wysiwyg

Showers have been rain/sleet/pellets here so far this morning. My parents 5 miles to my NE and 150 feet higher have had mainly wet snow. I guess I'm right on the border of the current marginality. Hoping for something colder and more organised later.

Happy New Year everyone - hope you're all enjoying the weather and the outlook!

I think that's a pretty good summary HotCuppa. However, I do think we will be colder by Saturday when the trough being modelled arrives here. I think the temperature variations you are seeing are still being caused by the remanants of the last couple of days and also your location relatively close to water that may also be having an effect. I am still in full agreement with you though. The further south and west you go in the region, the more marginal it becomes. The snow before Christmas was relatively localised and I see nothing different in this set-up. Just patience and keep our expectations under control so that we enjoy any bonus snow.

I share your pain Kent even though I'm further inland than you. Reality is that our coasts have a drastic effect on the local weather, warming, tides etc. My rule of thumb is that the colder it is the more likely that the cold will nulify any warming effect - looking at those ensembles the cold is looking good - it's just a case of now analysing the shorter term data 0-72hrs to start to put some detail on the overall synoptics being currently modelled. ( PS DO NOT FEED THE TROLLS!!!)

Yes that's pretty much spot on. It's more to do with the surface warm generated by the sun during daylight hours in clear conditions so any cloud cover will affect the rate that water evaporates from the sea's surface. The convective effect will die out with the sunset but any moisture already there will continue to move west. EDIT: Hehe just re-read that - you are spot in with your analysis is what I meant! Not in showing your ignorance lol - IMO it's not ignorance to ask questions. That's the whole point of learning!

Just to add to what JH said, my understanding of these models is that they are indeed "trained" using existing known conditions. In other words the coefficients in the algorithms are "tuned" on known data. I am only basing this on knowledge of other computational models that are used to model fluid and thermal dynamics. It is possible to use biased data to cause a training bias within these models, however I suspect that given the maturity of some of them that any bias will have been ironed out as more and more data has been used in each training run of the next "beta" version. As JH mentioned, the real achilles heel for these models is the lack of solid input data. The pre-screening process interpolates many of the points between each of the real data points, data has to be time shifted as it is not all collected at exactly T0, etc etc - bottom line for me is they are a valuable tool but frankly rather useless in isolation.

The radar is prone to showing false echos known as "anaprop" (or anomolous propogation in full) this is usually very light precip that causes radar echos but is being swept along in the breeze and never hits the ground - I had that virtually all day yesterday. Also the positioning of the echo data relative to the map can sometimes be a little suspect.

I'm not convinced we are going to see a true Nrly flow out of this just yet. Looking at the satellite imagery, the general flow to the north of the UK seems to be from the NNE i.e. roughly paralell to the west coast of Norway. Some of the upper winds are varying between NE and NW but the lower level flow looks set to be from the NNE for the next 48 hours or so. Having said that, the feature forming just off northern Norway now is likely to swing winds round to the NW for a time on Saturday and that could lead to convective snow showers off the Irish sea if the timing is right. The caveat here is that, as TWS mentioned, this will be prone to some modification by slightly warmer air to the west and may lead to marginality on the coast and very low ground. All fascinating stuff! BTW now the sun has gone it feels raw out there - I haven't got a thermometer handy but definitely a change in the "feel" of the air.

Yep - sit tight with the temperature drops - we are still mixed up with yesterday's system and there is still a fair bit of modification going on over the NW region. The low is definitely moving away now and the true cold is digging in hard. Yesterday as the front was advancing we had ground level and 850hpa wind vectors from the east but the higher wind vectors were still strongly from the south. Today we have NEerly wind vectors all the way up to around 600hpa and the 500hpa vectors pushing in from the NW with a northerly source. The cold mass is slowly but surely winning.

More than likely due to the cloud in the tail of yesterday's low spewing out over the north sea, blocking the sun and hence preventing convection.

It still looks likely to be a convective feature to me. There is no discernable WAA from anywhere other than the warm sea below that feature. Again I suspect that the precip band is modelled on a "likely to see showers" basis and will not necessarily be an organised frontal band of snow moving south. Also I think that the scottish highlands will take any sting out of the precip and the best chance for anywhere south of the Highlands is for local coastal convection as the feature moves south and temporarily modifies the flow direction. Having said all that - looking at the current satellite pics it does look quite organised already over Norway so who knows? - lamposts at the ready!

Sat24 animation shows the true NEerly flow digging in hard at the tail end of yesterdays low which is now making its way off to the south and forming a rather pretty spiral in the process. http://www.sat24.com...at=ir&type=loop Northern Scotland looks to be getting an absolute pasting and the first signs of the feature off Norway that is due on Saturday taking shape nicely too. (satcasting is a much underrated form of forecasting imo! ) As for the showers closer to home - it looks as though with the slightly more Nerly component in the flow than we had before Christmas that it's focussing the activity further to the north of the region. No sign of the streamer that set up off the tip of Denmark back then. Fascinating weather - especially when we are lucky enough to be able to view it from 700km above the planet

Yes! You can see that effect really well on the sat24 animation as well. Our current "lazy" low has been sat piddling about off SW Ireland for 48 hours and systems have been hurtling past below it headed for southern Europe.

