraging that model runs showing the pattern relaxing to unfavorable in the long range have been few and far between and the potential for a cold and potentially active first 10 days of Dec are on the table. 

 

If you look at the major TCs they have definitely painted quite a different picture compared to sensible weather. It makes one wonder if this is going to be a year of unexpected results. 

[donsutherland1]

Morning thoughts...

 

1. The latest data led to the partial teleconnection cases returning to the generally mild look they had maintained over the past two weeks (mild anomalies across much of the CONUS/cold readings across a large part of Canada/a fairly large area of cold anomalies in Europe), with yesterday having been an exception. December 2008 was the best fit. The possible variable responsible is that the ensemble guidance has again returned to a state where many members forecast a return to PNA- conditions after a brief period of PNA+.

 

2. The latest monthly CFSv2 forecast for December is warm in the East and across much of the southern tier of the U.S. It is cold throughout much of Canada. That's not dissimilar from the partial teleconnection cases, though those cases show more widespread warm anomalies than the CFSv2 does. The CFSv2 is now moving into a timeframe where its monthly forecasts have shown some skill.

 

3. The potential transitional period that has shown up repeatedly (yesterday being an exception) was the December 5-10 timeframe. The latest CFSv2 Week 4 forecast for the December 12-16 period shows warmth across the eastern half of the U.S., cold in the western third, and cold across much of Canada into Alaska.

[donsutherland1]

Severe November Cold Shot...

 

For some time, the November 22-30 period has looked colder than normal in the eastern U.S. (#40) and the ensemble guidance has suggested an unusually strong shot of cold at some point during the timeframe (#87). As the event has drawn nearer, the cold shot appears even more impressive than earlier modeled. The cold air that will blast into the region later Saturday appears likely to produce near record low maximum readings on Sunday (11/24) and near record low temperatures on Monday morning (11/25). A few areas could see new records.

 

The GFS ensemble mean shows 850 mb temperature anomalies of 2.0-2.5 standard deviations across an expansive area of the East for 11/25 0z.

 

 

That air mass appears only slightly warmer than the record cold air mass of 1938 (850 mb anomalies are below).

 

 

In terms of outcomes, the below charts show the kind of temperatures that are associated with the above-mentioned standardized anomalies, MOS and GFS operational forecasts, and records for Boston, New York City, Philadelphia, and Washington, DC.

 

 

In terms of outcomes, it appears possible that Boston and New York City could experience a high temperature at or below 32° on Sunday. Philadelphia also has a shot at approaching its record low maximum temperature on Sunday. All of the above cities will likely see low temperatures in the low 20s on Monday. Many outlying areas will see low temperatures in the teens. The possibility of a temperature below 20°, particularly in Boston or Philadelphia exists. Philadelphia has perhaps the best shot at approaching or reaching its daily record low temperature for Monday.

[Ottawa Blizzard]

Don, I was wondering what your thoughts were for Toronto and Ottawa? Do you think these two cities will see a mild build-up to Christmas, or will we be in the "battle zone" between the warm and cold air which often leads to snow?

[donsutherland1]

Don, I was wondering what your thoughts were for Toronto and Ottawa? Do you think these two cities will see a mild build-up to Christmas, or will we be in the "battle zone" between the warm and cold air which often leads to snow?

Those cities, particularly Ottawa, have a better chance at staying colder than normal longer. Ottawa has a good chance at finishing with cold anomalies for the month. Toronto will probably be nearer to normal for the month as a whole, but there's still quite a bit of uncertainty. Most of Canada will probably wind up colder than normal for the month as a whole. At least that's the way I see things right now.

[Srain]

Severe November Cold Shot...

 

For some time, the November 22-30 period has looked colder than normal in the eastern U.S. (#40) and the ensemble guidance has suggested an unusually strong shot of cold at some point during the timeframe (#87). As the event has drawn nearer, the cold shot appears even more impressive than earlier modeled. The cold air that will blast into the region later Saturday appears likely to produce near record low maximum readings on Sunday (11/24) and near record low temperatures on Monday morning (11/25). A few areas could see new records.

