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Medium Range Discussion Winter 2011-12


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Looking ahead to the first week in February, the GFS ensemble forecast for the Arctic Oscillation provides a great deal of complexity. There are two major clusters of ensemble members. One cluster is somewhat negative. The other is strongly negative. Assuming the other teleconnection forecasts e.g., PNA are reasonably accurate, the former would tend to promote a warm outcome in the East. The latter would provide a cold outcome in the East.

AO012120120z.jpg

In trying to draw up my map based on the expected teleconnection indices for the 2/1-7/2012 period (which I'll do tomorrow), I might need to choose from among one of those clusters. Of course, I'm hoping that the ensembles are in better agreement tomorrow.

Several pieces of evidence might provide some insight and, unfortunately, they would favor the higher cluster:

1. The ECMWF and ECMWF ensembles are not nearly as aggressive in promoting a strongly negative AO.

2. The long predominant AO+ regime is decaying after reaching a high point in December. The following are the % of days on which the AO was negative:

November: 6.7%

December: 3.2%

January: 19.0%

Indeed, this decay of the AO+ regime is part of the reason I expect the AO to average negative to neutral in February.

3. The ECMWF Ensembles forecast that the MJO will be in Phases 5 and 6 in early February (amplitude < 1). Since 1975, all February cases had a mean AO of -.075 with a standard deviation of 1.91. An AO of -3.000 would be more than 1.5 standard deviations from the mean. Put another way, a value of -3.000 would be in the lowest 6.5% of cases. Hence, my guess is that the GFS ensembles are probably overdone assuming that the MJO is in Phase 5 or 6 (amplitude < 1) during the first week in February.

If the AO does get -3.000 or lower the probability of seeing the coldest temperatures of the season or a snowstorm goes up soon after it happens...I agree with you about the AO for February...

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Some thoughts this morning regarding the southern cyclone this coming week. The Euro is a bit too progressive and is considered an outlier as is the Canadian. A slower ejection E of the U/L has been the pattern all season. There remain some questions as to the amount of phasing with the northern stream short wave and how that will affect our southern cyclone. The data gained from the RECON mission 22/00Z aided the 00Z GFS/NAM output and was ingested as that mission covered a large area from HI to AK to just off the California Coast. The GFS/UKMet blend with a bit of Euro early on seems like the best solution for now and the HPC mentions that in their very early morning update. I do want to mention the severe potential as well. The day 3 SPC is talking about an isolated tornado or two for S Texas as the Coastal low develops and slowly translates NE up the Coast. As has been mentioned, the atmosphere will be very moist through all levels in a very un January fashion (pw's 1.7+). The Sunday front will slowly retreat N across Central/E Texas and just where that boundary stalls will be key. We'll look at the operational data for the 12Z suite and hopefully have some more details as to what we can expect. I encourage everyone to follow the weather very closely the next several days as we are likely headed toward a very active couple of days beginning Tuesday through Thursday and will extend beyond the S Plains/Lower Mississippi Valley Regions into next weekend for those along the EC.

Edit to add...

HPC Morning Update:

PRELIMINARY EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD

859 AM EST SUN JAN 22 2012

VALID 12Z THU JAN 26 2012 - 12Z SUN JAN 29 2012

INCREASED RIDGING OVER THE ERN PACIFIC THIS WEEK SHOULD ALLOW FOR

MEAN TROUGHING TO STICK AROUND OVER THE PLAINS/MIDWEST UNDER A

PORTION OF THE POLAR VORTEX DEVELOPING OVER CENTRAL CANADA NEXT

WEEKEND. GUIDANCE AGREES ON THIS IDEA...BUT THERE ARE A COUPLE

LARGE ISSUES.

THE 00Z GFS/00Z GEFS MEAN MORE AGGRESSIVELY KNOCK DOWN THE TOP OF

THE RIDGE OVER THE WRN SUBTROPICAL ATLANTIC BY FRI THAN OTHER

GUIDANCE..WHICH ALLOWS A QUICKER FRONTAL PROGRESSION IN THE EAST.

