2024-2025 La Nina

[40/70 Benchmark]

5 hours ago, snowman19 said:

The region 1+2 warming is all consistent with a CP/Modoki Nina event

Doesn't really matter.

[brooklynwx99]

kinda insane how much the -PDO has been eaten into over the last couple of months. that likely continues over the next month or so aside from the brief jet overextension from Christmas-NYE

waters near Japan actually have negative anomalies. who could've thought

[40/70 Benchmark]

Looks like my main miss so far was the big +PNA Dec...I had it for January, but not December, so I will end up too warm this month. Looks like more of a 2020-2021 Dec-Jan mismatch, as opposed to the Jan 2022 type that I favored.

[GaWx]

  It’s interesting that we’re having the coldest first half of Dec in the E US overall in a good number of years (since 2010 in many cases) and that this is during a robust MJO 4-5, which has more often than not been mild in Dec and averages mild. The +PNA has been one of the strongest for this period on record.

 *Edit: For non-Nino since 1950 only these had a similarly strong +PNA during 12/1-15: 2020, 2017, 1989, 1988, and 1960.

*Edit 2: Of the above 5 strong non-Nino +PNA during 12/1-15, only 2020 and 1960 held on with a solid +PNA most of the rest of the month like is progged by the GEFS for 2024.

[40/70 Benchmark]

15 minutes ago, GaWx said:

  It’s interesting that we’re having the coldest first half of Dec in the E US overall in a good number of years (since 2010 in many cases) and that this is during a robust MJO 4-5, which has more often than not been mild in Dec and averages mild. The +PNA has been one of the strongest for this period on record.

Yea, I pinned my December call on the MC forcing that is just being overwhelmed by that potent PNA that is likely at least partially attributable to the ongoing +GLAAM. Hey, after these last couple of years, I would rather be too conservative in terms of east coast cold and snow.

[Terpeast]

1 hour ago, brooklynwx99 said:

kinda insane how much the -PDO has been eaten into over the last couple of months. that likely continues over the next month or so aside from the brief jet overextension from Christmas-NYE

waters near Japan actually have negative anomalies. who could've thought

Wow, that is quite the change. Should be reflected in the pdo numbers by end of month or early jan. Prob still negative, but not extremely so. Like -1 ish. 

[Maestrobjwa]

3 minutes ago, Terpeast said:

Wow, that is quite the change. Should be reflected in the pdo numbers by end of month or early jan. Prob still negative, but not extremely so. Like -1 ish. 

Now the question is...is this indicative of a larger change even beyond this season, or just a temporary one?

[snowman19]

[mitchnick]

39 minutes ago, snowman19 said:

 

 

 

 

 

I have to chuckle when these people who make these proclamations with such certainty regarding MJO projections and the effects. How'd this guy, Peyton, do in the fall with his MJO and Conus temp forecasts? As stated earlier, we've been in the process of going thru 4 and 5 and have had the coldest start in the east in December since 2010, and Peyton is certain with future MJO progression and the results. Just more proof you can find anybody to say anything on the internet. Personally, I  think the cooling of the warm pool (which continues) has something to do with the cool temps in the east despite phases 4-6, but you won't get any research on that since so many have predicted the world's demise because of it. Time will tell.

As for the PDO, apparently an historically negative state does not preclude a +PNA. But the worm has turned on the -PDO imho.

[EasternLI]

I think from a very broad perspective, all of the 00z ensembles basically showed the same thing. When you loop them. The North Pacific low retrograding to the dateline. Which causes the GOA low to break on the west coast. There would be an emerging ridge on the west coast in that scenario. Or wherever that wave breaks. Eps shows the same progression. Canadian ensembles are more aggressive. This is the 00z gefs 

[bluewave]

7 hours ago, GaWx said:

  It’s interesting that we’re having the coldest first half of Dec in the E US overall in a good number of years (since 2010 in many cases) and that this is during a robust MJO 4-5, which has more often than not been mild in Dec and averages mild. The +PNA has been one of the strongest for this period on record.