 

The GFS ensemble mean shows 850 mb temperature anomalies of 2.0-2.5 standard deviations across an expansive area of the East for 11/25 0z.

 

 

That air mass appears only slightly warmer than the record cold air mass of 1938 (850 mb anomalies are below).

 

 

In terms of outcomes, the below charts show the kind of temperatures that are associated with the above-mentioned standardized anomalies, MOS and GFS operational forecasts, and records for Boston, New York City, Philadelphia, and Washington, DC.

 

 

In terms of outcomes, it appears possible that Boston and New York City could experience a high temperature at or below 32° on Sunday. Philadelphia also has a shot at approaching its record low maximum temperature on Sunday. All of the above cities will likely see low temperatures in the low 20s on Monday. Many outlying areas will see low temperatures in the teens. The possibility of a temperature below 20°, particularly in Boston or Philadelphia exists. Philadelphia has perhaps the best shot at approaching or reaching its daily record low temperature for Monday.

 

Don, to follow up on your update regarding this weekend into the busy Thanksgiving Holiday travel period  we in the Central/Western Region are watching a unusually early Winter Storm developing that may have some significant societal impacts in the days ahead. This is a repost of my thoughts early this morning in our sub forum...

 

A complex and complicated forecast for much of Texas and Oklahoma is unfolding this morning regarding the timing of the arrival of the much talked about Arctic front and what we may see weather wise into the weekend extending into early Tuesday.

Currently surface observations suggest the Arctic boundary is moving faster than previously though and is running a good 12-18 hours faster than was expected. As is usually the case with a very dense and cold air mass, this is not too surprising that the computer model would under estimate the speed. First things first…showers are moving N to NE from the Gulf and that should continue today and increase in coverage across the Region and we should begin to see some storms develop to our NW across Oklahoma and N Texas later tonight. A line of showers and storms will sweep S during the overnight hours tonight ushering in the arrival of the coldest air of the season on Friday.

Wintry Weather Advisories have been issued across Texas Panhandle, Oklahoma/Kansas and will likely be needed later today across further S into the Permian Basin and the Big Country near Midland/Odessa. There is a chance that Winter Weather Advisories or even a Winter Storm Watch will be hoisted for the Dallas/Ft Worth area as freezing temps at the surface and over running precip begins to fall leading to an ice threat mainly on elevated surfaces by Friday afternoon into the evening hours.

We may see a brief break from the over running precip as the much talked about upper air cold core close low develops in Southern California. This feature is expected to deepen rather rapidly and there are some strong indications that this low will be near the 3 standard deviation below normal for late November standards making it a strong storm system that we usually do not see this time of year. Abundant tropical moisture from the Pacific will wrap up this storm system and indications are that it will be a bit further E over Arizona bringing flooding rains to the Phoenix area and heavy higher elevation snow to Eastern AZ into New Mexico.

This storm system appears to stay rather strong and remain a closed low as it cross New Mexico on Saturday and moves E into Texas on Sunday. The current projected storm track appears to be just S of Lubbock to near Austin and then very close to SE Texas during the morning hours of Monday. The latest run of the 06Z GFS brings this upper air feature very close to Bryan/College Station and Montgomery County, so it will be worth monitoring. There still remains relative good agreement that a Coastal Low will develop along the Middle Texas Coast on Sunday and slide NE toward Lake Charles on Monday into Tuesday. Currently the latest HPC/WPC Day 3 Outlook does suggest an icing potential for portions of Central and E Texas. Temperature profiles at the surface continue to drop with each run of the computer models, but warmer air above the shallow dense cold air at the surface do not support snow. What we may see is a chance of sleet as the cold air layer deepens a bit to about 3000 ft. Areas near Dallas may see heavy sleet thus warranting a Winter Storm Watch. Temps across SE Texas are expected to drop into the mid 30’s or very close to freezing Sunday night into Monday morning. Regardless, it is going to feel very cold with brisk N to NE winds and very chilly rain at the least.

