nick sussex

Lol! It’s an Amber Green combo ! The committee meets tomorrow morning to discuss going to green!

Another run ticked off with no major early dramas. Not the greatest week for the GFS with the overblown low crossing the south which is now just a shallow feature and its flat bias coming to the fore upstream. The shortwave to the nw still needs to be nailed down in terms of track and depth , that might still produce some interest. Overall coldies should be happy and we’ve seen quite a turnaround after the initial west based neg NAO trauma of last week.

Great ECM run for the Scottish ski resorts aswell as those across mainland Europe. After the mediocre GFS good to see the ECM continuing with its festive spirit. As long as the UKMO remains onside then confidence increases. Hopefully NOAA trash the GFS in their state forecasts!

I think we might be seeing changes upstream beginning to effect the brief model consensus . The ridge over the west coast of the USA is expected to break down early next week , in terms of the PV over Quebec which had stalled its what happens to that. Does this edge east as per the GFS or does this head more ne. The GEM goes with the ne helped by a bit more amplitude over Canada . Given the GFSs recent performance and it’s known upstream flat bias I’d tend to put more weight on the ECM. Its only a few days ago that the GFS made the wrong call within T120hrs. If the ECM goes flatter then fair enough but given tonights UKMO I’d be surprised if it follows the GFS.

I’d be a bit dubious of the GFS and that shortwave deepening that much. This is a known bias of it. These set ups are notoriously difficult to forecast accurately in terms of snow versus rain . The track will be effected by the depth of the low, so if you’re in the south you want a shallower feature in the north something a bit deeper as this will take it further ne. It’s a marginal set up regardless.

Thankfully the GFS 06 hrs run has a better shortwave track. It might be a case of rinse and repeat with another one heading se later. The key is to get low heights into Central Europe which hold there. As long as the PV over northern Canada remains stalled there with low heights over Europe that keeps the door firmly shut on any milder conditions . In terms of the possible snow earlier on I remember reading that the Met Office does take note of the Arpege model.

Not liking this mornings outputs which seem to be shifting things west . The shortwave needs to run se and end up to the se of the UK not the sw as that pushes a ridge north ahead of it into the UK. The UKMO is a shocker this morning both it and the GFS develop an even more west based set up. The latter eventually pushes the ridge to the se away but now we’re dealing with events well outside of the reliable timeframe which means even more time for more variables to pop up. ECM holds onto it’s Amber warning, the GFS and UKMO are now moved to Red!

As much as we've seen some good outputs I'd like to see the following corrections to the ECM. This would stop the chance of any milder air over the Med daring to show its face! The only issue I have with the ECM is the shortwave track, although we of course need the amplification initially too much of a good thing could cause issues. Remember here the shortwave can feed those low heights over mainland Europe, we don't want the shortwave dropping south as that pushes a ridge ne ahead of it, you can see on the T192 hrs that little high nosing into southern Europe. If the shortwave tracks too far to the west this ridge gets pushed in to the UK and theres less chance of some snow on the northern flank with that track too far to the west. Overall I am happy with the outputs but with this caveat re the trigger shortwave.

Overall lots of interest tonight but the ECM loses a mark for not delivering a better shortwave track. In terms of depth of cold we’re not seeing values that are that cold but this can change . Given what the outputs showed a few days back it’s hard to moan because it’s been quite a turn around .

Good ECM run so far but we don’t want too much amplification upstream. This might sound bizarre but you want the shortwave heading se into eastern France to feed low heights over mainland Europe. If the shortwave heads south too far west it will force a ridge to develop over southern central Europe.

Two more outputs with no major dramas! We’re inching towards the all clear re the trigger shortwave. The UKMO looks very good at T144hrs with more margin for error than the GFS. However after discussions at the CSAC. Cold Synoptics Action Committee the majority decided by 10 to 2 to maintain the Amber Warning . The 2 dissenting voices who wanted to go to green were a couple of cold rampers from net weather !

Yes I'll do that. The amber alert will remain till the trigger shortwave is at T96hrs! We've had some dramatic trigger shortwave dramas in the past, as long as the toughing over Quebec behaves we should be okay but its best to be cautious.

If you look at the ECM ensemble temps for De Bilt there are more colder options today than on last nights ECM. Of course if the flow was more northerly then northern parts of the UK would show colder values but as we're beginning to see a trend to topple the ridge towards Scandi De Bilt can be a decent guide in that situation:

Just caught up with the outputs. Nice to see the GFS climb down and overall good agreement on the pattern with a few minor differences in the earlier timeframe. It looks like the all important upstream troughing over Quebec is going to stall for a time, sending some shortwave energy into the Atlantic. The key timeframe is between T144 and T168hrs, the trigger shortwave is circled this needs to run se without any residual energy attachment to the upstream troughing. Once that happens you're in the clear to develop the ridge to the nw: ECM T144hrs ECM T168hrs I wouldn't look past T168hrs and worry about the later output, we need to get the trigger shortwave into the more reliable timeframe. For the timebeing my warning system remains at amber!