 *Edit: For non-Nino since 1950 only these had a similarly strong +PNA during 12/1-15: 2020, 2017, 1989, 1988, and 1960.

*Edit 2: Of the above 5 strong non-Nino +PNA during 12/1-15, only 2020 and 1960 held on with a solid +PNA most of the rest of the month like is progged by the GEFS for 2024.

The cold has really been muted in the Northeast due to the record warm Great Lakes temperatures along with the delayed freeze up on Hudson Bay. You can see how much colder the 850 mb temperatures were than the surface. Parts of Northern New England are close to average against the warmest 30 year normals. So the +PNA had much less cold to work with than in the past. 
 

 

[michsnowfreak]

4 hours ago, mitchnick said:

I have to chuckle when these people who make these proclamations with such certainty regarding MJO projections and the effects. How'd this guy, Peyton, do in the fall with his MJO and Conus temp forecasts? As stated earlier, we've been in the process of going thru 4 and 5 and have had the coldest start in the east in December since 2010, and Peyton is certain with future MJO progression and the results. Just more proof you can find anybody to say anything on the internet. Personally, I  think the cooling of the warm pool (which continues) has something to do with the cool temps in the east despite phases 4-6, but you won't get any research on that since so many have predicted the world's demise because of it. Time will tell.

As for the PDO, apparently an historically negative state does not preclude a +PNA. But the worm has turned on the -PDO imho.

It's hilarious really. Not to mention we will find the most random tweets in this thread from people many have never heard of. "If you want the best chance for snow in January...". Um, January is the coldest month of the year. He talks like its early November. Places north of 40N can have average snowfall with well above avg temps in Jan. It's about storm track and how active the pattern gets. MJO is overrated, especially forecasting it.

[michsnowfreak]

2 hours ago, bluewave said:

The cold has really been muted in the Northeast due to the record warm Great Lakes temperatures along with the delayed freeze up on Hudson Bay. You can see how much colder the 850 mb temperatures were than the surface. Parts of Northern New England are close to average against the warmest 30 year normals. So the +PNA had much less cold to work with than in the past. 
 

 

I haven't seen the actual up to date numbers, but I'd imagine the water temps have really cooled off with the cold weather. Streams and ponds and smaller lakes are already iced over even in southeast Michigan. So surface temps will likely start to more closely link with 850s.

[MJO812]

2 hours ago, bluewave said:

The cold has really been muted in the Northeast due to the record warm Great Lakes temperatures along with the delayed freeze up on Hudson Bay. You can see how much colder the 850 mb temperatures were than the surface. Parts of Northern New England are close to average against the warmest 30 year normals. So the +PNA had much less cold to work with than in the past. 
 

 

What cold has been muted ?it has been cold and the Euro and CMC are frigid for Christmas .

[bluewave]

16 minutes ago, michsnowfreak said:

It's hilarious really. Not to mention we will find the most random tweets in this thread from people many have never heard of. "If you want the best chance for snow in January...". Um, January is the coldest month of the year. He talks like its early November. Places north of 40N can have average snowfall with well above avg temps in Jan. It's about storm track and how active the pattern gets. MJO is overrated, especially forecasting it.

The MJO is an important piece of the forcing puzzle which we encounter in winter. This winter it’s been a part of the pattern but not the main driver. Most recent winters it was the main driver. It’s no coincidence that our last really snowy month near the northeast coast was in January 22 which was a solid MJO 8. That forcing configuration was able to weaken the Pacific Jet enough so the ridge axis locked in near the West Coast. That’s the opposite of what we have been seeing this winter as the ridge keeps drifting east instead of staying anchored out west. So we have been getting competing forcing elements between more Nino-like +PNA and La Niña faster Pacific Jet. So if the MJO remains in the background, then we may not see enough influence from a colder phase to really relax the Pacific Jet enough.

