snowking

In terms of stratospheric feedback, the early gains are certainly playing in to the realms of Fred's (and potentially, from the sounds of things, Roger's) suggested early winter bite... SK

I'm watching this thread from afar but it is already permanently a tab open on my phone to check each day and will continue to be with great interest. The reason I am generally holding fire for now is that I am all too aware of how much of a tease following a month-long index can be after a few years of SAI watching. May I say as ever some really brilliant analysis from the usual suspects - Steve in particular has really produced some top notch insight and some incredibly useful data. I would still urge caution for now, however for anyone wondering why the current reading shows such a negative index - taking in to account the fact that the OPI website takes forecast conditions for out to 10 days ahead too - it is worth comparing the current 500mb Anomaly forecast from the GFS side-by-side with the anomaly chart Steve provided with his analysis of October 2009: If we then take a look at the 8 and 10 day forecasts from the 12z: Note in particular the very strong anomalies present around The Aleutians and stretching in to the Pole in all three charts and you find your reasoning for the "current" state of the OPI. However caution should be urged as these are still forecast charts. That becomes even more apparent when we take a look at the ECMWF forecast for day 10: Whilst we may not have the strong anomaly suggestion in the same zone, we do still generally have positive height anomalies around that 65N mark, but the main point here is to highlight that much of this is still based around forecasts stretching out in to an unreliable timeframe. Something which may throw some forecasts out a little more in terms of the specific detail beyond a few days is a renewed MJO wave: Something worth bearing in mind when following the twists and turns of our new found favourite winter tool. All in all though a very intriguing watch this year and I must extend my thanks to Ricardo and the team for the monitoring tools. This thread will make fascinating reading in the weeks to come I am sure. SK

That's approximately 1' 8" or 20 inches

Just a thought RE: glosea I wonder whether it's most recent iteration had any sort of recent historic input in its initialisation phase? Jut going off the back of the Sept 13 forecast being a little northern blocking heavy (of course with usual caveat - it's a height forecast not an SLP one) following 12/13, and then this years resembling 13/14. Nothing concrete with a very small sample, but I'll try and remember to re-visit this the other side of the winter. SK

Thought I would set up a thread for all the model nerds out there (myself included) with a really significant upgrade coming to the GFS just in time for winter. I won't go too in depth here in terms of each specific change as this is not my area of expertise. You can find a full run down here: http://www.emc.ncep.noaa.gov/GFS/impl.php The single most significant change will be the horizontal resolution upgrade - we will see things improved from 23km up to 13km (switching at the same time from a Eulerian to a Semi-Lagrangian grid). This should bring things more on a par with the likes of the ECMWF (currently at a resolution of 16km), though the ECMWF itself is due an upgrade later this decade I believe. In addition to this I believe there is also a change due to the data assimilation process, once more designed (after consultation with the ECMWF) to bring the GFS more on a par with it's rivals. In addition to this the high resolution stretch of the operational run will be extended from its current 8 day period (+192) out to 10 days (+240). There is so much more to it than just this though. For the amateur forecasting community I cannot stress highly enough how significant this upgrade could be. If we bear in mind that up until last year many on here religiously followed the limited area 12km resolution NAE runs for just 48 hours ahead, which covered just the North-East Atlantic. Now take that idea and push it out globally, with many more parameters available completely free of charge. This really could be a game changing moment from that point of view. There is no concrete date set as yet for this other than some time in November 2014, though I believe the upgraded data will be ready to run in automated forecasts from next month. It will be fascinating to see how this upgrade improves things a we head in to the most eagerly followed time of the year here and we should all bear in mind when analysing runs that we cannot make the same old GFS vs the european runs arguments as before as we are entering totally unchartered waters with this one. There are also several stratospheric and o-zone improvements which I know will please many too. I'll try and post as soon as I can find a concrete date for the completion of the upgrade. In the meantime if anyone with more knowledge of the physics of modelling cares to chip in then please feel free to SK

The theory suggests that it is rate of increase during October that has the greatest impact (owing to a whole range of chain reaction factors which culminates in the formation of a stronger than usual Siberian HP - assuming a fast rate of advance - which in turn drives Wave 1 activity within the Stratosphere) So in fact a high base state in early October could be detrimental. As far as composites go I do not know of any specific parameters available on the NOAA website to map the rate of increase.

Sure recently, but with temperatures heading towards the mid 30's back in late July in the near continent the potential for temperatures pushing towards the 30's here would certainly have been there. Anyway, all theoretical! It was more of a tongue in cheek comment with regards to the winter that followed

As somebody who would likely melt in the heat that would have brought with it a month or so ago I am rather relieved I must say, and next week actually looks quite comfortable to me with some pleasant conditions around and some reasonable temperatures. However, I can understand the frustration for summer fans - it's just as annoying as last week's setup was for coldies given the time of year. SK

Current projections for Late August/September 2014 bear resemblance to September 2009....