I think the issue for the Met Office and other organizations which make LRFs is in terms of La Niña . If its a weak La Niña that helps colder prospects , a strong one would be a problem . You also have to factor in the MJO , that has much less impact with a strong La Niña. At this point I’d keep an open mind about December’s prospects . Theres also the issue of coupling which John Hammond alluded to in his excellent blog. I do think however that the UK needs to make the most of the current set up which is reluctant to stick the PV over Greenland . It’s quite unusual to see the PV so disorganized and reluctant to set up in its favourite place at this stage of the Autumn.

Even if you put aside the upstream differences downstream over the UK and Azores the GFS disagrees with the Euros at T96hrs and T120hrs hrs. It’s hard to back the GFS at T96 hrs against both models that verify ahead of it. We’ll see in the morning but I would be shocked if the GFS has got the right evolution.

Yes it’s new and good for a comparison . It’s a shame we don’t get that from the UKMO but that’s similar to the US fax chart going by the NH view . Given the GFS flat bias and the UKMO supports the ECM upstream I’d not lose any sleep over tonight’s GFS.

Heres the US forecasters fax chart for day 6: Next to that the ECM and the GFS: US FC ECM GFS You'll see the GFS is flatter with just one main low over the USA and Canada, that second low over the Great Lakes is important because as that runs east and phases it causes an anti clockwise motion on the main troughing further north which helps to keep the trough further west and not ejecting lots of energy into the Atlantic.

For the GFS to be right both the ECM and UKMO have to be wrong at T96 hrs. The GFS deals with low pressure over the UK differently and doesn’t split the energy near the Azores till much later. This together with its flatter upstream pattern and it’s too quick to push the Quebec troughing east later. NOAA expect that to stall into at least into Monday week.

In case people are wondering about this warning system! Lol it did appear a few years back but I shelved it because so few decent cold synoptics ever appeared in recent years there was nothing to warn about ! Red - low margin for error , liable to implode at any moment ! Amber- medium margin. Green- prepare to dust off the ear muffs, scarves and ice scraper. Green Plus- as above but include the sledge !

Not bad from the ECM but I’d like to see more amplification at T168hrs up stream to get more displacement nw of the high to the sw after that. Its crucial to clear energy between the high to the west and Greenland , the shortwave at T168 hrs is too flat . My margin for error warning system goes to amber for the ECM .

Still big differences between the ECM/UKMO and GFS at just T96hrs. Both to the sw and upstream , the GFS is much flatter over Canada . I’d be astounded if the GFS wins this early battle against the Euros at that timeframe. Moment of truth coming up at T168hrs on the ECM ! I can barely watch! Lol

A weeks a long time in politics and looks like a few days is even longer in terms of these outputs ! Perhaps for a change the UK will clutch a victory from the jaws of defeat rather than the other way around which often seems to be the case . Tonights GFS does get to some interest but we do see a difference of opinion earlier on two fronts, it doesn’t split the energy to the sw near the Azores and brings that ne into the UK and upstream it differs from the UKMO in terms of amplitude and phasing/timing. Interestingly NOAA prefer amplified solutions for the east USA for next weekend and that’s positive news for those hoping for something colder in the UK. It’s this upstream amplification that’s needed to help downstream. Tonight’s UKMO is offering support for this mornings ECM in terms of upstream timing and key features which is good although it’s a touch flatter than the ECM. The key timeframe though comes after T144hrs with the ejection of that shortwave , the one just to the sw of Greenland . That’s covered on page 152 , a bit more explanation as to what to look out for. So hopefully tonight’s ECM will keep the faith! I should add the GFS isn’t so interested n the Arctic high and Greenland ridge combo but goes with just keeping positive heights over the latter. As long as we get to cold I’m sure most members don’t mind how get there!

As promised here are the ECM T144 to T192hrs NH charts: Circled red is your main troughing, black your shortwave, as the shortwave runs east its phased with the troughing: When this happens this effects where the trough energy goes from the trough,because some amplification develops upstream this helps to sharpen up the energy ahead at T168hrs. That triangle ridge between the shortwave about to be released and the low over the Great Lakes is important because you need that sharp little ridge to help direct energy se. You need a clean release so at T192hrs you have a clearance of energy between low pressure near the UK and the US troughing, this allows ridging in between both after that to work in tandem with Arctic high pressure to help push those low heights into Europe. These types of forecast synoptics are very hard to verify and don't have a great track record. Not saying it can't happen but a lot needs to go right upstream aswell as to the ne of the UK.

Good grief the drama never ends! The ECM pulls out a great end with a big pattern change over Europe, limpet Azores high sent packing to be replaced by low heights which is essential for any meaningful longer lasting cold into the UK. Before then yet more changes to the handling of shortwave energy near the UK. Positively for coldies the models are agreed on splitting that energy near the Azores away from the UK troughing which helps to edge the pattern eastwards. Going back to the ECM I'd view that with a case of so many things have to go right that its a low probability solution. The UKs hopes to a large extent rely on the behaviour of troughing over the ne USA, this will eject shortwave energy into the Atlantic. Overall after a few horror runs for coldies a few days back we've seen some improvements but still a long way to go. PS for those that like my crayon jobs I'll put up a few charts soon to explain why that US troughing is crucial to cold hopes and especially for the ECM to have any chance of delivering the promised land!