nick sussex

It’s not that bad , look at the change of isobars between T144hrs and T168hrs , the lobe of high pressure to the west of the ridge near the UK has been pushed north ahead of the amplified wave working east out of the ne Canada . It’s difficult with the restricted view but it could have been worse.

The ECM run is a little disappointing towards the end and we’re back to discussing those shortwaves because the wheels come off when one of these shown to the sw of Greenland at T168hrs hrs doesn’t disrupt sending sufficient energy se to support the block. Indeed it could have been worse had it properly phased with the upstream troughing. That’s not to say the ECM is bad, it’s cold right to day ten but getting energy under the block would extend the cold and keep our options open. I think the critical timeframe is now looking around T168hrs to T192 hrs, energy distribution at that point will be the decider. You need energy disrupting off that shortwave allowing the ridge to get over the top of it.

Lets bet a virtual beer, wine whatever takes your fancy and await the T168hrs which comes out later. The direction of energy coming out of the ne USA is se then bouncing ne with those two more amplified little waves working across Canada and if low heights remain over northern Italy I think we'll see a squashing/ deflation but not a complete write off. Anyway lets hope that horrid mild ramper hasn't also hacked the ECM!

I think the UKMO is more a deflater than complete sinking of the high because of the upstream pattern at T144hrs. It manages to get the worst possible outcome , you either want the shortwave absorbed quickly by the next upstream low or energy heading se from it and disrupting. The UKMO was programmed tonight by a mild ramper who decided to pick the worst phasing outcome!

Positives and negatives this morning. The jet looks uninterested in firing up, the PV remains far enough to the nw so any attempt to breakdown the ridge will be a struggle and the ECM tries to take another chunk of the PV towards Scandi. We do though need to see an injection of deeper cold into the flow. On the negative side I think some patience is going to be needed because we don't have that deep cold close by ready to tap into. The models still diverge with their solutions however NOAA do not like GFS ops for upstream: REGARDING LEADING SHORTWAVE ENERGY REACHING WESTERN NORTH AMERICA BY EARLY MON, GFS RUNS CONTINUE TO OUTPACE OTHER SOLUTIONS INCLUDING THE GEFS MEAN ACROSS SOUTHERN CANADA. FROM THE START OF THE PERIOD THIS PRECLUDED USE OF THE OPERATIONAL GFS IN THE FORECAST BLEND. To see improvements in the ECM we need to see more trough disruption around T192hrs. We're missing some amplitude upstream which would help to elongate this low and send some energy under the block: The low circled red responds to the upstream flow, sharper upstream will help to amplify the low which in turn change its tilt to more negative allowing more forcing by the high pressure which in turn helps to disrupt energy se which allows that high to edge nw at the same time this will help pull the low ne of Scandi south to the east. Its a good thing to remember for newcomers every upstream change has a knock on effect downstream. Overall the outputs are good in terms of potential but expectations need to be managed this is no Dec 2010 at this point and the depth of cold isn't there. My best advice is to just see how things evolve, depth of cold might change and so could snow prospects.

The UKMO looks similar to the ECM at T168hrs. The complicating factor is that shortwave ahead of the main upstream troughing , that needs to disrupt se not head ne after T168hrs. That could still happen , energy distribution is poorly handled by models in the longer range .

Yes that’s possible but it would be more at the surface level rather than higher up. Even when we see those very cold easterlies , the deep upper cold doesn’t last forever and needs a topping up . What we’d like to see is a lobe of the PV ejected into the flow . Of course cold is cold even if it’s just at the surface and we’ve seen some snow battleground scenarios with 850’s not that cold. Convective snow showers need deep upper cold , frontal snow less so. Overall my glass is half full this evening and there’s room for positive changes in terms of the depth of cold.

Some interesting synoptics on show from the ECM but not the deeper cold to tap into. That might change though because there are bound to be more changes and it might be possible to get a lobe of colder air heading sw. The PV throughout shows no inclination to set up over Greenland which is very good news for coldies. Its hard to be too picky given what could have been on offer.

Good ECM so far, key moment coming up with whether some energy goes se at day 9. If you get that under the block then you lock in the cold.

The ECM at T72hrs looks better upstream than the UKMO for that time. AT T96hrs much better, not that flabby low but a cleaner deep feature.

One of the issues re the UKMO is the weaker low and then a shortwave runs ne and stops the ridge getting further north. You want a deep clean low over east Canada at T96hrs. The UKMO is a continuation of this mornings messier ECM run. The offending shortwave is that kink in the flow at T120hrs:

From what I've read of that La Nina research it doesn't distinguish between strong and weak La Nina but simply uses the rolling 3 month average of -0.5 or below. Its not clear whether it was the strength of the signal which tipped the balance rather than just the location of the biggest anomaly. The key component in terms of anomaly is that the greatest departure isn't situated in vector 4 but 3.4 towards 3. 150 to 120, the research saw the positive NAO because the greatest departure was towards 4. But I find it strange that the research didn't seem to divide up La Nina into strong and weak phases because that's critical in terms of the effects. The strong La Nina will often over ride other teleconnections so I'm not convinced by that research. Its like a piece of the puzzle was left out.