 

The WPC/HPC just updated their thoughts:

 

EXTENDED FORECAST DISCUSSION

NWS WEATHER PREDICTION CENTER COLLEGE PARK MD

1031 AM EST THU NOV 21 2013

VALID 12Z SUN NOV 24 2013 - 12Z THU NOV 28 2013

...LOW CROSSING THE SOUTH AND TURNING UP THE EAST COAST NEXT WEEK

A CONCERN FOR TRAVEL..

WITH THE UPPER TROUGH STILL HANGING BACK OVER NORTHERN MEXICO, THE

DETERMINISTIC SOLUTION SPREAD DOWNSTREAM REMAINS ENORMOUS. WHEN

THAT WAVE FINALLY EJECTS, ITS NORTHERN EXTENT WILL BE SUBJECT TO

THE PHASE OF THE PROGRESSION OF CLIPPER SYSTEMS SAILING ASTRIDE

THE CANADIAN BORDER. RELIED ON THE 06Z/21 GEFS MEAN AS A SYNOPTIC

BACKGROUND FOR THE FRONTS AND PRESSURES THIS PACKAGE. THIS

PARTICULAR ENSEMBLE MEAN KEPT MORE BAGGINESS IN THE ISOBARIC

PATTERN OVER THE SOUTHEAST TUESDAY NIGHT INTO EARLY WEDNESDAY--A

REFLECTION OF A CLUSTER OF ITS INDIVIDUAL MEMBERS THAT INDICATED A

SLOWER EJECTION. SLOWER IS USUALLY BETTER WITH REGARD TO THE

PROGRESS OF SUCH SOUTHWEST HANGBACK TROUGHS, SO WANTED TO HEDGE

BETS IN THAT DIRECTION. PERUSAL OF THE 20 ENSEMBLE MEMBERS

COMPRISING THE 06Z/21 GEFS MEAN SHOWED DRAMATIC VARIATION--SOME

DRY, COLD SOLUTIONS FOR THE EAST COAST--SOME SNOWY ONES FROM THE

TENNESSEE VALLEY TO THE MID ATLANTIC--SOME RAINY, WINDY ONES ALL

THE WAY INTO NEW ENGLAND. PRECIPITATION TYPE ASIDE, THE WAVE WILL

STILL AFFECT MAJOR AIRPORTS FROM DALLAS TO ATLANTA, AND PROBABLY

THE BIG HUBS OF THE MID ATLANTIC REGION ON THE ALWAYS-BUSY TRAVEL

DAYS BEFORE THANKSGIVING.

THE OTHER STORY WILL BE THE TWO EARLY SEASON ARCTIC OUTBREAKS FROM

THE MIDWEST TO THE NORTHEAST. THE FIRST SHOULD DELIVER A FRIGID

BLAST TO MUCH OF THE NATION EAST OF THE MISSISSIPPI SUNDAY. THE

SECOND IS SLATED TO BE DRAWN INTO THE SAME AREAS IN THE WAKE OF

THE SOUTHERN WAVE ON THANKSGIVING DAY. CALIFORNIA, THE GREAT

BASIN, AND THE PACIFIC NORTHWEST SHOULD BE IN A NO-MAN'S-LAND

REGION BETWEEN THE SPLIT STREAMS.

CISCO

 

[donsutherland1]

Don, to follow up on your update regarding this weekend into the busy Thanksgiving Holiday travel period  we in the Central/Western Region are watching a unusually early Winter Storm developing that may have some significant societal impacts in the days ahead. This is a repost of my thoughts early this morning in our sub forum...

 

A complex and complicated forecast for much of Texas and Oklahoma is unfolding this morning regarding the timing of the arrival of the much talked about Arctic front and what we may see weather wise into the weekend extending into early Tuesday.

