chionomaniac

I think it is time for a mid winter stratospheric assessment to see where we are and where we might be heading stratospherically. So, the story of winter so far, is one of an extremely cold stratosphere that has led to a powerful strong polar vortex that has dominated the outlook over the UK. But not everywhere due to the displacement of the vortex in the lee of the Pacific ridge, which has been an omnipresent feature this winter and has led to the east coast ogf the USA benefitting from the distortion. The cold stratosphere was expected this winter - but the extent of the cold that has coincided with the Pacific positive anomaly has been underestimated and we have seen a prolonged period at the end of last Year when we entered a period of Vortex Intensification (VI). When this occurs the effect on the troposphere below is strong and this leads to a positive AO and enhanced zonal conditions.This period is most ably demonstrated when looking at the mean zonal mean wind charts - especially at 1hPa- the VI period is highlighted and the mean zonal winds reached over 80m/s for almost 2 weeks - incredibly strong and that coincided with the festive storms. If we look further down the flux chart at the 30 hPa level mean zonal winds then another thing grabs my attention. These winds are about to reduce below 20m/s for the first time this winter. The wave 1/2 and 3 activity since the start of the year is beginning to take it's toll. One thing that I have noticed in previous years is that when the mean zonal winds at this level reduce significantly then the jet stream troposhericlally weakens and we see an increase in influence in blocking highs extending towards high latitudes. As the bike slows down it begins to wobble! So looking forward we are seeing a tropospheric pattern that I expected to see a few weeks ago (from the NW winter forecast) but the VI period has set this back a touch. The strong Siberian ridge appears to be growing in strength. The February part of my winter forecast offered 2 solutions - one based on strong stratospheric disruption and the other based on little stratospheric disruption. Well, it appears that so far we are somewhere in between. We have seen the strong wave activity so far this year that has led to the current tropospheric change in pattern and we have more wave activity forecast - but so far not enough to create a SSW. I still would not rule this out but we may not need one either. A SSW could be the difference between being at the junction where east flow meets west flow that we are seing now and putting is more towards the easterly side. We still see strong wave 2 forecast that could lead to a split in the vortex and this could just be the push and pressure that the Scandi high may need to push further west. This fits in nicely for the early to mid Feb forceast and coincides with the increase in tropospheric wave activity forecast by the Italian OPI forecast. The latest GFS Strat forecast show at 10hPa how this increase in wave activity could split the vortex by day 10 and this leaves us with a good deal of promise as to what could follow thereafter: This winter was always going to be a patient waiting game and it is now beginning to look as if that patience may be rewarded.

This is a great post because of the fact that it highlights the misconceptions that are often thrown around on here regarding the zonal regime. What is patently obvious is that the Atlantic will be a spawning ground for deep depressions and that these will move westwards towards the UK, hence the westerly regime indicated. It is because these are then stalling, slipping under the block or dissipating in the vincinity of the UK that the confusion arises. We are but at the end of the westerly line in this case, rather than along the main route that we have been all winter, and the difference between this has not been picked up by some members here - hence the confusion from some and the assumption that it will turn mild when the next westerly burst ends up and dissipates on our doorstep. A very encouraging set up for those who enjoy winter proper (after we get through this weekend).

I haven't time to post anything in detail, but to answer CH - I think that the strat is far more conducive now to allowing the forecast trop outlook to occur. Critically, we have lost the period of Vortex Intensification (VI) that has plagued the winter so far, and that leaves us with a vortex that is being bruised and battered by the forecast wave activity. We may not get a SSW or strong Greenland heights, however the disrupted vortex should be just enough to allow the Scandi block to persist. Will hopefully be able to post more thoughts later in the strat thread - but the promise is good and not unexpected and could improve further still by mid Feb.

Models please.....

Whereas Ian, the majority on here are searching for cold, I can assure you that the MOD thread is here to discuss all types of output and outcomes and that the type of winter storm brewing is another noteworthy one and worthy of discussion. It was for that reason that the off topic discussion was moved into another thread. I have witnessed only too closely the effects of the strong jet stream this winter and can certainly agree on its terrible disruptive nature. Please now keep on topic all, thank you.

There seems to be a lot of general winter chat getting into this thread. Please stick to the models, not winter weather preferences, thanks. Will be moving posts over to the winter thread shortly.

Wish I was in NYC! http://www.cnyclive.com/

JMA still bullish with the MJO forecast as well I note compared to the others, taking it into favourable phase 8 territory. (It was dated 19/1 yesterday and is 20/1 now - still waiting for an updated UKMO MJO forecast, though). http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/clivar_wh.shtml

I think it is too early and will be for a while yet to see any dramatic 'flip' in the models. But we are beginning to see the January pattern that I expected prior to winter. How strong any strat warming will be and how well it's effects will propagate are still an unknown quantity at this point, so I would suggest wait another week to see exactly where the strat is heading before getting too excited but it certainly looks like we are heading to that crossroads that I suggested for Feb on the winter forecast. Which path will we take? My thoughts regarding Atlantic ridging is that this will eventually lead to reinforcing a Scandi block, rather than a Greenland block and that a 1991 type Feb cold pattern could emerge towards mid Feb. (Just musings out loud btw.) But a lot of modeling to get through before then.