Thanks for the link I'll have a read.

Just looking at the latest ENSO update from NOAA . In terms of the current La Nina , after a big drop in ssts during October recent weeks have seen a stabilization which is good news. We want a weak La Nina with the coldest ssts centred over the central Pacific. This has in the past correlated with below average winters in Europe. This also means the MJO can play a bigger role rather than the signal being muted. Of course there are other teleconnections to factor in but we don't want to be facing an uphill battle against an unfavourable ENSO signal. PS for new members heres the ENSO regions:

After seeing the GFS 00hrs run I expected better from the ECM which adds a complication with a less clean evolution in its early timeframe. Todays ECM isn't as good as last night because the early messier set up doesn't get the high as north. It still looks cold with winds falling light later there could be some very frosty conditions, the UKMO looks much better at T168hrs with energy heading se. In terms of the upstream pattern lots of uncertainty with how amplified that might be and this has a knock on effect on how energy spills into the Atlantic. More amplified will help hold the PV further to the nw and with that a chance to get energy disrupting under the high. I'd not read too much into the later timeframe given comments from NOAA today: THE UPSTREAM PATTERN REMAINS AMPLIFIED ALOFT AS AN ENERGETIC ERN PACIFIC TROUGH THREATENS THE WEST COAST. THE MODELS NO LONGER OFFER A WELL CLUSTERED ENVELOPE OF SOLUTIONS WITH THE FORECAST STRENGTH/TIMING OF THIS FEATURE DAYS 3-7. MODEL RUN TO RUN CONTINUITY BECAME ABYSMAL TODAY WITH THE GFS MORE PROGRESSIVE THAN EARLIER RUNS AND THE ECMWF LESS PROGRESSIVE AND MORE DIGGY/AMPLIFIED. GIVEN ABOVE NORMAL UNCERTAINTY...PREFER AN ENSEMBLE MEAN APPROACH USING THE 12 UTC ECMWF ENSEMBLE MEAN AND TO A MUCH LESSER EXTENT THE 18 UTC GEFS MEAN. CONSIDERING WATER VAPOR FLOW/UPSTREAM FLOW AMPLITUDE AND CONTINUITY HOWEVER...OPTED TO LEAN STRONGLY ON ECMWF ENSEMBLES THAT OFFER LESS PROGRESSION/MORE AMPLITUDE THAN GEFS/NAEFS...ALBEIT NOT AS MUCH AS THE 12 UTC ECMWF. THE NEWER 00 UTC ECMWF HAS EASED FROM 12 UTC ECMWF AMPLITUDE. THIS FEATURE IS THE KEY TO THE SUBSEQUENT DOWNSTREAM FLOW EVOLUTION NEXT WEEK IN A PATTERN THAT GUIDANCE SEEMS TO BE EXTREMELY SENSITIVE TO THE DETAILS OF MID-UPPER LEVEL SUPPORT TO LEAD TO SURFACE CYCLOGENESIS

Welcome and no you’re not wrong in terms of the current depth of cold . However this far out the depth of cold might change. I tend to view the outputs from getting some favourable synoptics and then worrying later about depth of cold. And if you can hold onto those synoptics surprises can pop up in terms of snow. Given what could be on offer it’s a case of glass half full IMO.

The next thing to look out for in the outputs is whether this more amplified wave works across the USA and Canada. This could help to sharpen up the pattern in the Atlantic and send more energy se'wards. The ECM has this at T192hrs: This amplification has two effects, it phases with the PV chunk and helps to pull it a bit further away from Greenland, it could also help sharpen up the low sw of Greenland, preferably you want that low to elongate sending energy towards Iberia. This would then help support the block. The ECM almost delivers on days 9 and 10 but unfavourable phasing doesn't quite deliver the best outcome. Its still a good output but we could with a bit more amplitude than what it has at that point.

Good to see the GFS 18hrs run backtracking, still not quite as good as the ECM but we should be pleased that the day ends on a high note for those looking for some festive weather. We're not seeing however any deep cold currently modelled but 850s this far out are subject to change. There are still some uncertainties upstream past the initial shortwave which could effect whether enough energy can disrupt under the block by day ten however the CSAC (Cold Synoptics Action Committee) convened an emergency meeting where Code Green was given the go ahead!

Good stuff from the ECM tonight, almost a carbon copy of its 00hrs run. Its far ahead but at T240hrs if we get some trough disruption to send energy under the high that will lock in the cold and with the PV not interested in setting up in its normal place you couldn't really ask for more given some of the recent horror starts to winter. Overall I'm very happy with the outputs barring the misery GFS. Given the timeframes it would be good to see that making a decisive move towards the others on its 18hrs run.

