Evo

Looks like the real heavy stuff is over in the Channel Isles. http://www.meteox.com/gmapstatic.aspx?zoom=6&type=zoom&x=148&y=262 Jersey is now SNOCLO. [The airport is shut due to the weather]

The 1620 METAR for Jersey had rain, snow and ice pellets. Nice.

Think you may need your snorkel rather than shovel tonight, alas.

Anyone notice the 61mm 16 spot value on the 48 hour 12z NAE precipitation around the Taunton environs? Edit: Oops, sorry that's 16 <slaps wrists>

What an interesting satellite pic. Is that showing West Is Best's lawn? The bit underneath the word snow? From coast to coast? Bleeding heck, I wouldn't want to have to mow that lot

Just before Christmas I went for a wander around Spread Eagles Hill, by Compton Abbas. There was a fair bit of ice around then - managed to cut my hand up on some rather nice rusty barbed wire as I found myself sliding down the slope. Ended up walking back up the side of the hill from Compton back towards the airport & car park. I wondered then what it would be like to sled down the side there. Unfortunately I have niether the time or the cajones :lol: Oh and I had about 5 heart attacks walking up the hill. Can't keep doing that. I bet the folks down in Melbury Abbas "love" it when it's snowy and icy down there. As for this current load of rain/sleet and snow, I still haven't seen anything to grab my attention. Sure, lots of folks are going to see snow - it just isn't going to be anywhere near me [er, probably].

Fellow south coast Dorsetians will surely have a wry smile when they see the graphic for the MetO warning. Note that Bournemouth + Poole have been left as yellow !! If I had to stick my neck out, I would say that South of the Doreset Downs will be looking at a slushy mess at best. I just can't see sufficient cold advection to bring snow to low levels here. The deepening and North Western placement of the low should send the colder air further East and North IMO. Still, we won't know for sure for a while yet... That reminds me, I must update my location back to Bournemouth.

Little has really changed synoptically to cause the latest output. The shortwave may develop, it may not. There are too many variables to really know at this stage. We do know that the conditions seem to favour the shortwave to become organised, however. The possible side effect is that the initial precipitation will perhaps become more margnial as air from the channel becomes mixed in, however I'm not overly concerned about that. Anyway, to demonstrate that small changes on the synoptic scale make big changes in precipitation, I've been putting my IMBY glasses on and saving the Tue/Wed Net Weather GFS derived forecast for Bournemouth since the weekend (when the GFS first drived up that shortwave) Tuesday: Wednesday:

I don't think many of us that have been watching over the last couple of days will be surprised at the latest snow threat showing up. Both GFS and NAE are keen to close off the flow around the Western edge of the front. I've been pondering since the weekend what the driving factor for this is. I think it's a combination of things. There is jet forcing from a jet streak to the west - placing the western edge of the front on the difluent left exit - this favours cyclogenesis. Additionally the cold air moving out south over the warm channel water causes enhanced convection - i.e. uplift. In any event, whether this actually happens or not is another thing. It's certainly something the GFS has been keen on in an on-and-off fashion for some time. It could enable significant snowfall. However, massive emphasis is on *could*...

Compare these 2 super-ensemble outputs from here. See the explosion of scatter that just one day makes... 18th 19th

Looking at the UMNO-NAE meso output, it's fair to say that Kent has some potential for tonight. From an IMBY point of view I'm looking at an area of possible disruption around for M4/A34 area. There looks to be a line of precipitation from the wash down towards Salisbury. The first real precipitation moves in tonight and then carries on overnight. Could be interesting... You can see that the flow of upper cold pool aligns with the showers: The ouput has rendered it as rain but I think it's very likely to be of snow: Potential for visibility to drop below 8ks Temps likely to below freezing: Pricipitation accumulation indicates the potential for some disruption. Some impressive totals in the far SE: Lastly, predicted snow depth by the end of tomorrow:

