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carla
30 December 2013 20:26:44

528 dam or lower represents thickness levels making it possible for snow to occur (in a nutshell).

Originally Posted by: White Meadows 




Ahh thank you

Holton le clay lincolnshire
Gandalf The White
30 December 2013 20:31:32

What is the 528 dam line? Please

Originally Posted by: carla 


The 528dam line is a measure of the temperature of a specified layer of the atmosphere.  In this case the air between 500hPa and 1,000hPa.  That is roughly the airmass from near the ground up to about 30,000 feet.


528 is significant because it is a crude pointer to conditions favourable for snow to fall.   It's a bit more complicated than that and the guidance is usually that above 530dam snow is very unlikely and below 522dam rain is very unlikely.


There are other useful measures of thickness.  The NAE and Euro4 models in particular (available on WeatherOnline) give thicknesses for the bottom layer 850-1000hPa.  Here you need to see values below 130dam.


At the moment there's no cold air over us but the Europe-wide view shows it:


850-1,000hPa: http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/12/30/basis12/euro/th85/13123012_3012.gif


500-1,000hPa: http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/12/30/basis12/euro/tpps/13123012_3012.gif


 


Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


Matty H
30 December 2013 20:33:38


Another reminder. Links only, not charts.

Ta.

Originally Posted by: Quantum 


Can mine be an exception 😛 I couldn't find 10hpa wind anywhere online and since I generated them myself there won't be copyright issues.


Originally Posted by: Matty H 



No

Originally Posted by: Quantum 


Actually it doesn't matter, I can link to tinypic directly.


http://oi42.tinypic.com/73cily.jpg


 

Originally Posted by: Matty H 



Perfect thanks. It's not just copyright, it's also site bandwidth and it makes the threads look awful on the eye like NW.
Quantum
30 December 2013 20:44:44



Another reminder. Links only, not charts.

Ta.

Originally Posted by: Matty H 


Can mine be an exception 😛 I couldn't find 10hpa wind anywhere online and since I generated them myself there won't be copyright issues.


Originally Posted by: Quantum 



No

Originally Posted by: Matty H 


Actually it doesn't matter, I can link to tinypic directly.


http://oi42.tinypic.com/73cily.jpg


 


Originally Posted by: Quantum 



Perfect thanks. It's not just copyright, it's also site bandwidth and it makes the threads look awful on the eye like NW.

Originally Posted by: Matty H 


Sorry MattyH I just got so carried away with my new toy that I forgot that I could just link to the image server I uploaded too.  :P


 


Twitter: @QuantumOverlord (general), @MedicaneWatch (medicane/TC stuff)
2023/2024 Snow days (approx 850hpa temp):
29/11 (-6), 30/11 (-6), 02/12 (-5), 03/12 (-5), 04/12 (-3), 16/01 (-3), 18/01 (-8), 08/02 (-5)

Total: 8 days with snow/sleet falling.

2022/2023 Snow days (approx 850hpa temp):

18/12 (-1), 06/03 (-6), 08/03 (-8), 09/03 (-6), 10/03 (-8), 11/03 (-5), 14/03 (-6)

Total: 7 days with snow/sleet falling.

2021/2022 Snow days (approx 850hpa temp):

26/11 (-5), 27/11 (-7), 28/11 (-6), 02/12 (-6), 06/01 (-5), 07/01 (-6), 06/02 (-5), 19/02 (-5), 24/02 (-7), 30/03 (-7), 31/03 (-8), 01/04 (-8)
Total: 12 days with snow/sleet falling.
White Meadows
30 December 2013 20:47:02
...and it's not just screen grabs making those threads often so faecal in substance.
ITSY
30 December 2013 22:54:35

http://www.meteociel.fr/modeles/gfse_cartes.php?ech=204&code=0&mode=10&carte=1


Best stratospheric split so far, with the warming concentrated in the prime place for our liking. Just about the only positive in what was tropespherically a very drab output. 

EDIT: The stratosphere above Greenland warms by 70C in 6 Days! 

nsrobins
30 December 2013 23:04:26

...and it's not just screen grabs making those threads often so faecal in substance.

