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


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Posted
  • Location: Now moved to tropical Bradford on Avon
  • Weather Preferences: Cold, snow and summer heatwaves.
  • Location: Now moved to tropical Bradford on Avon
    1 minute ago, AWD said:

    It's a weird one mate, because if it does indeed miss us to the west, it wouldn't be the end of the world.  If the core of the PPN does indeed go west of the West Country, we remain cold and we get a second bite of the cherry on Friday ala GFS 12z and Arpege 12z.

    However, we a talking ridiculously small margins here, ie a 50 mile shift east on the GFS 12z and a lot more of us would be back in the heavy stuff.

    What is good is that a snow to rain event, even for those further south is looking less likely so far.

    I still think models are slowly picking up on signal met office are seeing and that is for the cold to hang on until Sunday/Monday with further opportunities? 

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    Sod the snow, Tom Baker is trying to steal your car. 

    I want to see this in the morning.  

    Good afternoon all ,with the passing of my beautifull wife last Autumn things have been rather busy at home but now starting to quieten down ,so today i,v been for a great walk up local woods .with th

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    Posted
  • Location: Longwell Green, near Bristol
  • Weather Preferences: Storms, Gales, frost, fog & snow
  • Location: Longwell Green, near Bristol
    Just now, Nights King said:

    I still think models are slowly picking up on signal met office are seeing and that is for the cold to hang on until Sunday/Monday with further opportunities? 

    Got to agree with that so far.  Still further 12z model data to come, but the colder weather lasting well into the weekend, away from the far south and south west is looking a good call for now, albeit not as cold as the next couple of days.

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    Posted
  • Location: Sunderland
  • Weather Preferences: Hot Summer, Snowy winter and thunderstorms all year round!
  • Location: Sunderland
    3 minutes ago, AWD said:

    It's a weird one mate, because if it does indeed miss us to the west, it wouldn't be the end of the world.  If the core of the PPN does indeed go west of the West Country, we remain cold and we get a second bite of the cherry on Friday ala GFS 12z and Arpege 12z.

    However, we a talking ridiculously small margins here, ie a 50 mile shift east on the GFS 12z and a lot more of us would be back in the heavy stuff.

    What is good is that a snow to rain event, even for those further south is looking less likely so far.

    if the whole series of fronts continue to trend southwards in their angle of attack, us here in the north east of the region will go from dry to dry event! :bad:

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    Posted
  • Location: Marlborough, North East Wiltshire 143M/469ft ASL
  • Weather Preferences: Cold and snow in the winter, warm and dry in the summer !
  • Location: Marlborough, North East Wiltshire 143M/469ft ASL
    3 minutes ago, AWD said:

    Looks like too much PPN there.  Probably to do with the grid resolution of the model.

    Unfortunately, I think you're probably right! Seems the GEM always overdoes the precipitation...

     

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    Posted
  • Location: Barton on Sea, Hampshire
  • Weather Preferences: Snowy winter, warm/hot summer with the odd storm thrown in
  • Location: Barton on Sea, Hampshire

    Being on the coast isn’t the most ideal in these situations. Hopefully that milder air can be delayed even further than it already has been. 

    Edited by matt111
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    Posted
  • Location: Barton on Sea, Hampshire
  • Weather Preferences: Snowy winter, warm/hot summer with the odd storm thrown in
  • Location: Barton on Sea, Hampshire

    -0.4°C DP -5.0°C. 

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    Posted
  • Location: Marlborough, North East Wiltshire 143M/469ft ASL
  • Weather Preferences: Cold and snow in the winter, warm and dry in the summer !
  • Location: Marlborough, North East Wiltshire 143M/469ft ASL

    Really looks like this is going to go down to the wire with changes right up to the event itself and even as it's happening!

    I'm sure there will be both upgrades and downgrades along the way, what a fascinating hobby we have :good:

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    Posted
  • Location: Longwell Green, near Bristol
  • Weather Preferences: Storms, Gales, frost, fog & snow
  • Location: Longwell Green, near Bristol

    12z High Res Hirlam good for a wide area of our region;

    hirlam-1-48-0.thumb.png.d6482de092acae3c04df655bd0b99f0b.png

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    Posted
  • Location: Longwell Green, near Bristol
  • Weather Preferences: Storms, Gales, frost, fog & snow
  • Location: Longwell Green, near Bristol
    2 minutes ago, Bristle boy said:

    Chucking it down! Heaviest snow of day. 

    It is all white everywhere. Settling on all surfaces.:yahoo:

    Just goes to show the locality of the showers.  Just a light flurry in the wind here.

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    Posted
  • Location: Stoke Gifford, Bristol
  • Location: Stoke Gifford, Bristol
    Just now, AWD said:

    Just goes to show the locality of the showers.  Just a light flurry in the wind here.

