Winter 2015-2016 Medium-Term Discussion

[donsutherland1]

Even as meteorological winter looks to get off to a mild start across much of North America, especially parts of central Canada, it is worth starting a thread for medium-term discussion.

 

Currently, one of the strongest El Niño events on record is underway. That event will likely play a critical role throughout the winter, even as the guidance suggests that it has peaked or is near its peak.

 

Teleconnections will be crucial. With the strong PDO+ underway and likely to persist through meteorological winter, the PNA+ should be favored. That coupled with a negative EPO could allow colder air to eventually overspread North America.

 

However, at present, the EPO is forecast to remain positive through mid-December.

 

In addition, the Arctic Oscillation (AO) is also strongly positive. Strong and expansive polar vortices usually require a measure of time before they erode. Indeed, 7 of the 8 cases since 1950 that saw the AO reach or exceed +3.000 during the November 20-December 10 period wound up with predominantly positive AO values for December. During such cases, December typically wound up warmer than normal across much of North America.

 

All of the major monthly guidance currently suggests that December will likely wind up warmer to perhaps much warmer than normal. The GFS ensembles are show widespread warmth through 15 days.

 

The big question concerns if or when the polar vortex will begin to break down. It has done so in a number of winters from the above sample, with 1972-73 and 2007-08 being exceptions.

 

In any case, below are some images from seven of the eight winters above that saw December's AO average > 0 (all and the El Niño subset) for the U.S. and Canada. The GFS ensemble forecast for days 6-10 and 11-15 are also posted.

 

[CAD_Wedge_NC]

Even as meteorological winter looks to get off to a mild start across much of North America, especially parts of central Canada, it is worth starting a thread for medium-term discussion.

 

Currently, one of the strongest El Niño events on record is underway. That event will likely play a critical role throughout the winter, even as the guidance suggests that it has peaked or is near its peak.

 

Teleconnections will be crucial. With the strong PDO+ underway and likely to persist through meteorological winter, the PNA+ should be favored. That coupled with a negative EPO could allow colder air to eventually overspread North America.

 

However, at present, the EPO is forecast to remain positive through mid-December.

 

In addition, the Arctic Oscillation (AO) is also strongly positive. Strong and expansive polar vortices usually require a measure of time before they erode. Indeed, 7 of the 8 cases since 1950 that saw the AO reach or exceed +3.000 during the November 20-December 10 period wound up with predominantly positive AO values for December. During such cases, December typically wound up warmer than normal across much of North America.

 

All of the major monthly guidance currently suggests that December will likely wind up warmer to perhaps much warmer than normal. The GFS ensembles are show widespread warmth through 15 days.

 

The big question concerns if or when the polar vortex will begin to break down. It has done so in a number of winters from the above sample, with 1972-73 and 2007-08 being exceptions.

 

In any case, below are some images from seven of the eight winters above that saw December's AO average > 0 (all and the El Niño subset) for the U.S. and Canada. The GFS ensemble forecast for days 6-10 and 11-15 are also posted.

 

Just curious ... what sort of look do you get when you roll those winters forward into Jan/Feb?

[donsutherland1]

Just curious ... what sort of look do you get when you roll those winters forward into Jan/Feb?

There's tremendous variability. While the above charts may have relevance to December, I don't think one can really extrapolate forward into January or February from them. 

[snowman19]

There's tremendous variability. While the above charts may have relevance to December, I don't think one can really extrapolate forward into January or February from them.

One thing is for sure, the NAO over the last 3 winters refuses to go negative for any sustained periods

[donsutherland1]

At the start of December, the Arctic Oscillation (AO) was +1.497 and the Pacific-North American Pattern (PNA) Index was +0.801. Over the next 15 days, both indices are forecast to remain generally positive to strongly positive.

 

Typically the kind of strong and expansive polar vortex responsible for the current AO+ regime is slow to break down. Therefore, it is likely that December will feature a predominantly positive AO. At the same time, the ongoing strong PDO+ typically favors a PNA+ pattern. It is probably more likely than not that the PNA+ will also predominate during December.

 

If one takes a trimmed set of 500 mb analogs from the 12/1/2015 0z run of the GFS ensembles (the years that showed up in both the 6-10-day and 11-14-day sets), those cases typically saw December’s AO and PNA average > 0. Perhaps reflecting the slow breakdown of the kind of polar vortex currently in place, January also typically saw an AO average > 0. However, the AO cannot be forecast accurately for more than a few weeks’ time, so the January outcome is speculative.

