swilliam
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Posts posted by swilliam
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That is some jet coming out of the US
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UK Outlook for Tuesday 15 Jan 2013 to Thursday 24 Jan 2013:
Sunny spells and wintry showers are expected to affect the UK on Tuesday and Wednesday. The showers are expected to be most frequent towards the east with snow likely to low levels, giving the risk of significant accumulations across some eastern counties. More prolonged rain, sleet and snow may spread into the southwest by Wednesday. It will be cold, locally very cold, with widespread overnight frost and ice. Thereafter, there is greater than average uncertainty, but central and western areas are likely to be mainly fine and dry although some rain and milder conditions may temporarily spread into the far west. Elsewhere, snow showers are expected and these spread further west at times. Generally cold with widespread frost, icy patches and freezing fog in places.
Updated: 1137 on Thu 10 Jan 2013
Seems the UKMO going with their model and not the ECM or the GFS although with the usual caveats about the uncertinty (who wouldn't)
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For the medium, term cold we seemt o be reliant on the shortwave near Iceland dropping SE. It is about to happen on the GEM but did not do this on the GFS.
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Control run FI is interesting in that it develops a sunstantial Sandi block -
might bring some super cold uppers if we get suitable undercutting
Sinks unfortunately
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Nice looking ensemble mean at 192 - split vortex, artic high, ridges in the Atlantic and alutieans
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If I had one gripe of the model output in general especially the ensemble mean is the relatively low pressure over Iceland and higher pressure over the Azores.
At +384 the mean SLP over Iceland is 995mb.
http://modeles.meteo...21-1-384.png?18
So going back to a concern of mine recently is the NAO and its positive phase. I realise the NAO isn't a driver but what if factors favour a positive NAO can the warming in the Stratosphere override this?
Over the next few days im eager to see an increase in SLP over Iceland but I would also like to see heights to our S decrease. During the Dec 2009 cold spell the ensemble mean was at 1030mb such was the strong signal for a GH!!
But as you said yourself the ensembles past the initial high pressure building over us are showing a wide variety of solutions - inlcuding having the PV right over or near us and some very deep depressions (terrible for the flood risk areas by the way). So it is no suprise that the mean shows lower pressure there and therefore on average a positive NAO. The deep depressions are deeper below average there than the high pressure is above average in the mid atlantic block solutions. There are also more solutions of this type than blocked.
So as I think SM once said to me the ensemble mean at that range is about as useful as a chocoate teapot. As long as some blocked options keep appearing I would not worry too much.
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I doesnt appear to be as many lows in 12z over 6z.
Look like the Northerly has gone though
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the first 14 days of this month were not mild
in this area the mean temperature was 2.2C the average is 4.6C
Hi John,
It seems, in this thread at least, anything that is not cold (enough for snow) is called mild or even very mild. I got told off for pointing this out a couple of days ago when someone said Christmas was going to be very mild when in fact the model predicition was for near or slightly below normal.
Stewart
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Happy with that, -4 covering most of the country on the MEAN is very impressive? Must be some very decent runs in there?
Lots of really good members but what is more impressive is the clustering.
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Control run from the GFS is looking very nice in FI.
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A very mild christmas period coming up if this run is to be believed http://modeles.meteo...nh-0-138.png?18!!
Who knows we may get the whole pattern to back westwards some more but unlikely enough to keep xmas cold unfortunately!! LOL Just goes to show what a crazy run the 12z was, good ol GFS!!
Still some interest in the hemespheric pattern i suppose, heres hoping for a chilly new year!!
Doesn't look in the very mild catergory to me except in the far S (even then just above average).
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Looking at the GEFS is seems pretty solid till the 13th then after the 16th anything could happen
Here in N Sweden (lulea) no problems. -14C and light snow with breeze. Major snow in Stockholm yesterday due to heavy snow causing problems geting here
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I think we want the low heading NE out of NA to head upthe W side of Greenland like it did on the 06 (and not underneath it)
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Disagree you compare the 6s to now not much change re Atlantic...
The difference is the trough to the S of Greenland is less favourably aligned to disrupt - let's hope it does though.
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Unless ive missed something here i don't believe windchill has any effect on the actual temp. It just makes it feel colder as the warm air from around your clothing is being blown away. Also a strong wind will cause moisture in your skin to evaporate faster and cause it to cool down.
The wind speed does have an effect on the actual temperature in an Easterly. With a slack flow the N Sea has a large influence - increasing both the dry and WB temps. With a strong wind the air from the continent has less time to increase in temperature so it is colder as a result. The direction is also important. If it is SE then there is a short sea track but this increases as it becomes E and then NE. This increases the temps but also increases moisture and convection producing more precipitation. The big advantage of low uppers is that we can get large amounts of convection and this remains as snow even on the coast.
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Anything pointing to anything more substantial further west or is it the same?!
If you bug him with will it snow in backyard questions every times he posts then the result will be that we will not get this inside info.
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Well ECM is very similar to the UKMO at t14 so I guess we will get to see it might evolve from here.
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Good signal, I think the end game will eventually be the same no matter what, its just do we take the LONG way round (like UKMO) with less cold pooling to tap into, or do we take the easier and probably colder method of getting into the great set-up.
Either way, its going to take a real botch job not to get very cold at some point this month!!
