My Winter Outlook 2020-21

[Isotherm]

On 1/16/2021 at 1:35 AM, 40/70 Benchmark said:

Tom, are you getting uneasy about your Feb call? Starting to look like the PV may not recover for at least through early Feb....

 

Ray, Not yet. Historically and probabilistically, from the standpoint of the background conditions/forcing agents extant at this time (e.g., one variable being the QBO), almost always yield a robust reversal of the NAM status in month 3 (we will now have seen two consecutive months, Dec-Jan, of fairly strongly negative AO status). From a forcing perspective, the putative rubber band snap typically (much more often than not) occurs when the winter-night is still lengthy, as it remains in late January, auspicious for re-intensification (as opposed to a late Feb or beyond SSW event, which is a more energy intensive process to regain potent vortex status). Further, the tropospheric pattern, unlike earlier in the winter, does not appear conducive for major wave driving/energy transfer into the stratosphere beyond the end of the month. So while there may be some plateauing at the end of January sufficient to hold vestiges of blocking into the early part of February, I still tend toward the idea that the direction we're headed is towards a +NAM state. The temperature departures of significant warmth in the East may be slightly more in question, if early month can include much more countervailing cold presses. But we'll see how it evolves.

[40/70 Benchmark]

3 hours ago, Isotherm said:

 

Ray, Not yet. Historically and probabilistically, from the standpoint of the background conditions/forcing agents extant at this time (e.g., one variable being the QBO), almost always yield a robust reversal of the NAM status in month 3 (we will now have seen two consecutive months, Dec-Jan, of fairly strongly negative AO status). From a forcing perspective, the putative rubber band snap typically (much more often than not) occurs when the winter-night is still lengthy, as it remains in late January, auspicious for re-intensification (as opposed to a late Feb or beyond SSW event, which is a more energy intensive process to regain potent vortex status). Further, the tropospheric pattern, unlike earlier in the winter, does not appear conducive for major wave driving/energy transfer into the stratosphere beyond the end of the month. So while there may be some plateauing at the end of January sufficient to hold vestiges of blocking into the early part of February, I still tend toward the idea that the direction we're headed is towards a +NAM state. The temperature departures of significant warmth in the East may be slightly more in question, if early month can include much more countervailing cold presses. But we'll see how it evolves.

What exactly does the NAM entail? I haven't used that....is it like North American Angular Momentum?

[Isotherm]

6 hours ago, 40/70 Benchmark said:

What exactly does the NAM entail? I haven't used that....is it like North American Angular Momentum?

 

Often used synonymously with the AO; Northern Annular Mode, a proxy which has geospatial overlap to the AO. I think we will flip to a +AO/NAO.

https://energyeducation.ca/encyclopedia/Northern_Annular_Mode#:~:text=Northern Annular Mode (NAM) also,the shape is more annular.

[40/70 Benchmark]

Just now, Isotherm said:

 

Often used synonymously with the AO; Northern Annular Mode, a proxy which has geospatial overlap to the AO. I think we will flip to a +AO/NAO.

https://energyeducation.ca/encyclopedia/Northern_Annular_Mode#:~:text=Northern Annular Mode (NAM) also,the shape is more annular.

Oh, agreed. Question is do we steal a week or two in early Feb...I think maybe a week.

[40/70 Benchmark]

Although I feel like we have seen stretches of +NAM last longer than 3 months often the past several years.

[40/70 Benchmark]

I think its time to concede that @Isotherm and I were too aggressive to break down the blocking this season.

[Isotherm]

20 hours ago, 40/70 Benchmark said:

I think its time to concede that @Isotherm and I were too aggressive to break down the blocking this season.

 

Monitoring the recovery of the z10-z50 stratospheric vortices as well as the subseasonal/MJO signal which will play a greater role in the month of February. At least, from the NAO perspective, it will flip positive early Feb (following the major storm/phase change threat, which finally showed up at the tail end of the Jan +PNA/-NAO pattern). Then the NAO may dip negative again in the Feb 5-9 time frame, but potentially only ephemerally. Coherent MJO 6-7 w/ magnitude is a +NAO signal, and depending upon the pace at which the SPV recovers, that may add adjunctively to a neutral or + NAO. The AO domain, I think may be a bit different, and that domain space will clearly go down as a miss this winter. The AO will probably average neutral to negative for Feb, if only by virtue of both residual +GP strat heights initially, but then the coherent MJO 6-7 assist will drive poleward EPO ridging into the Arctic domain. So the AO heights will receive assist from the Pacific induced intraseasonal alterations. My thinking at this time is the MJO expeditiously weakens in coherency beyond P7, so most of Feb should still feature the fairly robust SE-ridging in the means, and a colder Rockies/N Plains structure as forecasted. 

Another player on the field is that Feb will have legitimate arctic cold on the North American side, now that the SSW is over. So the cold shots that do slide through the Northeast US will be quite strong in February. Fascinating winter overall, and from a LR forecasting point of view, particularly on the AO domain, a very rare outcome in terms of opposing certain indicators.

I still think February will probably be a snowier than normal month for most of New England (although warmer than normal in the means). SNE coast points southward will be dependent upon the extent of countervailing blocking.

[40/70 Benchmark]

On 1/27/2021 at 9:29 AM, Isotherm said:

 

Monitoring the recovery of the z10-z50 stratospheric vortices as well as the subseasonal/MJO signal which will play a greater role in the month of February. At least, from the NAO perspective, it will flip positive early Feb (following the major storm/phase change threat, which finally showed up at the tail end of the Jan +PNA/-NAO pattern). Then the NAO may dip negative again in the Feb 5-9 time frame, but potentially only ephemerally. Coherent MJO 6-7 w/ magnitude is a +NAO signal, and depending upon the pace at which the SPV recovers, that may add adjunctively to a neutral or + NAO. The AO domain, I think may be a bit different, and that domain space will clearly go down as a miss this winter. The AO will probably average neutral to negative for Feb, if only by virtue of both residual +GP strat heights initially, but then the coherent MJO 6-7 assist will drive poleward EPO ridging into the Arctic domain. So the AO heights will receive assist from the Pacific induced intraseasonal alterations. My thinking at this time is the MJO expeditiously weakens in coherency beyond P7, so most of Feb should still feature the fairly robust SE-ridging in the means, and a colder Rockies/N Plains structure as forecasted. 