Looking at the UKMO-NAE output, the snow this morning is not totally unexpected. I've had a spare hour to lose before a fun filled day dealing with whinging customers. So, here's my analysis for our region based on the 6z UKMO-NAE. I've focussed on some of the parameters from John Holmes' "Will it snow guide". Looking at thicknesses for 500-100hPa: Sub 528dam covering south east of a line from Lyme Regis to the Wash initially. Higher thicknesses move in as the low sweeps down the North Sea such that by 6pm only Kent really has air with a thickness below 528dam. As the low sweeps South, the colder air moves in from a North East direction, bring sub-528dam air back to all of England and Wales, except for the far South West, by 9am tomorrow. That remains through to the end of the model run at 6am Friday. Only North West Scotland and Central Ireland Westwards remain in air above 528dam. Looking at 2m temperatures: South of a line from Bristol to the Wash, largely below 0 at 6am this morning and widely below freezing until mid-day. Warming up to 3-4c as the low moves South. Staying that way for us until the low clears away and by 6am Friday we're looking at -2 to -3 in our region. 850 temperatures: Starting off at -5 to -6 this morning and rising slightly as the low sweeps south. Staying below zero throughout though. Steadily falling as the colder air works in and by Friday morning we're looking at -10 to -11 at the 850 level. 850-500 thickness: Starting off between 1290 and 1300, with the lower thicknesses South East of a line from Weymouth to Norfolk. These thicknesses increase as the low moves South in the same way as the 500-100 thicknesses above. Sub 1290 thicknesses move back in Thursday and cover most of the region by mid-day. By midnight, the whole region is covered with thicknesses below 1280dam. Precipitation: A small amount falling pretty much anywhere, with larger amounts of preciptation in the North East corner of the region. No significant amounts though, likely to be mainly light to moderate showers. There's a chance of anyone in the region catching a shower throughout, however the more North East you are in the region, the higher the chance. Summary: Staying cold. Becoming colder from Thursday onwards. A chance of a shower anywhere, with more showers likely in the North East of the region. Conditions initially conducive to light sleet and slow showers this morning, especially on higher ground but those mostly turning to drizzle by the afternoon. Probably staying widely above freezing overnight tonight with isolated showers of drizzle in the North East and some mist throughout the region. From mid-day tomorrow onwards, any precipitation will be increasingly turning to snow, and by Friday morning I think snow anywhere rather than rain or sleet, save for a few areas right on the coast. Precipitation totals look small for this period but some areas may get a light accumulation of snow.

I apologise in advance for the ranting nature of this contribution! Due to time and other reasons I've been content to be a very irregular read-only patron of Net Weather for the last couple of years. I must say that this Autumn/Winter it has almost driven me to drink. I don't blame anyone in particular but this, to me, is nothing like the place it was 4-5 years ago. That is neither good nor bad, it's just progress I suppose. Without wanting to be patronising (but no doubt sounding like a pompous git), I feel a lot of the friction in the Model thread is caused by either young or inexperienced members. It's easy to forget that it is not mandatory, nor desirable, to share your every thought with the world. I've noticed that some members who used to irritate me in the past with pointless and childish posts now post with a great deal of eloquence and thought. I'm aware that this is as much a case of me being older and grumpier too. Too many people ask questions that have been answered at length many times before. If you can’t be bothered to search the forum, or type something into Google, why should anybody else bother to help you? I also think some people treat this forum a bit like MSN and expect instant gratification. It just irks me that if some of these people diverted their seemingly boundless energy from what is, brutally, a pursuit that is pointless as far as human advancement is concerned, to a truly worthy pursuit our race would be a lot better off. For instance, why not try to find a better way of approximating the Navier Stokes equations? Not only will it lead to an advancement in numerical weather prediction you can also pocket a million bucks from the Millennium Prize folks too. If you have no idea what the Navier Stokes equations are, you probably don't have any business criticizing a numerical weather prediction model... After getting all that off my chest, I do have a recommendation. Clearly from previous years separate threads die a death quickly. I remember trying to look in vain at various topics such as data assimilation weaknesses but these fall off the bottom very quickly. The same has/will happen with any technical thread. A new style of thread is wholly reliant on its users to make it a success. What I would propose is one of two things: i) A pinned in-depth thread where all contributions are pre-moderated and clear posting standards are set – minimum length, relevancy etc. Then a moderator can allow or disallow a post in that thread based on clearly defined standards that apply to everyone. That way everyone knows where they stand. I suspect that this would see little use, though. ii) Giving a filter option for the main discussion thread where one can click a button and view just the posts by the forecast team that have been made in that thread. More difficult but better would be where each user can create a “want to read posts by” list where they can add the users they want to read posts by in a thread. That way at a click of a button you can have the normal thread or your own customised thinned-down thread. I don’t like the ignore function for this as this is too permanent and rather than say who you don’t want to read posts by, say who you do want to read posts by. I also think it would be better that it’s something you can turn on when needed rather than something that’s always on. Ignoring someone in perpetuity because they may have annoyed you one day isn’t great for the community really. I’ll crawl back from whence I came now