THE LONGWAVE TROF OVER MID-CONTINENT FAVORS GRADUAL WRN ATLANTIC

RIDGE WEAKENING. THE OTHER BIG ISSUE IS HOW TO HANDLE THE

SOUTHERN STREAM CLOSED LOW NEAR TEXAS WED. 00Z ECMWF/ECMWF

ENSEMBLES ARE NOW THE QUICKEST OF THE GUIDANCE WHILE THE 00Z GEFS

MEAN/NOGAPS ARE THE SLOWEST. FORECAST SPREAD WITH THIS SYSTEM IS

SIGNIFICANT...WITH SOLUTIONS RANGING BETWEEN NRN MEXICO AND THE

EAST COAST BY FRIDAY DEPENDING ON THE EXTENT OF NRN STREAM

INTERACTION. THE 00Z GFS/UKMET AND TO A SLIGHTLY LESSER DEGREE

THE 00Z CANADIAN AND 06Z GFS/DGEX ARE ON THE SLOW SIDE OF THE

SOLUTION ENVELOPE...BUT NOT AS SLOW AS THE MOST EXTREME CUTOFF

SOLUTIONS. CLOSED LOWS IN A SEPARATED SRN STREAM TEND TO REMAIN

ON THE SLOW SIDE SO WILL DISCOUNT THE 00Z ECMWF THAT ALSO OFFERS

POOR RUN TO RUN CONSISTENCY. UNCERTAINTY THOUGH PROBABLY MAKES IT

PRUDENT TO NOT GO WITH THE SLOWEST GEFS ENSEMBLES/NOGAPS.

ACCORDINGLY...UPDATED HPC PRELIM PROGS HAVE BEEN PRIMARILY DERIVED

FROM A 50-50 BLEND OF THE 00Z GFS/UKMET DAYS 3-5 WED-FRI BEFORE

LEANING ON THE 00Z GFS NEXT WEEKEND...ALBEIT WITH LESS PRONOUNCED

EAST COAST/WRN ATLANTIC CYCLOGENSIS CONSIDERING UNCERTAIN SUPPORT

ALOFT.

post-32-0-28074600-1327240873.gif

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Consistent with yesterday's discussion on the AO (#691), the GFS ensembles have adjusted upward. The lowest cluster (smaller than yesterday's forecast) is generally in the -2 to -1 range as opposed to -3 to -2. In addition, numerous other members have trended higher. As a result, I have higher confidence that there likely will not be severe blocking during the first week in February.

The following charts show the temperature anomalies for the February 1-10, 1950-2011 timeframe for all cases with a La Niña Region 3.4 anomaly in the -1.45°C to -0.65°C range, AO in the -1.5 to 0.0 range, and PNA in the -0.5 to +0.5 range (top); the bottom chart shows the observed decadal trend in temperatures.

Feb1-72012.jpg

Adjustments:

In this case, the temperature adjustment relative to the composite temperature anomalies is sufficient to adjust the expected idea for the Northeastern U.S. to milder than normal. A similar adjustment would be applied to the eastern Great Lakes region.

In addition, if the strongest blocking in the AO forecast does not take place, the Northeast would also wind up warmer than normal. Severe blocking would lead to Northern New England/eastern Canada being warmer than normal. Overall, there is more risk of a warmer outcome than the raw composite chart (top) shows than a colder one.

Conclusion:

In sum, the composite temperature anomaly is what I expect for the February 1-7, 2012 timeframe except that Michigan, Ohio, Pennsylvania, New York, and New England would wind up milder than normal.

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The data gained from the RECON mission 22/00Z aided the 00Z GFS/NAM output and was ingested as that mission covered a large area from HI to AK to just off the California Coast. The GFS/UKMet blend with a bit of Euro early on seems like the best solution for now and the HPC mentions that in their very early morning update.