[mitchnick]

11 minutes ago, bluewave said:

The MJO is an important piece of the forcing puzzle which we encounter in winter. This winter it’s been a part of the pattern but not the main driver. Most recent winters it was the main driver. It’s no coincidence that our last really snowy month near the northeast coast was in January 22 which was a solid MJO 8. That forcing configuration was able to weaken the Pacific Jet enough so the ridge axis locked in near the West Coast. That’s the opposite of what we have been seeing this winter as the ridge keeps drifting east instead of staying anchored out west. So we have been getting competing forcing elements between more Nino-like +PNA and La Niña faster Pacific Jet. So if the MJO remains in the background, then we may not see enough influence from a colder phase to really relax the Pacific Jet enough.

Long range Eps says no more competing MJO forces.

[bluewave]

57 minutes ago, MJO812 said:

What cold has been muted ?it has been cold and the Euro and CMC are frigid for Christmas .

 

 

We have not had a cold December around the NYC Metro by historical December standards. Since December has experienced such a steep temperature rise over the years, the NYC average is 39.1° now. Years ago the average was in the mid 30s instead of close to 40°. So even a slightly colder finish than 39.1° would be close to average for a December earlier in the 2000s. NYC used to get a December averaging near 32° at least every 5-10 years as recently as 2010. Now we have gone a full 14 years without one. The cold coming in just before Christmas is being preceded and followed by near 60° warmth which wasn’t the case back in the old days when extended cold was much more common.  We saw a similar version of this back in 2022 when the cold before Christmas was preceded and followed by near 60° warmth.

[MJO812]

45 minutes ago, bluewave said:

We have not had a cold December around the NYC Metro by historical December standards. Since December has experienced such a steep temperature rise over the years, the NYC average is 39.1° now. Years ago the average was in the mid 30s instead of close to 40°. So even a slightly colder finish than 39.1° would be close to average for a December earlier in the 2000s. NYC used to get a December averaging near 32° at least every 5-10 years as recently as 2010. Now we have gone a full 14 years without one. The cold coming in just before Christmas is being preceded and followed by near 60° warmth which wasn’t the case back in the old days when extended cold was much more common.  We saw a similar version of this back in 2022 when the cold before Christmas was preceded and followed by near 60° warmth.

But this December will most likely end up colder than normal.  Alot of people forecasted a warm December which will most likely fail.

[michsnowfreak]

1 hour ago, bluewave said:

The MJO is an important piece of the forcing puzzle which we encounter in winter. This winter it’s been a part of the pattern but not the main driver. Most recent winters it was the main driver. It’s no coincidence that our last really snowy month near the northeast coast was in January 22 which was a solid MJO 8. That forcing configuration was able to weaken the Pacific Jet enough so the ridge axis locked in near the West Coast. That’s the opposite of what we have been seeing this winter as the ridge keeps drifting east instead of staying anchored out west. So we have been getting competing forcing elements between more Nino-like +PNA and La Niña faster Pacific Jet. So if the MJO remains in the background, then we may not see enough influence from a colder phase to really relax the Pacific Jet enough.

Fair enough. Though as you get into peak winter climo, which for many is mid Jan to early Feb, I have to imagine that for the "warmer" climates of the east coast and mid-Atlantic it takes less "to go right" for it to snow than it would in November or April.

[GaWx]

 The latest available bias corrected extended EPS, CFS, and BOMM ensemble means all have the MJO reaching the left side of the diagram mainly at moderate to weak amplitude in early Jan, which though not nearly always have more often than not been associated with a cold dominated pattern in the E US in the first half of Jan during non-Nino ENSO:

EPS bc:

 

CFS:

 

BOM:

 

 Here are non-Nino ENSO weak (near or inside circle) to moderate left side MJO dominated E US 1st half of Jan with diagrams shown for coldest:

2023 mild

2022 cool NE/mild SE

2002 slightly AN NE/cold SE

1999 cold:

1997 normal

1996 cold:

1994 cold:

 

1985 cool:

[bluewave]

21 minutes ago, michsnowfreak said:

Fair enough. Though as you get into peak winter climo, which for many is mid Jan to early Feb, I have to imagine that for the "warner" climates of the east coast and mid-Atlantic  it takes less "to go right" for it to snow than it would in November or April.