It didn't escape my attention that last week there were many Brixtons felt in Abingdon. This notion made me feel rather uncomfortable. It's like saying that there are several inches in a centimetre. Perhaps consideration could be given to revising the nomenclature? Anyway, here is a new definition for the dictionary: Snow Job: What a gentleman who is snow starved may be tempted to buy. Usually about £25 for a quickie. Consists of trawling the streets of less salubrious areas (such as Portsmouth or Carlisle) for purveyors of this particular act. The act itself consists of being taken to a darkened room which contains illegal snow imported from Russia. The gentleman can then entertain himself however he wants in said snow. Going all the way is about £40 and allows the chap ample time to build a snowman and/or get frost-bite. Gloves are recommended for "Safe Snow" to avoid the possibility of contracting a STD (Snow Transmitted Disease). As an aside, the snow smuggling rings that operate throughout Eastern Europe are thought to be operating under the control of a militant faction headquartered in the Peterborough region.

Great pics Iceberg and thanks for sharing. Interesting that down on the coast in Bournemouth there's been little settling snow. We did have constant snow for periods last week but the accumulations never made it over 1-2cm. I've often noticed a stark difference in weather when crossing the hills - (I suppose they're the Dorset Downs but I've never bothered to check) on the way up to Bath. Usually go on the top road from Blandford to Shaftsbury - through Melbury Abbas. Melbury can be pot luck in good weather, I wouldn't fancy that with the snow and ice around!!! Narrowly avoided getting taken out by a fast retreating burger van there once.

After some more digging it turns out my hunch, while not totally correct, had some mileage. It turns out that a research project called "The Greenland Flow Distortion Experiment" has recently completed field observations to investigate this issue (well not specifically but to get a better handle on the mesoscale processes that occur around Greenland). First, there are two background Met Office research papers which are worth a look. You need to complete a free registration to view them but I’ve summarised what I consider to be the salient points. Dumelow, R - "The impact of conventional observations on global and regional NWP forecasts" Available at http://www.metoffice.gov.uk/research/nwp/p...reports/516.pdf This paper looked at the relative importance in terms of forecasting skill of the differing types of observations that are assimilated into a model analysis. The author is coming from the angle of what would happen to the accuracy of the system if resources were concentrated on mainly satellite-derived data. The paper broke the observational categories into these groups: i) All available observations - COMB ii) Satellite derived data, GCOS, GUAN and buoys - BASE iii) BASE + Aircraft data - BPAIR iv) BASE + non GUAN radiosonde temperature and wind obs. - BPGTW v) BASE + non GUAN radiosonde wind observations - BPNGW GCOS = Global Climate Observing System GUAN = GCOS Upper Air Network The author points out that other papers have looked at denying entire classes of data or targeted field observations. An experiment was conducted during two periods - one in winter and one in summer. At T+48 in winter there is a marked improvement in forecasting skill by using COMB compared to BASE in a belt at 60N. This is explained as likely to be due to the density of observations in this region and the lesser difference between BASE and COMB data volume elsewhere. At T144 the areas of error are more widespread with only 30N to 30s showing little difference, however counter-intuitively the influence of the difference in observation use declines with increasing forecast range. In general using BASE over COMB produces a 5-30% decrease in accuracy depending on the time differential, location and season. The paper then looks at the effect of BPAIR, BPGTW and BPNGW. The order of effectiveness is: BPGTW (radiosonde temperature and wind observations) BPNGW (radiosonde wind observations) BPAIR (Aircraft data) So, adding aircraft air data is the least effective way of improving forecast skill over the base observations. However this has all using the UK Met Global model. When using the more localised UK Met NAE model, during winter no improvement can be seen by adding any of the extra data in! During summer adding the aircraft data is the most effective - giving a result similar to the complete data set. In the timeframe that most "model watchers" are looking at the NAE model would be of little interest even if it were published, though this is worth bearing in mind. Next, Bovis K, Dow G, Dumelow R & Keil M - "An assessment of deployment strategies for targeting observations" Available at http://www.metoffice.gov.uk/research/nwp/p...reports/515.pdf This paper looks at the potential benefit of deploying additional radiosonde observations within a targeted area to improve forecast accuracy for a specified region. In this particular context, they are looking at hurricane track prediction. There are two potential strategies for identifying areas that would benefit from additional observations - using a human forecaster and an analysis chart or by applying an Ensemble Transform Kalman Filter or ETKF, which in laymen’s terms identifies regions where forecast uncertainty is highest. It turns out that EKTF is far better at picking regions that would benefit from additional targeted observational data. Not surprisingly, when targeting these regions an improvement in forecast skill is observed. The authors note that that the single most important category in terms of forecasting skill is radiosonde data. Finally they note that additional work in this area has been undertaken called the Greenland Flow Distortion Experiment (GFDex). Rather than repeat the details of what GFDex is, I'd recommend a read of http://lgmacweb.env.uea.ac.uk/e046/researc...description.htm. The field observations have now completed and investigation of the collected data is underway. The key theme of each of these links is that improving upstream observations improves downstream forecast accuracy. This is obvious really when you think about it. The good news is that we can look forward to improvements in this area in the next couple of years as well as the continued improvements in model resolution. Whether this means more resources are allocated to creating fixed ascent stations or aircraft are used for dropsondes I’m not sure. In my opinion efforts to obtain more efficient and accurate use of satellite data will be the most likely course of action. Whether this will enable the GFS to accurately predict whether it will snow at T240 is anyone's guess!

