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Paul

Model output discussion - 16th Nov onwards

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Not only cold air temps on this weekend but a bitter wind making it feel even colder

 

63-290UK.GIF?18-1266-290UK.GIF?18-1272-290UK.GIF?18-12

78-290UK.GIF?18-1284-290UK.GIF?18-1290-290UK.GIF?18-12

 

:cold: :cold: :cold:

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This weekend's event may be classified as an 'enhanced toppler' in my book - (very) short lived but peaking with impressively cold upper air for the time of year.

The signs for a mobile westerly regime for the following week have gained ground over the past 48 hours with a risk of further very windy conditions for the north in particular. Also plenty of rain about which won't be welcome up there in particular, though at least polar maritime doesn't carry as much moisture as the TM air we've been seeing over the past few weeks.

 

The exact positioning of the longwave trough is a little uncertain though, with a trend slightly west over the past 24 hours but plenty of room for it to end up further east too. Shortwave developments on the western flank of maturing Atlantic storms will be an important player as outlined earlier today. Temperatures generally near average, though the GFS det. keeps things on the chilly side at night - clouds tending to be well broken at night as instability falls low. Following the weekend's cold snap, it looks to be enough to throw out the possibility of a record-warm November in the CET region and probably the majority of other locations too.

 

We should start to notice that unusually cold region in the North Atlantic again too, as it lowers temps by perhaps 1*C or so compared to what we'd usually expect from a westerly regime.

 

 

Seeing the pattern move back toward a more Nino-like state across the N. Atlantic and Europe serves as a reminder that we ought to be waiting until the back end of the season for our main chances of a more sustained outbreak of cold, snowy conditions. Yet with the AAM outlook from GEFS continuing to head negative beyond about 10 days range, there remains some suggestion that we could see deviations from that expected state of affairs in December. Those signs aren't as crazy as they were two days ago, but they're still there and must be kept an eye on.

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I am old enough to remember many of the classic bbc forecasts back in the 80's. Many of these winters featured bouts of northwesterly winds - very similar to what ECM is showing this evening. During these northwesterly episodes, I distinctly remember the forecaster saying on many ocassion that "If you think it feels cold now, wait until next week!!" Northwesterly periods very often preceded bitterly cold spells. For this reason, I expect quite a potent cold spell during the middle of December :) Nothing scientific I know, just a good memory :)

Which makes me think of December 1981, bitterly cold, lots of snow events but not particularly low uppers. Part of the PV having moved South over the UK stayed put for a couple of weeks, with small areas of LP undercutting as they moved in from the West, no Greenland high or scandi high that I can remember for that event.

                

If the PV is displaced our way and some sort of blocking takes hold in Siberia and Alaska up towards the pole as we have seen on some of the recent runs we could end up with this sort of scenario.

Edited by snowray

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A slightly colder set of extended ensembles from the ECM 12z tonight. The blue control run goes cold from day 10 and ends cold and snowy at day 15. It also ended on a snowy note on this mornings run :)

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[so the flow of Pm air, sometimes rPM with not much of Tm seems the most likely into December to me?]

What's that mean?

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[so the flow of Pm air, sometimes rPM with not much of Tm seems the most likely into December to me?]

What's that mean?

 

A diagram from the Met office which will explain - John's using the abbreviated forms.   http://www.metoffice.gov.uk/learning/learn-about-the-weather/how-weather-works/air-masses/types

 

Figure-6-Air-masses2_2.jpg

Edited by Nouska

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[so the flow of Pm air, sometimes rPM with not much of Tm seems the most likely into December to me?]

What's that mean?

Polar maritime and returning polar maritime with not much tropical maritime. In other words on the cooler side of average with winds from the west and north west more than south west.

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Some surprise snowfall this weekend for many I think, especially the East...if the fronts coincide with nighttime, lying snow at any level and latitude may be possible...

Latest GFS precip chart even has a snow event in the West/Sw on sun evening.

Edited by Ali1977

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Some surprise snowfall this weekend for many I think, especially the East...if the fronts coincide with nighttime, lying snow at any level and latitude may be possible...

Latest GFS precip chart even has a snow event in the West/Sw on sun evening.

yep  a lot more widespread on this run

Edited by weirpig

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Some surprise snowfall this weekend for many I think, especially the East...if the fronts coincide with nighttime, lying snow at any level and latitude may be possible...

Latest GFS precip chart even has a snow event in the West/Sw on sun evening.

yeh latest gfs moves things further west again for this weekend!!