The main thing we need to go right would be for the Pacific Jet to relax enough to prevent all the lows from tracking across the Great Lakes. Even marginally colder patterns like this month are still getting warm storm tracks with the cold arriving after the rains end. So we have very little snow to show for the colder departures relative to the means. The East Coast started getting warmer storm tracks even during colder intervals since the 18-19 winter. Last winter some spots were able to go over 10” in the snowfall department due the El Niño weakening the Northern Branch just enough for the STJ to dominate for a week in February. This wasn’t the case with the La Niña in 22-23. In January 2019 with lows near 0° in NYC and a monthly average near 32.0°, NYC only finished that colder month with an 1 inch of snowfall due to the warm storm track through the Great Lakes.

[beavis1729]

1 hour ago, bluewave said:

We have not had a cold December around the NYC Metro by historical December standards. Since December has experienced such a steep temperature rise over the years, the NYC average is 39.1° now. Years ago the average was in the mid 30s instead of close to 40°. So even a slightly colder finish than 39.1° would be close to average for a December earlier in the 2000s. NYC used to get a December averaging near 32° at least every 5-10 years as recently as 2010. Now we have gone a full 14 years without one. The cold coming in just before Christmas is being preceded and followed by near 60° warmth which wasn’t the case back in the old days when extended cold was much more common.  We saw a similar version of this back in 2022 when the cold before Christmas was preceded and followed by near 60° warmth.

This is a great point, and often gets overlooked in these discussions.  Another ridiculous stat on this: For the 1951-80 normals (which I grew up on), the normal low at ORD on 12/31 was 13F.  For the 1991-2020 normals, it's 21F.  So the normal low at ORD has increased by 8F in 40 years.  People should be rioting, but everyone just says "whatever" and moves on like everything is ok.  If ORD gets a winter month with a slight minus departure vs. the 1991-2020 normals, everyone says how "cold" it is...but such a month would be significantly above normal vs. 1951-80 normals.  

IMO, the worst outcome of the above is that everyone's standards have fallen so low.  It's like we've all given up on anything good, so we ratlionalize it by having low expectations.  Kind of like being a Bears fan. I saw a post in our sub-forum saying how great it was that 9 of the first 14 days in December 2024 had a high below 40F in Toledo...as if we should be excited about that.  Really?  It's annoying if any single day in Dec has a high over 40F, much less 5 of them. The days are shortest in Dec, so it should feel like it.  Currier and Ives would be rolling in their grave.

And while, technically, we can get a decent amount of snow in Jan north of 40N even with "mild" temps, we should expect more than that.  Dec 15th - Feb 15th is the core of winter, so snow shouldn't be melting every day or two.  Have our expectations really sunk that low?  Most of us wouldn't be happy with cold temps in July, but we're suddenly ok with snow-melting temps in Jan?  If we get slightly more snowfall than normal in Jan but it melts every few days, it's irrelevant. Yet another reason why total snowfall is misleading as a stat. We should be looking at SDDs, as it's a much better reflection of the tenor of a winter and would better exemplify the horrible winters we've seen since 2015-16 in the Midwest and Northeast.

We aren't asking for Alaska or Siberia, just seasons in seasons.  DJF should be winter, not an extended fall with a few weeks of occasional wintry weather here and there.  Last winter was a great example of this IMBY. For 2 weeks in January, we had really great wintry conditions...but nothing for the rest of winter. Do we ever have summers where it only felt like summer for two weeks in July? It's maddening to have to expect a perfect pattern to get wintry weather during winter.

[beavis1729]

30 minutes ago, MJO812 said:

But this December will most likely end up colder than normal.  Alot of people forecasted a warm December which will most likely fail.

But "normal" is very mild these days, compared to 30-50 years ago.  So a colder than normal December doesn't really mean much imo, unless the departure is -5 or more. 

