Jump to content


Supreme Wx Expert
  • Content Count

  • Joined

  • Last visited

  • Days Won


Isotherm last won the day on November 17

Isotherm had the most liked content!

Community Reputation

10,689 Excellent

About Isotherm

  • Rank
    Veritas Vos Liberabit

Personal Information

  • Location
    Colts Neck, NJ

Recent Profile Visitors

3,905 profile views
  1. Note, the November NAO value recently released was +0.28, thus positive for November. So, any statistical, numerical correlation attempted via a negative NAO November would be null. With respect to z500, correlational data, while often salutary, does not remove confounding variables. More essential is why the November pattern evolved as it did. November NAO data [far right]: 2019 0.59 0.29 1.23 0.47 -2.62 -1.09 -1.43 -1.17 -0.16 -1.41 0.28
  2. There were more systemic issues in my opinion. The key was the poor z700/z850 low placement, too far north, and a function of the pattern. Extracted from my post on the LR thread: "The key dilemma was the relatively northerly location of the z700/850 and concomitant lows, which yield maximum felicitous forcing/lift and snow growth approximately 100 miles to the north; hence, the historical snowfall near Albany is not surprising. The boundary layer warmth was an issue for the coast, due in part to poor forcing, in concert with climatological issues [early season]; sporadic banding is insufficient to maintain the necessary evaporative cooling processes as well. A more southward tracking low would have needed stronger PNA and/or NAO inducements, which the pattern did not support."
  3. First, @MJOP8 and @Event Horizon -- thanks for the expression of concern. All is fine, relatively, just have been very busy lately. This won't be a pleonastic disquisition but here are my present ruminations on the pattern: [1] The recent storm largely behaved pursuant to expectations, favoring significance across the interior Northeast, with generally minor, 1-3" amounts along the I-95 corridor. The key dilemma was the relatively northerly location of the z700/850 and concomitant lows, which yield maximum felicitous forcing/lift and snow growth approximately 100 miles to the north; hence, the historical snowfall near Albany is not surprising. The boundary layer warmth was an issue for the coast, due in part to poor forcing, in concert with climatological issues [early season]; sporadic banding is insufficient to maintain the necessary evaporative cooling processes as well. A more southward tracking low would have needed stronger PNA and/or NAO inducements, which the pattern did not support. [2] Pursuant to conversations hitherto, between myself and others such as @Bring Back 1962-63 and @Tamara, the negative NAO episode was quite ephemeral. The intraseasonally/extratropically forced perturbation yielded a transient diminution in the NAO from November 24th-November 30th, and both the AO and NAO are now strongly positive, in accordance with the base state forcing [and the variables underpinned in my NAO formula]. [3] Recent +EAMT episode will yield the ridge spike downstream, as evinced on medium range modelling; however, the underlying predilection will be for premature amplification and thus a continued propensity for hostile storm tracks for the East Coast/I-95 corridor. The aperiodic NPAC ridge spikes were highlighted in my outlook for December [and also repeated appearances during the winter], but the angular momentum transports will continue to promote circum-global sub-tropical ridging. FT has declined materially, and overall, the torque budget should remain near parity for the medium term, as GWO circuits again through the null. [4] Latest QBO value is slightly over +5 for November, again, pursuant to my expectations that this would be a slow descent of easterly shear stress. We have now fallen behind the pace of 2004, and it is unlikely to transition easterly until the end of January or later. This will have ramifications as far as persistently countervailing attempts at protracted blocking. [5] The pattern, from a sensible weather sense, should promote cold over the Mid-west/Plains, and surges of mild air pre-storm along the East Coast. The structures overall should be generally unpropitious/hostile to coastal significant snowfalls. [6] Recrudescence of lower geopotential heights near Alaska is expected following this EAMT induced ridge spike. Concomitantly, the NAM/NAO should remain generally positive throughout December. Hadley and walker cell behavior continues to operate in accordance with my initial thoughts several weeks ago. [7] Note, that the MJO was a largely minor component of my outlook, and the fact that it may be stationary over the IO for awhile does not impact the likelihood that December finishes warmer than normal. I still think the departure estimates set forth are reasonable. [8] Eventually, the MJO will regain coherency, as it propagates eastward [late December]. [9] Current ECMWF guidance indicates a fairly rapidly intensification of the stratospheric polar vortex in the medium term. Whether that happens or not --- is not dispositive as it pertains to the tropospheric structures. Summary: First, as a general caveat, to ensure to readers that I am not engaging in the very confirmation bias against which I impugn, here is what could enable a faster transition into sustained winter pattern than I delineated in the outlook: Since it is unlikely to receive assistance from the QBO in a material way for awhile in my view, the earlier assistance must have provenance in the tropical troposphere. A very potent MJO circulation through 6-7 in late December, ideally in concert with highly anomalous EAMT, would engender a significant momentum induction and further elicit rossby wave propagation poleward. This would, a priori, disrupt momentum budgets enough, in tandem with material SPV disruption, to loosen the effects of the stronger than average tropospheric vortex. However, the likelihood of that occurring is currently low, and the present base state momentum transports and forcing backdrop should continue to promote a +AO/NAO in the means. Spasmodic NPAC ridge spikes should deliver bouts of arctic/polar air, but unfortunately, the storm track should continue to be unfavorable for coastal areas. And I do not see any indication of this tendency reversing for the foreseeable future. As seen with the recent storm, I believe this tendency will persist, re: favoring interior Northeast. All in all, everything appears to be on track, at least from the standpoints of myself and a few others who I know accord with these thoughts. I realize this is an unpopular interpretation, but it is my objective interpretation of the pattern, and no one can unequivocally claim they know for certain what will transpire at this time. Below: QBO Data --> 2019 9.02 9.25 11.82 13.36 14.59 14.36 10.96 9.97 8.25 7.27 5.07