Currently surface observations suggest the Arctic boundary is moving faster than previously though and is running a good 12-18 hours faster than was expected. As is usually the case with a very dense and cold air mass, this is not too surprising that the computer model would under estimate the speed. First things first…showers are moving N to NE from the Gulf and that should continue today and increase in coverage across the Region and we should begin to see some storms develop to our NW across Oklahoma and N Texas later tonight. A line of showers and storms will sweep S during the overnight hours tonight ushering in the arrival of the coldest air of the season on Friday.

Wintry Weather Advisories have been issued across Texas Panhandle, Oklahoma/Kansas and will likely be needed later today across further S into the Permian Basin and the Big Country near Midland/Odessa. There is a chance that Winter Weather Advisories or even a Winter Storm Watch will be hoisted for the Dallas/Ft Worth area as freezing temps at the surface and over running precip begins to fall leading to an ice threat mainly on elevated surfaces by Friday afternoon into the evening hours.

We may see a brief break from the over running precip as the much talked about upper air cold core close low develops in Southern California. This feature is expected to deepen rather rapidly and there are some strong indications that this low will be near the 3 standard deviation below normal for late November standards making it a strong storm system that we usually do not see this time of year. Abundant tropical moisture from the Pacific will wrap up this storm system and indications are that it will be a bit further E over Arizona bringing flooding rains to the Phoenix area and heavy higher elevation snow to Eastern AZ into New Mexico.

This storm system appears to stay rather strong and remain a closed low as it cross New Mexico on Saturday and moves E into Texas on Sunday. The current projected storm track appears to be just S of Lubbock to near Austin and then very close to SE Texas during the morning hours of Monday. The latest run of the 06Z GFS brings this upper air feature very close to Bryan/College Station and Montgomery County, so it will be worth monitoring. There still remains relative good agreement that a Coastal Low will develop along the Middle Texas Coast on Sunday and slide NE toward Lake Charles on Monday into Tuesday. Currently the latest HPC/WPC Day 3 Outlook does suggest an icing potential for portions of Central and E Texas. Temperature profiles at the surface continue to drop with each run of the computer models, but warmer air above the shallow dense cold air at the surface do not support snow. What we may see is a chance of sleet as the cold air layer deepens a bit to about 3000 ft. Areas near Dallas may see heavy sleet thus warranting a Winter Storm Watch. Temps across SE Texas are expected to drop into the mid 30’s or very close to freezing Sunday night into Monday morning. Regardless, it is going to feel very cold with brisk N to NE winds and very chilly rain at the least.

 

The WPC/HPC just updated their thoughts:

 

EXTENDED FORECAST DISCUSSION

NWS WEATHER PREDICTION CENTER COLLEGE PARK MD

1031 AM EST THU NOV 21 2013

VALID 12Z SUN NOV 24 2013 - 12Z THU NOV 28 2013

...LOW CROSSING THE SOUTH AND TURNING UP THE EAST COAST NEXT WEEK

A CONCERN FOR TRAVEL..

