johnholmes

for newcomers who may get a bit lost with some of the terms you see used in here, the one above by Nick, I 'think', refers to needing to see the surface isobars orientated SE NOT E, this would, possibly, help in keeping the surface ridge and its governing upper ridge over the top of it either in situ or possibly building it. If I am wrong Nick please correct me.

try the Net Wx guide to this snow or rain. Fun doing it, helps your understanding of the complex processes at work, you might turn out lucky. Remember the model has to show PPN before doing all the clever bits and add on your height. ROUGHLY 1C per 300m or 1000ft, note I said ROUGHLY, and my item has no, I think as so long since I looked at it, allowance for cooling of the PPN, Evaporative cooling that can occur in mod+ rain with little wind. enjoy

sorry to repeat the whole text but it i srelevant to what I'll post, even though very brief. It is an average from whatever source, this can be GFS or whatever, but if you simply take it at face value, as I have generally done over the past 5-6 years, these 'changes' tend to even out. I have always said that great care is needed when using them and NOT to use them without looking at other outputs over the same or similar time scale. Do that and they will give good guidance for the overall weather pattern and the long wave upper air pattern over the 6-14 day time scale. They can and do give at least 5-6 days warning of significant changes in the long wave pattern, as they did with this incoming cold spell and its lasting longer than the synoptic models have suggested at times. Each to their own of course but I find them very useful throughout the whole year. They are a bit 'iffy' at the seasonal change overs, for about 10 days I find, and like every model are unreliable if a Tropical storm/ex hrricane get into the north Atlantic. An interesting post from Nouska-thank you for that

the link Nick provided, see above, shows as one would expect from similar sources, a very similar pattern to the 8-14 from NOAA last evening. What is interesting that it shows +ve heights across the large trough Canada/eastern US. looking back at the post from GP on longer term connections and the 500mb anomaly charts he suggests are quite similar again to the link that Nick gave above.

many thanks Nick

thanks for that Nick will bookmark the info, another source of data for checking the mid term forecasts. Can you give me the actual link for the charts please Nick?

a dry and fairly clear start, about 3/8 total cloud, a low of 2.0C just now so just starting to get some white showing on car windscreens as I look outside 0859=now down to 1.4C

Good to see an upturn in mood this evening. It really is funny reading some posts over the last few days. To me there has never been any doubt that the cold would arrive into England during today with Scotland already in the cold air over the past weekend, at least for many areas. I tend to look 6 days or more ahead so the showing today of the possible Tropical Storm is something that was mooted several days ago. What effect if it does become one is hard to predict, especially so at this time of the year. Almost unknown I would think. What effect this will have on the anomaly charts I follow is also hard to predict, that is other than confusion! Currently the NOAA output seems to be suggesting that somewhere between day6 and 14 the 'cold' ridge will have given way to a more mobile Atlantic type of flow. From past experience I would suggest later rather than sooner in that time scale. Interestingly the 8-14 shows some signal of rising +ve values in the entrance to the western English Channel, with the ridge still there, east of the UK now, and also the trough down into Europe. It does appear as if the Atlantic will win out but as to how long for I have no idea. I will leave that to others more aufait with later teleconnections. So cold for a week to 10 days becoming increasingly dry after whatever happens tomorrow into Thursday for some areas. That looks interesting and I suspect changes will occur in will it snow or not for any particular low lying area right up to T+6 hours. links http://www.cpc.noaa.gov/products/predictions/814day/500mb.php http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html the 12z run shows GFS reinventing ridging from the Azores area. How 'real' this will turn out to be remains to be seen

The penalty of believing the synoptic models when they 'appear' to promise deep cold and snow everywhere. One does need to treat these predictions with great care. At long term say beyond 168h and sometimes less always check one model run against the same time the day previous and keep doing this. IF it shows a particular scenario then it may well keep this and gives some confidence. If it keeps switching from one idea to another be very very wary of it showing the one you want.

The post from Steve above illustrates, largely, what the anomaly charts suggested recently. That is the cold remaining out to about 19-21 January. Prior to that and unlike the synoptic models at times they showed the cold starting around 11-12 for England (already there for Scotland) and possibly lasting out to about 16th. Beyond the 21st and I am afraid that both the ECMWF and GFS anomaly outputs show the block giving way with the cold weather being replaced by more Atlantic type weather. Currently, see below, NOAA at 6-10 shows nothing of this and even at 8-14 is not keen. If they both start to show a decrease in +ve heights and ridging which they have at the moment then we could be looking at the Atlantic returning. How long this might occur is impossible to say using the anomaly charts. links http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html http://www.cpc.noaa.gov/products/predictions/814day/500mb.php

Dry now after light rain earlier with a ground frost before that, cloudy at the moment and the low was 1.5C, its now 4.8C

sorry no I don't, that has always puzzled me

Perhaps one should realise they are produced for Exeter and other world weather centres. take a look at their output for civil aviation you may find some similarity in the orientation/shape/scale etc. We as the public are very small fry, however much that upsets, to their main money paying customers. NOT us although they are available for us. to add only this I have tried to explain why it is done. Now why not e mail them instead of making a fuss in here?

