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

[Frosty_wsm]

Snow falling, looks like that shower is just clipping my location. 

[Andrew_WsM]

Few flurries here at the mo, it's very bitter in the wind out there! 

[kumquat]

Looks like the current ppn over Bristol etc is tied in with the low moving SW through Wales. It's started to back fill in the Bristol Channel too now. (Very much what @Bringback1962 was saying in his post last night)

[Blizzardof82]

Light snow here, PPN seems to be building on radar 

[Zephyr]

06z EURO4

Edited February 27, 2018 by Zephyr

[PleaseSnow]

3 minutes ago, katemart said:

Showers maintaining intensity on the front edge and heading straight for Portsmouth and Southampton! COME TO MAMA!

(*Must remember how misleading the radar can be...*)

Oh how i hope that happens!!

[matt111]

10 minutes ago, fromey said:

From the mad thread Credit to Man with beard

ECM cluster report: No clusters after just T96 - Not because they are broken, but because they do not have a clue!!!!

I looked at individual ensemble members for D8/D9 on weather.us. Totally random!! In fact, the number of runs with minus 8C uppers or below probably outweigh the milder runs! 

The only pattern is low pressure very close to the UK, with a marked difference in coldness depending on whether the low is centred a few hundred miles west / east / south / north.

Little point, therefore, looking beyond the model mess of the end of this week IMO.

interesting!

That’s the one. Seems people talking about it becoming milder might be getting ahead of themselves. 

[EllyTech]

28 minutes ago, knocker said:

Morning Elly well it is apparent but the cloud to the north of is associated with the little wave (low) that has tracked south west from southern Norway and brought more consolidated snow showers to many places whist on route south west of Ireland. Forget about this Polar Low twaddle (not meaning you ) as the professional met people who apparently started this should have known better

Thanks Knocker. Yes, I too was a bit perplexed by the Polar Low factoid spurted out on the BBC. I always thought a Polar Low phenomenon was largely unpredictable and unfolded suddenly from the Arctic circle. If, on the other hand a PL in true/some revised, definition, was a low that forms alongside, to the North or within the PV. That would make sense currently.

 

[matt111]

8 minutes ago, katemart said:

Showers maintaining intensity on the front edge and heading straight for Portsmouth and Southampton! COME TO MAMA!

(*Must remember how misleading the radar can be...*)

I’ll join you there as there heading towards me as well. 

Edited February 27, 2018 by matt111

[fromey]

Little bit of snow falling now

[khodds]

2 minutes ago, matt111 said:

That’s the one. Seems people talking about it becoming milder might be getting ahead of themselves. 

Yes and this completely tied in with Meto long range thinking (well - I haven’t seen a recent update but last week was set for the cold to continue anyway..)

[EllyTech]

Snow flurries here.

[karlos1983]

Just now, matt111 said:

I’ll join you there as there heading towards was well. 

Will let you know when it’s hit Chichester!

had some flurries a little while ago which stopped quickly!

[jtay]

11 minutes ago, katemart said:

From what I can see on raintoday.com the ppn is tracking westward along the coast quicker than this. Hopefully that means we have more chance of showers today.

So wonderful this ppn popping up from the sea - usually with a low from the south-west if it arrives that means if blows through more quickly and is followed by the inevitable w*rm-up.

It'll be en francais time, so you're already an hour closer.

[Frosty hollows]

Minimum -5.9c last night. Now recovered to -3. Noticed a lot of convection about this morning oddly to my west but it's not budging. Guessing the cold dense air is keeping it in place. Bright and sunny ...even got a sweat on walking to the gym. Mind you I am dressed as an extra from real housewives of Siberia 

[MidnightSnow]

Nice little shower about to hit here. Pepped up out of nowhere really.

[Frosty_wsm]

Light snow again but the flakes are 20p size flakes, nice to see 

[MidnightSnow]

Really strange to see showers pepping up with every frame?? Is this what you were talking about kumquat?

[karlos1983]

Snowing ? now at work, just east of Chichester. 

[kumquat]

 

[Zephyr]

The showers seem to Pep Middleton up as they go past here  couldn't make it up.. *looks out window some more*

 

[Guest]

Good morning everyone. Let's not be too gloomy as there are still some decent snow prospects during this week and some good news. It is still too early to assess the potential for a significant snow event on Thursday onwards as there is considerable uncertainty in all the output with it being a highly complex set up and it may come down to a nowcast in the highly marginal conditions in the offing. I will give my view on it at the end of this post. Right now I want to focus on our opportunities before then. I will not repeat "all" the live charts again right now as they're still updating in my post on page 100. I will show the key ones that I want to comment on now.