WITH THE UPPER TROUGH STILL HANGING BACK OVER NORTHERN MEXICO, THE

DETERMINISTIC SOLUTION SPREAD DOWNSTREAM REMAINS ENORMOUS. WHEN

THAT WAVE FINALLY EJECTS, ITS NORTHERN EXTENT WILL BE SUBJECT TO

THE PHASE OF THE PROGRESSION OF CLIPPER SYSTEMS SAILING ASTRIDE

THE CANADIAN BORDER. RELIED ON THE 06Z/21 GEFS MEAN AS A SYNOPTIC

BACKGROUND FOR THE FRONTS AND PRESSURES THIS PACKAGE. THIS

PARTICULAR ENSEMBLE MEAN KEPT MORE BAGGINESS IN THE ISOBARIC

PATTERN OVER THE SOUTHEAST TUESDAY NIGHT INTO EARLY WEDNESDAY--A

REFLECTION OF A CLUSTER OF ITS INDIVIDUAL MEMBERS THAT INDICATED A

SLOWER EJECTION. SLOWER IS USUALLY BETTER WITH REGARD TO THE

PROGRESS OF SUCH SOUTHWEST HANGBACK TROUGHS, SO WANTED TO HEDGE

BETS IN THAT DIRECTION. PERUSAL OF THE 20 ENSEMBLE MEMBERS

COMPRISING THE 06Z/21 GEFS MEAN SHOWED DRAMATIC VARIATION--SOME

DRY, COLD SOLUTIONS FOR THE EAST COAST--SOME SNOWY ONES FROM THE

TENNESSEE VALLEY TO THE MID ATLANTIC--SOME RAINY, WINDY ONES ALL

THE WAY INTO NEW ENGLAND. PRECIPITATION TYPE ASIDE, THE WAVE WILL

STILL AFFECT MAJOR AIRPORTS FROM DALLAS TO ATLANTA, AND PROBABLY

THE BIG HUBS OF THE MID ATLANTIC REGION ON THE ALWAYS-BUSY TRAVEL

DAYS BEFORE THANKSGIVING.

THE OTHER STORY WILL BE THE TWO EARLY SEASON ARCTIC OUTBREAKS FROM

THE MIDWEST TO THE NORTHEAST. THE FIRST SHOULD DELIVER A FRIGID

BLAST TO MUCH OF THE NATION EAST OF THE MISSISSIPPI SUNDAY. THE

SECOND IS SLATED TO BE DRAWN INTO THE SAME AREAS IN THE WAKE OF

THE SOUTHERN WAVE ON THANKSGIVING DAY. CALIFORNIA, THE GREAT

BASIN, AND THE PACIFIC NORTHWEST SHOULD BE IN A NO-MAN'S-LAND

REGION BETWEEN THE SPLIT STREAMS.

CISCO

 

Very nice discussion, Steve. I'm happy you shared it in this thread.

[Chinook]

a bit of a historical analysis

 

In the last 30 days, the AO and NAO were highly positive. The Arctic Sea and Greenland had below-normal heights, and many areas in the mid-latitudes had above normal heights. The eastern United States had below-normal 500mb height and near normal or below normal surface temperatures. It is unlikely to have such a strong AO/NAO signal and get the "wrong" result in the eastern USA.

 

 

[ORH_wxman]

a bit of a historical analysis

 

In the last 30 days, the AO and NAO were highly positive. The Arctic Sea and Greenland had below-normal heights, and many areas in the mid-latitudes had above normal heights. The eastern United States had below-normal 500mb height and near normal or below normal surface temperatures. It is unlikely to have such a strong AO/NAO signal and get the "wrong" result in the eastern USA.

 

2013_10_19_to_11_19_anomaly.gif

 

 

Note the only real "dent" in the lower height anomalies north of 60N is around AK...a good spot for cold delievery into the CONUS. The main reason why the +AO hasn't produced warmer temps in this part of the world at mid-latitudes.

[HM]

I know a lot of the discussion has been regarding the signs pointing towards +AO, especially the first half of the winter, but what are people seeing in regards to the EPO. The AO and EPO certainly don't always go hand in hand, and it seems like some of the prominent analogs to this year had significant -EPO periods....especially from late December to early February.

 

I think every seasoned LR-forecaster knows all about the EPO, especially those who are professionally-employed. The reason the EPO does not get as much discussion as the AO is because its predictability is not as easy as the AO. Just because the EPO is doing something in the autumn, doesn't mean it will continue through the winter. If it were that easy, anyone could do this job and do it well. Again, I'm not making a statement here about 2013-14. I'm just saying, the EPO has just as low-predictability as the NAO at longer time scales. So why will the EPO be negative late Dec-early Feb?

