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Interitus

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  1. Interitus
    Here is their latest technical memorandum from October 2018 - "Evaluation of ECMWF forecasts, including the 2018 upgrade" https://www.ecmwf.int/sites/default/files/elibrary/2018/18746-evaluation-ecmwf-forecasts-including-2018-upgrade.pdf 50 hPa verification to day 5 only.
  2. Interitus
    There you go, CET anomalies for October 0.0, November +1.8, December +2.2 - Nov + Dec in particular good predictions matching the statistical analysis from a 5/6 month lead time. December came in at 6.9°C, another 6+ month making it 6 from the 13 coolest May/June SSTs in the area in the charts above, with 12/13 milder than average and only 2009 cooler.
  3. Interitus
    Wasn't sure where to post this, but there has been a lot of criticism of Chris Fawkes mild ramping, however on News 24 he just said -
  4. Interitus
    The 06z GFS para has really gone off on one, here are u1060 of the last 3 runs, the 06z has it's lowest of it's runs I've seen so far, -15.5 at T384 - The 850 mb zonal wind at 60°N is forecast to fall to -8.0 m/s at one point - this is lower than anything in the NCEP R2 reanalysis from Jan 1979 - Dec 2014 (struggling for more data with the government shutdown). The lowest in that period was -7.9 m/s from 09/02/85 - yes there was a notable SSW beforehand but over a month earlier. Interesting how the AO doesn't match this zonal wind especially well - the CPC AO value was -3.44 (NAO -1.06) whilst three weeks earlier on 19/01/85 the record lowest AO of -6.23 was recorded (NAO -1.64) with a 850 60°N wind of -6 m/s. Meantime, the reduction of wave propagation by the easterly flow allows the 1 mb wind to get back up to 40 m/s, quite some wind shear as it only reaches 4.5 m/s at 3 mb (Damn NaNs spoil plot!)
  5. Interitus
    GFS op, FV3 and NASA GEOS all go for reversal from Jan 1st midday onwards - these are 3 hourly instantaneous values, in each case if averaged for a daily value for the reanalyses then the reversal is from Jan 2nd.
  6. Interitus
    As posted above it looks like today's 00z. Regarding the longevity of the reversal, after 3 GFS op runs having a reversal at T384, the last 4 have all seen westerly winds return -
  7. Interitus
    The vortex ends up splitting but at time of reversal it is a displacement, it's not unusual for this to happen. There is some significance in the distinction because displacement would normally be seen to imply wave 1 forcing, as in this case, with a split being wave 2. Wave 1 tilts more westward with height which may be why any coupling from the 10mb split to our west looks like sending a northerly plunge to our east, compared to a wave 2 split which would have a more direct imprint on the surface.
  8. Interitus
    -10.6 m/s - think this is the strongest so far for this model.
  9. Interitus
    The ensemble mean minimum of the last run was -11.3 m/s so no, not really different from op now. That's a fair question and some researchers have used it for their SSW definition, but just using one pressure level and latitude whatever they are helps give some consistency for comparison purposes
  10. Interitus
    At 65°N - the GFS forecasts since 23/12 18z (last without SSW) for 60°N have been -3.4, -0.4, -3.6, -14.3, -13.4, -5.9, -9.2, -11.3, -6.5, -8.1, -11.4, -13.5, -10, -10.9, -10.7, -11.3, -11.9 and -11.2 m/s (up to today's 06z) Notably stronger than the FV3 which since 24/18 18z (last seen without SSW - missed a few runs) - -2.6, -, -, -6.1, -3.8, -4.3, -, -6.3, -9.5, -7.9, -7.7, -7.6, -5.4, -7.1 (to 06z today)
  11. Interitus
    Ok, an illustration. The last couple of GFS runs have toyed with a double dip reversal at 10 mb, here are the forecast zonal winds at 10, 100 and 500 mb from today's 06z - The first strong reversal has virtually no effect at 100 mb, and the 500 mb level shows typical variability. Looking at the geopotential anomalies for the maximum reversal on Jan 4th shows that there are some similar features but they aren't particularly well aligned at each level - At the second dip though there is a following reduction in zonal wind at 100 and 500 mb as the geopotential anomalies are more closely aligned -
  12. Interitus
    It is simplified - the need for westerly winds is for the vertical propagation of planetary waves (and then not too strong which limits propagation also as seen during the middle of the SH winter). The mean easterly wind field at 10 hPa for example doesn't tend to descend en masse through the strat into the troposphere at 60°N. At 150 hPa the mean zonal wind very rarely becomes easterly during winter, and then only marginally - In the MERRA data it has done so in the 45 days following SSW on 3 occasions and on one of those it had already been easterly in the days preceding the SSW. The zonal flow anomalies represent perturbation of mean flow which tends to be regionalised i.e. through the geopotential height field of the waves and associated geostrophic wind, and when the perturbations become well aligned then the zonal wind anomalies can appear to descend, but also ascend of course.