I would like to request the consideration for an investigation into the possibility of forming a comittee to comission a feasibility study for the generation of a new SATSIGS zone called the ZOSIIC. No, not the Zone of Southern Idiots In Corsets but the Zone of Snowwatch-esque Inane and Irrelevant Chatter. I would make no suggestion as for potential candidates to deliniate said zone - this is in order to preserve the integrity of my otherwise *ahem* unblemished character. In fact this may be more suited to a measuring instrument rather than a zone but I'm unable to adapt my rampometer since the needle snapped off by going off-scale high just recently. I would requisition another rampometer but my distinct dislike of hotpot, whippets and Emmerdale farm mean I am unable to transit into the ZOSNT to hand in the requisition slip.

Hi SS2 Hopefully this link will help! Haby Hints

I posted this a while ago in a Model Discussion thread but seeing as that was buried in about 10 seconds and the question will no doubt come up again, here are some brief details about the Met Office's own model output: It's also worth adding that ECMWF also run MOGREPS in a more long range configuration called MOGREPS-15, which runs out to 15 days and is used in TIGGE (more info)

Thanks for the replies chaps. I've attached the image I was referring to so you can see where I was coming from. It is certainly interesting how much preprocessing of this raw data has to happen before an analysis forecast can be produced - upon which the model run is initiated.