Originally Posted by: White Meadows 

Meaning?


 


Neil
Fareham, Hampshire 28m ASL (near estuary)
Stormchaser, Member TORRO
Quantum
30 December 2013 23:14:31

Still not quite, although PV has been severly displaced to svalbard and N greenland


http://i44.tinypic.com/2m6ojmw.jpg


 


Twitter: @QuantumOverlord (general), @MedicaneWatch (medicane/TC stuff)
2023/2024 Snow days (approx 850hpa temp):
29/11 (-6), 30/11 (-6), 02/12 (-5), 03/12 (-5), 04/12 (-3), 16/01 (-3), 18/01 (-8), 08/02 (-5)

Total: 8 days with snow/sleet falling.

2022/2023 Snow days (approx 850hpa temp):

18/12 (-1), 06/03 (-6), 08/03 (-8), 09/03 (-6), 10/03 (-8), 11/03 (-5), 14/03 (-6)

Total: 7 days with snow/sleet falling.

2021/2022 Snow days (approx 850hpa temp):

26/11 (-5), 27/11 (-7), 28/11 (-6), 02/12 (-6), 06/01 (-5), 07/01 (-6), 06/02 (-5), 19/02 (-5), 24/02 (-7), 30/03 (-7), 31/03 (-8), 01/04 (-8)
Total: 12 days with snow/sleet falling.
carla
30 December 2013 23:20:34

What is the 528 dam line? Please

Originally Posted by: Gandalf The White 


The 528dam line is a measure of the temperature of a specified layer of the atmosphere.  In this case the air between 500hPa and 1,000hPa.  That is roughly the airmass from near the ground up to about 30,000 feet.


528 is significant because it is a crude pointer to conditions favourable for snow to fall.   It's a bit more complicated than that and the guidance is usually that above 530dam snow is very unlikely and below 522dam rain is very unlikely.


There are other useful measures of thickness.  The NAE and Euro4 models in particular (available on WeatherOnline) give thicknesses for the bottom layer 850-1000hPa.  Here you need to see values below 130dam.


At the moment there's no cold air over us but the Europe-wide view shows it:


850-1,000hPa: http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/12/30/basis12/euro/th85/13123012_3012.gif


500-1,000hPa: http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/12/30/basis12/euro/tpps/13123012_3012.gif


 

Originally Posted by: carla 




thank you gandalf very helpfull..


Holton le clay lincolnshire
Gandalf The White
30 December 2013 23:59:06

ECM 12z ensemble chart for London:


http://www.weathercast.co.uk/services/ensemble-forecast.html


As with the chart 24 hours ago there remains excellent agreement between ECM mean and Op regarding temperature, rainfall and windspeed for the next 5-6 days.  GFS is pretty close as well.


After that the Op becomes very much a milder option, almost an outlier.


Beyond Day 10 the mean shows maxima of 5C and minima of 3C - but as I commented last night, the cool down keeps appearing at Day 11 and isn't moving forward, at least not yet.


50mm of rain by Sunday on the Op but a lot of the ensemble members don't develop the weekend's rainfall shown on the Op (and on the GFS runs).


 


Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


Quantum
31 December 2013 00:01:30


What is the 528 dam line? Please

Originally Posted by: Gandalf The White 


The 528dam line is a measure of the temperature of a specified layer of the atmosphere.  In this case the air between 500hPa and 1,000hPa.  That is roughly the airmass from near the ground up to about 30,000 feet.


528 is significant because it is a crude pointer to conditions favourable for snow to fall.   It's a bit more complicated than that and the guidance is usually that above 530dam snow is very unlikely and below 522dam rain is very unlikely.


There are other useful measures of thickness.  The NAE and Euro4 models in particular (available on WeatherOnline) give thicknesses for the bottom layer 850-1000hPa.  Here you need to see values below 130dam.