I think the most important thing to remember about Cohen's theory is that the correlation is between Snow Advance across Eurasia in October, and the overall winter AO index (the faster the rate of advance, the more likelihood of a negative AO index) - and that alone is fraught with difficulty in terms of pinning down the detail for our tiny little island. You won't need me to explain this one to you but for the benefit of any newbies reading, here's a nice image demonstrating the differences between a Positive and Negative AO index: As you can see the biggest effect is a change from net westerlies (positive phase) to net easterlies (negative phase) around the Arctic regions. This infers that high pressure is likely to be in place around these regions given the clockwise motion the flow follows under high pressure in the Northern Hemisphere. You may also notice this ties in closely with a sudden stratospheric warming event, where the winds change from net westerly to net easterly much higher up in the atmosphere and often such an event downwells in to the lower reaches of the atmosphere and leads to a negative AO index. The problem of using this to forecast for the UK alone is that there are plenty of examples in history of a negative AO index being in place but the UK simply being in "the wrong place" (doubtless for any newer members you will see examples once again this winter of one of Nick Sussex's Shortwave horror shows) with regards to the overall longwave pressure pattern setup. Usually this would result from a negative AO but either a positive or west-based negative NAO, leaving the UK out in the warm whilst other parts of the Northern Hemisphere bask in the glory of winter cold. But of course the crucial take-home from Cohen's theory is that a high Snow Advance Index significantly increases the chances of colder than average conditions during winte. That is about as far as we can take it for now. Of course there is also the October Pattern Index (OPI) from Italian researchers to take in to account, but as far as I can see there has been little progress on this over the last few months which is a shame as I believe we were awaiting a true English translation of the research so as to better understand the specific patterns suggested. Anyway, a little off topic but a fascinating subject and one that deserved further attention I feel SK

Only had a chance to have a brief look but in terms of the QBO drop, 62, 79 and 09 certainly stand out as having the closest parallels in terms of the scale and timing of the drops. Matching these against ENSO indexes and one would imagine the closest parallel we have will be 09-10. Most certainly not to be sniffed at, though it should be noted that solar activity has been, up until now, much stronger than back then...whether this remains the case going in to the winter (as some would have us believe) will be interesting to see, and I suspect we are now past the peak. I'll take a more in depth look for analogue years later in August when I have some time off. SK EDIT: Just adding latest IRI ENSO forecast to show the likely direction - seems like a mean peak around 0.6-0.9, which would sit somewhere between 79 and 09

One would suspect part and parcel of the reason for this change showing towards the end of model runs is this: I wouldn't be hedging too many bets on this just yet with the ECMWF signal by far the strongest (and quite honestly, given it's record this side of the Atlantic over the last 2 years, it can no longer be considered as any better than any other output), but still not supported fully, though the GEFS seems fairly close to it too. Whether the change is temporary or longer lasting is the question that follows, and one which we are some days yet from knowing. SK

It's certainly going to be a fascinating period for all involved...and I'm not just talking on this forum. Just to give an idea of how little even the likes of NASA are really able to project in to the future, this article provides interesting reading: http://www.noaanews.noaa.gov/stories2007/s2847.htm Elongated cycles were certainly the trademark of historical minimum periods, though they are by no means a feature exclusive to them either. Ultimately, right now it is a very brave person to call the exact progression beyond this point for the next 2 years or so, though I would suspect we are beyond the the maximum period now, contrary to certain reports. Of course we then have to interpolate the assumptions we make with whether there is enough strong evidence of the link between NW European winters and Solar Activity. On a VERY small scale, I would argue that the peaks aligned around the winters of 2011-12 and 2013-14 speak for themselves, but two winters in isolation hardly provides a credible sample size on a seasonal basis. On more of a decadal basis though there is certainly more encouraging evidence for the link between extensive periods of low solar activity and colder NW European winters, and the period of 2008-2013 should hopefully stand as testament to that. I'm sure we all suspect there is more than one factor at play here, but it seems to have a fairly distinctive effect at least. As ever only time will tell but the next couple of years could set a precedent for the years, and perhaps even the decades, ahead, as we start to get a glimpse of whether the sun really is entering a slumber. Happy sun-spotting. SK

Interesting to hear because most of the research I have read up until now has been based around a double-peak (as per the previous 4 cycles), and given that the cycle began in 2008 with an approx. 11 year life (though of course we should potentially heed warnings of an elongated cycle given the slump vs cycle 23 and previous such instances), by my estimates we are now beyond the expected maximum period, and en route to the minimum of circa 2019. Do you have any further reading on this as to where the expectation for a further uptick has come from as I always like to get a rounded view of these things and up until now most of the literature ha suggested a downtick between now and 2019. Thanks, SK P.S. - Sorry for taking things back off topic again, just a fascinating research area for climatology.

