swilliam

Also it is a long term forecast and we know how reliable they are - it certainly does not put anything to bed.

They cannot be that uncommon - the NH chart I posted for Jan 18th 2013 had one of 1050 hPa and in fact this grew to 1060 hPa by Jan 20th. Point taken about ECM overdoing heights in the later charts though.

HI TEITS, Yes you are correct - there were several undercutting scenarios producing significant snowfall without a big block e.g. 9th Jan 1020 mB and even more notably 23rd Jan 1015 mB The latter produced about 1 foot of snow here in Northampton. Interestingly the NH pattern shows a big Alaskan ridge along with the PV over NE Canada as is expected in the next few couple of weeks this year. Back then I remember a lot of discussion about whether these 'blocks' would resist the rampant PV and promote trough disruption - the naysayers were wrong again. Not saying this will happen again this year but is always a possibility which we should look out for to show up on the Ops and individual ensemble members (will not show on means)

Amazing temperature changes here in Northampton. At 18:00 it was 0.9 C and snowing. Temperature gradually rose to 6.7 C at 10:30 with a DP of 6 C - felt quite balmy. Both temp and DP dropped 2 deg in 1/2 hr and now temp down to 0.9 C again. A 12 degree change on 6 hrs.

After some snow earlier temp up to 5C but expecting that to drop as the depression moves SE. You can see where it is on XC weather http://beta.xcweather.co.uk/GB/observations heavy snow to the North - rain to the South. Problem is the precipitation is usually heavier when the low pushes into the cold air and becomes lighter as it moves away. We shall see.

That is not the control run it is the GFS 00Z Op.

Thanks Sylvain, Some significant improvements planned or early next year - especially the horizontal resolution. Not sure taking it out to 720 hrs as planned 2018 is a good idea - we will be discussing forever on here.

The pattern has not been flattened so much with HP still close by Leading to some cold frosty weather (at least in England and Wales) And therefore the potential that it could develop into something more interesting later.

The end of the high res GFS Op looks pretty weird to me - nothing seems to be happening - just a few small lows dotted about in the large PV Maybe the weather is in on its hols as well Edit Soon fires up in the low res though

Much as there is an overall improvement at 192 on the GFS (Op, P and Control) there is not much support in the ensemble. OP P Control Ensemble mean and spread - op and control outliers

Would certainly be windy and feeling cold Bust as Jason says no real snow - this is maximum extent of lying snow - 50 cm in the highlands but best for England is possibly a cm of probably wet slush. ECM would bring in some proper cold which could lead to some decent snow at a later date. Problem is these 240 hrs charts are not verifying but I would still rather take this chance. ECM still a mild outlier (along with the control)

Not sure why you are saying the GEM is an outlier to its mean. The Op shows a main low situated just SW of Greenland with a trough to Portugal, a Euro/Russian high with a ridge to S Scandi. Seems quite consistent with the mean to me with the same general pattern being shown.

It just about made it to S Northampton before dying - we had lots of thunder then torrential rain with hail. Looks like the cause was the overhang from the French storms getting this far N. http://www.sat24.com/include/images/trans.png

Yep - lots of flashes to the South near MK - should be here shortly

Doesn't mean that it is 'right' though - fortunately the weather does not run by averages

I think this illustrates two of the main otions open with the arctic high (if it appears) - it can link up with the Scandi high and then we have a chance of a major cold outbreak. This is illustrated by P1 although we do not quite the cold yet. The other option is that it links with the azores high through a mid atlantic ridge as shown on the ops. As NS and SM alluded to the first option is much better in terms of a real cold outbreak. With the second option because the PV is still located in NW Canada it is only a matter of time before it breaks down the ridge and we are back into more of the same mush. In addtion as NS suggested we have the worry that there is not quite enough amplification and the ridge is not enough to stop the low in NE US from phasing with the low over us - the result is no cold at all. The only route there to a major cold outbreak is if the mid atlantic ridge links up with the NW Russia high pressure through the latter ridging west - e.g. P7 So for me I would much prefer the 1st option. The main worry with this would be that it sets up to far East and the cold does not reach us or the Scandi high parks its bottom in the E Med. So lots of interest to see how it all pans out but I know what I am rooting for. Edit - of course anything is better than what we have just seen from the18Z

The ensemble mean has changed quite a bit a might be expected (especially for the 850s). However the debilt ensembles still showing some cold runs so still some possibilities although the METO 10% is probably about right. The mean at 240 still shows to my untrained eye a split jet to the WEST of the Uk - perhaps someone more expert could clarify. It also shows the PV moving menacingly towards Greenland

If you must worry about how long something will last which has not even happened you should read the guide for forecasters on Scandi highs posted by JH yesterday. It clearly states that the longevity of the block does not depend on its size. Quote 'The intensity of the anticyclone on the day of formation has no effect on persistence'. The main factor is the mobility to the East of the block. There are then someguidlines as to what factors affect the persotence of this set-up. I reattached it in case you did not see it yesterday. Empirical rules for scandinavian high to developc.doc This was also borne out last January when we had a small block with central pressure of only about 1015 mb which proved quite resilient. http://www.meteociel.fr/modeles/archives/archives.php?day=17&month=1&hour=0&year=2013&map=0&mode=2 It is the orientation and placement of the block which is most important in my view.

Don't forget Steve Murr

Yes it seems GFS is having nothing to do with the inland track of the US low and the consequent sharp mid atlantic ridge which leads to the weak Scandi ridge on the ECM. However it does seem to be favouring more robust buildng of heights to the NE in general. However it seems unlikley that this pattern could give us anything very interesting from a cold perspective in the medium term as it allows the reforming vortex to take up residence close to NW UK. Maybe some cold zonality due to its close proximity which I think was what the Meto were alluding to in the 15-30d upate yesterday regarding more wintry conditions - especially for the North.. I think I know which option I would prefer but the odds seem stacked against this. Were it to happen though (and it obviously possible) there would some very incorrect forecasts knocking about at present.

Wrong

I prefer 7 and 8 myself

Modified data I think is the phrase but indicates possibilities only and of course the averages are used to give the most likely solution at this range rather than the ops (as JH keeps telling us)

Pertubation 2 is interesting and demonstrating the sort a thing we are looking for( or hopecasting for depending on your pov) I see Mucka beat me to it.

Hope this does not come off for Christmas day!