Just to clarify, the other operational centers get the RECON data as well. For example, here's the observation distribution from the EC at 00z today (not the green dropsonde observation profiles in the pacific):

dcover!Temp!00!pop!od!mixed!w_coverage!latest!chart.gif

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Don, the 10 day euro ens mean has the Ao very weakly negative and the pna negative while the 06Z gfs ens mean really looks like the nao goes more positive with time. There sin't much skill in the forecasts as the models were showing the ao and nao being pretty positive looking only a day or so ago. Makes me think your stats are the best way to go using a benign middle of the road AO, NAO and PNA guess. Like you I think that probably would end up giving the mid atlantic warmer than normal temps but only a degree or so above normal. My confidence factor is down as I think the period is a low confidence one.

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My confidence factor is down as I think the period is a low confidence one.

I agree, Wes. The lack of continuity on the guidance and the large spread among some of the ensemble members makes this a very challenging guess.

And, for those who forgot the beauty of snow in this unseasonably warm winter to date, I uploaded a number of photos from yesterday at: http://wintercenter.homestead.com/photojan2012h.html (2 pages).

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Overnight, parts of the southern U.S. experienced severe weather. CNN reported:

Severe weather tore across the Southeast early Monday, spreading damage through at least two states, emergency officials said.

A powerful string of storms stretched from southern Louisiana to eastern Tennessee, National Weather Service radar showed. Tornado watches and warnings were in place across the region.

http://www.cnn.com/2012/01/23/us/severe-weather/index.html

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February 2012 Thoughts:

- The La Niña will likely slowly weaken during February. No rapid collapse appears likely. The ENSO Region 3.4 anomaly fell to -1.1°C for the week centered on January 18 from -0.9°C a week earlier. Since the Southern Oscillation Index (SOI) fell to negative levels earlier this month, the index has rebounded. The 30-day moving average is registering a steady decline, indicative of a weakening La Niña event down the road. The SOI has been negative the following percentage of days:

November: 13.3%

December: 3.2%

January: 30.4% (through 1/23)

Both the CFSv2 and ECMWF forecast a somewhat weaker La Niña event during February. The International Research Institute's (IRI) modeling also indicates a continuation of the La Niña event for the January-March timeframe

The core assumption is that the La Niña will continue, but weaken during February.

- The PDO is likely to remain solidly negative during February. A negative PDO correlates well with a negative PNA. As this winter has seen the PNA average higher than what might have been expected during the strongly negative PDO that has predominated, the February assumption is a PDO that will remain locked in a fairly narrow range close to neutral (-0.5 to +0.5).

- February will likely have the most blocking of any of the winter months (December, January, February). The predominant AO+ regime has continued to show signs of decay. The following is the percentage of days on which the AO has been negative:

November: 6.7%

December: 3.2%

January: 26.1% (through 1/23)

Although the GFS ensembles have had a tendency to rush to extremes with the AO in some recent runs, I believe the general idea of more blocking down the road is reasonable. The ECMWF ensembles have been less aggressive with forecast blocking. Given the amount of uncertainty that exists, my assumption is an AO that will generally range somewhere between -1.5 to +0.5.

Unfortunately, to get a colder outcome for the East/Great Lakes Region/Midwest, one would need to see a more strongly negative AO (generally -2.0 or below) and/or a more strongly positive PNA (generally +1.0 or above).

The composite map for February that I have come up with based on the above assumptions is:

Feb2012.gif

Adjustments based on the observed decadal change in temperatures for February would be a somewhat warmer outcome than what is shown for New England and the eastern Great Lakes region and a somewhat cooler (but still mild outcome) for the Southeast. The Pacific Northwest would also be adjusted to somewhat milder but still have cooler than normal temperatures.

In sum, I believe February will likely wind up warmer than normal across much of North America, including southern Ontario and southern Quebec. The Pacific Northwest (Oregon, Washington, British Columbia) could have another cooler than normal month. Alaska/extreme western Canada also look to remain colder than normal, on average. In the warm areas, cold shots will generally be short-duration events. Some opportunities for snowfall might exist.

