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General Model Output Discussion Tuesday December 22Nd:

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Generally I can see the mean trough coming down into Scandinavia as well but my main concern is the jet doesn't quite line up correctly and we end up with a Euro high still and a trough over Scandinavia with higher pressure over Greenland but because of the angle of the jet the cold remains locked up further north, sort of the ultimate screw over set-up!

Saying that I can see a trend for a northerly shot for New Years, after that and there is a lot of spread, ome ensemble members follow the ECM and develop a stronger PV, if that happens odds of a cold first half to Jan go down quite hugely...

However I agree with GP as well that all the teleconnections would suggest a decent cold shot again towards the back end of the month, if we can get some sort of Stratospheric warming then that will help as well...

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I think it's worth stating that the atmosphere might also be working 'bottom'-up' w/r/t mean zonal east wind propagation due to upwelling waves. It's not possible to discern these at the moment because the stmopshere is still in a deeply -AO state. This upwelling should reach its peak mid to late January and steadily decline thereafter.

In so far as El Nino, I would regard this as our friend right now. Remember how La Nina denied us the full impacts of the SSW last year? What goes around comes around and this Nino should help deflect the polar vortex along the lines of the long range models dropping the trough into Scdnainavia with a ridge further west.

That said, as the tropical convective signal starts to work its way back into the Indian Ocean (where SSTAs are +1.5C right now), that is likely to be the trigger for a warming of the stratosphere. Everything is culimanting towards a severe spell of weather mid to late January. But the period before holds huge interest, not least because the cold air has not really gone anywhere and remains closeby.

It certainly appears that way. The whole vortex split this December has been very much a lower stratosphere and troposphere event rather than an upper event propagating down. To me it does look like the negative mean zonal winds are acting like a barrier to the upper positive anomalies. With last winter's SSW it proved very difficult to see the 'blues' that we are seeing in the troposphere now - they always seemed to be held in the stratosphere. The ECM has been keeping the positive wind propagation held in FI and long may that continue!

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Decided to pin this topic (like the previous one) as otherwise it may get lost.

My main interest continues to focus on Christmas Eve/Day and it will be interesting to see if the models throw up any more changes even though Christmas Eve is only two days away. Precipitation type and distribution is still up in the air.

I agree with the others that the longer-term looks very interesting indeed. The back end of December is increasingly looking like it will be cold in the north but mild in the south, and at some point this cold air is likely to spread down from the north.

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It certainly appears that way. The whole vortex split this December has been very much a lower stratosphere and troposphere event rather than an upper event propagating down. To me it does look like the negative mean zonal winds are acting like a barrier to the upper positive anomalies. With last winters SSW it proved very difficult to see the 'blues' that we are seeing in the troposphere now - they always seemed to be held in the stratosphere. The ECM has been keeping the positive wind propagation held in FI and long may that continue!

yes i think this el nino is helping us but not meaning to do so, its like sort of confused in some someway if u get me, by bringing us a different scenario to things.

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GP alluded to this earlier via GEM and GEFS ens height anomolies, but the NAEFS 00z run is superb in FI. parts of the UK are under mean uppers below -4c with the trough firmly into scandi. to have this level of upper temp at such a long range is something i havent seen on this output. remember, we are talking about the mean of all 50 ensemble runs from GEFS and GEM. This past week may well be just the starter .............

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Here is hoping that this week has been just a taster.

I hope that GP's thoughts for January are correct and that we could be on the cusp of something a bit special.

The ensembles for GFS are looking good right now let's hope this trend continues.

My wife doesn't understand my obsession with winter weather but standing in london on the shortest day of the year with the snow tipping down was just magical.

Now if we could get a freeze up like they have just had on the east coast of the USA that really would send this place into melt down, over twenty inches in Manhatten- crazy !

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Here is hoping that this week has been just a taster.

I hope that GP's thoughts for January are correct and that we could be on the cusp of something a bit special.

The ensembles for GFS are looking good right now let's hope this trend continues.

My wife doesn't understand my obsession with winter weather but standing in london on the shortest day of the year with the snow tipping down was just magical.

Now if we could get a freeze up like they have just had on the east coast of the USA that really would send this place into melt down, over twenty inches in Manhatten- crazy !

In 1978 blizzard, would the snow have been deeper and driftier than that usually on the east coast of usa at times. I remember reading that in 1963 that drifts were recorded of up to 20 ft and i havent even heard of anything like that on the east coast for example?

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It certainly appears that way. The whole vortex split this December has been very much a lower stratosphere and troposphere event rather than an upper event propagating down. To me it does look like the negative mean zonal winds are acting like a barrier to the upper positive anomalies. With last winter's SSW it proved very difficult to see the 'blues' that we are seeing in the troposphere now - they always seemed to be held in the stratosphere. The ECM has been keeping the positive wind propagation held in FI and long may that continue!

I think we have got accustomed to 'what usually happens' after a cold spell so that after such a relatively potent one as this one it is easy to look for the hangover after the party so to speak. The expectation becomes as such that the default position of the polar vortex is always back to Greenland. Hopefully the current eliptical shape of the vortex is retained and doesn't change if/when the negative zonal winds are flushed out

But saying that, just perhaps the atmosphere is working in reverse from bottom to top? - afterall not all warming events that begin at the upper 10mb levels, sometimes 30mb, propagate in any uniform way (some don't at all)

Regarding the ECM, I couldn't agree more!

