Backtrack

Dunno what everyone is fussing over. Have you seen the upper air profiles and the precipitation charts for us? Much of the south of the region looks to be RIGHT in the firing line for a good 6 hours of snow before the front moves away. After that we have the potential for some wintry showers off the Irish Sea the next day. All in all a very positive outlook. Cheer up.

Merry Christmas everyone! Streamer went through, containing rain, hail & grauple. Thought I saw some snow too but I feel I was mistaken.

With uppers of -2C in the associated warm sector? Perhaps not.... Too far away to even discuss in detail anyway!

Yes, this would bring snow to some areas in the north and east. As a general rule, the contours (white lines) of high pressure are followed clockwise, whereas low pressure is quite the opposite, we follow these anti-clockwise. So as you can see from the chart in question, we have lower pressure to the east and high pressure to our west ridging towards Greenland. The high pressure moving toward up to Greenland is a sign of the jet-stream diving south and WAA (warm air advection) happening, where warmer air is being pumped up towards Greenland thanks to this high pressure cell, this acts as a block, blocking off the Atlantic, for a time at least from having a major influence to our weather. We see the low pressure to our east drawing down colder air from the North East, with the influence of that higher pressure also dragging down colder air from our north. As a general rule for snow, we look at the 850hPa charts. These reflect the temperature high up in the atmosphere (at 850hPa), we need these to USUALLY be at -5C or lower, unless there are exceptional circumstances. The above chart is not an exceptional circumstance, and as seen from the chart below (of the 850hPa temperature), we unfortunately have a warm sector associated with the colder air. This would hinder the chances of snow for some, but it will eventually move away or fill out, and with the low pressure in such a close proximity, we are likely to see some great shower action near to North Sea coasts, blowing significantly inland on a flow that strong (look how close the contours are together). We also see those isobars (contours/white lines) creating a slight westerly element to the flow over on the western side of the country, this would aid convection from the Irish Sea too, giving some western areas wintry showers, North Wales especially on that chart in question. So in summary, away to the north of that warm sector (where we see a warmer pocket of air away from the cold) we will see some potent, frequent wintry showers, across much of the country with the flow being as strong as it is. The weaker the flow (calmer) the less likely that showers will penetrate the Pennines. But it's certainly charts like this that illustrate and paint a great picture for those living in the North East, who are likely to get absolutely pasted! It's of course 6 days away though, which is far too far to be pinning down precipitation amounts or just where exactly that warm sector will be (if it even materializes!). So yes, snow for some, not for others!

Someone bring me some snow

Given that we've not had a below average month in about a year, I'm gonna stick with the trend. 5.0C, cool start, mild rest.

"In mathematics and physics, a deterministic system is a system in which no randomness is involved in the development of future states of the system." I'm still no wiser as to what that might mean mate haha! Sorry!

Operational run maybe? I honestly can't work out what that might mean either.

Blue screen of death? Could be a hard drive error, usually a reboot sorts it unless there's something internally wrong, start it up in safe mode and do a recovery to an earlier restoration point, you'll lose any saves you've made since the last point but it could save your hard drive.

Said I wouldn't post in here, but I lied. The way I see it, EVERY model (except short to medium range models such as the UKMO) are showing heights building over Greenland, via WAA, or another route. And whilst we may not have cross model agreement on an exact time stamp for a nailed on cold spell, we have fantastic agreement across 95% of major models for Mid-Atlantic blocking at some time in the near future. In the famous words of Glacier Point 'Get set, it's coming'.

Hardly fair post BD, I contribute what I can, I don't know a great deal, but when I see something that I think may add some sort of value or discussion point to the thread, I'll post it. If every user reading the topic were looking for posts from the likes of Nick Sussex, Ian F & Lorenzo etc, then there would be about 50 pages just overlooked, just because some members are new to this, or like myself have a fairly limited knowledge base compared to some others, does this mean I'm talking as you say 'absolute b*!!@xs'? I don't see you contributing to this thread. It's posts like yours that prevent people from posting, or scare people away from this thread. So tell me, because I prematurely called out the 12z as a mild run when it showed MILDER synoptics for Christmas & Boxing Day, when compared to the 06z, how does that make my post rubbish? I'm done posting in this thread now. Have fun.

Rapid cyclogenesis.

I was far too quick to judge man, not a half bad 12Z afterall. That storm looks fun, blizzards for all!

I take back my post. Later frames now show WAA up to Greenland with the low sinking to our south east to re-introduce colder air from the north. What get's me though, is that the same thing has stayed constantly around T+162 and beyond for about 3 days now, it just doesn't seem to be getting any closer. Still not looking great though for Christmas & Boxing Day

That model is either broken, or onto something. It's consistency is amazing. I can't see that being right though, despite it's trend, too many other models now going against it.

12Z looking worse already, quicker to introduce mild air from the SW thanks to the Azores High...

Fantastic write up Nick, I certainly didn't know the part about the energy process, from the liquid to the gas. Will certainly help newcomers! Worth adding too, the heavier the precipitation, the quicker the process, lowering the temperature even further. Hail is a supreme example of evaporative cooling at its best!

Really can't understand who is feeding the fire, but telling people to discount a run just because it's an 06Z or an 18Z because it doesn't have balloon data is just plain wrong, and this is coming from a non-bias point of view, whether the models are showing the deepest cold or the mildest December synoptics ever seen. A run cannot simply be overlooked, the GFS is ran four times a day for a reason. Instead of discounting a run, compare the four which run each day and take the average, and that's more than likely the closest to accurate one can get. Sorry for the rant but it's annoying, especially when I see EXPERIENCED members who have been here for years asserting people to 'BIN' a run for whatever stupid reason that may be.

And alas the start of some WAA toward Greenland on that second chart, with Mid-Atlantic blocking likely to establish later on in the run. Fantastic charts.

It'll be a fantastic upgrade when they fully get it up and running, I assume like all new things, there will be niggles and things which need tweeking before it's on top-form, but I can't wait for the official release. A great addition to the already groundbreaking data we have available to us

You know it's Christmas when this theme returns, thanks Paul! Woo!

But John, years of GFS at standard resolution, vs what, a month of GFS Parallel? Quantifiable evidence to currently use the GFS OP over the parallel, despite the higher resolution, surely?

You've answered your own question it's not fully officially operational yet and it's performance as of yet is questionable, compared to years of GFS OP verification stats. It may have a higher resolution, but in my book that doesn't mean it's better, there's been many models run at higher resolutions than the GFS, yet we follow the GFS, ECM & UKMO year in year out, there's good reasoning for it!

The low has been removed on today's 12z

That's the Parallel, the OP is the center of discussion right now, which isn't great compared to yesterday's runs.