I'd best start this off with a disclaimer - I'm not an expert in any of the following so some, or all, of it may be pish! I've been pondering the issue of model data assimilation since looking at the Kalnay book I mentioned in John Holmes' pinned GFS data thread and reading J07s interesting contribution in that thread. In the book there are a couple of maps showing the actual observations incorporated into a particular GFS run. It's only recently dawned on me that the observations that are assimilated into the analysis forecast (which forms the basis of the model run) vary by quantity and location from run to run. There is a much higher density of observations near human habitation - which seems intuitive. The main area that attracted my attention, though, was Greenland. There was a scant amount of data input from this region on that particular run. The potential sources that data can be assimilated from can be summarised as: i) Land (surface) based observations - both manual and automatic ii) Sea (surface and sub-surface) observations - such as buoy data iii) Ascents - observers on land or at sea release 1-2 balloons a day per location iv) Aircraft - automated and manual observations v) Satellite - remote sensing of wind and temperature, radiance and vapour While many stations incorporate automated measuring and reporting equipment, some information is derived from manual observation such as ascents. These require human input obviously and this human input means that occasionally there will be a problem with getting this done in a timely and accurate fashion! Some data is assimilated from aircraft, but on average aircraft spend a large proportion of their flights at cruise level so the information will typically be from 30,000 to 40,000 feet and (this is an educated supposition) be composed of temperature (adjusted to factor in the effect of speed), wind speed/direction and static pressure. There are some weaknesses with the aircraft observations - aircraft will generally follow set routes called airways. Data will be concentrated along these airways, whilst outside of the airway system there will be little or no data. If you look at the ACARS (aircraft) data on Kalnay's map, you'll notice that the observations over the Atlantic line up vertically. This is because the aircraft crossing the Atlantic follow a movable set of airways called the North Atlantic Track system (or NAT tracks). The NAT tracks are fixed each day and will compose 5 westbound tracks and 7 eastbound tracks. The actual tracks will take into account factors such as the Jetstream. In general the westbound tracks will be more to the North to avoid the Jetstream and in general the eastbound tracks will be more to the South to enlist the help of the Jetstream. This will obviously vary by season and prevailing synoptics. Westbound flights tend to happen in the first half of the day GMT, while eastbound flights tend to happen overnight. Each track is made of up waypoints which are latitude and longitude coordinates. ACARS reports are made at these waypoints, which will usually be at 50W 40W 30W and 20W - you can see the effect of this in the vertical lines in Kalnay's ACARS map over the Atlantic. So, the location, time and quantity of ACARS data will vary each and every day. Other data are derived from satellite soundings as J07 has illustrated but as far as I (as an interested amateur) can establish the information from these satellites is rather generic and interpolated. The satellite derived data will not be anywhere near as specific and accurate as an ascent. Finally there are many other issues with the data assimilation process, as J07 has highlighted - getting the data measured and incorporated in a timely fashion, blending different (and potentially conflicting!) observations and the issue of extrapolation into areas where there is a low amount and quality of data available. Where I'm leading to is this question - Although technology and resources will no doubt have improved since Kalnay's 1997 maps, if there is an inadequate amount and quality of observations in the Greenland region, how can a model hope to resolve the energy balances in the so-called sub-polar field correctly? I find it hard to believe that such an obvious hole would be left, or that this would not have been considered by those more learned that I but it does pose an interesting what-if question, especially given the importance [to our weather] of the energy flows in the GIN corridor! Sources: http://mason.gmu.edu/~phouser/houser_files...NAL_22Jan08.pdf http://www.goes-r.gov/downloads/GOES%2520U...conf5_moore.ppt http://www.emc.ncep.noaa.gov/gmb/ens/THORP...gfs_thorpex.pdf http://www.emc.ncep.noaa.gov/mmb/data_proc...cumentation.htm While not directly relevant, interesting as an under-the-hood look at the GFS model while the Indian met agency implemented the GFS model: http://www.ncmrwf.gov.in/ncmrwf/gfs_report_final.pdf

Unfortunately personal circumstances don't allow me to read or post much any more but during a quick peek this morning saw this topic which is certainly interesting. I'd recommend those interested in this suject to take a look at the Google Books preview of "Atmospheric Modeling, Data Assimilation, and Predictability" by Eugenia Kalnay here: Google Books ... in particular pages 13 and 14 and note how a short term forecast is used to populate model grid points due to the lack of available observations. There are also some interesting details on the evolution of the modelling process and the problems associated with increased resolution. There's plenty of heavy maths in there too for those inclined!

I really enjoy reading the bantering of the CET threads. All of the regular contributors debate with a great deal of restraint and respect on the whole. The only time it becomes tiresome is when an inadvertant agent provocateur (who may not appreciate or understand the good natured ribbing) jumps in and manages to rub people up the wrong way. As analogues are all the rage, I see this as the analogue of a bunch of bearded middle aged men in a pub having a good natured debate on something as important as whether dark navy blue is blue or black. Oh and err, 10.7c.

Thanks for the input BF. Your analogy does make a lot of sense! The problem I have is not being sufficiently clued up to be able to judge if the case he is making is a valid one (he seems to imply that there's a better corrolation with his index). It does seem logical that atmosphere, surface and deep water are related and interact, so I suppose it comes down to the same old chicken and egg question. As for the GLAAM, it seems that everybody has a different opinion as to what it's really saying so it's nice to read a coherent discription that I can understand - much appreciated.

A while ago, there was an interesting piece of research posted over on easternuswx.com: http://www.easternuswx.com/bb/index.php?showtopic=140902 The theory is that subsurface thermocline anomolies play the driving role in determining the El Nino/La Nina state, rather than the conventional opinion that it is boundary layer interactions being the dominant factor. It's well worth a read and I'm interested to hear what some of Net Weather's experts think about this. I think I'm right in saying that if this was the case, we could've actually been in a La Nina phase for the last couple of months. The disparity between surface waters (end hence ENSO index) and the observed weak Nina pattern being explained by the wild negative GLAAM index?