 

Nevertheless, the current polar vortex leaves open the possibility that the AO could be predominantly positive for the winter as a whole, even if blocking develops in January or February. It’s too soon to make that call given the forecasting limitations on the AO.

 

Finally, the trimmed analog pool features a lot of warmer than normal anomalies in North America with near normal or cooler anomalies in parts of the West. That idea is similar but not identical to the last CFSv2 forecast for December (11/30/2015 run). Moreover, toward the end of their range, the GFS ensembles suggest that a generally zonal and warm pattern across North America may begin to yield to a cool West/warm East scenario.

 

[winterymix]

Don:  Nice, unbiased essay.

 

It makes sense that if and when the pattern changes to allow cool or cold air into the eastern US,

patience and the fullness of time will allow achievable expectations.

 

I've attached some graphics below.  Everyone can notice that we have a long path ahead.

 

 

[donsutherland1]

Don:  Nice, unbiased essay.

 

It makes sense that if and when the pattern changes to allow cool or cold air into the eastern US,

patience and the fullness of time will allow achievable expectations.

 

I've attached some graphics below.  Everyone can notice that we have a long path ahead.

 

 

Thanks Winterymix for the kind words and for posting the graphics.

[raindancewx]

NOAA has a big drop in the PDO from Oct to Nov - it's 0.47 in Nov 2015.

 

https://www.ncdc.noaa.gov/teleconnections/pdo/

[Bob Chill]

NOAA has a big drop in the PDO from Oct to Nov - it's 0.47 in Nov 2015.

https://www.ncdc.noaa.gov/teleconnections/pdo/

We'll see how the ssta plots look at the end of Dec but right now it appears the +pdo is strengthening again. Hopefully the warm anoms sandwiched between the cooler areas in the wpac continue to shrink. The epac looks good.

[40/70 Benchmark]

We'll see how the ssta plots look at the end of Dec but right now it appears the +pdo is strengthening again. Hopefully the warm anoms sandwiched between the cooler areas in the wpac continue to shrink. The epac looks good.

No way it won't rise again.

The fall was transient, and MJO induced.

[jdrenken]

Debating on a post...keep in mind...the first graphics are for the last on the WPC.

 

OPC 500mb North Pacific...note the split flow in the Sea of Okhotsk?

 

November 20th

 

00z

 

12Z

 

November 21st

 

00z

 

12z

 

 

WPC 500mb Day 3-7 forecast

[jdrenken]

Continued...

 

November 22nd

 

00z

 

12z

 

Finally...November 23rd

 

00z

 

12z

 

 

WPC 500mb Day 3-7 forecast

[donsutherland1]

December has started with much above normal readings in a large part of North America with the exception of parts of the West. The trimmed objective analog pool from the GFS ensembles still favors warmth across much of December as a whole.

 

Recently, there have been some changes in the long-term teleconnections forecast.

 

1. The PNA, which had been forecast to go negative is now forecast to remain generally positive. This outcome is what one would typically see during a strong PDO+ (October value: +1.47).

2. Numerous ensemble members forecast the AO to go negative. It remains to be seen whether that forecast will hold or blocking will prove transient should it develop.

3. The EPO is forecast to remain generally positive.

 

Both the teleconnection cases for the 12/15-25/1950-2014 period and the extended range of the GFS ensembles point to a reasonably consistent 500 mb pattern:

 

 

Finally, it should be noted that some of the teleconnection cases e.g., December 1965, evolved into a colder January. The trimmed objective analog pool had fewer cold outcomes in January. Nevertheless, it's too soon to really speculate on January, but December's largely warm outcome has been reaffirmed by the early data coupled with the latest guidance (objective analogs, ensembles, and teleconnection cases).

[Ginx snewx]

Isn't that a negative PNA?

[donsutherland1]

Isn't that a negative PNA?

In the West, it resembles the negative PNA. My guess is that other factors related to the El Niño e.g., powerful Pacific jet, will lead to something that resembles the PNA- during the timeframe in question regardless of what the indices show.

[Ginx snewx]

A positive PNA features west coast ridging with the semi permanent intermountain high the discernable feature. That GEFS map is a negative PNA

[donsutherland1]

A positive PNA features west coast ridging with the semi permanent intermountain high the discernable feature. That GEFS map is a negative PNA

We don't disagree about the map. However, the GEFS ensembles show somewhat positive.