[Maestrobjwa]

46 minutes ago, beavis1729 said:

This is a great point, and often gets overlooked in these discussions.  Another ridiculous stat on this: For the 1951-80 normals (which I grew up on), the normal low at ORD on 12/31 was 13F.  For the 1991-2020 normals, it's 21F.  So the normal low at ORD has increased by 8F in 40 years.  People should be rioting, but everyone just says "whatever" and moves on like everything is ok.  If ORD gets a winter month with a slight minus departure vs. the 1991-2020 normals, everyone says how "cold" it is...but such a month would be significantly above normal vs. 1951-80 normals.  

IMO, the worst outcome of the above is that everyone's standards have fallen so low.  It's like we've all given up on anything good, so we ratlionalize it by having low expectations.  Kind of like being a Bears fan. I saw a post in our sub-forum saying how great it was that 9 of the first 14 days in December 2024 had a high below 40F in Toledo...as if we should be excited about that.  Really?  It's annoying if any single day in Dec has a high over 40F, much less 5 of them. The days are shortest in Dec, so it should feel like it.  Currier and Ives would be rolling in their grave.

And while, technically, we can get a decent amount of snow in Jan north of 40N even with "mild" temps, we should expect more than that.  Dec 15th - Feb 15th is the core of winter, so snow shouldn't be melting every day or two.  Have our expectations really sunk that low?  Most of us wouldn't be happy with cold temps in July, but we're suddenly ok with snow-melting temps in Jan?  If we get slightly more snowfall than normal in Jan but it melts every few days, it's irrelevant. Yet another reason why total snowfall is misleading as a stat. We should be looking at SDDs, as it's a much better reflection of the tenor of a winter and would better exemplify the horrible winters we've seen since 2015-16 in the Midwest and Northeast.

We aren't asking for Alaska or Siberia, just seasons in seasons.  DJF should be winter, not an extended fall with a few weeks of occasional wintry weather here and there.  Last winter was a great example of this IMBY. For 2 weeks in January, we had really great wintry conditions...but nothing for the rest of winter. Do we ever have summers where it only felt like summer for two weeks in July? It's maddening to have to expect a perfect pattern to get wintry weather during winter.

"Rioting?" Lol So "Man riots at cloud?"  Listen man...what else is there to do but just be grateful for what we get? We certainly don't control the weather...We don't know whether things will/can improve or not in this unknown era of climate whatever we're in. So when what what we expected becomes few and far between, we oughta become much more appreciative of what we do get. Because again...we can't control it. Does it suck that we haven't been getting what we used to? Absolutely. Are the snowfall numbers and the number of consecutive seasons where crap in the atmosphere doesn't work? Absolutely. 

But...keeping the "standards" high despite the current reality only brings more frustration. Better to adjust the standards to what is as opposed to what we wish it could be. Otherwise it's bad for the brain, lol

I feel your frustration and I get it. I've blown up and whined and complained on this site plenty and driven folks crazy--so yeah I get it! But I know for me I've been working to get to a place where I don't dwell on it, and if something like a cold December is what we get, hey it's better than a torch. Just gotta be grateful 

[michsnowfreak]

2 hours ago, beavis1729 said:

This is a great point, and often gets overlooked in these discussions.  Another ridiculous stat on this: For the 1951-80 normals (which I grew up on), the normal low at ORD on 12/31 was 13F.  For the 1991-2020 normals, it's 21F.  So the normal low at ORD has increased by 8F in 40 years.  People should be rioting, but everyone just says "whatever" and moves on like everything is ok.  If ORD gets a winter month with a slight minus departure vs. the 1991-2020 normals, everyone says how "cold" it is...but such a month would be significantly above normal vs. 1951-80 normals.  

Been waiting for your annual copy and paste rant that Chicago doesnt annual get a repeat of their most severe 1970s winters on record. At no point in Chicago's climate history has the avg low on 12/31 ever been 13°. In fact, the 1951-80 avg winter temp is just 1.1° colder than 1991-2020, not 8° lmao.