At the moment there's no cold air over us but the Europe-wide view shows it:


850-1,000hPa: http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/12/30/basis12/euro/th85/13123012_3012.gif


500-1,000hPa: http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/12/30/basis12/euro/tpps/13123012_3012.gif


 


Originally Posted by: carla 


I'm being overly pedantic here, but thickness isn't a measure of temperature. Its a measure of, well, thickness (or height). Dam is short for decametre, so 528dam is 5280m; that is to say that in the 'full thickness' there would be 5280m between a pressure of 1000mb and a pressure of 500mb. Gandalf is correct though that it can be used as a snowfall indicator because volume is proportional to temperature (pV=nRT for idealised gas) so a smaller thickness implies a smaller volume of gas which itself implies a lower average temperature of the gas between the two levels. In the UK the 522,530 rule that gandalf mentioned works well, though for somewhere like canada you wouldn't need a thickness so low. The partial thickness is more useful than the full thickness, because the 750-500mb is virtually guaranteed to be subzero so it really doesn't matter what goes on there, all the action happens much closer to the surface. 130dam is a pretty good guide provided the wind is light, I would go with 129.5dam in a moderate breeze and 129dam for the gusty conditions on a cold front.


Twitter: @QuantumOverlord (general), @MedicaneWatch (medicane/TC stuff)
2023/2024 Snow days (approx 850hpa temp):
29/11 (-6), 30/11 (-6), 02/12 (-5), 03/12 (-5), 04/12 (-3), 16/01 (-3), 18/01 (-8), 08/02 (-5)

Total: 8 days with snow/sleet falling.

2022/2023 Snow days (approx 850hpa temp):

18/12 (-1), 06/03 (-6), 08/03 (-8), 09/03 (-6), 10/03 (-8), 11/03 (-5), 14/03 (-6)

Total: 7 days with snow/sleet falling.

2021/2022 Snow days (approx 850hpa temp):

26/11 (-5), 27/11 (-7), 28/11 (-6), 02/12 (-6), 06/01 (-5), 07/01 (-6), 06/02 (-5), 19/02 (-5), 24/02 (-7), 30/03 (-7), 31/03 (-8), 01/04 (-8)
Total: 12 days with snow/sleet falling.
Gandalf The White
31 December 2013 00:09:16



What is the 528 dam line? Please

Originally Posted by: Quantum 


The 528dam line is a measure of the temperature of a specified layer of the atmosphere.  In this case the air between 500hPa and 1,000hPa.  That is roughly the airmass from near the ground up to about 30,000 feet.


528 is significant because it is a crude pointer to conditions favourable for snow to fall.   It's a bit more complicated than that and the guidance is usually that above 530dam snow is very unlikely and below 522dam rain is very unlikely.


There are other useful measures of thickness.  The NAE and Euro4 models in particular (available on WeatherOnline) give thicknesses for the bottom layer 850-1000hPa.  Here you need to see values below 130dam.


At the moment there's no cold air over us but the Europe-wide view shows it:


850-1,000hPa: http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/12/30/basis12/euro/th85/13123012_3012.gif


500-1,000hPa: http://expert-images.weatheronline.co.uk/daten/proficharts/en/nae/2013/12/30/basis12/euro/tpps/13123012_3012.gif


 


Originally Posted by: Gandalf The White 


I'm being overly pedantic here, but thickness isn't a measure of temperature. Its a measure of, well, thickness (or height). Dam is short for decametre, so 528dam is 5280m; that is to say that in the 'full thickness' there would be 5280m between a pressure of 1000mb and a pressure of 500mb. Gandalf is correct though that it can be used as a snowfall indicator because volume is proportional to temperature (pV=nRT for idealised gas) so a smaller thickness implies a smaller volume of gas which itself implies a lower average temperature of the gas between the two levels. In the UK the 522,530 rule that gandalf mentioned works well, though for somewhere like canada you wouldn't need a thickness so low. The partial thickness is more useful than the full thickness, because the 750-1000mb is virtually guaranteed to be subzero so it really doesn't matter what goes on there, all the action happens much closer to the surface. 130dam is a pretty good guide provided the wind is light, I would go with 129.5dam in a moderate breeze and 129dam for the gusty conditions on a cold front.


Originally Posted by: carla 


Yes you are Quantum (being overly pedantic). 