    It has just turned into a whiteout - i am not exagerrating.

    Just in time for rush hour and around here that is a nightmare!

    Edited by Bristle boy
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    Posted
  • Location: Redlynch, Wiltshire / 110m asl
  • Weather Preferences: Cold snowy winters, warm springs, hot summers, warm then stormy autumn
  • Location: Redlynch, Wiltshire / 110m asl

    Looks like the next showers are set to arrive in around 40 minutes around here, according to the Home and Dry radar. Will have to head out for that.

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    Posted
  • Location: Barton on Sea, Hampshire
  • Weather Preferences: Snowy winter, warm/hot summer with the odd storm thrown in
  • Location: Barton on Sea, Hampshire

    Decent looking shower going thorough @*Stormforce~beka* Land. 

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    Just a shorter (EDIT: hardly :D) update from me. As promised, I'll take a look at temps this time but first of all  there's some excellent news. Everything is looking great for "tomorrow" (we can worry about Thursday a little later on). The Met O briefly dropped their yellow warning for Wednesday but they quickly put it back as an amber warning for south Devon and South Cornwall (but read on). The dropping was most likely to have been an error anyway. So, what about "our" Channel streamer. Well  it's currently out there bashing Guernsey and Alderney.  Their airports were closed. Some reports (perhaps exaggerated, perhaps not) suggested about 25 cm of snow in under 6 hours and it's still snowing there. Do we have a member who can give us an unbiased account?  For headings and explanations about these type of charts, please refer to several of my earlier posts (eg: the one on page 106).

    lastsnowradar_uk.gif   anim_ir_color.gif   anim_ir.gif

    The snow showers are becoming much more frequent and some are reaching into our region. This will continue. With the pool of lowest temps (surface and 850s) about to move in from the east later this evening and overnight when the whole country "might" see an increase in shower activity. Just look at that expanse of thicker cloud over northern and north-west Europe. That contain a lot of snow showers that will be further enhanced as they cross the North Sea. Remember that this "low level convection" is caused by frigid air crossing a much warmer sea and is why the showers do not lose intensity overnight (unlike standard convection which depends on the solar heating of land surfaces).

    Whilst all that is very encouraging, I have suggested in all my posts so far that "Wednesday" will be important in terms of snow for many of us. I think of "our" streamer waiting out there in the Channel, gathering in intensity, biding its time, until it heads straight at us. This requires the flow to veer from just north of east to just south of east. I posted the "live" and the "GIF 24 hour to 0850"  pressure maps in my last post. So let's focus on two "frozen" (not literally but in this pattern perhaps they are :D) charts:

                      Feb 27th 0050                                              Feb 27th 1550                             Met O Fax for 0600 Feb 28th                     Met O Fax for 1200 Feb 28th 

    pression2_eur2-00.png    pression2_eur2-15.png    20180227.1030.PPVE89.png    20180227.0521.PPVG89.png

    It might look like very little change but there are key differences - all going in the right direction for us. The Scandi  HP continues to intensify more or less in situ. A great trend if it continues to help maintain the cold block against the Thursday attack from the south and to ward off any less cold intrusions (one to monitor closely). Then the increased isobar gradient, strengthening the easterly flow just as the coldest air moves in. A bitter combination and I would expect windchill temps to be well below those currently forecast (of -7c to -10c) perhaps sub -15c or even lower (see later). If that's all good, the most important change is the direction of the flow. Look how over the nearby continent it has already shifted from east-north-east to east-south-east. Over the eastern Channel it has shifted into the east and is halfway there. This has just cut off and stopped their snow streamer.

    The Met O faxes for tomorrow complete the change with the east-south-easterly flow now blowing straight out of NW France and across the full length of the Channel.  Remember, the air flow only has to cross about 10 miles of water to pick up sufficient moisture from the sea in its lowest layers to produce low level convection - initially building clouds, then light showers and then much heavier showers. Look at the standard satellite imagery along all of the north-west European coast and you can see that there is a short clear zone and then with increasing cloud. As I said this morning this will push our streamer right up to our south-western shores but it is not just the streamer. Just as the east coast benefits from their on-shore easterlies from the North Sea with snow showers pushing a long way inland, then we will too. That means that roughly from Brighton westwards "should" be in the firing line and the further west one goes the longer the sea fetch is. Another reason why Channel streamers in our region are so rare, is that convective easterlies need a very cold source and northwest France is often not as cold as slightly further north. Not this time though, the coldest 850s and lowest surface temps that are moving across the UK tonight and tomorrow are moving right down into central France too (which is also further help for Thursday's LP to pick up some early dense cold air into its circulation before it gets anywhere near to us - every little helps :)). As long as this convection source is there and the flow remains just south of east (both of which now look to be odds on)  we may get over 24 hours with this exposure.