Another player on the field is that Feb will have legitimate arctic cold on the North American side, now that the SSW is over. So the cold shots that do slide through the Northeast US will be quite strong in February. Fascinating winter overall, and from a LR forecasting point of view, particularly on the AO domain, a very rare outcome in terms of opposing certain indicators.

I still think February will probably be a snowier than normal month for most of New England (although warmer than normal in the means). SNE coast points southward will be dependent upon the extent of countervailing blocking.

NAO does't look to cooperate through at least mid month....seems we both may have missed the boat on that, at least to a degree.

 

[Isotherm]

On 2/3/2021 at 2:57 PM, 40/70 Benchmark said:

NAO does't look to cooperate through at least mid month....seems we both may have missed the boat on that, at least to a degree.

 

 

 

Indeed. While there is significant uncertainty as to the pace at which the NAO neutralizes in the medium to long range, I believe it's high probability as this point that DJF will average negative for NAO (barring an anomalous positive episode from mid month through the end of Feb, which isn't out of the question). The NAO finished -1.11 for January and -0.3 for December. January was expected, but the inter-monthly duration of the NAO was unexpected. The DJF NAO miss will go down as my first NAO formula miss in about a decade. And of course the AO domain, likely the most glaring aberration from the indicators I've quite frankly ever seen. The QBO finished +10 for January, continued strongly westerly. And while that in and of itself is not the sole determinant, there were other robust indicators pre-season that strongly suggested a neutral or positive AO mean winter.

I have been speculating/hypothesizing as to provenance -- the 2020 Australian fire induced aerosol dispersal may have been a factor in changing things up, possibly in concert with record low Arctic sea ice. But I think more likely the former. Regardless, the mean circulation flow altered significantly in the Arctic once December began.

As to February temperature departures, as you delineated in a recent post, it is possible the East Coast still finishes warmer than normal, depending upon the second half. The core of the cold will clearly be centered in the N Rockies-N Plains for the first half of the month. Overall forecasted temperature departures DJF still may fare very well; we will revisit that at the end of Feb. Snowfall -- New England looking good for a SWFE threat next week (potentially). And we'll need to monitor the window around mid-month as the blocking structure degrades.

 

[Isotherm]

One note on snowfall:

Snowfall is invariably the most stochastic, capricious and therefore most difficult variable to prognosticate from the long range, which is why I assign more weighting to temperature departures than snowfall at final verification. That said, the snowfall tally through 2/5/2021 has NYC at 28.0", slightly above my seasonal snowfall range. It is almost certain that this value will be increased, via, at least, light or moderate opportunities in the coming 10 days. Boston, currently around 22", has a ways to go to arrive at my range of 40-48", though that is still within the range of outcomes, certainly. The Mid-Atlantic cities are nearing my seasonal projections at this time. We will see how the remainder of this period progresses. However, for those certainly in the NYC area, it appears certain that a "positive" snowfall error will be occurring this winter, namely, more snowfall than forecasted. NYC will likely get into the 30s as far as snowfall. The evolution of the mid-month threat is subject to a number of different permutations and mechanisms. The equatorward/southwestward degradation of the block toward the Pacific is not ideal, as it could invite height rises in the Southeast US. Further to that, the MJO is somewhat out of phase and may tend to force SE-ridge resistance in the means. Contemporaneously the TPV will press from the north, as the SSW mediated block decays to its northwest. Overall, a highly convoluted and difficult to prognosticate variables. However, the rapid multi-standard deviation rise in the AO & NAO invite another large precipitation event opportunity. The PNA may not be as conducive this window, however, and that must be monitored. I'm not nearly as optimistic about this window as I was for Jan 31-Feb 2 along the Northeast/Mid-Atlantic coast, due in part to the more favorable mechanics of the block degradation in Jan 31-Feb 2. That said, Feb 12-14 is a window to monitor in the East.

[40/70 Benchmark]

Tom, any wrap up post in the works?

Thanks for all of your efforts...always a pleasure to read.

[thunderbolt]

On 11/10/2020 at 12:03 PM, Isotherm said:

My winter outlook for the 2020-21 season can be read on my website, linked here, for those interested:

https://www.lightinthestorm.com/

Tom are you doing a 2021/22 winter outlook?

[40/70 Benchmark]

2 hours ago, thunderbolt said:

Tom are you doing a 2021/22 winter outlook?

I thought this was this year's....I started reading it and was like...what? Disagree...lol

His should be out in about two weeks.

[thunderbolt]

I guess Tom’s not doing a winter outlook I checked his website and it is shut down

[40/70 Benchmark]

1 hour ago, thunderbolt said:

I guess Tom’s not doing a winter outlook I checked his website and it is shut down

I checked last night, and it looked like the last post was October 12th.

[dmillz25]

Hey @Isothermno winter outlook this year? I usually look forward to reading your and @40/70 Benchmarkoutlooks 

[stadiumwave]

Is @Isotherm OK? I haven't seen one post from him on any forum. 

[40/70 Benchmark]

On 11/27/2021 at 10:04 AM, stadiumwave said:

Is @Isotherm OK? I haven't seen one post from him on any forum. 

I PMed him last week...read it, but did not reply. May just be going through some stuff...