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  1. Hello everyone, I've just introduced this new topic about Greece. As you may know Greece doesn't mean just sun, fair weather and beaches. Furthermore, the very complicated orography can affect the weather from a place to another even if the distance is just a few Kilometers. So, I will use this topic to prove what I said . Of course, if anyone has any comments, queries or even matterial from Greece, he/she can upload.
  2. QBO was moderate westerly in Autumn 2010 and became borderline strong westerly during winter 2010/2011 so the weak WQBO analysis for the up coming winter is not likely to be relevant to another December 2010. It was one of the outliers in my moderate WQBO analysis of Autumn's preceding the winter CET values. Most of those options came out milder than average. Talking of the QBO I feel it is time for another update since there appears to be more developments since my last one I shall start with the QBO phase plot from NASA Singapore site 1 - The highest part of this chart is now consistently showing EQBO at 10 hpa so it is only a matter of time now before this begins to descend and as we have had no southern hemisphere SSW to mess things up this time around and no strong ENSO to throw in another issue to think about then I see no reason why the EQBO won't descend this time around 2 - The middle layer is consistently showing WQBO of varying strengths each day and just refuses to do one. It seems to the cold lovers annoyance that this winter is now going to be a definite WQBO winter thanks to the southern SSW last September messing things up 3 - The last remnants of the easterly anomaly are still clinging on at the lower end of this chart but overall these values have been getting weaker and should disappear within the next few weeks which should make way for the WQBO to move down and in turn allow the new EQBO to descend too. 4 - With the state of the plot chart I feel it won't be long before this text reads East - Descending phase once again unless there's another twist in the tale of the QBO this year Next I will show the QBO progression chart This chart shows what the cold winter lovers feared and that was a quick return to the WQBO once more. However the good news is that we appear to be rapidly progressing through this WQBO and it would appear that this WQBO could end up just as short as the mini EQBO did earlier in the year and a bit weaker than average too but no where near as weak as the EQBO was. The next chart is the 10 to 100 hpa chart 1 - This shows up clearly how the EQBO appears to be back in business at 10 hpa now with consistent greens and blues showing up at this level now. It also appears to be gaining in strength too but is still some way off where it was at late last year in terms of strength at 10 hpa. Hopefully it will begin to descend soon but maybe a short delay wouldn't be a totally bad thing as it would increase the chances of winter 2021/22 being an EQBO winter rather than a EQBO to WQBO transitioning one which would be better for cold chances 2 - The annoying lingering WQBO still looks to be expanding both upwards and downwards and some of the yellow colours are beginning to show themselves in the speed chart. This no doubt shows speeds in excess of 10 m/s and strong WQBO values being achieved on some days. Not a good sign for winter 2020/21 if you want cold weather unless we get another December 2010 3 - For a while a week or two ago it looked like the easterly anomaly was fast running out of steam when you see that big brown area that suddenly descended into this region but it looks like it is making a bit of a comeback. Are we seeing another disturbance but this time down between 70 and 100 hpa which could explain why the WQBO is expanding upwards as well as downwards. I hope another EQBO disruption events ISN'T going to happen again, surely not another one. The final chart I want to show is the 3 hpa to 100 hpa chart 1 - The first of the two main reasons I included this chart today is what can be seen at 10 hpa. Notice how the next darkest green area has begun to appear at 10 hpa which is the 15 - 20 m/s colour. This shows that the EQBO is continuing to build at 10 hpa but like with the last chart this is still no where near what the EQBO reached during last year when the 30 - 35 m/s colours appeared at 10 hpa for a time. Still time for the EQBO to roughly double in strength at this height then before it descends. 2 - Not good news for winter 2020/21 anymore with the obviously strengthening WQBO on this chart. It has been descending clearly at the base but refuses to let go of its grip on levels below 15 hpa. Hope there's some movement of the WQBO downwards before the end of the autumn at least so we can then average out as a weak WQBO in the autumn which based on my analysis came out as the coldest option overall for the following winter CET 3 - The bad news is that the QBO at 3hpa didn't stay easterly for very long and has in fact turned back westerly again. Hope this doesn't descend so rapidly that it neutralises the EQBO at 10 hpa and pushes us into an even longer period of WQBO at 30 hpa. Then again maybe the change to WQBO high up could help push the EQBO down towards 30 hpa and start us off on the next EQBO sooner rather than later
  3. Ian Docwra

    Snow Moon

    Home in NE Surrey. Snow fell heavily on 24 January 2021 and the sky cleared that night to allow a waxing gibbous moon to shine brightly.

    © Ian Docwra

  4. Ian Docwra

    Piled High

    From the album: Ian Docwra

    Our garden when we lived in Epsom, Surrey, just after the exceptional snow of February 2009 had stopped falling.

