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    South West and Central Southern England Regional Weather Discussion 22/02/2018 Onwards

    in Regional

    Posted

    50 minutes ago, kevvo said:

    Sounds like someone is throwing  dry rice against my windows. Guess that's freezing rain arriving, whilst we still have Met Office forecast for heavy snow. 

    Hi Kevvo. For info about freezing rain. I grew up in the north cotswolds and was at secondary school in the 1962/3 winter. We had about three weeks of freezing rain.  When you were out in it it was just rain but all the trees, paths, telegraph wires etc.were coated in about an inch of ice. The wires and branches would keep snapping off. The previous drifted snow was rock hard and covered in a layer of solid ice. We used to walk right over the hedges as the snow was like concrete. Not seen freezing rain now for about 20 years. We have a place on the south coast in Christchurch and none of the neighbors had a clue what we were talking about when I mentioned freezing rain - its that rare and and its deadly so I hope you don't get much if any.

    • Thanks 1

    Earthquake Activity Thread

    in Space, Science & nature

    Posted · Edited by musician

    11 hours ago, Chris K said:

    Was noticeable here North of Bristol. I was in my room and it felt like everything had been shuffled about all at once. Could here faint rumbling outside and it was like a large lorry going by, but instant rather than gradual.

    My thoughts exactly. I'm in Stroud, Gloucestershire. I was in the house when suddenly all the doors and windows started to vibrate and there was a rumble akin to a heavy vehicle going past the house. I remember thinking "Earthquake" as a similar thing occurred many years ago when I was playing the piano in the top floor of a house and the piano moved. It was an earthquake then also.

    South West and Central Southern England Regional Weather Discussion 09/12/2017 onwards

    in Regional

    Posted

    1 hour ago, SilverWolf said:

    Hi, you’re right about the Stroud district, microclimates and elevation! I live in Rooksmoor, which is lower than Stroud town, but I’m below Rodborough common in a frost hollow. It has rained now, but there is still 3 inches of snow here. Worked up on Rodborough common yesterday and there was 6 inches there. Looking out to May Hill across the Vale of Gloucester (for those who don’t know it - it’s pretty high up) there was hardly a dusting up there, when sometimes it can be covered with snow with nothing here at all. 

     

    1 hour ago, SilverWolf said:

    Hi, you’re right about the Stroud district, microclimates and elevation! I live in Rooksmoor, which is lower than Stroud town, but I’m below Rodborough common in a frost hollow. It has rained now, but there is still 3 inches of snow here. Worked up on Rodborough common yesterday and there was 6 inches there. Looking out to May Hill across the Vale of Gloucester (for those who don’t know it - it’s pretty high up) there was hardly a dusting up there, when sometimes it can be covered with snow with nothing here at all. 

    Yes I've noticed that sometimes. Though when I lived in the Forest near Cinderford the snow didn't seem to want to thaw under those trees. Always seemed very icy over there. My photos from today were from a site near The Camp just North of Bisley.

    South West and Central Southern England Regional Weather Discussion 09/12/2017 onwards

    in Regional

    Posted

    Chris55 is so right about elevation affecting snow in his earlier message. I was in Stroud town centre this morning and you would not know it had snowed. The roads were dry. Whereas where I live in Thrupp Lane nearby, at 350 ft we still have a couple of inches. However, I needed to go to a Nature Reserve just five miles north of Stroud this afternoon as I volunteer there for Butterfly Conservation and these images were taken there at 2 pm today, I kid you not. I was unable to get the car into the car park so to get it off the road I had to use a warning triangle while I dug myself a parking space to get the car off the busy road. The site is around 800 ft at the highest point and I estimated the snow depth was approaching a foot in places. It was a winter wonderland.  Anyway, I thought I'd show you a few pictures to make you salivate. 