I really do think people should stop guessng what will come after the UKMO 144. Looking at it those small LPs they could move in a variety of ways and we will never know who is right/wrong as it is extremely unlikley to verify exactly like this anyway. None of the models are showing the link up at this juncture so I do not know why people think the UKMO should. Also remember that IF said last night that the UKMet do not use their GM beyond day 5 anyway.
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The CFS is giving the vortex to us for Christmas
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Just a reminder, if you are getting a bit annoyed with someone's posts, we have the ignore function so you can stop them from appearing for more stress free model thread viewing
Except they then appear in someones irritated reply to them - can we switch someone's reply to an unwanted poster off as well?
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I must say there are some rather silly posts on here tonight; talking about how can the ECM be so far out, saying it is a battle between ECM + minors agsinst GFS/UKMO and depending on the outcome one is right and the other wrong etc.
There are two basic solutions for the period t120-144. One is that we have extensive blocking to our N and a cold solution for a protracted period (i.e. GFS/UKMO). In this case the Canadian low goes N/NW up the W coast of Greenland and does not send enough energy eastwards to break the Atlantic ridge.
Eventually this minor remnant energy moves SE as a potenial slider.
The other is that the Canadian low sends energy eastwards and does not go up the W of Greenland - a small difference in positioning of this low.
This energy then breaks the link between the Atlantic ridge and the N blocking. The result of this is the Atlantic ridge falls over and the energy from, and substantial remnants of, the Candian low link up with euro low and we end up with mildsih westerly winds over us. Blocking and splitting vortex remain to the N but we loose the blocking in our immediate vicinity (only).
Thereafter there is the possibility of blocking reestablishing near to us.
The differences between these two solutions is very small and therefore marginal but the consequences for our weather >t144 is massive. So whichever way it goes (and no-one knows at present) does not mean one model got it hugely wrong or right - both options are quite plausibe at present - further small changes will determine which way it goes. These two solutions have been showing on the ensembles in the last few runs and on one or two of the GFS ops (when it was derided).
Some less hysterical or emotional posting would make this thread rather more enjoyable.
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Short term 18z ensembles look rock solid for cold
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Would be some interesting weather for Canada if something like this happened
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Its not the BBC but the Met O Fred, and simply highlights my post last evening about not doing knee jerk reactions. To me the Met O have not done any knee jerk reaction, simply refined the outlook. They always stressed the uncertainty, showed where ONE model had the rain and said keep watching.
Again I have no idea why weather systems from S-SSW give so much trouble. I would be very surprised if a small team are not working away trying to discover what is the problem from that direction.
By this time tomorrow the actual system can be tracked by surface and upper air observations as well as satellite so back to 'seat of the trouser' type forecasting for me. However I don't think Met staff have that luxury and have to accept the model outputs.
adding to the above after looking just quickly at the GFS output at 500 and 300mb along with the 3 latest Fax charts from UK Met.
These shows a path consistent with the upper air on GFS for the next 48 hours, that is running ENE from its 00z position, initially not deepening possibly even filling slightly before starting to deepen a little but not much.
The upper air pattern is looking consistent with no major deepening.
The next system - surface and upper air is perhaps the one that shows signs of deepening?
HI John,
I am not sure that the models do have more difficulty with depressions from this direction - it is just that small changes have large effects on the weather (especially in Southern England but we won't go there). If you look at a typical depression most of the weather is to the S of the centre. Typically there will be fronts dangling many hundreds of miles S of the depression often with strong winds and following on behind a large area with showers. So if one of these depressions moves to the North of Scotland most of the UK will get a spell of wet and windy weather followed by showers. The forecast is easy and if there is small variations in the track of the depression nobody notices much.
To the N of the centre of the depression though the area of rain and strong winds is often aligned either SE-NW or even E-W associated with the occluded or occluding fronts. This area of rain is therefore aligned with diorection of travel so if the depression track varies by relatively small amounts the change in the weather in a particular locality can be quite marked. The result is that the changes in the track of the depression are noticed much more - like the one on Sunday.
This can be seen on the fax chart for Sunday.
The depression in question extends all the way from N France to S Portugal so for most of France small changes in the track will have relatively little effect on the weather. Near the depression centre though the fronts are aligned E-W (the same direction that the depression is travelling in) so small changes in the path will have a big effect on the weather in the extreme N of France (and also of course S England). This general effect can be seen even more so for the deep depression near S Greenland. If you happened to be living on the tip of S Greenland (plenty of interesting weather there I should think) then the track of this depression would have a major effect on your weather. To the S of it though the weather is essentialy the same for more than a thousand miles - so you would not care to much about track - it going to rain and then there will be heavy showers.
Having said all that the tracks from this area may be somewhat less predicatble for couple of reasons
1 - The depression coming from this direction are often rather small with a low overall energy and so can have tendency to wander - e.g. Sundays depression
2 - Similarly and probably because of this they are often associated with a rather weak jet so the direction is less well determined. This can be seen by looking at the jet profile for Sunday
The jet with this depression is quite weak so the steering is not very forceful. Compare that with the much more energtic low to the S of Greenland - here the jet is very strong and everything will probably be quite predictable with this system.
Winter Model Discussion - 12/01/13 06z Onwards
in Spring Weather Discussion
Posted
Even the NOGAPS looks ok - decent block at +144
Begins to undercut at +180