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danm

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Posts posted by danm

    General Model Output Discussion

    in Spring Weather Discussion

    Posted · Edited by danm

    Have a look at the UKMO 00z.............

    S

    If im looking at the most recent update, it seems to show the low getting up to north wales by t96, then rapidly moving south east, drawing in the colder air. Am i right?

    EDIT: I was looking at the 00z link thats on this website, i think that might be yesterdays 00z. Not sure if im looking at the correct charts

    General Model Output Discussion

    in Spring Weather Discussion

    Posted

    LOL- Well so far this morning the GFS has handed the biggest can of xmas whoop ass ever to the UKMO & every other model.....

    Patiently awaiting the end of the week.... :(

    Do you think the fact that the GFS is sticking to its guns in the short term means that it may be correct in its modelling of the low pushing further north? Shouldnt the fact that all the other models are going against the GFS mean that its being far too progressive with how far north it is projecting the low to go?

    Model Output Discussion - 26Th Dec 21:25-->

    in Forecast Model Discussion

    Posted · Edited by danm

    Well if the ECM and METO charts come off times are changing for the UK winters,there was a hint of this last year in DEC and FEB,but the DEC cold spell never really got there.Its just astonishing how much blocking is taking place this winter,as a child in the 80s i remember seeing an Easterly on the BBC weather MANY TIMES and just used to to think it was a normal part of UK winters, untill 1987 when they just suddenly became very tame and infrequent.Lets just hope these charts really happen because after so many let downs, mild winters,lame easterlys,48 HR cold snaps my god we ALL deserve it.

    :p:)

    A Decade Of Weather

    in Spring Weather Discussion

    Posted · Edited by danm

    Down here in the London area i'd pick out these events:

    Jan 2003 Thames streamer snow event.

    August 2003 heatwave - 38c! Can't forget that week in early August, i had to sleep with 3 fans!

    Jan 2004 thundersnow event - left central London on the tube, it was dry and cold, walked out of the station half an hour later near home and there was an almighty blizzard with over an inch having already fallen in just over 20mins. The snow stopped within an hour and there was mayhem on the roads. Probably around 4 inches of snow by the end.

    June & July 2006 heatwave - Incredible heat. Day after day of intense heat, with countless days over 30c.

    Feb '09 snow - The heaviest snowfall in this area since the legendary Feb '91 cold spell. 7 inches of snow fell in this area overnight, which is a rarity.

    General Model Output Discussion

    in Spring Weather Discussion

    Posted · Edited by danm

    I thought id tag this one onto the model output this eve-

    Since the advent of the internet & the 'archives' on the forum every year since around 2000- even back in the snowatch days on the BBC forum ( some will remember this) we have all referred to Winters of old, the 63's, 47's, 79's ,85's etc etc- We place these with fond memories close to our hearts & are we are all very quick to post up images of what used to be-

    Brilliantly informative post, especially for someone like me who is just learning what exactly to look out for beyond the blatantly obvious. Let's hope it all pans out in the way you are describing. We are long overdue a classic winter. Me being one month shy of 24, the only real severe cold spell i can remember is Feb '91. Feb '09 was the closest we've got since then down here in the SE, but not close enough.

    Thanks Steve!

    In Depth Model Discussion, Analysis and Summaries

    in Spring Weather Discussion

    Posted

    I thought id tag this one onto the model output this eve-

    Since the advent of the internet & the 'archives' on the forum every year since around 2000- even back in the snowatch days on the BBC forum ( some will remember this) we have all referred to Winters of old, the 63's, 47's, 79's ,85's etc etc- We place these with fond memories close to our hearts & are we are all very quick to post up images of what used to be-

    Since the advent of this -

    http://www.wetterzentrale.de/archive/2009/brack/bracka20091216.gif

    some 10 days ago where the first pressure rise over greenland developed -this winter has had a whiff of a classic about it-

    Weary seasoned posters would have been sceptical about the pattern redeveloping in such a short space of time- especially with such familiarity as the last evolution, however as we edged to Christmas day & now almost beyond we see a potential 'classic' pattern developing- which in my opinion has a BETTER chance of sustaining cold & the UK seeing widespread snow- ( we havent done half bad this time round though)more of that in a moment & the reasons why-

    Firstly the evoltion thats being progged for the early part of next week is marginal at best, dont get me wrong we have a chance of something widespread, but as it stands the angle of attack, surface cold ahead of the front & upper air conditions do NOT favour a widespread snow event-

    If we take the ECM 120 which seems the middle ground-

    ECH1-120.GIF?25-0

    We see that the system moving along the channel bears the resemblence & hallmarks of that classic snow event in the making- but we are missing the vital ingredient- HP to our NE...

