Isotherm

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About Isotherm

  • Birthday 09/24/1990

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  1. 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.
  2. 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.
  3. My brief thoughts w/ attendant illustration. The difference in outcomes b/t the 00z ECMWF and yesterday's 12z run (and by extension, other guidance), is largely predicated on the behavior of the short wave trailing the target short wave. Yesterday's solutions maintained significant magnitude/coherency w/ the trailing short, thereby keeping the front-running target short wave deamplified, and thus unlikely to "connect" with the Canadian PV lobe. The off-West Coast s/w trough is a key ingredient as to raising the putative ceiling on the downstream outcomes, as it provides the wave spacing to ensure deamplification until the "right" time, additional ridging in the Rockies, which aids in phasing and amplification at the most propitious times. The new set of solutions would still yield a winter event in the Northeast, but a lower-ceiling event. Which solution has more credence? The answer at this point is stochastic and effectively anyone's conjecture. The macro-scale features, inclusive of a westward retrograding, slowly degrading blocking structure, concomitant 50/50 positioned vortex, set condition precedents which significiantly increase the probability of wintry weather in the Northeast, as has been targeted for the month. The question as to the specifics of the actual system will be a function of the behavior of the incoming Pacific short waves. For snow enthusiasts, the solution to desire is a return to a larger trailing short wave which deamplifies the front-running initially, obviating early phasing. Full-latitude Western trough solutions would yield lower ceiling, energy transfer/SWFE type outcomes.
  4. The second dip and z10 split w/ mean zonal wind reversal for several days+, if it verifies, would attain the definition I described for major. As far as the real-world impact: it would aid in prolonging the +GP action center near Greenland, countervailing any increased SE-ridging resistance via the almost inevitable retraction of the upstream ridge by the end of January. The conducive north atlantic paradigm would thus maintain favorability in the Northeast/Mid-Atlantic beyond an ephemeral/short term window and potentially extend possibilities through the end of January. As it stands, these stratospheric outcomes do not alter my overarching thinking that mid-late January will provide heightened potential for snowfall in the Eastern US. Details remain indeterminate given the highly stochastic nature of snowfall, but I do not see any reason to abandon the notion that January will eventually produce wintry weather, to varying degrees depending upon locations.
  5. Ray, indeed and I hear you re the internal conflict going forward. Certainly after the past few benign winters, it would be nice to have a longer wintry period. February's more canonical Nina z500 structure should tend to favor the northern and potentially even central New England at times for snowfall. So I don't think your area has as much concern to maximize the upcoming 2-3 weeks of potential (though the coming period should offer best opportunities).
  6. @frd, see my outlook thread for continued updates (below). As emphasized awhile ago, I would repeat that stratospheric warming events are a reaction/product of tropospheric forcing, and the feedback outcome is dependent upon tropospheric receptivity, more integral than whether a subjective major definition is reached or not. In this case, the troposphere is well coupled, so it will promote at least a few weeks of blocking before disintegration. I still believe the coming period (through the end of Jan) provides heightened opportunity for snowfall in the E US. An important factor I'd monitor, esp. for the Mid-Atlantic and SE, is PNA tendencies upstream. It will be positive in the means, but the retraction toward the EPO domain/W PNA should occur later month, there will be more resistance in the far SE US via height rises.
  7. @40/70 Benchmark, the definition of sudden stratospheric warmings has been elusive, subjective and often capricious throughout the decades (see this paper, at least 9 different definitions): https://www.arl.noaa.gov/documents/JournalPDFs/Butler_et_al_2015_bams-d-13-00173.1.pdf You are correct that the common WMO definition of 'major' will be reached [mean zonal wind reversal to easterly at 10 hpa / 60N]. Other definitions, one of which I prefer for major ascertainment, is 60N/10hpa mean zonal wind reversal to easterly for a minimum of 5 consecutive days (see Simon Lee's blog: https://simonleewx.com/2019/01/24/the-january-2009-ssw/). I've been monitoring this event, and it seems we may have an interruption in the zonal wind reversal in the coming 1-2 days [see ECMWF below]: [note that the 10 hpa/60N zonal wind will probably hit or exceed 0 in the coming 48 hours, before slipping back easterly again]. https://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/ts.php?plot=fluxes&alert=1&lng=eng&hem=nh So, we'll have to watch that interruption. But regardless, the technical, subjective definitions don't matter much to me, as what is more integral is the tropospheric receptivity, downwelling potential, and resultant tropospheric response. The existing z30 westerly stress from the +QBO will tend to promote a more robust post-SSW recovery in my view, as well. @LibertyBell, I believe there's high probability of NYC finishing in the upper portion of my snowfall range (low/mid 20s) with some potential for higher/toward average, depending upon the outcomes of the next few weeks (which I think provide the best opportunities for snowfall). In March, wavelengths are much shorter, and thus typically unfavorable winter patterns can become more serviceable - so I wouldn't be surprised if we had an event in March. I would still lean toward around 30" total or lower for the seasonal total. We shall see how it evolves.