Yep, as mentioned in my last post Still a very low overall count though when compared with Cycle 23....it should also perhaps be noted that the two peaks of the double-peak cycle 24 co-incided with the winters of 2011/12 and 2013/14...two notably poor winters for NW Europe from a cold lovers perspective, but of course two instances does not a trend make. Anyway, I feel that I am probably moving a little off topic here... SK

That would certainly help, although whilst not to the same extent it is worth noting we did briefly see a return to a +PDO index through Autumn 09. Potentially, although of course it is a little naive of us to assume that matching index values will automatically equal similar conditions, especially when considering what while solar activity is rapidly declining, it will not be at the near-zero levels it was at during 09/10. However for me the most encouraging signal heading in to the winter will be -QBO, given the role it plays in terms of zonal winds. Of course all still a long way ahead of us yet but a fascinating one to start looking at, and a sure sign that last winter was this poor when we are already looking for any signal that might suggest something opposing this year. SK

Combine that with declining solar activity and a negative QBO, and dare I say that excitement levels in here on the approach to winter 2014/15 may well be on the high side...

Hmm, not so sure I would describe Saturday as a great day for much of England and Wales on the 12z GFS: Visibly some sort of frontal disturbance there, fairly apparent from the pressure charts too: Of course I am in no way advocating the use of a single operational run 4 days away SK

They tried... MJO forecasts fairly coherent in terms of the overall phasing (heading towards 7/8) but still some uncertainty on amplitude - ECM least keen on taking us into something Amp >1 territory, where as UKMO and GFS forecasts more bullish on this. Phase 8 tends to offer the direction in which I think we are headed, particularly with falling AAM projected too: That leaves the UK still under the force of a persistent trough (yawn) but it's which side of this trough we end up which could prove crucial. Current ensembles would tend to suggest our humble little island is left on the cooler side of the trough, with rising pressure and falling heights to our North-West: I still remain cautious over this given recent tendencies to over-egg any height rises around the Greenland locale in recent months, but we can only work with the tools we have available and to derive a 10 day ensemble mean such as those above there must be fairly good consistency within each suite for the above signal. This is backed up by some consistent 100mb forecasts from both suites too: With the suggestion, as reflected in closer to the surface NWP projections, of the main thrust of the vortex being displaced towards the Siberian half of the Northern Hemisphere with an upper ridge heading towards Canada/W Greenland - of course this is something else we have seen projected a few times in the last 18 months or so, but with the warming that has already taken place: I would suggest this signal may actually bear fruit this time around. So where does that leave the UK? Well unfortunately the signals at present would suggest cool and damp - the chance of something wintry over hills in the North, but it would take something really exceptional (such as the trough over Siberia dropping through in to Europe just to our East) to inject anything significantly cold at this late stage. Instead it looks likely to have a whiff of a West-based negative NAO...a little further East based than perhaps we have seen in previous years but the general theme of rather dull and cool would be my punt in around 10-15 days time. SK

Certainly a wide divergence in solutions at day 10. Of course that's not necessarily uncommon but such a wide divergence between ensemble means at that range as we have at present: ECM: GFS: With the ECM's mean Easterly solution vs the GFS's mean South-Westerly, which is usually a sign that something high-pressured will be taking place somewhere to our North. I think it's worth remembering just how poorly the ECMWF has dealt with Northern blocking at the 10 day range (or for that matter the 6 day range at times this winter!) during the last 18 months or so - yes that does stretch back to winter 2012/13 with the failed December beast from the East. Whilst global verification statistics sometimes prove useful and have shown consistently for many years now the ECMWF to outperform the GFS it is always worth bearing in mind shorter-term regional trends (for example I have colleagues in New Zealand who swear by using the GFS because it outperforms all others). I suspect the overall ECMWF picture has been caused by the exceptionally higher resolution vs the competition - something which will of course be levelled somewhat before the end of this year with the GFS upgrade (as well as an upgrade the initialisation methodology based upon consultation with the folks at the ECMWF). This point I am making here though in a very long-winded way is be wary of pressure rises shown at this range to the North-West of the UK by the ECMWF - it has consistently over-egged heights and SLP in the GIN corridor, particularly on the Western periphery, for these last 18 months. Even during the cold spells of January and March 2013 there were consistent (consistently wrong!) signals for pressure to rise significantly around the Greenland locale. In reality we ended up with a much weaker pressure rise than modelled but still ended up with a good result courtesy of a Steve Murr sausage special. Of course when you see divergence from ensemble suites like this: With a number of colder solutions there's always hope for a little flurry of something colder and indeed there was a cluster of solutions on the 0z ECM EPS suite heading for something colder towards the day 10-15 range, but ultimately we have been lead down this path a number of times now and without the full backing of other suites it becomes a little difficult to believe. Can I end on something more positive for collides? Well there is certainly an impressive amount of cold bottling itself up to the North-East of the UK, so if we can get a bit of luck with the pattern - always possible with an increasing stratospheric thermal profile and therefore a higher chance of higher pressure at more Northerly latitudes than during the winter itself - the depth of cold is certainly there to throw up a few surprises. It just needs something to advect it. For now I remain rather dubious of ECMWF day 10 outputs and am looking forward to the upgrade cycles of the next couple of years...could it be that through the second half of this decade we finally have two suites that give us some reliable insight behind day 4-5? An exciting prospect! Regards to all, SK