     5a303c7ac949d_RoughBankSnowatAccessStripgate.thumb.jpg.edec485135a4ca339448b55c8c1f4563.jpg5a303c908769a_RoughBankSnowtopofBank2.thumb.jpg.35e485a9b38cf00bfd663545782a12e1.jpg5a303ca2e02af_RoughBankSnowandAnthill.thumb.jpg.f622a0ce3ec41a8c82a0c1bba24851d7.jpg5a303cb61243c_RoughBankSnowlookingwestfrombank.thumb.jpg.cd068d0a4bd715168f818cb7b5e56175.jpg5a303d0f9a088_RoughBankSnowlookingwestfromBank2.thumb.jpg.25207a26b2af6ff6553b0eebdb4a0631.jpg5a303cf05e304_RoughBankSnowlookingEastmiddlepath.thumb.jpg.0f0634955d7b75d2beda4b05ca2871c9.jpg5a303cdd6c31b_RoughBanksnowtopofBank.thumb.jpg.90fe5d601033e03ceb2baf14a7e4b127.jpg5a303cc963e21_RoughBankSnowonBeechbranches.thumb.jpg.c4b1db7831b267b0f169b6dfed03f803.jpg

    • Like 4
    • Thanks 1

    Model Output Discussion - cold spell to end Autumn

    in Forecast Model Discussion

    Posted

    39 minutes ago, TEITS said:

    Having followed all the output and read all the posts these past few weeks I thought I would make my first post of the winter. A few points I wish to raise.

    1. Current output does not suggest a major cold spell.

    2. The NW,ly this Fri/Sat will bring snow showers to the favoured locations and may even spread SW through the cheshire gap towards even London. However many locations will remain dry and sunny with max temps of 2/3C. The snow showers will not be as extensive as some have suggested.

    3. Beyond NW,ly the jet stream does appear to be taking a NW-SE track so slider low pressure systems bringing a risk of snow is possible. Remember though your location dictates whether a model run is good or bad based on the track of the low.

    4. The risk of cold and snowfall from this pattern looks likely to extend into mid Dec. However I fear beyond this a return to a milder weather, flatter jet stream, lower heights to our NW/N is likely towards xmas. Love to be wrong.

    So a summary is this is much better than last year but certainly no repeat of 2010!

    I've really missed you TEITS. As a learner and still a learner I always looked forward to your posts as they seemed to me to be the most reliable and balanced.  I've been really put off by all this recent bickering ansdwas thinking of taking a break from this site for a few days until things calmed down - that is unless you are going to be posting on here! Thanks.

    • Like 4

    Model Output Discussion - cold spell to end Autumn

    in Forecast Model Discussion

    Posted

    2 hours ago, o0herbie said:

    As a long time lurker and non-poster, I'd like to highlight this post as one of the most useful I've ever read on here and implore other posters to use this as an example of something that helps those of us who don't completely 'get it'. Thank you Quicksilver1989

    Agreed! it so good to be able to follow what is being said, represented by step by step charts. I'll look forward to further posts from you Quicksilver 1989.

     

    2 hours ago, o0herbie said:

    As a long time lurker and non-poster, I'd like to highlight this post as one of the most useful I've ever read on here and implore other posters to use this as an example of something that helps those of us who don't completely 'get it'. Thank you Quicksilver1989

     

    • Like 1
    • Thanks 1

    Model output discussion - 5th December 2016 - Into Winter we go

    in Forecast Model Discussion

    Posted

    1 hour ago, ManiaMuse said:

    +1

    As a lurker who doesn't understand most of the technical posts but still enjoys reading them anyway to get an idea of which way things may be swinging, it's getting really annoying having to sift through all the petty bickering and overly optimistic/pessimistic one liners that don't add anything to the thread.

    (Yes I'm aware this post is also breaking the rules so warn/ban me if needs be)

    Agreed. I'm trying to learn more from those far more knowledgeable than myself but have to trawl through reams of bickering instead of backing up thoughts with models. Its become so bad that if I don't see a chart I tend to disregard the one-liners. PLEASE lets return to serious discussion! 

    Model Output Discussions 06z 04/11/16

    in Forecast Model Discussion

    Posted

    2 hours ago, IDO said:

    Come on guys, the UK D6 charts are woeful when it comes to HP -v- LP, they are akin to D10 ECM charts. I rarely pay any attention to them as clearly they have issues.