 

[OSUmetstud]

The gefs pna is slightly pos because the pna index is centered in the canadian rockies not the us rockies. Theres slightly above normal heights there.

[andyhb]

1. The PNA, which had been forecast to go negative is now forecast to remain generally positive. This outcome is what one would typically see during a strong PDO+ (November value: +1.47).

 

That is the October value.

[donsutherland1]

That is the October value.

Thanks. I corrected the typo. November's value isn't available yet.

[raindancewx]

The thing with the PDO is that it isn't just a warm tongue in the Gulf of Alaska. I think of it as a "C" around Alaska that is either warm/cold punctuated by the opposite signal in the opening of the C. If you look compared to last Nov/Dec the tongue is much warmer - it looks to me like the western part of the Pacific is moving into the -PDO phase while the eastern part of the Pacific is still in the +PDO phase. The +PDO phase is still stronger as the tongue is still relatively cool vs. the "C".

 

 

 

 

[donsutherland1]

During the 12/10-13 period, very warm air is forecast to sweep across the Northern Plains into the eastern U.S. The latest GFS ensembles suggest that 850 mb temperatures and 500 mb height anomalies will be 1-2 standard deviations above normal. That outcome would result in temperatures in the middle and upper 50s and perhaps even into the 60s across a number of cities from Chicago eastward to New York City.

 

That outcome could still change, but there has been a consistent signal on the ensembles for just such warmth.

 

[donsutherland1]

The latest guidance has grown even warmer for the December 10-13, 2015 period. The highest readings on the 12/7 0z MOS for the cities shown in #22 are as follows:

 

Albany: 53°

Chicago: 59°

Detroit: 62°

New York City: 60°

Pittsburgh: 69°

 

Although the pattern is likely to slowly evolve toward possible less exceptional warmth toward the end of December, it still appears likely that most of the cold will remain locked up in Alaska and extreme northwestern Canada. That would imply that Christmas Day in such cities as Chicago, Detroit, and Toronto could be milder than normal.

 

The latest CFSv2 guidance:

 

Below are the GFS ensembles through 360 hours. Afterward, I rolled forward the trimmed objective analog pool from the GFS ensembles to see what is implied.

 

 

It should be noted that one should not place much weight on the values themselves. Instead, what's relevant is the idea that at this point in time, the guidance hints at a milder outcome. A lot can still change,

[donsutherland1]

The overnight MOS readings remained impressive.

 

Highest Readings (12/10-13):

Albany: 60°

Chicago: 59°

Detroit: 61°

New York City: 61°

Pittsburgh: 66°

 

Overall, the repeated warm signal on the operational guidance and ensembles provides high confidence that some of the above cities could experience temperatures that could approach daily records in some cases.

 

Despite the 12/8 6z run of the GFS, which depicts a turn toward colder weather and a fairly significant snowfall for parts of the eastern U.S., the GFS  ensembles have remained largely consistent with their prior runs. That scenario would favor only transient shots of cooler weather, no significant Arctic intrusions for the eastern half of the CONUS, and a generally mild pattern for Christmas Day.

 

For purposes of illustrating the stability of the GFS ensemble runs, the implied high and low temperatures for Washington, DC for 12/15 using the trimmed objective analog pool are 50° and 37°. During the last 3 days, the implied high temperature ranged from 48°-50° and the implied low temperature ranged from 33°-37°.

 

These figures should not be taken as point estimates, but merely to illustrate the stability of recent runs of the GFS ensembles in showing a milder pattern. Nothing, of course, is cast in stone from that far out. But given the context of fairly consistent ensemble guidance, it would not surprise me if the 12z GFS run flips to milder conditions at the end of its range.

 

Finally, the latest ensemble guidance shows a large spread among members concerning the evolution of the Arctic Oscillation (AO):

 

 

The very large and expansive polar vortex would argue that any drop to negative values could be short-lived. Since 1950, seven El Niño events featured AO+ conditions through the first 8 days of December followed by some negative values that developed between 12/9 and 12/15. There was one El Niño case (1951-52) that saw the AO remain positive throughout all of December.

 

Among the seven cases in question, all saw AO+ values return for at least a time during the second half of December. The median number of days during which the AO was positive during the second half of December was 11.