    We have seen a lot of Southerly tracking lows already- both this year & last year- the shallow shortwaves that skip along the coast- however the South & south east have seen rain events from ALL these- even central areas havent favoured much better-

    Take this chart for instance from the 8th of Feb this year-

    http://www.wetterzentrale.de/archive/ra/2009/Rrea00120090208.gif

    The UK in a cold run of Northerlies & very cold surface air prevailing over the UK- that shortwave undercut some of the UK but the cold got lifted out to quickly for most- it was a quick snow to rain event for nearly all- snow lasting less than 20 mins!!

    This has been the plight of the UK for some time-

    now look at a couple of classics-

    http://www.wetterzentrale.de/archive/ra/1982/Rrea00119820108.gif JAN 1982- the Irish & welsh should have fond memories here-

    http://www.wetterzentrale.de/archive/ra/1996/Rrea00119960206.gif Widespread snow over the central belt of the UK-

    http://www.wetterzentrale.de/archive/ra/1978/Rrea00119781230.gif THis lead to one of the most significant blizzards over the UK for many many years-

    So what have we learnt-

    Undercutting troughs- even if they are elongated require HP DIRECTLY to the NE to force the dry air undercut at the surface- with the only exception being if a shortwave is traversing EAST under a East based iceland block ( again more about that later)

    Back to the ECM 120-

    ECH1-120.GIF?25-0

    The trough over Norway is cutting the supply of cold off from the Scandi region- where the coldest airmass originates from-

    Sure we have a cold feed from the East but just not cold enough-

    taking the 18z at face value its a total rain event for the UK, taking the ECM at face value its a rain event for most in the South - with snow over the North & west & elevation a great assist here-

    Is there still hope for the mid part of next week- well yes- but we will need to be VERY VERY lucky with a quick flip back from the models to a track along the brest peninsula through & out East- even then thats not the end of the story - we will need minimal north sea track as well from an upper air perspective-

    Excluding what I think is dodgy outputs this eve I think there is a zone from yorkshire through to wales that does see snow ( mainly away from the East coast), although PERHAPS not as significant as initially touted ( I hope im wrong with that)

    This wasnt the reason of this post though really- its the background signal though & for the people that want to decipher things into more detail the finite differences between a Greenland block & Iceland block- Also how the amplification of the jet determines a Northerly over an Easterly- even though the blocking seems to be in the same place- ( & why a circular iceland block favours a Channel low as opposed to a Greenland block which favours a polar low)

    The background NH signal is a negative AO which if by now you dont know I will breifly summarise-

    High pressure at the pole & low heights forced into the mid lattitudes- by definition this then means that theres LOTS more air coming south out of the pole: in this situation as you will usually have 3 or 4 standing waves along with the higher polar pressure zone- - The eastern sides of the standing waves have huge amounts of COLD air advection moving South & the western sides have lots of warm air advection moving North-

    Note:- this is why in negative AO months the UK can be warm as we can still be on the wrong side of any potential blocking-

    What we are seeing now at day 5-10 is a rapid change in the modality of the NAO ( after a brief rise ) -

    http://www.esrl.noaa.gov/psd/forecasts/teleconn/images/nao.png it will appear here in the next few days-

    The modality change is showing that Greenland has a rapid rise in Pressure & areas towards the azores will drop pressure- the significance is that the AO is dropping to 3/4 Standard deviations below zero & the NAO is heading that way-

    this is the PERFECT menu of cold for NW europe-

    Teleconnections however do not give us 'local detail'-- local being the United Kingdom- this boils down to what type of blocking actually exists- as there are Many types-

    East based NAO, West Based NAO, mid atlantic block, iceland block-....