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February 2012 Thoughts:

- The La Niña will likely slowly weaken during February. No rapid collapse appears likely. The ENSO Region 3.4 anomaly fell to -1.1°C for the week centered on January 18 from -0.9°C a week earlier. Since the Southern Oscillation Index (SOI) fell to negative levels earlier this month, the index has rebounded. The 30-day moving average is registering a steady decline, indicative of a weakening La Niña event down the road. The SOI has been negative the following percentage of days:

November: 13.3%

December: 3.2%

January: 30.4% (through 1/23)

Both the CFSv2 and ECMWF forecast a somewhat weaker La Niña event during February. The International Research Institute's (IRI) modeling also indicates a continuation of the La Niña event for the January-March timeframe

The core assumption is that the La Niña will continue, but weaken during February.

- The PDO is likely to remain solidly negative during February. A negative PDO correlates well with a negative PNA. As this winter has seen the PNA average higher than what might have been expected during the strongly negative PDO that has predominated, the February assumption is a PDO that will remain locked in a fairly narrow range close to neutral (-0.5 to +0.5).

- February will likely have the most blocking of any of the winter months (December, January, February). The predominant AO+ regime has continued to show signs of decay. The following is the percentage of days on which the AO has been negative:

November: 6.7%

December: 3.2%

January: 26.1% (through 1/23)

Although the GFS ensembles have had a tendency to rush to extremes with the AO in some recent runs, I believe the general idea of more blocking down the road is reasonable. The ECMWF ensembles have been less aggressive with forecast blocking. Given the amount of uncertainty that exists, my assumption is an AO that will generally range somewhere between -1.5 to +0.5.

Unfortunately, to get a colder outcome for the East/Great Lakes Region/Midwest, one would need to see a more strongly negative AO (generally -2.0 or below) and/or a more strongly positive PNA (generally +1.0 or above).

The composite map for February that I have come up with based on the above assumptions is:

Feb2012.gif

Adjustments based on the observed decadal change in temperatures for February would be a somewhat warmer outcome than what is shown for New England and the eastern Great Lakes region and a somewhat cooler (but still mild outcome) for the Southeast. The Pacific Northwest would also be adjusted to somewhat milder but still cooler than normal temperatures.

In sum, I believe February will likely wind up warmer than normal across much of North America, including southern Ontario and southern Quebec. The Pacific Northwest (Oregon, Washington, British Columbia) could have another cooler than normal month. Alaska/extreme western Canada also look to remain colder than normal, on average. In the warm areas, cold shots will generally be short-duration events. Some opportunities for snowfall might exist.

You stated previously that you thought the la nina will strengthen.

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You stated previously that you thought the la nina will strengthen.

Three quick things:

1. My quote concerning the February La Niña was:

The ongoing La Niña remains relatively stable. Region 1+2 has actually cooled a little in the past week. Region 3.4 continues to hold steady at -1.0°C. Coupled with the guidance on ENSO conditions, it appears to be a reasonable bet that the La Niña probably won't fade rapidly in February.

See #522 in this thread.

Back in December I had noted that some of the model guidance showed the La Niña strengthening through January. That's not the same thing as suggesting that it would strengthen during February.

2. In #424 in this thread, I stated, "The actual outcome for February will depend on the continuing evolution of the La Niña and the teleconnections. For now, there are some hints from the objective analogs and also MJO forecasts that a mild February, at least in the East, is a possibility."

3. Most importantly, when one draws closer to a possible event, one should take into consideration any new data that is relevant. Hence, if there were indications that the La Niña would rapidly fade, then my February idea would have taken that into consideration. Instead, the initial thought that the La Niña wouldn't fade rapidly remains unchanged based on the new data.

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Three quick things:

1. My quote concerning the February La Niña was:

See #522 in this thread.

Back in December I had noted that some of the model guidance showed the La Niña strengthening through January. That's not the same thing as suggesting that it would strengthen during February.

2. In #424 in this thread, I stated, "The actual outcome for February will depend on the continuing evolution of the La Niña and the teleconnections. For now, there are some hints from the objective analogs and also MJO forecasts that a mild February, at least in the East, is a possibility."

3. Most importantly, when one draws closer to a possible event, one should take into consideration any new data that is relevant. Hence, if there were indications that the La Niña would rapidly fade, then my February idea would have taken that into consideration. Instead, the initial thought that the La Niña wouldn't fade rapidly remains unchanged based on the new data.