Carla asked for an explanation and a simple one seemed best - thickness does measure the temperature, exactly as you describe, through looking at the density of the air - colder air is denser, warmer air less dense.  If the distance between two levels is smaller then the air is denser and therefore it's colder and vice versa.


As regards 129 v 129.5 and 130, it is similar to the other thickness values, i.e. there are other variables to consider - but again I was trying to keep it simple.   We know that with a very cold flow from the continent you can get snow with higher values and particularly for the 500-1,000 hPa values.



Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


some faraway beach
31 December 2013 00:27:04

I nearly always try to type decametre rather than dam, because it took me ages to realize what "528 dam" meant on here. Got lazy today on the previous page and typed "528 dam". At least it prompted some good explanations.


Worth memorizing that Ideal Gas law which Quantum mentioned (PV=nRT, or "Pivnirt"). Pressure x volume = number of moles of gas x constant number x temperature. For dealing with weather in the atmosphere, pressure x volume = temperature is precise enough in practical terms. Once I concentrated on this equation, suddenly a lot of mysterious terms and numbers started to make sense, and I could start to follow the workings of the atmosphere and its weather.


2 miles west of Taunton, 32 m asl, where "milder air moving in from the west" becomes SNOWMAGEDDON.
Well, two or three times a decade it does, anyway.
Gandalf The White
31 December 2013 00:41:12


I nearly always try to type decametre rather than dam, because it took me ages to realize what "528 dam" meant on here. Got lazy today on the previous page and typed "528 dam". At least it prompted some good explanations.


Worth memorizing that Ideal Gas law which Quantum mentioned (PV=nRT, or "Pivnirt"). Pressure x volume = number of moles of gas x constant number x temperature. For dealing with weather in the atmosphere, pressure x volume = temperature is precise enough in practical terms. Once I concentrated on this equation, suddenly a lot of mysterious terms and numbers started to make sense, and I could start to follow the workings of the atmosphere and its weather.


Originally Posted by: some faraway beach 



It seems we have trodden similar paths.


I have to say I wouldn't ever type 'decametre' because all I ever see is 'dam' on charts and explanatory comments.


Anyway, it would be nice to get something under 528 decametres overhead for a few days. At the moment we're about 10 above that and heading higher....


 


Location: South Cambridgeshire
130 metres ASL
52.0N 0.1E


Quantum
31 December 2013 00:51:03



I nearly always try to type decametre rather than dam, because it took me ages to realize what "528 dam" meant on here. Got lazy today on the previous page and typed "528 dam". At least it prompted some good explanations.


Worth memorizing that Ideal Gas law which Quantum mentioned (PV=nRT, or "Pivnirt"). Pressure x volume = number of moles of gas x constant number x temperature. For dealing with weather in the atmosphere, pressure x volume = temperature is precise enough in practical terms. Once I concentrated on this equation, suddenly a lot of mysterious terms and numbers started to make sense, and I could start to follow the workings of the atmosphere and its weather.


Originally Posted by: Gandalf The White 



It seems we have trodden similar paths.


I have to say I wouldn't ever type 'decametre' because all I ever see is 'dam' on charts and explanatory comments.


Anyway, it would be nice to get something under 528 decametres overhead for a few days. At the moment we're about 10 above that and heading higher....


 


Originally Posted by: some faraway beach 


the trouble though, with typing 'decametre' is you might fall into the trap of typing 'decimetre' which = 1/10 m as opposed to the 10m decametre. Kinda puts my 'bering' problem in perspective (and I can probably imagine sometime in the late ninties deep in a NOAA conference room everyone got so irratated at a poor guy named quantum mispelling decametre as decimetre they just said F%@* it we'll call it dam).  


Twitter: @QuantumOverlord (general), @MedicaneWatch (medicane/TC stuff)
2023/2024 Snow days (approx 850hpa temp):
29/11 (-6), 30/11 (-6), 02/12 (-5), 03/12 (-5), 04/12 (-3), 16/01 (-3), 18/01 (-8), 08/02 (-5)

Total: 8 days with snow/sleet falling.