         LIVE (RAIN) SNOW RADAR                        LIVE ANIMATED INFRA RED SATELLITE                     LIVE STANDARD SATELLITE                      INFRA RED SATELLITE 0815 26.2.18

                                               

Well, as you can see in the current charts, the more organised band of snow and snow showers has just skirted to the north of our region. A smaller pocket of snow showers (on the southern edge of the band) just clipped parts of the north Devon coast around 4 am with perhaps several centimetres - is there anyone on here who have reports on that?. The immediate forecast is not that good for snow chances in our region for today but I think a few of the heavier ones in the east will filter down our way this afternoon but most (perhaps not all) of these will be fizzling out as they arrive. You'll see that I added a second infra red chart above from the archives. I have set it for this time yesterday as I want to compare it with the live chart. Remember the bright colours are bands of much thicker cloud which is not necessarily precipitation baring but in this extremely cold pattern it mostly represents areas of heavier snow. These charts will be fascinating to view from late on Wednesday into Thursday when many of us may well be glued to our PCs (unless, of course we are too busy enjoying Wednesday's snow ). I will add the "France view" radar then so that we can see the progress of the northward push of that LP and what's in its circulation (hopefully one to look forward to). Look at the difference in the two charts. There is far more action over the Baltic and moving out into the North Sea  this morning. The coldest uppers and surface temps will arrive late today and into tomorrow. I'm hoping that this might produce a trough or cold front with a more organised band of snow moving westwards and south westwards - certainly a possibility. At the very least the convective activity and shower intensity should increase and the pressure gradient will tighten. Which leads me onto the pressure and a full house of charts that I want to analyse.

   1   MET O FAX FOR 0000 27.2.18    .     2      MET O FAX FOR 0000 28.2.18         3     MET O FAX FOR 1200 28.2.18           4    MET O FAX FOR 0000 1.3.18    

       

   5      MET O FAX FOR 1200 1.3.18             6     MET O FAX FOR 0000 2.3.18            7     MET O FAX FOR 1200 2.3.18          8      MET O FAX FOR 1200 2.3.18    

          

  9     MET O FAX FOR 1200 3.3.18             FRONTS & TROUGHS AT 0700 27.2.18            PRESSURE at 0750 27.2.18           GIF PRESSURE 24 HOURS TO 0850  

            

I was brought up on these fax charts and have been obsessed with them since age 6 in 1959 following a long hot summer. I studied all the Daily Telegraph weather reports which were much more thorough in those day with full Atlantic and British Isles pressure charts. I used to cut them out but I learnt to do this after my father had finished with the paper  Fax charts reveal so much more than the models show providing you know what to look for. These are the charts which were produced at 0000 this morning, accept the last two which are updated much later in the day and explains why the 7th and 8th charts are for the same date and time. Even this is useful as it reveals an interesting change (for the better).

Right, let's go through them. Chart 1 shows our powerful Scandi HP centred over Lapland with the extremely cold easterly flow sourced from Siberia pushing around it, through Europe, the UK and now more than halfway across the Atlantic. You can see the minor disturbance that gave that area of snow  just to our north last night with the kink in the isobars and the Met O show it with a small set of fronts pushing into eastern Scotland and north-east England. That cleared through overnight. Notice the trough shown just behind the fronts. I believe that's there really to show that it is introducing even cold air in its rear. These features are an approximate representation of the micro detail and the boundary of some (often minor) changes in the air flow. Really another small step down in the temps towards tomorrow's low point. The trough lines show up in the eastern and western English Channel. When troughs like this are spiked, that means that they have become quasi stationery and, in this case, demonstrate the areas where there are active streamers. With the flow just north of east right now, our trough is far out in the.mid-Channel and the Channel Islands should see some large snow accumulations today. There is another interesting little feature starting to show up as a pair of minor troughs on the Baltic Sea coast just east of Denmark. That little feature "may" become more significant as time passes. It's partly associated with the increased shower activity shown on the live infra red satellite image. Jumping over to the "Fronts & Troughs" chart we can see all the features that I described at 7 am today. Meteoceil show that Baltic feature slightly further south and with a small LP starting to show up in the air stream. One to monitor during today. Very significantly for us (a little later on), see how the flow over the low countries, northern France and through the Channel has already veered very slightly from just north of east to due east.in just  7 hours. The last 2 charts show this too, where I have frozen the pressure at 0750 this morning and the GIF showing the 24 hours to 0850 this morning. This veering is very good news for our snow prospects later tonight and through tomorrow. 

Chart 2 for midnight tonight shows that the flow is veering a little more (not quite there) to just south of east. Our streamer is just starting to edge northwards. The eastern Channel streamer has gone as the south-east is now getting a direct continental flow with a very short sea crossing. They'll be getting some of the lowest temps (apart from any clearer, less windy parts of the north-west which may see some of the severest frost tonight over their snow covered areas). There's another interesting feature, a trough just off East Anglia which is not a quasi stationery streamer. It's there with a kink in the isobars - another very small area of LP. That'll beef up their snow showers and it's possible that that kink moves through towards us and it may be associated with what I mentioned above - the wave of the coldest air of all moving in (both surface temps and the 850s). This "might" produce a small area of more organised snow showers and could reach us in the small hours or towards dawn on Wednesday. Another one to watch. There's another trough moving into Scotland, probably there for similar reasons. There's a continuing feature of Denmark.