1991-2020: 27.1
1981-2010: 26.3
1971-2000: 25.9
1961-1990: 25.1
1951-1980: 26.0
1941-1970: 26.8
1931-1960: 28.0
1921-1950: 28.1
1911-1940: 27.9
1901-1930: 26.8

Avg low on 12/31 in chicago

1991-2020: 21
1981-2010: 21
1971-2000: 19
1961-1990: 17
1951-1980: 19
1941-1970: 19
1931-1960: 23
1921-1950: 22
1911-1940: 22
1901-1930: 21

[bluewave]

1 hour ago, MJO812 said:

But this December will most likely end up colder than normal.  Alot of people forecasted a warm December which will most likely fail.

The monthly forecasts issued near the start of December weren’t warm. But the main issue this month is that the model forecasts underestimated the strength of the Pacific Jet. So the ridge axis in the means for the whole month will end up further east than forecast. Very active storm track through the Great Lakes with warm ups ahead of the storms with rain and cool downs behind the lows. Very little snowfall near the East Coast with this pattern. 

[donsutherland1]

Yesterday, I noted that the 46-day ECMWF ensembles show the development of an EPO-/PNA- pattern during the first half of January. Statistically, following a PNA+ December, a PNA- January is uncommon:

December PNA: +0.5 or above: 31 cases
January PNA < 0: 29% cases
January PNA > 0: 71% cases
January PNA +0.50 or above: 48% cases
January PNA +1.00 or above: 19% cases
Lowest January PNA: -1.14, 1954
Highest January PNA: 2.02, 2016

December PNA: +1.00 or above: 13 cases
January PNA < 0: 8% cases
January PNA > 0: 92% cases
January PNA +0.50 or above: 62% cases
January PNA +1.00 or above: 31% cases
Lowest January PNA: -1.14, 1954
Highest January PNA: +1.51, 2001

If one assumes that the PNA will average > 0 during January, especially as the December PNA could average near or even slightly above +1.00, the idea of a predominant ridge in the West and trough in the East pattern with warmth in the West and cold in the East is not anything close to a slam dunk. The predominant patterns show a wide range of diversity.

Trough in the West Patterns: 42% of cases

Ridge in the West Patterns: 33% of cases

Trough across much of the CONUS: 25% of cases

The classic ridge in the West, trough in the East pattern has occurred with mean January PNA values -0.95 or below, as did the second type of trough across the CONUS cluster (most were +1.00 or above). All of the other clusters had mean January PNA values below -0.75. The first trough in the West, ridge in the East pattern actually produces a temperature anomaly pattern that is very similar to an EPO-/PNA- pattern.

Overall, even if one assumes a predominantly positive PNA for January, which would go against the 46-day ECMWF guidance, one can't automatically assume that the eastern third or half of the U.S. would wind up colder than normal. Keeping in mind the 3-month seasonal guidance, which is more skillful than the month-by-month guidance over seasonal timeframes, a milder January outcome may be somewhat more likely than a colder one for the eastern third or half of the CONUS and southeastern Canada (Ontario and Quebec). There will likely be variability, which has been an important theme through December 14th and is likely to continue throughout the month based on a consensus of the latest guidance.

[mitchnick]

4 minutes ago, donsutherland1 said:

Yesterday, I noted that the 46-day ECMWF ensembles show the development of an EPO-/PNA- pattern during the first half of January. Statistically, following a PNA+ December, a PNA- January is uncommon:

December PNA: +0.5 or above: 31 cases
January PNA < 0: 29% cases
January PNA > 0: 71% cases
January PNA +0.50 or above: 48% cases
January PNA +1.00 or above: 19% cases
Lowest January PNA: -1.14, 1954
Highest January PNA: 2.02, 2016

December PNA: +1.00 or above: 13 cases
January PNA < 0: 8% cases
January PNA > 0: 92% cases
January PNA +0.50 or above: 62% cases
January PNA +1.00 or above: 31% cases
Lowest January PNA: -1.14, 1954
Highest January PNA: +1.51, 2001

If one assumes that the PNA will average > 0 during January, especially as the December PNA could average near or even slightly above +1.00, the idea of a predominant ridge in the West and trough in the East pattern with warmth in the West and cold in the East is not anything close to a slam dunk. The predominant patterns show a wide range of diversity.

