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Vorticity0123

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Vorticity0123 last won the day on December 22 2015

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    Stratospheric meteorology and stratosphere-troposphere connections, interannual variability, tropical cyclones, operational meteorology

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  1. To get a quick idea of the 3D-structure evolution of the stratospheric polar vortex, I like to use the 'ellipse profile' plots found here. The GFS-forecast for the upcoming warming episode nicely show how the polar vortex might behave both horizontally and vertically during the next 10-15 days. Note that the plots are from Sunday 20-12, as the plots from 21-12 were not yet available. At first (situation 20-12), you can see the polar vortex is nicely structured - it is both vertically well-stacked and circular in shape. GFS ellipse Polar Vortex profiles from the run of 20-12, va
  2. At day 12, the GFS is showing the polar vortex to be displaced towards Eurasia. At the same time, this brings temperatures of around -80 degrees to Western and Northwestern Europe at 10 hPa (about 30 km altitude). From what I have read these conditions are favorable for Polar Stratospheric Clouds, so this may be something to watch for in just under two weeks if the GFS turns out to be accurately forecasting the cold stratospheric temperatures. The area highlighted shows the cold spot that could be favorable for the formation of Polar Stratospheric Clouds. Source: stratobserve.com
  3. Interesting and cool animation - it nicely shows how the troposphere in this case is forcing the polar vortex aloft to be 'squeezed' by effects induced by two tropospheric ridges. The animation also made me wonder - would it be insightful to create a similar animation of the polar vortex in terms of temperature? I would expect that if you visualize the edges of the polar vortex via temperature, you should be able to see the ascent and descent of warmings that propagate from the troposphere/upper stratosphere to the mid-stratosphere or vice-versa. In other words - it could give more insigh
  4. Not sure whether this is the right topic for this - but what has been interesting lately, is the large amout of small-scale cut-off features that are located in/passing through the subtropics. These cut-off features are evident as small southward-extending 'drops' of low heights (green colours; equivalent to upper-level troughs). For this post I will mainly focus on the Atlantic sector, because that alone is already pretty interesting to consider In the Atlantic, the cut-off lows have already been present from August onwards. These cut-off lows have been the breeding ground for several (
  5. Quite interesting to see the looping motion within Matthew evolving. It could indeed be the onset of a northward turn. Would it also mean that the track of Matthew would turn out to be further to the east given the eastward looping of the eye? What does appear new to me is the spiral banding structure to the west of Matthew. This could indicate that shear is lessening and outflow is developing on that side of the circulation. At least it appears that Matthew is becoming healthier again. Whether this is a prelude to more intensification remains to be seen though, especially since sub
  6. Things can change pretty quickly; the ECMWF does develop the wave again in the 00Z run. Though it does so quite a bit later compared to the GFS. It definitely appears that we will be watching a potentially interesting storm in the Caribbean in the 5-10 day range. Things can change quickly, still, but the model support appears quite large. ECMWF run 24-09 00Z 5 days out (top) and 10 days out (below). The 00Z ECMWF runs shows the system just west of the Lesser Antilles as a weak low pressure area, and as a potent hurricane just east of Nicaragua 5 days later. Of course it
  7. Much appears to be dependent on the intensity of Fiona, with a stronger system most likely ending up further north. With respect to intensity, it seems that Fiona will be having to go through a 'wall' of dry air on its west-northwestward track. As long as wind shear remains low, this air will penetrate the storm only occasionally. However, once wind shear kicks in (and according to the NHC that will happen in a couple of days) this dry air will be more easily entrained into the core of Fiona. Saharan Air Layer analysis by CIMSS. Yes, it appears that the storm is able to sust
  8. The 2016 Atlantic hurricane season has just given birth to a new system, being tropical depression Six. The tropical cyclone is a typical Cape Verde system, developing from a tropical wave that left the coast of Africa a few days ago. Satellite imagery shows TD Six has a well-organized satellite appearance, with a comma-like cloud pattern evident. IR satellite image from TD Six taken around 06 UTC 17-08. Courtesy: Colostate University hurricane page Such a cloud pattern is rather associated with a strengthening tropical storm than a tropical depression, so it would not be surpr
  9. Still much chopping and changing to be expected, since this morning's ECMWF run (14-08 00Z) shows two different systems developing in a significant tropical system, The first one peaks in about 5 days: ECMWF surface pressure and anomalies (colours) 00Z 14-08 T+120 This system, probably only being a weak tropical depression at best, is located in the East Tropical Atlantic just to the west of the Cape Verde islands. In subsequent timeframes the system weakens while travelling northwestward. The second, more vigorous system, 'peaks' in 240 hours (10 days): ECMWF s
  10. A WINDSAT scan of this morning (07:19 UTC) showed that 97L did not have a closed surface circulation yet. There was a sharp wind shift visible around the black line indicated in the figure below. Yet the wind shift was elongated on a NE-SW axis, and no true westerlies could be observed. WINDSAT image of 97L at 07:19 UTC 01-08 Yet given the convection sustaining itself over the system for quite some time now, it would not surprise me if a surface circulation would have closed off and become less elongated. There is no data available as of writing, but one could argue that
  11. After a lull of nearly one month of tropical cyclone activity, one could argue that we are on the verge of obtaining the first tropical cyclone of the 2016 North Indian tropical cyclone season. The cyclone is currently just off the east coast of India. However, owing to its large size and effects of easterly shear, it is causing a lot of precipitation over India. Visible satellite animation of invest 01B From this visible image, one would conclude that this is clearly a tropical cyclone given the rotation noted at all levels and the abundance of convection. The effects of shear
  12. After an underwhelming end of April in terms of temperature (which I have more throughly described here) May seems to start off quite differently, as alluded to by Captain Shortwave above. What's interesting though, is the confidence which is associated with the pattern change - like also occurred in the end of April with the cold being forseen many days before. Are we again heading towards a blocked scenario? Let's find out! Unsettled UK Before we get there, lets take a look at the actual situation. And that situation looks very unsettled for the UK! ECMWF surface pressur
  13. A wintry spell in late April - not exactly what one would expect! Many places in Western Europe have experienced wintry temperatures and even snowfall, for instance in the Netherlands people could greet a wintry landscape with snow actually settling! This caused quite some traffic jams and accidents on the road. Snowy landscape in the Netherlands on the 24th of April. Source: Weeronline. Snow did not only reach the Netherlands, but also in low-lying areas of Switzerland some snow fell, although only somewhat higher up the landscape got a wintry white colour. Slide o
  14. Winter is now well underway, though it is all feeling more like mid-Autumn. The UK has been soaked over and over again, sometimes by bands of moisture-loaded conveyor belts originating all the way from the tropics. For much of Europe, December has also been a record-shattering month. In the Netherlands, the average temperature record high was literally crushed by an astounding 2.3*C! After this extremely warm and for the UK very wet December, hopes are up that probably the rest of the winter may deliver some wintry weather, or at least some dry spells. Will this finally be bound to come?
  15. I’ve just been catching up with this thread; there are quite some interesting thoughts and contributions about this matter. Great to see this all being collected in this thread. The atmospheric angular momentum – although I understand the general concept – is still too difficult to get my head around, but I think this will improve over the course of the year with some extra study and reading contributions on this site. What piqued my interest is the relationship between the cooler-than-average sea surface temperatures in the Atlantic and lower geopotential heights there. In fact,
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