[HM]

Strongly agree and this is what I talked about in my winter outlook thread. +AO/-EPO patterns have shown since 1950 to be quite cold for the northern tier. Even a winter like 1992-93 which was one of my analogs, had a +1.7 AO for DJF yet temps for DJF finished normal to slightly below in NYC due to the EPO.

 

http://www.americanwx.com/bb/index.php/topic/41743-my-winter-outlook-2013-14/

 

What happens if the EPO block retrogrades into the WP domain? If this were to occur and the +AO continues, the northern-tier would blowtorch. How are you sure that this won't occur and that the -EPO will sustain?

[HM]

Let's pretend we don't know anything about teleconnections or how cold it has been in the USA.

 

Suppose the giant 500mb high anomaly in the North Pacific is not really an entity of cause, but really an effect. The very strong PV, extremely high AO, might be soooo anomalous that the "ring" of above normal heights around it is an indication of just how tightly wound-up things are. So, once we get a winter like expansion in the height field, is it possible this block will simply go away? Or at the very least be crushed and morphed into something else?

 

Below are the 500mb anomalies and mean for the month so far. Try to envision what I'm saying and keep the other stuff from affecting your perception.

 

[Isotherm]

What happens if the EPO block retrogrades into the WP domain? If this were to occur and the +AO continues, the northern-tier would blowtorch. How are you sure that this won't occur and that the -EPO will sustain?

 

 

The EPO in late autumn has shown to have a stronger correlation with the ensuing DJF EPO than the AO or NAO.  I have found the North Pacific state of November to have a .79 positive correlation with DJF overall. The SAI has a .81 correlation with winter AO values. So that's pretty comparable. The Northeast Pacific low or high height anomaly at this time of year is usually fairly stable going forward. The reversal years tend to be stronger ENSO either cold or warm. There haven't been many neutral ENSO seasons with a drastically different NE PAC/EPO signal from Nov moving into DJF overall. The EPO will probably break down at times and during those periods the CONUS should torch given the AO/NAO states. What you mention could very well happen, but history dictates that the -EPO will in the overall sense probably remain most of the winter.

[HM]

The EPO in late autumn has shown to have a stronger correlation with the ensuing DJF EPO than the AO or NAO.  I have found the North Pacific state of November to have a .79 positive correlation with DJF overall. The SAI has a .81 correlation with winter AO values. So that's pretty comparable. The Northeast Pacific low or high height anomaly at this time of year is usually fairly stable going forward. The reversal years tend to be stronger ENSO either cold or warm. There haven't been many neutral ENSO seasons with a drastically different NE PAC/EPO signal from Nov moving into DJF overall. The EPO will probably break down at times and during those periods the CONUS should torch given the AO/NAO states. What you mention could very well happen, but history dictates that the -EPO will in the overall sense probably remain most of the winter.

 

That's a pretty substantial correlation. If you wouldn't mind, could you post the data? As you know, I am a big proponent of Aleutian Highs being more poleward during +QBO/cooler ENSO years. So, I'm curious about the  more neutral years.  

 

There aren't many neutral years. But of the most -EPO and +EPO Neutral Decembers, they both seemed to  have a more -EPO depiction in the N PAC during November. So while I agree that the -EPO Decembers do tend to continue the -EPO from late-autumn, it seemed like the +EPO years also had the -EPO late autumn, too.

 

Sample size is clearly an issue and I know I am breaking it down monthly, which further weakens it.

[Isotherm]

That's a pretty substantial correlation. If you wouldn't mind, could you post the data? As you know, I am a big proponent of Aleutian Highs being more poleward during +QBO/cooler ENSO years. So, I'm curious about the  more neutral years.  

 

There aren't many neutral years. But of the most -EPO and +EPO Neutral Decembers, they both seemed to  have a more -EPO depiction in the N PAC during November. So while I agree that the -EPO Decembers do tend to continue the -EPO from late-autumn, it seemed like the +EPO years also had the -EPO late autumn, too.

 

Sample size is clearly an issue and I know I am breaking it down monthly, which further weakens it.