The ECM so far is very similar to this mornings run at T168hrs. Interestingly it disagrees with the UKMO/GEM over the central USA and Canada at T144hrs, no amplified trough but crucially they agree on one deepish low over ne USA at T120hrs which will run ne and help develop the ridge ahead. The GFS has a lack of phasing, no single deepish low and isn't supported The good thing about this is if the ECM adds more amplification at T144hrs the knock on effect will drag the high further north, even without that it looks fine. The GFS has no support and a very unlikely solution. I would be astounded if the GFS is correct.

No! lol Look upstream, keep the faith the GFS is cat litter at the moment.

Whats interesting about the possible evolutions is the ECM this morning managed to deliver some decent output without making much of that amplified upstream trough past T144hrs. Because its earlier timeframe was already much more solid than the GFS it wasn't a problem. If it follows the UKMO and GEM with more amplification then it could get more interesting. Of course at this point the main thing is getting the shortwave se without any dramas.

We're not the only ones underwhelmed by GFS ops. NOAA think its flip flopping too much! In terms of the upstream pattern : AN ACTIVE MOIST PATTERN WILL REMAIN IN PLACE FOR THE PACIFIC NORTHWEST/NRN CA AND THE NRN INTER-MOUNTAIN WEST/ROCKIES THROUGH THE UPCOMING WEEKEND, AS A SERIES OF ERN PACIFIC IMPULSES ALONG MULTIPLE STREAMS LIFT INLAND FROM THE SOUTH AND WEST. THEN ON CYBER MONDAY, A VERY PRONOUNCED AMPLIFIED UPPER TROUGH WILL FOLLOW UP THESE FEATURES ALOFT AND SPREAD THROUGH THE WEST TO REACH THE INTER-MOUNTAIN REGION AND FRONT RANGE OF THE ROCKIES. MEANWHILE, THE UPPER RIDGE INITIALLY OVER THE WEST SAT MORNING, STRETCHING FROM BAJA CA NORTH THROUGH THE INTER-MOUNTAIN WEST... WILL GRADUALLY PRESS DOWNSTREAM FROM THE INFLUENCE OF HEIGHT FALLS SPREADING INTO THE WEST TO REACH THE MIDDLE TO EASTERN THIRD OF THE COUNTRY. THIS MEANS THE INITIAL AMPLIFIED COLD UPPER TROUGH OVER EAST OF THE MS RIVER WILL SWEEP OFF THE EAST COAST, AS HEIGHTS ATTEMPT TO REBOUND SOME. BY NEXT TUES AND WED, THE PROGRESSING BUT AMPLIFIED UPPER TROUGH EJECTS OUT INTO THE PLAINS/MS VALLEY BUT INCREASING SPREAD KEEPS SOME UNCERTAINTY ON WHETHER A RATHER DEEP CYCLONE FORMS OR WHETHER THE SYSTEM REMAINS PROGRESSIVE WITH JUST SOME LEFTOVER UPPER DYNAMICS POSSIBLY CLOSING OFF TOWARDS NORTHERN MEXICO. THE ECMWF IS TRENDING TOWARD A DEEPER SOLUTION, WHILE THE GFS RUNS FLIP FLOP BACK AND FORTH. THE MEANS OF BOTH GLOBAL MODELS PRETTY MUCH SUPPORT THE LATEST OPERATIONAL SOLUTIONS. The GFS is much quicker with the amplified trough, both the UKMO and GEM are slower and more amplified with that, the issue of how much it deepens is still uncertain but the GFS has the fastest solution and given its recent performance I'd bin it. As this amplified trough moves east it should engage that chunk of PV , the amplification should help to pull the chunk further to the nw with some energy heading se into the Atlantic, but in this case it won't be what the GFS does with the PV being pushed east to fire up the jet.

Just to explain a bit more re the ECM/GFS differences. If you look at the ECM 00hrs for T96 and T120hrs. You can see the one low in the northern jet stream and the shortwave running ne from the southern, the ECM phases these into one deeper low, this is what you want to see: Now if you look at the GFS 06hrs T90 and T114hrs charts, you have the shortwave in the southern stream but see what happens at T114hrs:

Just when you think model consensus is approaching the GFS pulls the plug! The domino effect of failing to develop a single low over the ne USA downstream impacts how far north the ridge gets. These differences starts between T96hrs and T120hrs, indeed the big 3 disagree on what happens but the UKMO still manages to run the energy ne not more east like the GFS. We often see these issues when you have the jet flow merging, and then how much deepening occurs, in this instance you want the deepening because this causes a more ne track. In the New Hampshire state forecast they had this to say: In general, expecting a mid level longwave trough to linger near our region Friday into Saturday. As previously note, this is more of a split flow during this time. Majority of the guidance merges this flow into a deeper mid level trough Sunday into Monday. This mid level trough expected to finally move over the Maritimes toward the middle of next week. That on the face of it is positive but it seems as if we've overcome the trigger shortwave to now be met with another problem! It's slightly concerning that given the timeframes the GFS 06hrs run hasn't even made a partial backtrack so we'll have to wait for this evening. I'd tend to have more faith in the ECM given this difference is between T96 and T120hrs and it generally handles these split flows merging better than the GFS upstream but we'll have to see tonight.