 

Those with more than 11 AO+ days during the 12/16-31 period all saw January come out with a positive AO average (Mean: +0.982; Range: +0.356 to +1.359). All of those cases then saw February wind up with an AO- (Mean: -1.091; Range: -1.806 to -0.195).

 

Those with more than 11 or fewer AO+ days during the 12/16-31 period all saw January come out with a negative  AO figure (Mean: -0.879; Range: -2.066 to -0.148). Most of those cases then saw February wind up with an AO- (Mean: -0.290; Range: -1.473 to +1.429).

 

Cautiously, given sample size limitations, an above median number of AO+ days for the second half of December might suggest that sustained blocking could be delayed until late January or February. In contrast, the median number or below median number could favor earlier sustained blocking, with the greatest blocking focused on January.

[griteater]

Appreciate your posts in here Don, nice work

[leo2000]

The overnight MOS readings remained impressive.

 

Highest Readings (12/10-13):

Albany: 60°

Chicago: 59°

Detroit: 61°

New York City: 61°

Pittsburgh: 66°

 

Overall, the repeated warm signal on the operational guidance and ensembles provides high confidence that some of the above cities could experience temperatures that could approach daily records in some cases.

 

Despite the 12/8 6z run of the GFS, which depicts a turn toward colder weather and a fairly significant snowfall for parts of the eastern U.S., the GFS  ensembles have remained largely consistent with their prior runs. That scenario would favor only transient shots of cooler weather, no significant Arctic intrusions for the eastern half of the CONUS, and a generally mild pattern for Christmas Day.

 

For purposes of illustrating the stability of the GFS ensemble runs, the implied high and low temperatures for Washington, DC for 12/15 using the trimmed objective analog pool are 50° and 37°. During the last 3 days, the implied high temperature ranged from 48°-50° and the implied low temperature ranged from 33°-37°.

 

These figures should not be taken as point estimates, but merely to illustrate the stability of recent runs of the GFS ensembles in showing a milder pattern. Nothing, of course, is cast in stone from that far out. But given the context of fairly consistent ensemble guidance, it would not surprise me if the 12z GFS run flips to milder conditions at the end of its range.

 

Finally, the latest ensemble guidance shows a large spread among members concerning the evolution of the Arctic Oscillation (AO):

 

 

The very large and expansive polar vortex would argue that any drop to negative values could be short-lived. Since 1950, seven El Niño events featured AO+ conditions through the first 8 days of December followed by some negative values that developed between 12/9 and 12/15. There was one El Niño case (1951-52) that saw the AO remain positive throughout all of December.

 

Among the seven cases in question, all saw AO+ values return for at least a time during the second half of December. The median number of days during which the AO was positive during the second half of December was 11.

 

Those with more than 11 AO+ days during the 12/16-31 period all saw January come out with a positive AO average (Mean: +0.982; Range: +0.356 to +1.359). All of those cases then saw February wind up with an AO- (Mean: -1.091; Range: -1.806 to -0.195).

 

Those with more than 11 or fewer AO+ days during the 12/16-31 period all saw January come out with a negative  AO figure (Mean: -0.879; Range: -2.066 to -0.148). Most of those cases then saw February wind up with an AO- (Mean: -0.290; Range: -1.473 to +1.429).

 

Cautiously, given sample size limitations, an above median number of AO+ days for the second half of December might suggest that sustained blocking could be delayed until late January or February. In contrast, the median number or below median number could favor earlier sustained blocking, with the greatest blocking focused on January.

 

 

Hi Don, actually the 12z gfs shows at the end of its run a piece of the polar vortex coming down. It's colder than the 6z is. Seems like the last few runs 00z, 6z and 12z have been showing a colder trend. 

[donsutherland1]

Hi Don, actually the 12z gfs shows at the end of its run a piece of the polar vortex coming down. It's colder than the 6z is. Seems like the last few runs 00z, 6z and 12z have been showing a colder trend.

 

 

This is somewhat encouraging. We'll have to see if this holds up in coming days and model/ensemble support grows. Hopefully, what one sees toward the end of the most recent GFS runs is, in fact, the first hint of a meaningful pattern change. It's too soon to be sure right now.

[donsutherland1]

The biggest story over the next seven days will be the near-record to record warmth that will spread eastward from the Midwest to the Middle Atlantic and southern New England areas. The latest GFS ensembles point to 500 mb height anomalies that will range from 2.0-2.5 standard deviations above the norm.

 

The MOS guidance is now showing a number of temperatures that would tie or break daily record high marks.