  13. Interitus
    This morning's GFS Op has a deeper reversal starting a full 24 hours before the parallel FV3, a noticeable difference at 4-5 days but both ending at day 10 -
  14. Interitus
    Yes, it was high level blocking from a large anticyclonic wave break to the north of the UK which caused the cold blast and was implicated in the ensuing SSW - as posted upthread https://www.netweather.tv/forum/topic/88772-stratosphere-temperature-watch-201718/?page=45&tab=comments#comment-3918352
  15. Interitus
    Oh no, there it is look
  16. Interitus
    That's a sun dog - https://en.wikipedia.org/wiki/Sun_dog
  17. Interitus
    Just a quick comment, there has been a lot of criticism of the GFS but note the FV3 has been showing quite similar forecasts. The ECM itself has been solid but has retreated in time a few days. It would be interesting to compare models if they ran with exactly the same initial data assimilation. Regarding the heat flux, little surprised that Amy focuses on the 100 hPa flux quite so much - yes it has been shown for a number of years to be related but is it causative? - one of her collaborators on the SSW compendium, Jeremiah Sjoberg has in a couple of papers questioned the significance of this. Also nearly everybody looks at the 10 hPa temperatures / heat flux - it is a matter of simple observation from the data to see that reversals at 10 mb are actually closer linked to 30 mb temperatures oddly enough.
  18. Interitus
    Differential planetary wave 1 forcing causing a westward tilt of the vortex with height creating a baroclinic region with descending air resulting in adiabatic warming (closer observation of the charts will also show that the area of lowest temperatures become cooler at the same time where air is ascending).
  19. Interitus
    No
  20. Interitus
    Missed grabbing the data for this run unfortunately but subsequent run minimum u1060 were -2.1 and +4.6 m/s with the vortex reforming to +12 and +24.2 m/s by t384.
  21. Interitus
    See also Regarding the FV3, the 06z minimum was +1.9 m/s for 3/1 0z but was +7 m/s by the end as the split vortices retreated northwards slightly. It was like a stronger split version of the 00z where the min was 7.1 m/s and 18.9 m/s at the end as the vortex reformed and slightly displaced from the pole and back to square one.
  22. Interitus
    GFS 12z has a similar looking split with a reversal down to -7.9 m/s - but 1 hPa is very different -
  23. Interitus
    The 06z fv3gfs had a min zonal wind of +0.1 m/s but it was sporting a convincing looking split - Prompted by a tweet, here it is at 1 hPa and 0.4 hPa - For the lower strat the main vortex heads to Eurasia, but upper strat wanders to N. America.
  24. Interitus
    Nobody knows lol
  25. Interitus
    1. There was no misquotation. 'Cherry-picking' is the selection of pertinent points which undermines the main tenet. Anything out of context or misunderstood is because of your inability to post with clarity and accuracy in over 1000 words! Apologies in advance for abbreviating the above quote, but the forum will be thankful. 2. I do not dismiss this paper, though note there are issues with the model used (WACCM) which is investigated in numerous papers. Their own control charts show some differences from reanalysis climatology which may or may not be significant. FWIW I linked to the paper on April 6th on this thread which I believe is prior to it's appearance on the other board - https://www.netweather.tv/forum/topic/88772-stratosphere-temperature-watch-201718/?page=35&tab=comments#comment-3846840 3. Good, this is the jist of the mechanism, yet from the previous two posts this does not appear to be your understanding - As explained, this is not how it works. Further, the paper looks at seasonal integrations of zonal EP flux and refractive index and does not describe locations or timing of forcing. For instance the current wave 1 forcing involves a fairly typical north Atlantic/European pattern of blocking episodes. 4. Any evidence of this? 5. Once again, your overall point appears to be at odds with the takeaway from the paper. 6. Lack of clarity necessitated some assumptions to be made, but given the quote - it was not unreasonable to make a comparison of the pre- and post-SSW periods given the remarkable nature of that winter. Regarding the Russian HP, there was no retrogression of this following the 2010 SSW, Arctic HP developed in situ.
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