 

 

Yeah I'm not looking at it monthly, I'm looking the NPAC signal of November and comparing that to the ensuing winter NPAC signals. So the correlation would definitely weaken significantly by shortening the time scales.

 

Since you asked about neutral ENSO years, here's a look at negative EPO neutral ENSO seasons for November's 500mb pattern:

 

 

 

The ensuing winters while not exact of course, featured a fairly similar NE PAC positive anomaly.

 

 

* NOTE - this is for negative EPO years.

 

 

Some neutral ENSO, neg height anomaly in NPAC Novembers:

 

 

 

And the winters.

 

[tacoman25]

What happens if the EPO block retrogrades into the WP domain? If this were to occur and the +AO continues, the northern-tier would blowtorch. How are you sure that this won't occur and that the -EPO will sustain?

 

For a good number of pattern/ENSO/QBO analogs it did for a time in December. But the stats show that -EPO in November usually results in -EPO overall for the winter following. With a strong signal for mid winter...especially weak/neutral ENSO years like 2013.

[tacoman25]

Let's pretend we don't know anything about teleconnections or how cold it has been in the USA.

 

Suppose the giant 500mb high anomaly in the North Pacific is not really an entity of cause, but really an effect. The very strong PV, extremely high AO, might be soooo anomalous that the "ring" of above normal heights around it is an indication of just how tightly wound-up things are. So, once we get a winter like expansion in the height field, is it possible this block will simply go away? Or at the very least be crushed and morphed into something else?

 

Below are the 500mb anomalies and mean for the month so far. Try to envision what I'm saying and keep the other stuff from affecting your perception.

 

nov1-19h5nh.JPG

 

 

I get what you're saying. But the northeast Pacific/-EPO ridging has been a dominant feature for most of the year. Well before the +AO set in. This makes me doubtful that the +AO is forcing it.

 

 

[SnowGoose69]

The most interesting thing I see in those 500mb anomalies is that the NAO was positive for the composite Novembers of 67, 78, 79, 80, 85, 90, 92, 93, 96 yet the composite for the ensuign DJF shows the NAO is largely negative...I took a closer look at the years and 67, 78, and 79 all made up years where the NAO became markedly more neutral or negative after November. 80-81, 92-93, and 93-94 it never reversed, 85-86 and 90-91 it was actually negative in Nov and then flipped positive the rest of the winter...96-97 was largely negative all winter except for February, 96-97 was always an odd winter to me, not a bad Pacific nor Atlantic yet the winter as a whole sucked....the good news I take out of this is that we may be able to toss out what happened in 85-86, 90-91, 92-93, and 93-94 with the NAO as those all fell during the 15 year raging +NAO period...67-68, 78-79, and 79-80 all fell more so in a period where the NAO was tending to be negative more than positive during the winters, so perhaps, just perhaps we will see a flip that direction more so as the last 5-6 winters we've seen a -NAO frequently.

[QcSevereWx]

ftp://ftp.cdc.noaa.gov/Public/gbates/teleconn/epo.reanalysis.t10trunc.1948-present.txt

when the EPO goes very negative, like it is right now,  don't expect the EPO to return to a very negative state for the next months.  -250 november 13th, I don't think you will see another -250 for the entire winter. Usually, the very negative state of the EPO can fit inside 45 days.

[donsutherland1]

Evening thoughts...

 

1. The severe November cold shot remains on track for the 11/24-26 period as per the 11/22 0z run of the GFS.

 

2. Looking ahead to December, this morning, I noted that the partial teleconnection cases returned to a milder look (#102), though the month will likely start off on a cold note. Those cases had some similarities to the CFSv2, but featured more widespread warm anomalies. This evening, I factored in ENSO.

 

The map from this evening alongside the latest CFSv2 December forecast is below.

 

 

3. There remains uncertainty as to how much blocking might occur in December, even if the AO is predominantly positive. Neither idea is cast in stone just yet, but this is a timeframe where the ideas have started to show some skill.