    © Ian Docwra

  5. From the album: Ian Docwra

    Our then garden in Epsom, Surrey after an exceptional snowfall in February 2009.

    © Ian Docwra

  6. Hi I had a question about Freezing fog that I don't seem to be able to find the awnsers for by google searching. Its my favourite type of weather phenomenon but I don't get to see it very often in my part of the world (Thames Valley/Marlborough Downs) We get plenty of fog here, autumn and winter, and there are many frost pockets and hollows but getting frost and fog at the same time always seems to be rare. I know freezing fog is brought about obviously by sub zero temperatures and areas of clear high pressure in winter, by why is that some clear some frosty highs produce freezing fog occaisonally while many more usually don't? What are the exact conditions needed for it to form other than clear highs and very low temps? During December 2010 we had almost 3 weeks of lying snow under both cloudy and clear conditions and freezing fog formed on only one of those nights. It was neither the mildest or the coldest night either. I see a lot of people mention on forums when looking at certain charts that due to what they see, freezing fog could definitely be a risk. What is it about a particular chart that makes a cold frosty high more likely to produce FF than another? It would be a great help if anyone could explain the partiuclar conditions that create the right sort of environment for FF to occur locally. Does it have to do with relative humidity? direction of source of cold air? How moist the ground is? Thank you for any helpful explanation.
  7. Here we go then, already plenty of interest in the strat this year, and with a La Nina likely, perhaps a less hardcore strat than last year can be expected? @chionomaniac will be along soon to fill in his thoughts on where things may be headed this year, but in the meantime, I've copied his excellent strat guide from 2015 below. For more info you can also read his full tutorial here: https://www.netweather.tv/charts-and-data/stratosphere/tutorial Ed's opener from 2015/16 As ever, the first post will become both a reference thread and basic learning thread for those wanting to understand how the stratosphere may affect the winter tropospheric pattern, so forgive me for some repeat from previous years, but it is important that those new to the stratosphere have a place that they can be directed to in order to achieve a basic grasp of the subject. The stratosphere is the layer of the atmosphere situated between 10km and 50km above the earth. It is situated directly above the troposphere, the first layer of the atmosphere and the layer that is directly responsible for the weather that we receive at the surface. The boundary between the stratosphere and the troposphere is known as the tropopause. The air pressure ranges from around 100hPa at the lower levels of the stratosphere to below 1hPa at the upper levels. The middle stratosphere is often considered to be around the 10-30hPa level. Every winter the stratosphere cools down dramatically as less solar UV radiation is absorbed by the ozone content in the stratosphere. The increasing difference in the temperature between the North Pole and the latitudes further south creates a strong vortex – the wintertime stratospheric polar vortex. The colder the polar stratosphere in relation to that at mid latitudes, the stronger this vortex becomes. The stratospheric vortex has a strong relationship with the tropospheric vortex below. A strong stratospheric vortex will lead to a strong tropospheric vortex. This relationship is interdependent; conditions in the stratosphere will influence the troposphere whilst tropospheric atmospheric and wave conditions will influence the stratospheric state. At the surface the strength and position of the tropospheric vortex influences the type of weather that we are likely to experience. A strong polar vortex is more likely to herald a positive AO with the resultant jet stream track bringing warmer and wet southwesterly winds. A weaker polar vortex can contribute to a negative AO with the resultant mild wet weather tracking further south and a more blocked pattern the result. A negative AO will lead to a greater chance of colder air spreading to latitudes further south such as the UK. AO chart The stratosphere is a far more stable environment then the troposphere below it. However, the state of the stratosphere can be influenced by numerous factors – the current solar state, the Quasi Biennial Oscillation (QBO), the ozone content and distribution and transport mechanism, the snow cover and extent indices and the ENSO state to name the most significant. These factors can influence whether large tropospheric waves that can be deflected into the stratosphere can disrupt the stratospheric polar vortex to such an extent that it feeds back into the troposphere. Ozone Content in the stratosphere Ozone is important because it absorbs UV radiation in a process that warms the stratosphere. The Ozone is formed in the tropical stratosphere and transported to the polar stratosphere by a system known as the Brewer-Dobson-Circulation (the BDC). The strength of this circulation varies from year to year and can in turn be dictated by other influences. The ozone content in the polar stratosphere has been shown to be destroyed by CFC's permeating to the stratosphere from the troposphere. The overall ozone content in the polar stratosphere will help determine the underlying polar stratospheric temperature, with higher contents of ozone leading to a warmer polar stratosphere. The ozone levels can be monitored here: http://www.cpc.ncep.noaa.gov/products/stratosphere/sbuv2to/index.shtml One of the main influences on the stratospheric state is the QBO. This is a tropical stratospheric wind that descends in an easterly then westerly direction over a period of around 28 months. This can have a direct influence on the strength of the polar vortex in itself. The easterly (negative) phase is thought to contribute to a weakening of the stratospheric polar vortex, whilst a westerly (positive) phase is thought to increase the strength of the stratospheric vortex. However, in reality the exact timing and positioning of the QBO is not precise and the timing of the descending wave can be critical throughout the winter. Diagram of the descending phases of the QBO: (with thanks from http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/qbo/index.html ) The QBO has been shown to influence the strength of the BDC, depending upon what phase it is in. The tropical upward momentum of ozone is stronger in the eQBO , whereas in the wQBO ozone transport is stronger into the lower mid latitudes, so less ozone will enter the upper tropical stratosphere to be transported to the polar stratosphere as can be seen in the following diagram. http://www.atmos-chem-phys.net/13/4563/2013/acp-13-4563-2013.pdf However, the direction of the QBO when combined with the level of solar flux has also been shown to influence the BDC. When the QBO is in a west phase during solar maximum there are more warming events in the stratosphere, as there is also during an easterly phase QBO during solar minimum, so the strength of the BDC is also affected by this – also known as the Holton Tan effect . http://strat-www.met.fu-berlin.de/labitzke/moreqbo/MZ-Labitzke-et-al-2006.pdf http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50424/abstract http://onlinelibrary.wiley.com/doi/10.1002/2013JD021352/abstract The QBO is measured at 30 hPa and has entered a westerly phase for this winter. As mentioned warming events are more likely during solar maximum when in this westerly phase – with the solar flux below 110 units. Currently, we have just experienced a weak solar maximum and the solar flux heading into winter is still around this mark. This doesn’t rule out warming events, but they will not be as likely – perhaps if the solar flux surges then the chance will increase. Latest solar flux F10.7cm: http://www.swpc.noaa.gov/products/solar-cycle-progression Sudden Stratospheric Warmings: One warming event that can occur in the stratospheric winter is a Sudden Stratospheric Warming (SSW) or also known as a Major Midwinter Warming (MMW). This, as the name suggests is a rather dramatic event. Normally the polar night jet at the boundary of the polar vortex demarcates the boundary between warmer mid latitude and colder polar stratospheric air (and ozone levels) and this is very difficult to penetrate. SSWs can be caused by large-scale planetary tropospheric (Rossby) waves being deflected up into the stratosphere and towards the North Pole, often after a strong mountain torque event. These waves can introduce warmer temperatures into the polar stratosphere which can seriously disrupt the stratospheric vortex, leading to a slowing or even reversal of the vortex. Any SSW will be triggered by the preceding tropospheric pattern - in fact the preceding troposheric pattern is important in disturbing the stratospheric vortex even without creating a SSW. Consider a tropospheric pattern where the flow is very zonal - rather like the positive AO phase in the diagram above. There has to be a mechanism to achieve a more negative AO or meridional pattern from this scenario and there is but it is not straightforward. It just doesn't occur without some type of driving mechanism. Yes, we need to look at the stratosphere - but if the stratosphere is already cold and a strong polar vortex established, then we need to look back into the troposphere. In some years the stratosphere will be more receptive to tropospheric interactions than others but we will still need a kickstart from the troposphere to feedback into the stratosphere. This kickstart will often come from the tropics in the form of pulses and patterns of convection. These can help determine the position and amplitude of the long wave undulations Rossby waves - that are formed at the barrier between the tropospheric polar and Ferrel cells. The exact positioning of the Rossby waves will be influenced by (amongst other things) the pulses of tropical convection, such as the phase of the Madden Jullian Oscillation and the background ENSO state and that is why we monitor that so closely. These waves will interact with land masses and mountain ranges which can absorb or deflect the Rossby waves disrupting the wave pattern further - and this interaction and feedback between the tropical and polar systems is the basis of how the Global Wind Oscillation influences the global patterns. If the deflection of the Rossby Wave then a wave breaking event occurs – similar to a wave breaking on a beach – except this time the break is of atmospheric air masses. Rossby wave breaks that are directed poleward can have a greater influence on the stratosphere. The Rossby wave breaks in the troposphere can be demonstrated by this diagram below – RWB diagram: https://www.jstage.jst.go.jp/article/jmsj/86/5/86_5_613/_pdf This occurs a number of times during a typical winter and is more pronounced in the Northern Hemisphere due to the greater land mass area. Most wave deflections into the stratosphere do change the stratospheric vortex flow pattern - this will be greater if the stratosphere is more receptive to these wave