  8. Mid-winter checkpoint w/ my updated thoughts here: Winter progressing in accordance w/ outlook thus far. Everything remains on track w/ respect to colder and more active January; most conducive multi-week period forthcoming.
  9. Mid-Winter Checkpoint: December = Thus far, the winter is progressing mostly in accordance with expectations. December finished +1.7 in NYC (within the range provided for in the outlook, +1.5 to +2.5). Most of the Northeast/Mid-Atlantic finished similarly. The core of warmth centered over the Rockies/NW Plains as anticipated, with a cool zone near Florida. The +PNA verified as expected, along with the +EPO. The NAO for December was merely slightly negative. The principal error was the AO domain, which finished -1.7 (negative); this aided in permitting the significant snowfall for the NE corridor. January = the forecasted mean +PNA/-NAO looks to verify. I see no reason to depart from the temp. anomalies forecasted. The highest probability for medium+ impact events of the winter exists in the coming multi-week period. The occurrence of the SSW is immaterial to the overall forecast, and a byproduct of the antecedent tropospheric forcing. This will likely be a significant, not major, SSW, and a non-vortex destruction event. This, too, has implications. The EPO may briefly move negative in the latter part of the month. The most conducive period for the SE US/Mid-Atlantic will likely be 12th-20th. Beyond the 20th, more resistance should develop in the far SE US via PNA diminution, implying the target zone may shift northward along the East Coast. The details are indeterminate and will be predicated upon wave/timing/propagation. Therefore, January 10th-31st should provide for greatly enhanced probabilities of wintry weather. February = I expect a rapid disintegration of the coming multi-week pattern, with the genesis of +NAO/AO in concert w/ -PNA/Nina-esque Pacific structure. The delay of any negative PNA phase until February was/still is expected from my standpoint. It's possible the PNA may beginning transitioning as early as very late January. Sub-seasonal forcing should constructive interfere w/ low frequency forcing near the Maritime Continent, retracting the jet and forcing a more canonical Aleutian High/NW US trough paradigm. The stratospheric vortex should expeditiously redevelop to at least near average intensities by early February, and subsequently couple rapidly. Thus, I continue to think February will favor locations further north [N/C New England] for meaningful snowfall.
  10. As you know, examination of one variable in a vacuum is typically complex given there are always/invariably numerous constructively and destructively interfering forcing agents. That said, all else being held equal, generally +EAMT events are a net positive as far as enhanced favorability for downstream z500 patterns in the E US. The overall momentum budget right now is one of near parity to slightly above neutral, so we do not have a situation akin to 2016 w/ extremely high momentum precluding all ridge formations upstream (note, even in Jan 2016's very high momentum, the PNA was positive). Furthermore, the subseasonal forcing [e.g., MJO incoherence] also argues against prolonged -PNA. The mean state forcing thus far has promoted a neutral to positive PNA (which I expected until Feb) with a positive EPO. I would err toward model guidance improving on the PNA as we move past the New Year. As to your other inquiry - the location of the daughter vortices post split (or vortex post displacement) would govern location of coldest anomalies, but there are also gradations of SSW events -- some which briefly reverse z10/60N zonal winds, and those (more rare) which destroy the vortex. The latter tend to be better at creating their own regimes for about a month, sometimes even 40-45 days. But yes, hypothetically, sufficiently robust AO/NAO domain blocking would be able to countermand a much less conducive Pacific. Right now, modelling depicts the blocking action center slightly too far south on the Atlantic side to countermand. I think you'll find some of these z500 depictions changing somewhat over the next several days. Model chaos is further heightened in times of significant vortex assault as well.
  11. @frd, not sure if you have been reading my updates in my winter outlook thread, but my thoughts remain the same as those expressed there (and not much disparate then initially w/ January). January still appears to offer the most conducive wintry potential in the Northeast/Mid-Atlantic of the winter, in my view (my initial thoughts were normal to snowier than normal and slightly colder than normal - I don't see compelling reason to abandon this). Those thoughts were, and continue to be expressed irrespective of the outcome of any SSW technical event, a phenomenon which receives too much focus in my view. Speaking generally in the meteorological community, I think sometimes there is a propensity for expectations to be set too high, and when modelling doesn't accord with those overly heightened expectations, disappointment ensues (E.g., it was never wise to set the bar at "epic" January - while that outcome can happen - it's still somewhat low probability). The current contemporaneous wave-1 hit on the SPV + multiple robust Siberian high descents-->+EAMT--> jet extension should be more than sufficient to tilt the NAO/AO negative for much of January. As the initial jet extensions begin to relax post the medium range, I anticipate amelioration in the PNA domain beyond the 5th or so of January. The "good" news is that the troposphere has evidenced receptivity to stratospheric alterations this winter, meaning, coupling and feedback strat-trop is present, so even if a technical SSW occurs (again, not needed to reach my expectations for a decent January), it will tend to feedback and promote/maintain tropospheric blocking. Overall, I do not see substantial reason to panic from a winter enthusiast's perspective for the month of January in particular.