Would'nt the nina weakening help (especially when we do get blocking) get some more cold and snow for feb and march?

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A faster deterioration of the La Niña would be better for cold and opportunities of snow in the East. Absent that, a stronger PNA+ and/or AO- would be helpful.

The latest CPC discussion about enso did not suggest it was weakening. The ONI was 0.80 for the 3 months ending In Dec and looks to be the same for Jan or maybe slightly cooler. I could see a 0.9 reading.

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February 2012 Thoughts:

- The La Niña will likely slowly weaken during February. No rapid collapse appears likely. The ENSO Region 3.4 anomaly fell to -1.1°C for the week centered on January 18 from -0.9°C a week earlier. Since the Southern Oscillation Index (SOI) fell to negative levels earlier this month, the index has rebounded. The 30-day moving average is registering a steady decline, indicative of a weakening La Niña event down the road. The SOI has been negative the following percentage of days:

November: 13.3%

December: 3.2%

January: 30.4% (through 1/23)

Both the CFSv2 and ECMWF forecast a somewhat weaker La Niña event during February. The International Research Institute's (IRI) modeling also indicates a continuation of the La Niña event for the January-March timeframe

The core assumption is that the La Niña will continue, but weaken during February.

- The PDO is likely to remain solidly negative during February. A negative PDO correlates well with a negative PNA. As this winter has seen the PNA average higher than what might have been expected during the strongly negative PDO that has predominated, the February assumption is a PDO that will remain locked in a fairly narrow range close to neutral (-0.5 to +0.5).

- February will likely have the most blocking of any of the winter months (December, January, February). The predominant AO+ regime has continued to show signs of decay. The following is the percentage of days on which the AO has been negative:

November: 6.7%

December: 3.2%

January: 26.1% (through 1/23)

Although the GFS ensembles have had a tendency to rush to extremes with the AO in some recent runs, I believe the general idea of more blocking down the road is reasonable. The ECMWF ensembles have been less aggressive with forecast blocking. Given the amount of uncertainty that exists, my assumption is an AO that will generally range somewhere between -1.5 to +0.5.

Unfortunately, to get a colder outcome for the East/Great Lakes Region/Midwest, one would need to see a more strongly negative AO (generally -2.0 or below) and/or a more strongly positive PNA (generally +1.0 or above).

The composite map for February that I have come up with based on the above assumptions is:

Feb2012.gif

Adjustments based on the observed decadal change in temperatures for February would be a somewhat warmer outcome than what is shown for New England and the eastern Great Lakes region and a somewhat cooler (but still mild outcome) for the Southeast. The Pacific Northwest would also be adjusted to somewhat milder but still have cooler than normal temperatures.

In sum, I believe February will likely wind up warmer than normal across much of North America, including southern Ontario and southern Quebec. The Pacific Northwest (Oregon, Washington, British Columbia) could have another cooler than normal month. Alaska/extreme western Canada also look to remain colder than normal, on average. In the warm areas, cold shots will generally be short-duration events. Some opportunities for snowfall might exist.

Don't know much about weather forecasting yet,

But wouldn't that be like the warmest Febuary ever recorded, just because of that wouldn't it be unlikely to turn out that way just by averages? Not saying that if will not be warm though. Just not a record, I hope. lol

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Don't know much about weather forecasting yet,

But wouldn't that be like the warmest Febuary ever recorded, just because of that wouldn't it be unlikely to turn out that way just by averages? Not saying that if will not be warm though. Just not a record, I hope. lol

The pattern of anomalies is far more relevant than the actual numbers. If you note, there were also adjustments that I suggested:

Adjustments based on the observed decadal change in temperatures for February would be...somewhat cooler (but still mild outcome) for the Southeast.

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The latest CPC discussion about enso did not suggest it was weakening. The ONI was 0.80 for the 3 months ending In Dec and looks to be the same for Jan or maybe slightly cooler. I could see a 0.9 reading.

I don't believe there will be rapid weakening. My guess is that there will be a slow fade during February, possibly with the Region 3.4 anomalies starting out in the -1.2°C to -1.0°C range and ending in the -0.9°C to -0.7°C range.