I think it's down to how much moisture it can pick up from the North Sea before the fronts cross Scotland. Also how much of that moisture is deposited over the Scottish highlands will determine what is left for areas to the south. As TWS mentioned earlier, I believe the greater potential is for coastal shower activity as that trough moves south and temporarily modifies the flow direction.

Nothing IMBY about that at all imo. To me it's a well put together analysis that shows that the latest GFS 06Z run is trending towards the favoured (by NOAA) ECM predictions. Just a side note to put all the model predictions into perspective. Technically they are all "FI" (for want of a better term) even before the start button is pressed. None of the input data will be synchronised in time, variations will occur due to time shifted samples, obscured readings (particularly satellite and airborne). Again, we see ensembles diverging widely after only 4-5 days indicating that the extrapolation that these models predict is currently highly sensitive to minor variations in initial data. These errors multiply rapidly as the iterations progress so, for example, if snow fall is predicted at T+x and doesn't occur, then the remainder of the run is severely compromised due to inaccurate surface temperature modelling. I think it's worth also re-iterating (during the wait for the 12zs) that there is a whole host of other info on here that is objective and gives a pretty good summary of the outlook. If we start being too agressive with off-topic posts in this thread then no-one will ever ask questions or present their own analyses. In other words there has to be some tolerence of different views and differing levels of understanding of the models and the interpretation associated with their output. Enjoy the synoptics though - they are rare for winter :smiliz46:

RAMPER! Hehe just kidding - add to that the fact that there are three major models and a raft of "lesser" models all struggling to cope with unusual synoptics, initial conditons, wider teleconnected signals, etc etc etc The most important trend for me is that all the predicted output shows the trend for remaining cold - it is utter folley to try and tack on any details wrt actual ground temperatures and precipitation levels for specific locations after T+48 hours. We have seen some of the rarest winter synoptics and weather patterns in recent years in the last three weeks - savour these and enjoy what is about to happen

Who would wanna be a meto forecaster eh? To be fair to them they issue warnings for people who would be inconvenienced or endangered by the snow and ice potential from the current setup. Had they failed to issue a warning and it had turned out that snow was widespread there would have been a lot more complaints from people not interested in building snowmen! For me the interest in this cold spell continues on after today. The last 24 hours has shown northern height rises and a negative Arctic Oscillation index are fundamental building building blocks for a sustained cold spell. The system that produced the mush would have been a different beast entirely had it been energised by the full force of the jet stream. As it happened it was a weak affair that had already had to negotiate its way around the Greenlland high so that by the time it ran into cooler air over the uk it ground to a halt off SW Ireland and its only remaining energy was rotational about its core. The same scenario with a deeply entrenched pool of cold over the UK, fed by a strong flow from, say, Siberia would have resulted in a very different picture this morning. In summary, the pattern already seen over the last couple of days looks set to reload several times in the next ten days or so. I wouldn't expect this to result in much snow for my part of the NW but the key is: Building blocks in place + UK cold pool being reinforced = potential there for snow just about anywhere.

When did they move the english channel?????

Looking at the Meto 12z analysis fax and the T+24 chart would suggest that they think that this system is going to stall sometime overnight with the warm front stretching east from Cumbria and the occluded front stretching east from mid Wales. The T+36 chart then indicates the occlusion slowly heading back south as cold air digs in behind it. Although the whole set-up is clearly quite marginal - the potential was and still is there for quite heavy snowfall if the fronts stall for long enough to drop their moisture through the cold air as it undercuts the warmer air we are currently seeing now in the NW. I'm not holding my breath for my location as I think by the time the conditions are conducive for snow, most of the moisture will have gone from the system. However, I still think that there is potential here for a few cm and more in areas with more favourable elevation. I think today we have witnessed a classic cold vs warm battle ground over the NW. Unfortunately it was a tame storm versus a lazy cool airmass instead of an aggressive atlantic system pitched up against entrenched cold backed up by a polar or siberian feed. All in all these are encouraging signs and the fact that it looks likely cold will win out yet again is good news as we head into January. (if the ecm 12z T+240 verifies we are in for a shock! :lol: )

It doesn't seem to be showing anyone's location at the moment whilst the server maintenance is ongoing - might be worth putting locations in posts temporarily until it's sorted. And yes believe it or not - it's snowing in Chorley!! :lol:

I'm far too busy trying to find my house!!!!

Shows up nicely on this sat image

Trouble is with snow risk forecasts in these showery setups is that you could see a single 30 second snow shower and the 100% risk is fulfilled

LOL it goes to Chorley's stats when I click on that link - cookies anyone?

You can get decoded METARs here http://weather.noaa.gov/weather/GB_cc.html (Note that the times are US EST - UTC is shown in brackets) I would guess that the manchester airport ones would be closest to you but have a look at the list and you might recognise somewhere a bit closer