    My thoughts are that we remain in a holding pattern where the PV remains subdued but there is no forcing to create a more prolonged amplified pattern. It shows that even with a weak PV you need the right synoptics to get long term cold. 

    We have gone from the Russian/Siberian High & Azores mid-latitude quasi block setup to an Azores & Pacific HP combo.But again both haven't the heart to be anything but topplers if they do venture into semi-higher latitudes, so effectively still a rather mobile NH pattern within those confines.

    Of course as time passes the PV gains a bit more energy just to make any meridional pattern a little bit tougher.

    It looks pretty clear we have a sinking high around D8-D10 and its direction of fall will define the upper flow over the UK, with GEM bringing us a warming (average T850s >8c above normal) whilst the GFS a mild flow (T850s +4c above average). As that sinks the cycle starts again, and the next wave from the Azores pushes towards the UK. I am sure the FI GEFS will have some producing  stellar runs, but that has been the modus operandi for weeks and it may be better to assume the status quo until one of these elusive background signals change the pattern. However that has low confidence as the second pulse from the Azores after D10 and the sinking high could be difficult to model at this range. 

    Being honest it is hard to see any cold/snowy pattern developing by mid-December but the potential remains clear and hopefully its just a matter of time.

    gfs-15-216.png

    gem-15-222.png

    At last! someone who can spell STELLAR correctly!

    • Like 1

    Model Output Discussion - 1st February Onwards 12z--->

    in Forecast Model Discussion

    Posted

    We have had an interesting period last week, with a brisk northerly delivering snow on several places across the UK. There seems to be a change in the pattern underway, with high pressure activity probably taking foothold over Western Europe. How does this pattern evolve, and how can high pressure activity still cause a lot of uncertainties? In this post, I will try to give an answer to these questions.

     

    For the first 96 hours, I will use the GFS 12Z/18Z runs as a general guide.

     

    Current synoptics

     

    For the current situation, take a look at the GFS chart below:

     

    attachicon.gifGFS_00_EDIT.png

    GFS surface level pressure and 500 hPa heights (Colours) 18Z run T0

     

    As can be seen from the image, a large 500 hPa trough (blue colours) extends over the center of Europe down to the Mediterranean. A complex area of low pressure at the surface is associated with this feature.

     

    This trough has been influencing our weather over the past few days. Northerlies blew on the western side on the trough. Also, because the 500 hPa temperatures (not shown here) were very cold at the center of this trough, the air was very unstable (expressed by a big difference in temperature between the surface and aloft). This made formation of showers possible, which were carried southward by the northerly flow, bringing rain and snow toward the UK.

     

    Aside from this trough, a 500 hPa ridge can be seen building over the Atlantic (orange colours edging northward), also visible by high pressure at the surface. This ridge will be important for our weather over the next week.

     

    Transition to high pressure activity

     

    Looking 48 hours later, the same general pattern as described above is maintained, but with a few crucial differences.  Check the GFS chart for 2 days ahead below:

     

    attachicon.gifGFS_48_EDIT.gif

    GFS surface level pressure and 500 hPa heights (Colours) 18Z run T48

     

    The 500 hPa trough located over central Europe is still there. However, there are two important things happening, being:

    • The trough is weakening, as the dark blue colours (indicative for very low 500 hPa heights) are now longer visible.
    • A piece of the trough is willing to dive southwestward (indicated by the black arrow). This movement will be very important for future developments.

    Also, the 500 hPa ridge (orange colours edging northward) is still visible, but has moved some westward and is now located just to the west of the UK. Also note the orientation of the high has shifted some into a NE-SW orientation, basically pushing itself over the piece of the trough (over France) which is trying to move southwestward under the ridge.

     

    Another 48 hours later, the developments mentioned above have continued, as can be seen below:

     

    Rtavn961.gif

    GFS surface level pressure and 500 hPa heights (Colours) 18Z run T96

     

    The ridge which was located to the west of the UK 2 days before has now moved over the UK, yielding a strong area of high pressure at the surface (up to 1035 hPa).