Perhaps one should realise they are produced for Exeter and other world weather centres. take a look at their output for civil aviation you may find some similarity in the orientation/shape/scale etc. We as the public are very small fry, however much that upsets, to their main money paying customers. NOT us although they are available for us.

I think they are so orientated as they are/were in my day, taken of the some chart layout as the senior man uses for drawing his charts?

True at longer time scales, say beyond 168h sometimes 144h. Below that then the convergence of the different models and consistency start to be more important.

A rotten cold damp morning with slight rain and drizzle at times with the clouds clearing to clear skies by mid afternoon. The high of 4.2C made it the coldest day since 5 February 2015.

To 'try' and get some normality or perhaps objectivity into what may or may not happen. The synoptic models have shown some degree of, shall we say, volatility over the last few days. From deep artic to mild SW'ly. The truth lies between the two but erring more towards the cold specctrum rather than the mild one. My use of anomal charts gets derided by some but they remain the most likely upper air outcome in the 6-15 day time scale. 2 years of research winter and summer proved this with something like a 70% accuracy at the 10 day mark. If you look at the synoptic models, Gibby gives their statistics usually, and ECMWF almost always leads at any time scale and 10 days is no exception, sometimes a bit under 40% sometimes 40-45% accurate. So the figures show which version/model gives the most accurate end product at 500mb. Getting the surface pattern is even less accurate and, for various reasons of physics with moisture a major clulprit is much much more difficult. The NOAA outputs have consistently since last Sunday/Monday kept the cold air over the UK, ECMWF anomaly has much of the time but not as consistently; GFS has given different ideas, especially latterly. To me the cold is on its way from those parts of Scotland that have been 'cold' for 2-3 days now. It will last into next week but gradually become mostly dry as both the upper ridge and its surface partner edge into the UK area. Currently, and I do not try to predict beyond 14-16 days ahead, it looks like remaining 'cold or rather cold' by meteorological definition for latish January over almost all the UK to 20-21st January, maybe a bit longer. Remember also that once cold is established trying to move it is usually a slow job. Forecasters have struggled with his dilemma for decades, long before the advent of computers. Since their arrival and the increasingly complex data they can assimilate and the accuracy very slowly increases with each new model this remains one of the problems that remains-moving mild air in too quickly. Sorry if this post upsets some folk but I hope it gives as balanced a view without all the complex words and phrases that can be used but which, judging from some pm's I get, puzzles some folk. links below for various sites that are worth watching http://www.weathercharts.org/ukmomslp.htm http://www.cpc.noaa.gov/products/predictions/610day/fxus06.html http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html http://www.meteociel.fr/modeles/naefs_cartes.php?code=0&ech=240&mode=0&map=1&runpara=

Nothing has changed in decades, ALMOST always if a cold spell lasts 3 or more days, the longer the more effect it has, then milder Atlantic air is predicted to move across the whole UK too quickly.

A ground frost earlier but cloudy now although dry, a low of 0.6C

And through the ups and downs on the synoptic models the NOAA anomaly charts continue along the same lines they have for the whole week, link below http://www.cpc.noaa.gov/products/predictions/814day/500mb.php IF they are correct, especially the 8-14, then the cold lasts at least until 24 January it seems. By then of course just dry cold.

I think it is so amusing reading the highs and lows in the model thread as the synoptic models chop and change. What 'blink' and you will miss it Bb? Nothing I have seen has ever predicted deep long lasting cold. Cold by meteorological definition yes, length of spell, still open to doubt but 5 days as a minimum with most areas (if with clear skies) getting air frosts, and some even getting snow. Just when the cold leaves is still not definite, I would suggest 7-10 days unless the cold settles in sufficiently to slow down or even stop the return of the Atlantic for a while longer. Of course time will show us all how wrong we may have been but a more relaxed approach might be an idea for some folk in the model thread.

not at all, it is not that often one model is so far out near the UK but correct for the rest of the northern hemisphere. The stats are for the upper air pattern NOT the surface, long wave patterns are not minor peturbations.

Nor should we be swayed by adherence to GFS outputs IDO. Check the 1, 3, 5 or 10 days 500mb statistics for the northern hemisphere and GFS is almost always behind UK met out to 120 and ECMWF to 240h and by increasing margins as one gets further from T=00. A careful overall look at all outputs beyond about T+144h and looking, not for detail, but consistency in the upper air, not the surface. From experience it is hard enough to get the right pattern at 500mb but infinitely harder to get it at the surface, even without making it even more complex by the addition of moisture.

From the anomaly charts, not the GFS version, but NOAA and ECMWF, they both suggest that the 6-10 day outlook from now is for cold to be still over the UK. My own interpretation of these 500mb charts is that the cold will by then be largely a dry cold with both the upper ridge and a surface high beneath it governing the weather. How long post 10 days is open to doubt. Over many years the feeling is, and proven when working, that we try to shift cold air too quickly. The NOAA 8-14 suggests this may be starting in that time frame. Time will tell of course.