breaks (and if they are substantial enough, then a SSW can occur). The change in the stratospheric flow pattern can then start to feedback into the troposphere - changing the zonal flow pattern into something with more undulations and perhaps ultimately to a very meridional flow pattern especially if a SSW occurs - but not always. If the wave breaking occurs in one place then we see a wave 1 type displacement of the stratospheric vortex, and if the wave breaking occurs in two places at once then we will see a wave 2 type disturbance of the vortex which could ultimately squeeze the vortex on half and split it – and if these are strong enough then we would see a displacement SSW and split SSW respectively. The SSW is defined by a reversal of mean zonal mean winds from westerly to easterly at 60ºN and 10hPa. This definition is under review as there have been suggestions that other warmings of the stratosphere that cause severe disruption to the vortex could and should be included. http://birner.atmos.colostate.edu/papers/Butleretal_BAMS2014_submit.pdf A demonstration of the late January 2009 SSW that was witnessed in the first strat thread has been brilliantly formulated by Andrej (recretos) and can be seen below: The effects of a SSW can be transmitted into the troposphere as the downward propagation of the SSW occurs and this can have a number of consequences. There is a higher incidence of northern blocking after SSW’s but we are all aware that not every SSW leads to northern blocking. Any northern blocking can lead to cold air from the tropospheric Arctic flooding south and colder conditions to latitudes further south can ensue. There is often thought to be a time lag between a SSW and northern blocking from any downward propagation of negative mean zonal winds from the stratosphere. This has been quoted as up to 6 weeks though it can be a lot quicker if the polar vortex is ripped in two following a split SSW. A recent paper has shown how the modelling of SSW and strong vortex conditions have been modelled over a 4 week period. This has shown that there is an increase in accuracy following weak or strong vortex events – though the one area that the ECM overestimates blocking events following an SSW at week 4 is over Northwestern Eurasia. http://iopscience.iop.org/article/10.1088/1748-9326/10/10/104007 One noticeable aspect of the recent previous winters is how the stratosphere has been susceptible to wave breaking from the troposphere through the lower reaches of the polar stratosphere - not over the top as seen in the SSWs. This has led to periods of sustained tropospheric high latitude blocking and repeated lower disruption of the stratospheric polar vortex. This has coincided with a warmer stratosphere where the mean zonal winds have been reduced and has led to some of the most potent winter spells witnessed in recent years. We have also seen in recent years following Cohen's work the importance of the rate of Eurasian snow gain and coverage during October at latitudes below 60ºN. If this is above average then there is enhanced feedback from the troposphere into the stratosphere through the Rossby wave breaking pattern described above and diagrammatically below. Six stage Cohen Process: The effect of warming of the Arctic ocean leading to colder continents with anomalous wave activity penetrating the stratosphere has also been postulated http://www.tos.org/oceanography/archive/26-4_cohen.pdf As ever, I will supply links to various stratospheric websites were forecasts and data can be retrieved and hope for another fascinating year of monitoring the stratosphere. GFS: http://www.cpc.ncep.noaa.gov/products/stratosphere/strat_a_f/ ECM/Berlin Site: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/index.html Netweather: https://www.netweather.tv/charts-and-data/stratosphere Instant weather maps: http://www.instantweathermaps.com/GFS-php/strat.php NASA Merra site: http://acdb-ext.gsfc.nasa.gov/Data_services/met/ann_data.html Previous stratosphere monitoring threads: 2016/17 https://www.netweather.tv/forum/topic/86485-stratosphere-temperature-watch-201617/ 2015/16 https://www.netweather.tv/forum/topic/84231-stratosphere-temperature-watch-20152016/ 2014/2015 https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/ 2013/2014 https://forum.netweather.tv/topic/78161-stratosphere-temperature-watch-20132014/ 2012/2013 https://forum.netweather.tv/topic/74587-stratosphere-temperature-watch-20122013/ 2011/2012 https://forum.netweather.tv/topic/71340-stratosphere-temperature-watch-20112012/ 2010/2012 https://forum.netweather.tv/topic/64621-stratosphere-temperature-watch/?hl=%20stratosphere%20%20temperature%20%20watch 2009/2010 https://forum.netweather.tv/topic/57364-stratosphere-temperature-watch/ 2008/2009 https://forum.netweather.tv/topic/50299-stratosphere-temperature-watch/
  8. Looking towards the Howgills, Whinash Ridge and the Yorkshire Dales from Cunswick Scar in the Lake District. Today's snow showers from the NE didn't get any further west than the Howgills. What is interesting is how the altitude has made such a difference to where the snow is lying. The River Kent valley is green whilst the surrounding hills are white. The snow event earlier this week was marginal which is so often the case here, the influence of Morecambe Bay is strong.

    © Kate Willshaw

  9. BruenSryan

    28 Feb 2018

    © Sryan Bruen

  10. BruenSryan

    28 Feb 2018

    © Sryan Bruen

  11. From the album: Bempton

    Saw icicles here in 2010, but very unusual this late in the season
  12. Small drifts forming behind ant hills...
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