     

    Furthermore, the 500 hPa trough which was located over central Europe has been separated into a part that has shifted out of Europe, and another part which has become partially cut-off over Italy (blue colours). As a refresher, a cut-off low is a low pressure area that is separated from the mean flow by means of high pressure activity to the north of it.

     

    The result is a high-over-low situation, which can be seen as a blocked pattern. This can also be seen on the Jetstream patterns as given by Netweather, which can be found in the following image:

    hgt300.png

    Netweather Jetstream analysis from the 12Z GFS run valid for 96 hours out.

     

    Note that the jet stream is very wavy and inactive, indicative of a blocked pattern.

     

    (Un)certainties in future outlook

     

    The situation described in the previous outlook is not expected to change much over the days to follow. However, small differences develop between the models, which may have significant implications for the weather across the UK. For example, compare the GFS and ECMWF MSLP forecasts for 7 days out:

     

    http://www.wetterzentrale.de/pics/Recm1681.gif ECMWF

    http://www.wetterzentrale.de/pics/Recm1681.gif GFS

     

    As can be seen from the models, both agree that a strong 500 hPa ridge will be present over the UK (as indicated by the orange colours).  This provides enough certainty to conclude that high pressure activity will be likely by the end of next week.

     

    However, there are small differences in the placement of the surface high pressure, with the GFS being much further east with the high pressure area than the ECMWF. Also, the 500 hPa ridge (and associated surface high) on the ECMWF is somewhat stronger  than on the GFS.

    What makes these differences so important is that placement of the surface high to the east or west of the UK has major implications on the weather expected there. If the ridge would appear to be located to the east of the UK, a southerly flow will be present over the UK bringing mild weather. On the other hand, placement of the ridge to the west of the UK would result in a cool northerly. This uncertainty is reflected nicely in the wind distribution of the ECMWF ensemble for the Netherlands:

     

    epsroos_260.png

    ECMWF wind distribution of 50 individual calculations 00Z run, 1 February.

     

    The image indicates a set of wind vanes, each for a different time step. Each sector stands for a different wind direction. For example, the upper segment indicates northerlies, while the right-hand sector denotes easterlies, analogously for the lower and left sector. The distance from the center is the strength of the wind expected. The further away a run from the center is, the higher the wind speed will be. The green triangles denote a single ensemble run forecast for the wind speed and direction. The blue and red triangles are the Control and the OPER run, respectively.

     

    When the triangles are very close together, it means there is a high certainty of the expected wind, while a large spread indicates uncertainty.

     

    What can be seen is that from about 168 hours, a large disagreement between the various ensemble members develops regarding wind direction. Basically everything except a southeasterly is possible, with equal chances for each of the other wind directions. All models do agree, though, that the wind speed will not be high.

     

    This spread can be linked to the synoptic situation discussed earlier by the high pressure area positioning near the UK. A very small deviation in the positioning of the center of the high may result in a complete turnaround of the wind direction to be expected, and the expected temperature.

     

    Regardless of this spread, the fact that high pressure activity seems to be dominating our weather for a significant period of time is pretty certain. To illustrate this, take a look at the precipitation ensemble ‘pluim’ from the ECMWF:

     

    eps_pluim_rr_06260.png

    ECMWF ‘pluim’ of precipitation for the Netherlands, showing 50 individual model calculations of the ECMWF model regarding precipitation (green lines). The red line is the operational run, while the blue line is the ‘control’ run.

     

    Over the next 15 days, almost no model is calculating any precipitation to fall. It does take up to 13 February to see some members calculating a decent amount of precipitation. As high pressure is often accompanied by a lack of precipitation, this is good evidence that high pressure activity will dominate for the next several days.

     

    Boundary-layer and high pressure activity

    Of a final note, even if the location of the high pressure is certain, the weather over the UK can still be uncertain even up to the day itself (say, 12 hours out). This has to do with boundary layer dynamics, which are crucial in high pressure activity. The boundary layer, in general, comprises the lower 100m to 1 km of the atmosphere (the area where we ‘live in’).

     

    Questions like: “What will be the height of the subsidence inversion caused by the high pressure area?†and “What will be the humidity of the surface air and?“ are of high importance. This can be the difference between a day full of sunshine, a day of cloudiness, or in the worst case a day of only fog. Therefore it has to be kept in mind that even if the general synoptic pattern is clear, the forecast for the actual weather being observed may not be that certain at all.