Actually for those who have tracked this warming from its inception at 1hPa it is now starting at day 6 on the latest GFS run. In a theoretical SSW case study, if this forecast was correct than it takes around 10 days for mean zonal reversal to occur at this level and then up to another 5-6 for reeversal at around 10 hPa. From then on in, depending on whether the vortex splits or displaces and whether propagation occurs, potential tropospheric affects will take anything from 6 days to 6 weeks to occur if at all. So if we see a warming at T+384 at 1 hPa on a GFS run, and, if that is going to go on and lead to a SSW and then tropospheric disturbance it may take a full month from that very first sign.

Ripe for just 1 more kick SK, and that kick is being delivered at 1 hPa at that time!

Yet again - this is my bugbear this season - that is a temperature chart - can you tell where the vortex is on it? I know I can't!!

First complete vortex destruction forcecast at 1 hPa by the end of the run!! Best strat chart of the season - though this is very, very high up!!

II think that the negative tilt of the Atlantic low hitting the stronger Scandi block is far better in this run at T=132 - but not a lot in it otherwise..

I don't see Draztiks Exc ens 10-15 chart as a truly zonal setup. For that I would expect to see more of the negative anomaly towards the southern tip of Greenland. And neither is it a blocked set up either. In my eyes it is somewhere in between, which as he says will give us below average temps - and it is a start to a more blocked set up should the strat deliver downwards, which currently is the big 'if' for the rest of winter.

That is not what that chart is showing though. It is showing the forecast temperature way out in FI at a height in the stratosphere where any warming may or may not influence events further down towards the troposphere in a period after that. The forecast vortex position at T+384 at 10hPa is just east of Greenland and only slightly displaced off the pole. I think that you may be confusing the temperature chart for polar vortex positioning and also charts in the upper area of the stratosphere for tropospheric ones.

Hi Tony Did you ever get around to completing composites for Feb?. If I remember correctly the phase 7 MJO has a flattened Azores ridge so we would like to push through to phase 8 - otherwise the carrot may be left dangling!

The ensemble trend also is for reduced energy crossing the Atlantic between T+168 and T+240. Not quite clear cut yet though.

Just catching up with the models (before reading this thread), but what I have noticed with the ECM is that when clicking between T+ 168 > T+192 to T+216 the evolution jumped wrt to the Atlantic low moving east between the latter two, so much so that I assumed that I had not clicked correctly and missed a day out. What I had expected to see was more in line with the JMA. So I think that there could be some surprises in store in this respect. Also, another thing to take note of is that the JMA Atlantic ridge pattern follows it's own MJO forecast, which is different from all the other models as the JMA shows the MJO entering phase 8 whereas all the other models stall in phase 7 - http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/clivar_wh.shtml The strat disruption is certainly leading to a more disrupted tropospheric vortex pattern and I believe that this will only increase when the FI strat forecasts are taken into consideration. I am certainly not as downbeat as some on here today, though having viewed the JMA MJO forecast I am slightly circumspect about how quickly an Atlantic ridge will disrupt the trough, no matter how 'wrong' the latter evolution of the ECM looks. One to check the ensemble mean later for any clues I think.

I have been away most of the weekend, but I see that we are edging closer to the notional SSW. The amount of residual warming would pretty much do the job on this 10 hPa chart.

Does it mean 'to get easily beaten by Arsenal'? Ps I like more innovative language in a world where everything is dumbed down.

End result of the ECM today is probably what those who thought laterally, envisaged yesterday evening. We have three possible height sources around day 10 - the Azores ridging northwards, the Arctic high and the Scandi high. The relative strength of each and how they interact will determine whether we will hit a cold bonanza or not. For the first time this winter we at least have bought a ticket for the lottery.

Cynicism is fine, purga, but using it as an excuse to wind up others is not. Please remember that.

I think that this chart highlights a very disturbed polar vortex, it is not in the reliable timeframe and the split shows that any zonal conditions could be interupted very easily. Zonal for us perhaps in this timeframe but with potential that the disturbed vortex could lead to alternative possibilities - can you not see this Purga?

That is all very well but we know that charts at T+240 do not necessarily show what actually occurs by the time that becomes T+0. One of the skills in looking at the charts is finding the trends that lead up to T+240 and encorporating this into the other signals that are becoming evident around this time and then using this to determine what may actually occur. Sometimes these signals do not verify, but at other times a high degree of uncertainty suggests that these should not be ignored. Now could just be one of those time to look at the changing background signals to see what else could be possible. Firstly we can look at the strat output - At long last the extreme cold strong vortex conditions are waning and further attacks on the polar vortex are forecast to continue. This is leading to splits in the vortex which, even though there are strong unfavourable tropospheric temperature differentials across north America, the split could end up hindering any resultant jet streams progress across the North Atlantic. This could be further encouraged by the MJO forecasts which suggest that there will be amplification of any pattern across the North Atlantic which is showing that any Azores High will disrupt the jet stream progress across the North Atlantic with a trend to link with Arctic heights. The 10- 15 day outlook is looking as promising as it has all winter and we are as close as we have been all winter to see colder meridional conditions take hold come February. Watch this space for further updates - but certainly do not base forecasts on the rest of winter on the ECM 32 dayer - we need to be a little bit more lateral in our thinking I suspect.