    Those (mostly) light snow showers and flurries that have been reaching all the way down here today (I just had my first very light shower just now but not enough to settle) have crossed all the way from around the Lincolnshire and north Norfolk coasts and the Wash and originated from a few miles off north Holland. Imagine us being much nearer to the source and just do the maths. If the Met O doesn't extend our amber warning further east along the south coast or even produce at least a yellow warning, then I will right now :D Here's a badly annotated chart. I had to use print screen, then save it into paint, edit it there, crop/enlarge/annotate, save it as a PNG doc and upload it into the pre-submit part of this post. Despite using loads of charts, I still think that I'm doing something wrong in this process and I'm unsure if you can enlarge it to view it properly (and the white run through arrows may not work either). If so, I can only apologise. I have annotated the map to demonstrate my points. The dreadful looking red arrows should be the approximate direction of the on-shore winds - they might even be very slightly more easterly than south-easterly but this is near enough. The green line is my minimum impact line - how far inland the showers go before fizzling out.  The purple line is my estimate for their maximum extent. if anything, I may have been too conservative with this. using today as a yardstick, even the north Somerset coast may get some decent showers and then our friends in south Wales (who have generally done better than us so far) will benefit from the flow picking up more moisture again as it passes over the Bristol Channel. I have stuck my neck right out with this forecast and only time will tell. If you want to shoot the messenger tomorrow, I've just emigrated to the South Pole :) 

              5a957c222665a_snowchart.thumb.png.ad50697af9df6a096c204207648d0eb7.png    sstuk.gif     2018-02-22uk.gif

    Now that I've hinted at the sea surface temperatures (SSTs), i do not want anyone to be curious. i did a full review of these in my Eurasia temperature report on the MOD last week. While I was just using that chart to do the annotations, I noticed that the SSTs had fallen back already by about 1 c in the last 4 days all around our southern and eastern shores. They would normally take a few weeks to drop back this far. This just shows the effect of the very cold air stream. For our sea to freeze close to our coasts, we would need another month or more of this level a cold. Only in the end of our epic winters (like in '62/'63) does this happen. That story this morning about the sea freezing over at Weston-Super-Mare is ridiculous! I imagine what happened was the tide was out, the very low dew points dried out the beach rapidly and then a heavy snow shower dumped several centimetres there. The tide comes in very quickly over those long flat beaches. So, just near the tide line there would be pieces of slush and snow caught up in the advancing waves for a few minutes before they melted. A photographer could show ice flows but don't believe the news reports. Was it the Daily Express (other "usual" suspects are available) who stated this?

    Finally, some of the latest temperature charts (without comments for a change):

                         Live 2 M Temps                            2 M Temps GIF 24 hours to 1610                             Live 2 M Temps                                   2 M Temps GIF 24 hours to 1610      

    temp_uk.png      tempresult_hqm5.gif        temp_eur2.png         tempresult_miy8.gif

              Live Dew Point Temps                            Dew Point Temps GIF 24 hours to 1610            Live Windchill Temps                                 Windchill GIF 24 hours to 1610      

    pointrosee_eur2.png      tempresult_vbh0.gif        windchill_eur2.png        tempresult_ldt2.gif

    Well just one comment! The UK "GIF" temp map should end near to the daily maximums but look how the temp has already dropped for the last 2 hours or so - an early indication of the coldest air moving in. I'll let someone else post an 850s chart. Will we see lower than sub -14s - perhaps some sub -16s early tomorrow? 

    I'll be back with a really brief update around 11 pm or so. 

    David

    EDIT: My annotated such does work properly. Now we just need it to be right :) 

    Edited by Guest
    Correct typos and check charts
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    Posted
  • Location: Lytchett Matravers - 301 ft ASL
  • Weather Preferences: Snowy Winters, Torrential Storm Summers
  • Location: Lytchett Matravers - 301 ft ASL

    Looks as we were to me at the moment, no significant changes going by the 12z so far! 

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    Posted
  • Location: Winterbourne, South Glos
  • Location: Winterbourne, South Glos
    1 minute ago, Bristle boy said:

    Just as i've typed that last post it is dying out:D

    Yep blue skies behind :D

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    Posted
  • Location: Caerphilly
  • Location: Caerphilly
    1 minute ago, karlos1983 said:

    Looks as we were to me at the moment, no significant changes going by the 12z so far! 

    I don't understand what they're saying in the model thread mate, surely the met office wouldn't upgrade to an amber without real concern.

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    Posted
  • Location: Weston-Super-Mare, North Somerset
  • Weather Preferences: Thunderstorms in the summer, frost fog & snow in winter.
  • Location: Weston-Super-Mare, North Somerset

    Massive heavy shower ncoming, been watching it getting  closer on  the radar. 

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