     

    Conclusion

     

    A pattern change is about to occur at the beginning of next week, with high pressure activity taking over. There seems to be a fairly high level of confidence that this will last for a week or even more. However, there are still small disagreements on the placement of the surface high, which will have major implications for the weather experienced across the UK; directly by means of wind direction and indirectly by boundary layer dynamics. Therefore, the models can be watched with interest.

     

    Sources:

    http://www.weerplaza.nl/15daagseverwachting/?type=eps_pluim

    http://www.netweather.tv/index.cgi?action=jetstream;sess=

    http://www.wetterzentrale.de/topkarten/fsecmeur.html

    http://www.knmi.nl/exp/pluim/kansverwachtingen_staafdiagram.php?run=00&type=precip0618

     

    Just catching up on last evening's posts and, as someone who does not feel qualified to reply in depth to many of the posts. I have to say that this is possibly the best post I've ever read on here in the past few years. A beautiful explanation of your thoughts, which took me quite some time to read as I was able to click on and digest your explanations at every stage. A perfect post for those who might be new to this thread.

     

    Thank you so much Vorticity 0123. You have restored my faith in this forum!

     

    Peter

    Stroud

    Model Output Discussion; into 2015

    in Forecast Model Discussion

    Posted

    Trying to find some positives from tonights operational outputs upto day ten. :whistling:

     

    I maybe some time.......................................................

     

    Okay I've waved the white flag! The operationals are all in agreement for a spell of mild mobile weather upto day ten, any signs of life re cold are showing up on a few GEFS ensembles but well into FI.

     

    I think we're left with two options barring the emergency trip to Lapland , the MJO I'm actually more interested in than the current modelling and so we wait to see of this can survive and move into phase 7 at a decent amplitude. So far this winter its hit a brickwall ,  annoyingly at present even with this current strat warming Berlin Uni which has some key charts hasn't updated, the effect if any of that warming seems hard to quantify.

     

    One of course could look at the PV and think what strat warming, I mean could the output have looked any worse anyway!

     

    Whether theres some effect on the PV during the rest of January we'll just have to wait and see, of course waiting and patience seems the mantra that's been in evidence for the last 5 weeks for cold and snow lovers.

     

    I think realistically we should just view the next ten days as likely to deliver little if any cold interest, I'm willing to give it to next week and then hope the output upto T240hrs begins to show a bit more interest if not expect to see a plethora of these clogging up my posts :help: .

    You are our only hope, Frosty. Its only your optimistic posts which keep me on this forum!

    The GEFS 12z mean trends colder between T+240 and the end of the run, another good sign. I think beyond mid month we could be looking at a wintry pattern.

     

    Sorry, posted in the wrong place just now, but you need to know that its only your optimism which keeps me on this forum!

    • Like 1

    South West/Central Southern England Regional Discussion 03/02/13 12z ------->

    in Regional

    Posted

    Currently 6.2°C with decent sunshine for most of the day.

    I've got my 'near realtime' graphs set up on my index page now and i've edited the file to show the last four hours of data.

    Have a gander and bookmark if it helps to see my data during interesting weather events, links in my signature. smile.pngdrinks.gif

    Thanks for this. I'm thinking of setting up something similar so have bookmarked this. Also, we spend quite a lot of time in Dorset so it will prove useful.

    Peter

    Stroud

    South West/Central Southern England Regional Discussion 18/01/13 16z ------>

    in Regional

    Posted

    Normally when watching a front move in you watch it track where it's going, but this is literally exploding to life , ahead of what looks to be the band breaks out ppn out of nothing, it wouldn't take a huge jump 40miles to get us lot in the fun, looking at the bbc I'm literally within touching distance of it , but I feel we will at least see some , maybe an inch?

    Well, even if we don't get any more this winter, I'm happy with what we had on Friday. I measured a level six inches, which is, I think, our heaviest fall since February 1998. Have some great photos for my next home made Christmas Card!

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