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Take GFS ppn charts with a large dose of salts, especially this far out but being in the west I like this "kinky" chart.  :laugh:

 

gfs-0-78.png?18gfs-2-78.png?18

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A diagram from the Met office which will explain - John's using the abbreviated forms.   http://www.metoffice.gov.uk/learning/learn-about-the-weather/how-weather-works/air-masses/types

 

Figure-6-Air-masses2_2.jpg

 

There's also a really good guide to air masses over in the guides area. which John wrote:

https://forum.netweather.tv/topic/12371-guide-to-uk-airmasses/

 

And for some additional reading for those interested, Ian (TWS) wrote a nice guide on UK winter weather setups:

https://forum.netweather.tv/topic/56318-guide-to-uk-winter-setups/

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Take GFS ppn charts with a large dose of salts, especially this far out but being in the west I like this "kinky" chart.  :laugh:

 

gfs-0-78.png?18gfs-2-78.png?18

Yeah, one to watch for definite. I think by the end of tomorrow we should get a better idea of potential disturbances within the cold - some of the more accurate models come within their timeframes.

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A slightly colder set of extended ensembles from the ECM 12z tonight. The blue control run goes cold from day 10 and ends cold and snowy at day 15. It also ended on a snowy note on this mornings run :)

 

The 10 day ECM ensembles for Reading show the deterministic to be right at the top of the envelope, control less so. Scope to see colder solutions in subsequent runs.

 

epsgram_at_reading!epsgram.gif

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Take GFS ppn charts with a large dose of salts, especially this far out but being in the west I like this "kinky" chart.  :laugh:

 

gfs-0-78.png?18gfs-2-78.png?18

yes  the gfs tonight brings the nw wales w mids and the sw into the game  all for fun off course :)

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The ecm T240 tonight is as already been described. By the end of the ext period there is a trough Alaska with a more zonal flow across N. America but the Greenland trough is still the main player so unsettled with incursions of Pm airstream that has been the consensus this evening.

 

 

post-12275-0-35009200-1447885191_thumb.p

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away from Scotland, I don't think there will be much in the way of snow, maybe one or two flakes.

You have posted this in the wrong thread. More suited to General Weather chat or Regional threads :D

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The 10 day ECM ensembles for Reading show the deterministic to be right at the top of the envelope, control less so. Scope to see colder solutions in subsequent runs.

 

epsgram_at_reading!epsgram.gif

Indeed :) I think we could just about class it a mild outlier.

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The GFS has been boasting a N/W Pm type flow into December for a good few days now. Some potent cold shots can come of these, Atlantic Lows and cool air mix well ☺

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Seeing the pattern move back toward a more Nino-like state across the N. Atlantic and Europe serves as a reminder that we ought to be waiting until the back end of the season for our main chances of a more sustained outbreak of cold, snowy conditions. Yet with the AAM outlook from GEFS continuing to head negative beyond about 10 days range, there remains some suggestion that we could see deviations from that expected state of affairs in December. Those signs aren't as crazy as they were two days ago, but they're still there and must be kept an eye on.

 

I enjoy reading your in-depth posts very much. However, maybe we should wait for Winter to begin before saying our best chance of seeing sustained cold is at the end of Winter. After all it is the 18th of November and you say things looked more promising two days ago. Things can change again

 

This isn't a dig but this is the model thread. This happens all the time. I wish this thread was for the reliable time frame and we had a separate fantasy island thread.  We have posts saying what will happen in 11-15 days time when we don't even know what will happen day 10. Thanks once again not a dig at anyone. It just gets confusing.

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a more Nino-like state across the N. Atlantic and Europe

 

With its base in 1600s science and the relatively short time span since overlapping the LIA and all we've learnt since, I'd like to think we're pretty much just in another period of general cooling for this part of the NH. All bets are off in terms of micro-scale. As we head towards the borders of macro-scale climate change and all that human input has effected into these models, it's pretty much unknown country.

What would have used to have taken centuries, might well take decades.

What might take decades might change from year to year.

One shouldn't take too much stock in medium - to - long-term drivers when predicting a 3/4 month period.

Anything could happen and probably will. A calving off of an Ice cliff into the thermohaline conveyor could start the chain reaction to the next Ice Age.

 

I'm sorry, I'm just very sceptical of the academic boundaries placed on the global model due to such long-era peaks and troughs.

They are not invalid, of course. I just think absolutely ripe for censor.

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