Een verrukkelijk stukje proza van onze vriend Judah Cohen, vanaf de andere kant van de plas. Een sterke winterverwachting, toen ik hem drie maanden geleden zag, dacht ik: wat een zooitje. Maar in de praktijk scoort hij wonderwel goed, gezien de complexiteit van deze winter. Een ding ontbreekt in zijn analyse, dat is de positieve IOD. In plaats daarvan besteedt hij aandacht aan de sterk negatieve PDO, een driver die ik over het hoofd gezien.
Treffend ook zijn sentiment over deze winter, die in de VS net zo teleurstellend is verlopen als hier in Europa. Hij is er wel zo'n beetje klaar mee, ik ook. Daarom kost het hem (en ook mij) moeite aandacht te besteden aan de SSW die ophanden is. Symptomatisch voor zijn sentiment is de scepsis over de verwachte hogedruk boven Groenland, die het al zo lang af heeft laten weten deze winter. Een van de weinige missers in zijn winterverwachting ook, druk en dus ook de temperaturen waren lager dan normaal in die cruciale regio.
O ja, mooi die metafoor van de Titanic.
It is my impression that in the fall the consensus was how challenging forecasting the upcoming winter would be given so many different strong boundary forcings, the incredible warmth in the atmosphere but especially in the ocean. We also had a competing strong El Niño coupled with a strong negative Pacific Decadal Oscillation (PDO). And the weak Arctic boundary forcings compounded the challenge at least for me. Of course, during the winter, it is my impression at least we had a hyperactive polar vortex (PV) quickly pinballing from one disruption to the next creating crisscrossing currents and interring PV influences and many weather extremes. We ended the winter with a wild February with the models failing spectacularly. Longer range forecasting is difficult for human and model alike but this February was still a noteworthy for the flameout from the weather models.
I can’t claim to be objective and unbiased but that is a very good seasonal forecast (humbly understated) and will only look better when compared with the dynamical model forecast from the leading North American and European forecast centers included in the late November blog. Enough for now and I will discuss more once the final numbers are known.
I have to admit that emotionally I am done with winter and ready to move on to summer (a sentiment I shared last week as well). And as I prefaced with a tweet, what I right next may be best described with the metaphor as “rearranging deck chairs on the Titanic.” Across the NH there was winter to be found and from Figure i, it is easy to pick out where but for Europe outside of Scandinavia and around the Baltics and the Eastern US, winter made at most a cameo appearance so why expect anything differently now that climatological spring begins at the end of the week?
The annoying or nagging fact is that a very large PV disruption is ongoing and the most closely associated tropospheric response to a sudden stratospheric warming or SSW (the zonal mean zonal wind at 60°N and 10hpa did reverse from westerly to easterly/from positive to negative) is Greenland blocking. In the latest North Atlantic seasonal polar cap geopotential height anomalies (PCHs), Greenland blocking is strongly suggested, (see Figure ii) consistent with most weather model forecasts. But seeing is believeing.
https://www.aer.com/science-research/cl ... cillation/
Judah Cohen prog.png
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