  12. Full snow cover maintained here through Christmas Eve. Will be gone later today, but a solid period for early winter (16th-24th).
  13. @griteater, thanks for your reply. Regarding the evolution: the amount of momentum which ultimately will be added to the system via the torque processes should not be superfluous/overpowering to the extent that all semblance of +GP heights are extirpated in W North America. January 2016 is an exemplar of what one might consider the epitome of an extreme +AAM regime, complete with anomalously coherent GWO circuits. Even in that paradigm, the PNA domain was positive (actually, strongly so), and even the EPO neutral to slightly negative, w/ a GOAK trough immediately west of the W North American Coast. Of course the +ve momentum regime extant is much less anomalous, and the z500 is multifactorial, but it's an example of what can happen. I think modelling (e.g., EPS depiction for early January) should eventually morph into a depiction wherein we see positive geopotential heights in the PNA domain, and close to neutral or positive heights extending northward on the W Coast of North America. We should see the lower GP heights retrograde somewhat, but I'm not yet sold on a massive -EPO in conjunction with a +PNA/-NAO. My original thinking for January was +PNA/-NAO and EPO closer to neutral or pos., as preseason factors did not appear favorable for prolonged -EPO. One factor to aid the EPO heights, possibly, is stratospheric alterations - however - will need to monitor. So, in short, I think we'll see data back off somewhat on driving the Pacific jet through W NA, and eventually by early January, begin to see the +PNA reform with at least near neutral EPO. That pattern along with the Atlantic changes should be sufficient to make the pattern interesting for many. It's far out, but the end of the EPS seems to begin these changes to which I refer in the PNA domain.
  14. Additionally (supplement to your good points here) regarding the United States "average" snowfall, left unsaid is whether that average is derived via a population weighted calculation. The raw average may be somewhat deceptive. A comparison of moderately-highly populated cities rather than an incorporation of all towns in the entire United States would likely yield NYC well above the 50th percentile. Locally, I've calculated a 31.0" average snowfall for 1990-2020. It's been an excellent 20 year period in interior Monmouth County. Like portions of central LI, here, we tend to benefit from late developing Miller Bs, further mesoscale enhancement from the Sandy Hook Bay on NELY flow during winter storms, and proximity to the Atlantic Ocean, but not close enough to materially lower the snowfall average. Hence Monmouth County features a fairly interesting climate, and frequently steep snowfall gradient NW-SE/NNW/SSE in numerous storms. There's about a 9-10" differential in average snowfall across the county; 30-31" in the N/W and close to 20-21" in Manasquan. (My website here: https://www.lightinthestorm.com/nj-snowfall ). Newark Airport also has a 31.1" 30-year running average 1990-2020 per latest data. My median 30-year snowfall is 29.0", which is not far from the mean, and it suggests the frequency of above and below normal snowfall winters aren't too dissimilar. Contrast to locations farther south (for example, DCA) wherein snowfall medians are quite a bit lower than means. Also, possibly axiomatic, but the average for a given place is deceptive in how that average arrives. Most of the Mid-west outside of the Lakes region derives those 25-35" averages via frequently low end snowfall events (as you know). I think the region 39N-41N on the eastern side of North America has some of the most significant and fascinating variability in winter-time weather.
  15. My brief thoughts on the coming multi-week period (reposted in my outlook thread as well main board); rapidly increased favorability should initiate at the tail end of December. "The GFS based guidance is likely rushing the genesis/realization of the auspicious pattern; the ECMWF/EPS are more congruous with the physical drivers. z50 geopotential heights favor a positive NAO from now through circa Dec 28th; as the Canadian 'warming' occurs in the stratosphere and z50 restructures w/ a wave-2 paradigm, geopotential heights will begin to respond within a few days over the NAO domain, with diminution there in the final 1-2 days of December/beyond. The classical Siberian high descent initiates December 26th +/- a couple of days which will induce a +EAMT and jet extension event at the very end of December, and thus ameliorating the downstream Pacific/PNA/EPO domain pattern by the early days of January. Therefore, the December 28th-January 2nd period should feature expeditious amelioration of the hemispheric pattern, first, with improvement in the NAO domain at the very end of December, then, shortly followed by the Pacific. If there is a storm threat of significance in late December, it would likely favor the interior Northeast/New England, in my view, with a threat for I-95 beyond that time-frame (sometime in the first 10 days of January), but we'll see how it evolves."