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It looks like some sort of a +PNA is trying to set up shop in Feb.

The EC ensembles in the 11-15 day take this image....

and also try to retrograde back towards the Aleutians. Once again though, we see the Euro is very stubborn of letting go the AK vortex, and floods the country with milder Pacific air before hand. The image above clearly shows that. In any case, if the vortex does retreat, it will probably leave Canada warmer than normal. Thus, any cold shot will not be arctic, but perhaps enough for more wintry wx...if this did materialize. Also, the MJO seems to want to at least try and develop convection closer to the dateline, although not there quite yet. However, at least most models show this. Forecasts are still not in complete agreement, but it does seem to want to hint at moving east just a little.

http://www.cpc.ncep....clivar_wh.shtml

IMO we still can't get a well defined -NAO and that seems to want to continue for at least the next two weeks. So if this pattern does develop, it may be more of a "tainted" kind of +PNA pattern with not the most coldest air we've seen, but could be cold enough for some. Other things like various torques and AAM tendency seem to try and hint at this as well.

I bring this up as something to watch going forward. The details are still not east to figure out.

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Don, I was wondering what your ideas are for precipitation for February across the U.S. Thanks!

The eastern third of the U.S. will likely have somewhat above normal to above normal precipitation, especially in an area running from the Gulf States to the Great Lakes region. The Gulf States will probably be wettest relative to normal. The Pacific Northwest might be somewhat drier than normal.

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It looks like some sort of a +PNA is trying to set up shop in Feb.

The EC ensembles in the 11-15 day take this image....

and also try to retrograde back towards the Aleutians. Once again though, we see the Euro is very stubborn of letting go the AK vortex, and floods the country with milder Pacific air before hand. The image above clearly shows that. In any case, if the vortex does retreat, it will probably leave Canada warmer than normal. Thus, any cold shot will not be arctic, but perhaps enough for more wintry wx...if this did materialize. Also, the MJO seems to want to at least try and develop convection closer to the dateline, although not there quite yet. However, at least most models show this. Forecasts are still not in complete agreement, but it does seem to want to hint at moving east just a little.

http://www.cpc.ncep....clivar_wh.shtml

IMO we still can't get a well defined -NAO and that seems to want to continue for at least the next two weeks. So if this pattern does develop, it may be more of a "tainted" kind of +PNA pattern with not the most coldest air we've seen, but could be cold enough for some. Other things like various torques and AAM tendency seem to try and hint at this as well.

I bring this up as something to watch going forward. The details are still not east to figure out.

Good observations, I have noticed the difference in the models as well. The Euro is a little more Niña like, but the tropical forcing is trying as you commented. Also, the current -AO, a consequence of the late December, and first 20 days of January stratospheric warming, which helped weaken the PV gives us a little of hope, though I'm not sure the warming will be enough to overhelm the Niña pattern, and it may prove brief. These are the very reasons that in a post a few days ago I thought the very end of Jan and early Feb could bring a window of opportunity for a colder pattern for the eastern half for a couple of weeks (three if lucky), before going back to a warmer pattern.

Also of note, is that any hope for cold will come from the Pacific, as the Atlantic will underperform, once more, IMO.

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Good observations, I have noticed the difference in the models as well. The Euro is a little more Niña like, but the tropical forcing is trying as you commented. Also, the current -AO, a consequence of the late December, and first 20 days of January stratospheric warming, which helped weaken the PV gives us a little of hope, though I'm not sure the warming will be enough to overhelm the Niña pattern, and it may prove brief. These are the very reasons that in a post a few days ago I thought the very end of Jan and early Feb could bring a window of opportunity for a colder pattern for the eastern half for a couple of weeks (three if lucky), before going back to a warmer pattern.

Also of note, is that any hope for cold will come from the Pacific, as the Atlantic will underperform, once more, IMO.

It's still kind if ugly imo, especially if the vortex tries to hang around which it might. However some very weak ridging across nrn Hudson Bay may be enough to give the nrn tier some wintry wx. It's too bad the -NAO continues to fail.

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