Trough in the West Patterns: 42% of cases

Ridge in the West Patterns: 33% of cases

Trough across much of the CONUS: 25% of cases

The classic ridge in the West, trough in the East pattern has occurred with mean January PNA values -0.95 or below, as did the second type of trough across the CONUS cluster (most were +1.00 or above). All of the other clusters had mean January PNA values below -0.75. The first trough in the West, ridge in the East pattern actually produces a temperature anomaly pattern that is very similar to an EPO-/PNA- pattern.

Overall, even if one assumes a predominantly positive PNA for January, which would go against the 46-day ECMWF guidance, one can't automatically assume that the eastern third or half of the U.S. would wind up colder than normal. Keeping in mind the 3-month seasonal guidance, which is more skillful than the month-by-month guidance over seasonal timeframes, a milder January outcome may be somewhat more likely than a colder one for the eastern third or half of the CONUS and southeastern Canada (Ontario and Quebec). There will likely be variability, which has been an important theme through December 14th and is likely to continue throughout the month based on a consensus of the latest guidance.

So what's your forecast, without hedging?

[michsnowfreak]

3 minutes ago, donsutherland1 said:

Yesterday, I noted that the 46-day ECMWF ensembles show the development of an EPO-/PNA- pattern during the first half of January. Statistically, following a PNA+ December, a PNA- January is uncommon:

December PNA: +0.5 or above: 31 cases
January PNA < 0: 29% cases
January PNA > 0: 71% cases
January PNA +0.50 or above: 48% cases
January PNA +1.00 or above: 19% cases
Lowest January PNA: -1.14, 1954
Highest January PNA: 2.02, 2016

December PNA: +1.00 or above: 13 cases
January PNA < 0: 8% cases
January PNA > 0: 92% cases
January PNA +0.50 or above: 62% cases
January PNA +1.00 or above: 31% cases
Lowest January PNA: -1.14, 1954
Highest January PNA: +1.51, 2001

If one assumes that the PNA will average > 0 during January, especially as the December PNA could average near or even slightly above +1.00, the idea of a predominant ridge in the West and trough in the East pattern with warmth in the West and cold in the East is not anything close to a slam dunk. The predominant patterns show a wide range of diversity.

Trough in the West Patterns: 42% of cases

Ridge in the West Patterns: 33% of cases

Trough across much of the CONUS: 25% of cases

The classic ridge in the West, trough in the East pattern has occurred with mean January PNA values -0.95 or below, as did the second type of trough across the CONUS cluster (most were +1.00 or above). All of the other clusters had mean January PNA values below -0.75. The first trough in the West, ridge in the East pattern actually produces a temperature anomaly pattern that is very similar to an EPO-/PNA- pattern.

Overall, even if one assumes a predominantly positive PNA for January, which would go against the 46-day ECMWF guidance, one can't automatically assume that the eastern third or half of the U.S. would wind up colder than normal. Keeping in mind the 3-month seasonal guidance, which is more skillful than the month-by-month guidance over seasonal timeframes, a milder January outcome may be somewhat more likely than a colder one for the eastern third or half of the CONUS and southeastern Canada (Ontario and Quebec). There will likely be variability, which has been an important theme through December 14th and is likely to continue throughout the month based on a consensus of the latest guidance.

With all of the model changes, ups and downs, and typical nina climo (even tho nina underperformed), variability and up and down has been my thoughts all along. Any remote guess of when the ups and downs will be....I'll pass on making that guess haha. But the key is variability. Anyone expecting all cold or all mild will be disappointed. 

[mitchnick]

10 minutes ago, bluewave said:

The monthly forecasts issued near the start of December weren’t warm. But the main issue this month is that the model forecasts underestimated the strength of the Pacific Jet. So the ridge axis in the means for the whole month will end up further east than forecast. Very active storm track through the Great Lakes with warm ups ahead of the storms with rain and cool downs behind the lows. Very little snowfall near the East Coast with this pattern. 

He was talking temps, not snow. Why change the subject to snow or model forecasts? Unless you can show a model that showed colder than what has occurred, flawed modeling has literally nothing to do with it.