As has been mentioned on here in recent days, with the GEM now second in the pecking order in terms of NH SLP verification for days 3 through 8 it remains more than a bit of a niggle: After the very disappointing and troublesome winter experienced a period of high pressure and some warm days would be a very pleasant way to welcome in the meteorological spring, but just as we had to remain cautious beyond 5 days in the frustrating (non)winter, such advice should be adhered to now too. As strongly behind the scenario of high pressure building across at least the Southern half of the country as even the ECMWF EPS is at the moment we have seen on a number of occasions that even these are far from infallible beyond a few days. Very strongly hoping for something a bit drier and warmer now but until we see a consistent cross-model consensus the wise money is to remain cautious for now. SK

The track of the aforementioned Tuesday storm on the ECMWF det.: Northern and Western areas of the UK getting it bad enough but on that track it would be the Irish Republic that would see the absolute worst of the winds - current projections suggest 90kt max. gusts off the South-West coast of Ireland (104mph). Still strong enough for the UK though with max. gusts of 70kt (~80mph) around Irish Sea coasts from that. The slightly better news from overnight (though I would emphasise the word slightly) is the slight downgrading of peak gusts for Saturday from deterministic modelling, with the suggestions from yesterday of 80kt gusts down the Bristol Channel now reduced to around 65kt - still severe enough but hopefully a decent trend for the poor folk in the South-West. SK

That's a bit harsh on the block isn't it

The trouble is picog even when averaged over the course of a few days it tends to throw out every scenario possible and so eventually it will prove correct but only because it is playing the lottery with a ticket containing every number combination possible! Perhaps a little harsh but I remember back in October and November it was throwing out 10 day averages with some huge positive height anomalies for February over Greenland for example, fairly consistently too for a few weeks. Therefore it is difficult to use a predictive tool because whilst it throws out lots of different scenario's (one of which usually proves correct) it's difficult to know which of the scenarios will ultimately prove to be correct - which is supposed to be the entire point of NWP I will add the caveat I have not got the evidence to hand to support this but I remember posting quite a few examples of the above from WeatherBell in the winter discussion thread at the time. SK

Hi Victor The 850 temps are given as a broad-brush guideline to be honest and I think sometimes they are taken too much as the be all and end all of snow potential. Essentially it all comes down to lapse rates - how quickly the temperature increases between the 850mb layer and the surface. This is dependant upon a whole host of different variables but in short the lower the heights are (the 'blue' colours shown on the 500mb charts) the shallower the system is and therefore the lower the lapse rate is. What does all that mean? Well it means that under certain circumstances the atmosphere will be at a temperature supportive of snow at the surface even with the 850mb at say only -2c. This generally occurs when we get a shallow flow from the East, and so in the upcoming scenario the only requirement we really need to look for is for the 850mb temperatures to be below 0c - as long as the air between the 850mb layer and the surface is cool enough all the way down snow will fall. What happens when we get Northerlies/North-Westerlies is we tend to get higher lapse rates, hence the temperature differential between the 850mb layer and the surface is higher, so whilst we might see -5c at the 850mb layer, it could be +5c or greater at the surface. But as a general rule of thumb under a shallow flow (blue colours on the 500mb charts) from the East, you simply look for sub zero 850mb temperatures. A much better guide to rain/snow discrimination (and one I tend to use more prominently) is dew points. The general requirement here is for the dew points to be at or below 0c (occasionally we can see wet snow with a dew point up to 1c, but generally use 0c as a guide), as without this is doesn't matter what the 850mb temperature is, it won't be falling as snow at the surface. Of course the problem there is that dew points even as far away as 36 hours can be incorrect and this is why snowfall is always so complicated to forecast. The Met Office tend to use the Wet Bulb freezing level, but this in itself can cause some issues with a rather liquid requirement (if you'll pardon the pun) for the height. It can snow with a WBFL at 400m depending upon evaporative cooling, but generally you want it at 200m or below. Hope this helps, Regards SK