    What we saw develop last week was Clearly a Greenland block- Very central to Greenland---- this & west based Greenland Highs favour the NW UK & Scotland & NI- as they generally end up with NW winds over the UK-

    Fax for the 20th- 2009

    http://www.wetterzentrale.de/archive/2009/brack/bracka20091220.gif

    Reanalysis for 9th dec 1981-

    http://www.wetterzentrale.de/archive/ra/1981/Rrea00119811209.gif

    Note the central Greenland blocking - almost west based NAO-

    note the flow over the UK is generally NW- with the trough also west over scandi-

    Going back to last week the reason the pattern loaded to a Northerly & even N.westerly was because of the initial jet profile & the fact that it was VERY amplified North / South-

    We got a flow that went directly north up western greenland then returned sharp south southwards over iceland- hence the Northerly flow & how the vortex got shunted to the NE part of the UK-

    Also importantly here - note how close the shortwaves got to the southern part of the UK in the southern arm of the jet--- they didnt....

    because the Northerly flow kept them a long way South-

    http://www.wetterzentrale.de/archive/2009/brack/bracka20091221.gif

    look towards Portugal......

    We now though see a different pattern setting up which as I mentioned earlier seems to be the same- but with a couple of key differences-

    *) NAO block (high pressure) looks to be positivly tilted & circular as opposed to the squashed sharp North /South oval shape it had last week-

    *) at a SLIGHTLY more favourable locale V last week ( we are talking more EAST based)

    *) Pressure core looks to be centred towards the SE coast of Greenland

    *) THe jet flow off the states is less amplified over the top & doesnt look to cut a sharp gradient back directly south through iceland like it did before-

    What does this all mean-

    Look at these 3 charts-

    ECM 168- ECH1-168.GIF?25-0

    GFS 168-http://91.121.94.83/modeles/gfs/run/gfsnh-0-168.png?18

    GFS ENSEMBLE MEAN at 144-

    http://www.wetterzentrale.de/pics/Rz500m6.gif

    They all agree on a curved East ISH based NAO block that is in closer proximity to Iceland than we have seen in many a year...

    What does this all mean-

    It means the background signal for cold for the UK is developing at around 96-144, once completed it will force the pattern to where we want it & because of THIS angled flow of set up- ( note the waeker amplified flow off the states)

    http://91.121.94.83/modeles/gfs/run/gfsnh-0-96.png?18 IE more positivly tilted -

    the net result will be a more Easterly component in the air as its curving westwards on the southern side of the high as opposed to southwards before-

    this will eventually deliver for everyone, with a HIGH chance of a snow event coming up from the South west into Southern UK- this is why both models- ECM & GFS are modelling this-

    GFS 192-

    http://91.121.94.83/modeles/gfs/run/gfsnh-0-216.png?18 notice the block centring more over Iceland- ICELAND BLOCK= Perfect for the UK-

    ECM-

    ECH1-240.GIF?25-0 Almost an Iceland block- but the key is the curved flow over the atlantic- the shortwave will roll & Spin eastwards because its pathway is being vented & circulated from inflow on the NE quadrant > NE >SW & inflow from the SW quadrant >SW> NE-

    In Summary then-

    I think we are on the eve of a very special period in UK weather- MAYBE a classic in the making, I think the classic charts come though in the latter half of next week towards the weekend with an attack from the NE & the south west-

    If we get a wdespread snow event from the inital low pressure tracking along the channel then treat it as a bonus for the UK.............

    fingers crossed this could be the one-

    If we get the iceland block I would rate a higher chance of seeing a temporary link up with a Siberian /arctic type high pressure that has been lurking all winter-

    S

    Brilliantly informative post, especially for someone like me who is just learning what exactly to look out for beyond the blatantly obvious. Let's hope it all pans out in the way you are describing. We are long overdue a classic winter. Me being one month shy of 24, the only real severe cold spell i can remember is Feb '91. Feb '09 was the closest we've got since then down here in the SE, but not close enough.

    Thanks Steve!

    East Anglia & South East Cold Spell Discussion

    in Spring Weather Discussion

    Posted · Edited by danm

    I think this is where the over-reliance on the exact details of the BBC weather graphics needs to be cut out

    Think of it like the good old days pre-fancy graphics - just because it had a sleet shower symbol over all of EA and SE England it didnt mean that would be the exact weather all over that area

    SK

    I agree, however she also said herself that it would fizzle out. I wasnt just going by the graphics.

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