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Teleconnections: A More Technical Discussion

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16 hours ago, Isotherm said:

Alas, an opportunity to disagree; it's been far too long...

 

There are misconceptions that I often see floating around regarding SSW behavior and their attendant time-lags in my opinion. Each SSW is idiosyncratic, non-linear, behaving differently as far as its manifestations. Be that as it may, the notion that one begins the clock and must wait 2-3 weeks for tropospheric effects of SSW events is  not supported by historical data, IMO, per my research. In fact, seemingly paradoxically, most cases of splits and displacements since 1955, tropospheric high latitude blocking actually preceded the SSW event, and thereupon, positively feeds back, reinvigorating the -NAM. Often times there is about a 5-7 day period of weak +NAM around the time of the event itself. The troposphere creates the event in the first place. I've found that winters which feature predominate +AO / strong polar night jets, and the enthusiasts are waiting for the 2-3 week downward propagation of a SSW to occur - it rarely happens. 2001-02 is a pertinent exemplar of this. 

 

While, no doubt, there will be some not insignificant destructive interference from the intraseasonal MJO signal in the medium range, contemporaneously, the high latitude blocking will be evolving, in my opinion, fairly instantaneously in this particular circumstance. Not severely so at first; that will wait until the AAM and tropical forcing reinvigorate. But the NAM is already moving negative now, and there is unanimous concordance on data, with a trend slightly negative each day actually, for the remainder of the month.

 

The engagement/coupling of the stratosphere/troposphere will be very expeditious in this instance, due to enhanced "receptibility" from the troposphere, and other exogenous forces constructively interfering. 

 

Today's  data continues to correct toward the notions delineated in prior days: geopotential height increases in both the EPO / NAO domain spaces. While the severity of the pattern may increase in January, the pattern will be sufficiently cold and potentially favorable pursuant to the same time periods I've mentioned, beyond the 23rd. As @brooklynwx99 astutely noted in a post today, the NAO domain will be integral as a countervailing force to the destructive interference via the intraseasonal MJO signal during Christmas week. This is something I have been noting, too, that the flow Christmas week would go largely zonal due to a countervailing -NAO, and the blowtorch pattern would largely fade.

 

I'm not guaranteeing any winter events, but I continue to hold that the pattern increases in favorability beyond the 23rd. The putative "gradient" structure for a handful of days 24-28th, followed by Nino-esque structure incipient thereafter. 

 

The following was updated several days ago per AER, and is merely to evince the rapid coupling of the strat/trop via positive PCH:

 

Significant changes are occurring and will be occurring in the troposphere in the last 10 days of December.

 

 

Nice post, Tom. I think we agree much more than most would assume, especially regarding the changes that begin to occur in the troposphere and stratosphere during the last 10 days of December. Our main disagreement stems from the last several days of the month, particularly from 12/23 onward, which was once discussed to be a period of favorability. Changes to the hemispheric wave guide are much less favorable at this juncture and, to me, the pattern is not truly conducive for winter weather in our area. I would consider this a pattern of "slightly below average" favorability for winter weather - which is in stark contrast to some of the thoughts that were evolving and laid on the table by both yourself and myself included. This was one of the "head-fakes" referenced above in my earlier post, and I have no problem with that - I think the pattern is evolving as we thought all along, but the changes were pushed up a little too far in time. 

 

The pattern through 12/29 features a retrograding trough, which is only briefly in the Aleutians. This allows a North Pacific ridge anomaly to expand, with above normal heights moving into the Gulf of Alaska and toward the West Coast. Pacific energy should be able to undercut this into the Southwestern USA. While the NAO domain and associated modality is changing to a more favorable state, the wave breaking events as currently modeled are insufficient to create a sufficient response that would buffer the Southeast Ridge - which is supported by tropical forcing in multiple sources.  With that said, I think that's the main difference in our forecasts - I don't see the late month period being as favorable for winter weather. Could something work out? Sure, but it would be a bit of luck, IMO...and not the result of an overly favorable pattern (or at least not the one that I thought it would be for a brief period of time). 

 

Still, I digress a bit, because I think our thoughts come together again immediately after 1/1 as the pattern begins to transition toward a more favorable one - which, to me, is especially indicated from 1/7 onward...perhaps even into the end of the month.

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45 minutes ago, earthlight said:

 

Nice post, Tom. I think we agree much more than most would assume, especially regarding the changes that begin to occur in the troposphere and stratosphere during the last 10 days of December. Our main disagreement stems from the last several days of the month, particularly from 12/23 onward, which was once discussed to be a period of favorability. Changes to the hemispheric wave guide are much less favorable at this juncture and, to me, the pattern is not truly conducive for winter weather in our area. I would consider this a pattern of "slightly below average" favorability for winter weather - which is in stark contrast to some of the thoughts that were evolving and laid on the table by both yourself and myself included. This was one of the "head-fakes" referenced above in my earlier post, and I have no problem with that - I think the pattern is evolving as we thought all along, but the changes were pushed up a little too far in time. 

 

The pattern through 12/29 features a retrograding trough, which is only briefly in the Aleutians. This allows a North Pacific ridge anomaly to expand, with above normal heights moving into the Gulf of Alaska and toward the West Coast. Pacific energy should be able to undercut this into the Southwestern USA. While the NAO domain and associated modality is changing to a more favorable state, the wave breaking events as currently modeled are insufficient to create a sufficient response that would buffer the Southeast Ridge - which is supported by tropical forcing in multiple sources.  With that said, I think that's the main difference in our forecasts - I don't see the late month period being as favorable for winter weather. Could something work out? Sure, but it would be a bit of luck, IMO...and not the result of an overly favorable pattern (or at least not the one that I thought it would be for a brief period of time). 

 

Still, I digress a bit, because I think our thoughts come together again immediately after 1/1 as the pattern begins to transition toward a more favorable one - which, to me, is especially indicated from 1/7 onward...perhaps even into the end of the month.

 

 

John, I concur that we're not really all that different here, and good write up on the last page as well. The only slight curveball to me, has been a bit more destructive interference than anticipated from the MJO signal, but each successive cycle continues to lessen the influence of the intraseasonal induced SE-ridge post Christmas, as stratospherically elicited EPO/NAO concurrent blocking aids in locking confluence across southern Canada. That pattern, to me, is a recipe for energy transfers and at the very least, a potentially more wintry outcome for New England and New York State for the 27th-28th event (which is still nearly 200 hours away). Like I discussed yesterday with a couple others in the discussion thread -- the negative NAO development would be integral to any opportunity in that 27th period (there may be something light around the 24th, we'll see). Further, I expect that any blowtorch will continue to be suppressed in the post Christmas period, and I'll stick w/ my temperature evolution forecast for near normal to "cold enough" in the 23rd-31st period.

 

Either way, this SSW event appears to be a virtual lock, and it's been awhile since I've been positive about a winter; I'm more interested about prospects than I've been in 4+ years, going forward for this winter. :) 

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5 minutes ago, Isotherm said:

Either way, this SSW event appears to be a virtual lock, and it's been awhile since I've been positive about a winter; I'm more interested about prospects than I've been in 4+ years, going forward for this winter. :) 

 

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