 

 

It still appears that cold shots in the eastern half of North America will likely be transient for the next 10-15 days. No significant Arctic intrusions appear likely. Somewhat more sustained cooler readings could develop in the western half of the U.S.

 

As for 12/25, the trimmed objective analog pool rolled forward remains remarkably similar to what it showed two days ago. For example, the implied readings would include: Detroit: 37-25 (vs. 38-23 from 2 days ago), New York: 44-34 (vs. 45-32 from 2 days ago), and Washington, DC: 49-36 (vs. 49-34 from 2 days ago). In terms of probabilities, they continued to indicate that the day would likely be milder than average across parts of the Midwest and eastward. In contrast, there were near equal chances of warmer or colder anomalies in the Pacific Northwest. The GEFS mean anomalies at 12/25 0z, the end of their range, were forecast to be cool in the western half of the CONUS and somewhat warmer than normal in the eastern half of the CONUS.

 

Finally, the current AO+ regime appears likely to yield to at least a period of AO- values within the next 5 days or so. Whether the forecast AO- period will be short-lived or more sustained remains to be seen.

[bigtenfan]

The biggest story over the next seven days will be the near-record to record warmth that will spread eastward from the Midwest to the Middle Atlantic and southern New England areas. The latest GFS ensembles point to 500 mb height anomalies that will range from 2.0-2.5 standard deviations above the norm.

 

The MOS guidance is now showing a number of temperatures that would tie or break daily record high marks.

 

 

It still appears that cold shots in the eastern half of North America will likely be transient for the next 10-15 days. No significant Arctic intrusions appear likely. Somewhat more sustained cooler readings could develop in the western half of the U.S.

 

As for 12/25, the trimmed objective analog pool rolled forward remains remarkably similar to what it showed two days ago. For example, the implied readings would include: Detroit: 37-25 (vs. 38-23 from 2 days ago), New York: 44-34 (vs. 45-32 from 2 days ago), and Washington, DC: 49-36 (vs. 49-34 from 2 days ago). In terms of probabilities, they continued to indicate that the day would likely be milder than average across parts of the Midwest and eastward. In contrast, there were near equal chances of warmer or colder anomalies in the Pacific Northwest. The GEFS mean anomalies at 12/25 0z, the end of their range, were forecast to be cool in the western half of the CONUS and somewhat warmer than normal in the eastern half of the CONUS.

 

Finally, the current AO+ regime appears likely to yield to at least a period of AO- values within the next 5 days or so. Whether the forecast AO- period will be short-lived or more sustained remains to be seen.

Thank you  so much for  the work that you must do to make these posts. it is very educational to a total novice like myself.

 

When you change the title of your thread to the one that you had a few years ago "The emperor of warmth" I will then start to panic. Meanwhile hope springs eternal..

[Great Snow 1717]

The biggest story over the next seven days will be the near-record to record warmth that will spread eastward from the Midwest to the Middle Atlantic and southern New England areas. The latest GFS ensembles point to 500 mb height anomalies that will range from 2.0-2.5 standard deviations above the norm.

 

The MOS guidance is now showing a number of temperatures that would tie or break daily record high marks.

 

 

It still appears that cold shots in the eastern half of North America will likely be transient for the next 10-15 days. No significant Arctic intrusions appear likely. Somewhat more sustained cooler readings could develop in the western half of the U.S.

 

As for 12/25, the trimmed objective analog pool rolled forward remains remarkably similar to what it showed two days ago. For example, the implied readings would include: Detroit: 37-25 (vs. 38-23 from 2 days ago), New York: 44-34 (vs. 45-32 from 2 days ago), and Washington, DC: 49-36 (vs. 49-34 from 2 days ago). In terms of probabilities, they continued to indicate that the day would likely be milder than average across parts of the Midwest and eastward. In contrast, there were near equal chances of warmer or colder anomalies in the Pacific Northwest. The GEFS mean anomalies at 12/25 0z, the end of their range, were forecast to be cool in the western half of the CONUS and somewhat warmer than normal in the eastern half of the CONUS.

 

Finally, the current AO+ regime appears likely to yield to at least a period of AO- values within the next 5 days or so. Whether the forecast AO- period will be short-lived or more sustained remains to be seen.

Don,

  Yesterday on the Weather Channel they were forecasting mild and wet in the east for Christmas week so their thoughts are similar to the GEFS for that week.