And regarding a big reload later in January as GP suggests is possible - a huge amen to that !!cold.gif

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In 1978 blizzard, would the snow have been deeper and driftier than that usually on the east coast of usa at times. I remember reading that in 1963 that drifts were recorded of up to 20 ft and i havent even heard of anything like that on the east coast for example?

I think I remember reading that the East Coast had its very own blizzard the same year; heavy snow (heavy snow on the East Coast makes heavy snow here look like a flurry!) for two days with very strong winds. It does happen; quite often as the storm pulls away very strong winds pull in from the North West which blows the lying snow around.

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interesting that the bbc are not forecasting any wintry weather for christmas eve like the gfs show! However paul hudson says christmas eve cold with rain sleet and snow likely!!??

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The ensembles for GFS are looking good right now let's hope this trend continues.

They are indeed quite interesting, there seems to be decent agreement on a northerly flow for the start of Jan...however I'm increasingly concerned on what I'm seeing on the ensembles and from the ECM with regards to the reduction of heights over the pole and importantly a stronger PV developing near Greenland, which over rides the signal for a Scandi trough and indeed such a set-up would lock us into a possible Euro high set-up...equally if the PV were to end up further west then we'd probably end up in a pattern akin to the 06z GFS...its quite a tight set-up...all or nothing!

As for the ECM, I believe there is only one way that chart would eventually evolve given the high moving NE from the Azores and deepning LP swing NE as well and thats for a broad SW flow to eventually develop, the south could get lucky and stay under high pressure but I can't say I'm a great fan of the 0z ECM long term prospects for Jan...

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interesting that the bbc are not forecasting any wintry weather for christmas eve like the gfs show! However paul hudson says christmas eve cold with rain sleet and snow likely!!??

their charts are very very terrible. they change all the time. on the tv they have snow shoers for north of england scotland, on the website it is rain and no mention of snow on bbc 5 day froecast

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well looking at the gfs since this morning the so called warm spell has gone instead it seems to be very wintry again if the models and the weather man can,t see more then 2 days ahead even then you look at the next run its changed again at the moment the gfs is saying now its staying cold deep in to f1 now up yo jan 2nd no sigh of any mild weather coming

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well looking at the gfs since this morning the so called warm spell has gone instead it seems to be very wintry again if the models and the weather man can,t see more then 2 days ahead even then you look at the next run its changed again at the moment the gfs is saying now its staying cold deep in to f1 now up yo jan 2nd no sigh of any mild weather coming

Yes but its model out put discussion so people can talk about trends even if in F1 and even if they dont come off.

Maybe the models are are prone to go back to default mode, lets face it last 20yrs the default would generally be South Westerly.

Were 3 days away from xmas day and even now people (TV etc) are 'scared' to put their kneck out. If it was 10c with drizzle it would be easier.

Forcast for reading today was 4c its 1c with snow still everywhereunsure.gif

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It looks as though the less cold trend is locked and loaded now to begin slowly pushing north during the next 2-3 days with a thaw in the south and precipitation turning to rain except on the higher hills. Scotland, N.Ireland and the far north of england will probably remain on the cold side with a wintry mix right up to the weekend, especially scotland and it's from sunday and into next week when colder and more wintry weather could push south again. Hopefully the 12z runs will continue to offer hope of renewed cold and snow potential next week.

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It looks as though the less cold trend is locked and loaded now to begin slowly pushing north during the next 2-3 days with a thaw in the south and precipitation turning to rain except on the higher hills. Scotland, N.Ireland and the far north of england will probably remain on the cold side with a wintry mix right up to the weekend, especially scotland and it's from sunday and into next week when colder and more wintry weather could push south again. Hopefully the 12z runs will continue to offer hope of renewed cold and snow potential next week.

So you think this very different forcast is tosh whistling.gif

http://www.netweather.tv/index.cgi?action=other;type=xmas;sess=

Any link to support your 'assumption'

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So you think this very different forcast is tosh whistling.gif

http://www.netweather.tv/index.cgi?action=other;type=xmas;sess=

Any link to support your 'assumption'

It's not an assumption, it's how the met office see it and I happen to agree with them, it will become less cold in southern england and probably further north as well, face reality. :)

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Potential for flooding on Wednesday night? Could be a lot of rain in the south, combined with snow melt it could be a nasty combination:

http://212.100.247.145/viewimage.pbx?type=gfs;date=20091222;time=12;ext=33;file=ukprec;sess=8f187d40dbdaf99165ba2eb5f95c9595;

Will certainly be rain, uppers of -2, positive dew points and temperatures.

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Potential for flooding on Wednesday night? Could be a lot of rain in the south, combined with snow melt it could be a nasty combination:

http://212.100.247.145/viewimage.pbx?type=gfs;date=20091222;time=12;ext=33;file=ukprec;sess=8f187d40dbdaf99165ba2eb5f95c9595;

Will certainly be rain, uppers of -2, positive dew points and temperatures.

I havent seen any charts showing how this will progress north yet? how far north is it going to get

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Potential for flooding on Wednesday night? Could be a lot of rain in the south, combined with snow melt it could be a nasty combination:

http://212.100.247.1...ba2eb5f95c9595;

Will certainly be rain, uppers of -2, positive dew points and temperatures.

Why does our local forecast suggest then that the rain could turn back to snow in the early hours of thursday? cc_confused.gif

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