  4. Yes. This synoptic evolution has occured many a time heretofore, and almost always doesn't work out in mid winter, let alone the beginning of December, at the coast. If the primary maintains circulation too long, the mid levels are typically unrecoverable until very late in the game. Even after the energy transfer occurs at the sfc level, this is the type of situation wherein one needs to worry about z700 and z850 lows still maintaining a circulation with the primary. By the time the mid levels have recovered via a rapidly intensifying secondary, the next step is cooling the boundary layer, even more difficult given the time of year, and the fact that the ULL is rather quasi detached from the PJ, rendering cold air source diminutive. All in all, anything more than minor accum at the coast is a long shot in my view.
  5. Other proxies of northern hemispheric, vortex status indicate the predilection for lower-geopotential heights in the Arctic domain, but particularly the NAO domain in the means, as delineated in my outlook. November 2019 ozone data evinces generally lower concentrations near/over Greenland to the north of Europe. When juxtaposed with the mean November climatological ozone, it has generally been less extensive in those domains. Moreover, the polar vortex area is now running well above normal, circa 30 million km^2. Expansion in vortex area is generally a precursor / presages tropospheric NAM significant incline. Again, as Don alluded to above, while aesthetically pleasing stratospheric maps continue to be circulated, it's integral to examine exactly what is transpiring in the troposphere as far as the veridical data. SPV intensity diminution doesn't always correlate directly to tropospheric vortex status.
  6. @rb924119, I may not have been clear with the intent of my post -- that composite was merely to illustrate a corroboration of Don's point that +EPO/PNA regimes still tend to be warmer than normal in the East. 1992 is not an analog of mine, and the z500 depicted in that composite is not what I'm anticipating the evolution to look like.
  7. Precisely, Don. I was going to make a post to this effect earlier today. Historically speaking, +AO/NAO/EPO/PNA regimes still tend to feature warmer than normal conditions in the E US. One example of which was Jan-Feb 1992. That's of course operating under the assumption that the PNA is predominately positive, which is controvertible at this juncture.
  8. Approximately a 250 mile WNW adjustment in z500 fields due in large part to slower propagation of the s/w initially, which permits downstream +GPH over Greenland to depart slightly more expeditiously. This is a correction to cognize going forward.
  9. Right, agreed - and the occlusion is really a function of the more macro-scale pattern structure to force premature intensification over the US Plain States. Trough amplification in the W US will tend to intensify and occlude systems well before they reach the East Coast -- so even if a decent block is in place downstream, it merely forces the remaining, weak low underneath [devoid of dynamics]. While the more felicitous outcomes can't be ruled out, I think there's more countermanding than supporting an outcome of > minor accum at the coast.
  10. Early for more definitive answers, but cold air damming is typically more resilient in interior PA, which will aid matters on the front-end, at minimum. The synoptic driven snowfall would be a function of mid level low paths.
  11. @rb924119 - I don't disagree w/ those concerns, and your concerns are further evinced on the ECMWF. The problem w/ an already occluded system traversing ewd is that advective processes are diminished or nearly shut off, as you noted in your post. The minor front-end accumulating is likely the best opportunity for frozen at the coast with this, IMO. The orientation of the 50-50 and trough in NE Canada was more consolidated as well, and thus farther north, so the block does not press equatorward as much here. Overall, I think the ECMWF is a fairly meteorologically reasonable outcome.
  12. @rb924119. My thoughts tend to accord with you on this - good points. An additional important point is as follows. The most significant disparity when juxtaposing the EPS and the GFS valid the same times is the orientation of the upstream ridge axis. The GFS, to me, is a thread the needle type evolution for the coast, as it keeps the upstream ridge farther east but more importantly positively tilted, thereby forcing a more positively tilted s/w, which becomes neutral at just the right moment near the Mid-Atlantic coast. The upstream positively tilted ridge also forced the more southerly track, in contrast to the EPS. Furthermore, while there is a precursor 50/50, the block action center is in the Atlantic with extension into eastern Greenland, so a bit unorthodox, though not totally unfavorable. As you alluded to, the initial northerly path through the N plains, historically, renders it quite difficult to end up with the result the GFS depicts, which actually evinces an east-south-easterly path of the z500 low from the lower Lakes to the coast [yet another depiction with low probability]. So to me, there are a couple of variables depicted by the GFS that are more likely than not to be erroneous. Beyond which, the precursor airmass is poor too. While I can see how the coast might pull off a light accumulation here, I think the current GFS run is the most favorable depiction we will see in this tracking period. I think the synoptics strongly favor an interior Northeast wintry weather opportunity. We'll see.
  13. The weeklies were generally positive AO, NAO, neutral to positive EPO, and neutral to negative PNA throughout the period. So, I'm not sure I see improvement other than potentially being a bit more ambiguous at certain intervals. In viewing model z500 data post circa Day 7-8, I think one of the most integral features to keep in mind is the error bar depiction. For example, the EPS EPO long term prognostication has error bars spanning over 10 standard deviations; that's effectively a "no clue" type of forecast. Note the expeditious increase in those error bars beyond day 5, redolent of the extreme uncertainty in model data. I continue to be skeptical of any progged persistently favorably -EPO/+PNA couplet given the present backdrop of forcing and AAM trends.
  • Create New...