Chart 3 shows just what we want. The flow has now veered to the east-south-east and the trough is now hugging the coast from Dorset to Cornwall and out beyond the Scilly Isles. I refer you back to what I and Knocker alluded to yesterday. The streamer should be near it's strongest and most expansive and will produce almost continuous snow shower activity. Not just on the coast as the flow will push those showers well inland. perhaps for 30 to 40 miles and the heavier ones might make it right across to the Bristol Channel. Furthermore, you have seen how the snow showers form about 10 miles off shore from France (clearly shown in the "standard" satellite image above). Well anywhere from around Brighton westwards should get some snow showers (that's away from the actual streamer zone) and some of those might be quite beefy and move some distance inland. Yet another one to keep an eye. Out of all the possible snow events, I feel that this one for tomorrow is perhaps the one that we can "most rely on" to deliver. Nothing is 100% certain and the veering might not play ball but I believe that it will.

The convective easterlies may well be cut off as we move into Thursday depending upon how quickly the LP moves up from the south. Chart 4 shows the LP itself making slower progress than before but still pushing up fronts well ahead of it. Remember at this stage (0000+ on Thursday morning) not only the UK will be bathed in extreme cold but so will northern and central France. The chart shows what I call a "ghost" warm front. The one which isn't blacked out ahead of the other fronts and troughs. This shows that any milder (or rather less cold) air associated with the front has not penetrated through to the surface layers. If (pretty likely given the pattern shown) or when this happens, depending on how far above the surface the milder air is uplifted, "can" produce some extremely heavy snowfall "or" a period of freezing rain (please refer to my MOD on page 20 of that thread for a full analysis of this possible event).  At this stage the fronts do not seem to have much northerly impetus and so any snowfall  or freezing rain on early Thursday is likely to over central France. With a further tightening of the isobars near us, we may see a final bout of snow showers before the wind veers too far and cuts off the convective source.

Now it gets really uncertain in terms of timing, progress, the path of the LP and how it reacts to hitting our incredibly deep cold block. One would think with sub -14c uppers engulfing the UK,  surface temps well below zero, the deep cold extending over much of France and a weaker jet stream pushing far to our south that our cold spell is not going to give up without one hell of a fight. I have gone through all these reasons one way or another, in my last 4 MOD posts.Frankly, nobody knows, no model can handle the general set up let alone the micro detail. All we can do is watch how the pattern evolves. Expect some huge swings in the output over the next 2 days right up to the (possible" event. I will be surprised if we do not see at least some snowfall and may be a very large amount of it.

So, I'll briefly describe the remaining fax charts as they are subject to significant changes. Chart 5 shows that "ghost" warm front just approaching us. Possible blizzards or possible freezing rain but will it actually be there by Thursday lunchtime - the LP itself is still far to the south, off north-west Iberia. Chart 6 shows that 12 hours later, the LP has deepened and moved north into southern Biscay. meanwhile the ghost warm front has pushed north-westwards into Wales and the Midlands. A whole succession of "surface" fronts are shown. probably with each one associated with marginally less cold air. The first main warm front still has a lot of south-east flow off northern France in it and I would imagine that temps would still be close to freezing or even below. Remember there will be an incredibly tight gradient in the 850s aloft but even if an area of sub 0c temps moves overhead it does mean that the deep surface cold layer has been fully penetrated (at that stage).  By chart 7 (for 1200 on Friday) this LP seems to be giving up the battle and is filling well to our south and moving towards central France. . The fronts are stalling - if this is anywhere near correct, it could be a sign of a longer period of real cold for almost all of the UK. Now, as I said above, we can see the identical chart for the same time but from yesterday. There is a big difference - the LP "was" in the south-west approaches. Then in chart 8, the last run did show the front stalling to our north and possibly returning south again. So, definitely a recent trend moving away from an early end to our cold spell but far too uncertain to judge if this will continue or change back nearer the time. I haven't had a chance to look at the other output this morning and frankly, one could get excited or disappointed - we must just hang for at least another day. 

Meanwhile enjoy what we should get tomorrow (or even later tonight) and also this epic battle coming up. I'll do a much briefer update this afternoon and take a closer look at the temps. I'll be pretty busy this evening but if it gets exciting, I'll do a very late report tonight (almost in the small hours).

David  .   

[Climate_Eyes]

Popped out for half an hour with the radar looking pretty empty, come back and WOW! Few tiny flakes blowing in the breeze and it's clouding up. C'mon!

 

[jessandjon]

1 hour ago, festivalking said:

I have some seen some forecasts in my time but the suggestion of 3 hours of heavy snow in plymouth tomorrow is frying my brain!! 

This is the event for this locale this week as on current modeling (can all change) friday might not be as impressive for snow as tomorrow!

@jessandjon @SNOW CRYSTAL 

It won’t let me like the comment....... looking good isn’t it ?

[fromey]

Snowing nicely now, can see it blowing along the road and paths