2022/2023 Snow days (approx 850hpa temp):

18/12 (-1), 06/03 (-6), 08/03 (-8), 09/03 (-6), 10/03 (-8), 11/03 (-5), 14/03 (-6)

Total: 7 days with snow/sleet falling.

2021/2022 Snow days (approx 850hpa temp):

26/11 (-5), 27/11 (-7), 28/11 (-6), 02/12 (-6), 06/01 (-5), 07/01 (-6), 06/02 (-5), 19/02 (-5), 24/02 (-7), 30/03 (-7), 31/03 (-8), 01/04 (-8)
Total: 12 days with snow/sleet falling.
some faraway beach
31 December 2013 01:15:08

The 528 dam line regularly flirts with us even on the GFS 18z horror show. This might be wind and rain at 90 hrs:


http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=90&mode=0


But it won't feel mild, once the position of the 528 dam line is calculated:


http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=90&mode=3


This train of storms must be removing more and more heat and energy from the Atlantic as each one passes over. The resulting fall in sea-surface temperatures is going to result in colder and colder wind and rain for us, I feel.


In the end, I suppose there won't be enough heat left on the ocean surface to promote these storms, and the pattern will change. But as Gandalf points out, the ensembles keep calculating hints of this at 10 days out, which never seem to come closer. But one day they will. Maybe while the days are still short enough to get some fun out of it.


2 miles west of Taunton, 32 m asl, where "milder air moving in from the west" becomes SNOWMAGEDDON.
Well, two or three times a decade it does, anyway.
Retron
31 December 2013 04:16:40


I'm being overly pedantic here, but thickness isn't a measure of temperature.


Originally Posted by: Quantum 


Yes it is. 564dam means a mean temperature between 1000 and 500hPa of +5C, 546dam means a mean temperature of -4C, 528dam is a mean temperature of -13C and so on.


You can learn more about thickness, including snow probabilities and all sorts of other goodies, here:


http://weatherfaqs.org.uk/node/152


 


Leysdown, north Kent
Retron
31 December 2013 05:00:46
Last night's 12z ECM-15 control run was a thing of beauty (for cold fans, anyway) - an Atlantic ridge at 240 migrates over Scotland at 264 and then by 300 NE'lies cover the UK (with cold air entrained). Low pressure then spins up over the North Sea and remains there until the end of the run at 360. Cold air remains over the UK throughout and there would be fairly widespread snow as a result.

The ensembles show it was one of the colder runs, but not entirely without support, there still seems to be around a 15% risk of a cold spell from the east, as has been the case for a while now.
Leysdown, north Kent
Retron
31 December 2013 05:21:57
Just had a look at yesterday's ECM-32 control and it also shows Atlantic ridging at 240 and by 300 there's a Scandinavian High with easterlies and SE'lies over the UK.

A spell of SSE'lies then follows as two troughs attempt to move in from the Atlantic and disrupt over the UK.

The Atlantic breaks through at 432, then it's zonal mush all the way to 768, with further gales and rain dominating.
Leysdown, north Kent
Whether Idle
31 December 2013 06:38:57

http://www.meteociel.fr/modeles/ecmwf.php?ech=168&mode=1&map=0&archive=0


Meanwhile at the edge of reason the ECM says it will be very unsettled wet and windy, even out to 7 days.


 


Even stormier at 168 from GEM


http://www.meteociel.fr/modeles/geme_cartes.php?&ech=168&mode=0&carte=0


And for the sake of balance the GFS


 


http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=168&mode=0


 


Summary: 


 


 


Dover, 5m asl. Half a mile from the south coast.
Retron
31 December 2013 07:38:42
Back with the ECM and it's noteworthy that the op also shows a ridge to the west at 216 (yesterday's 240!)

http://www.wetterzentrale.de/pics/Recm2161.gif 

In this case it doesn't really do much as it soon collapses, but it's interesting nonetheless that ECM is keen on at least a temporary lull from this zonal crud.
Leysdown, north Kent
Charmhills
31 December 2013 07:45:09

The next low pressure system is already waiting to move in after 240hs on the ECM!


http://www.wetterzentrale.de/pics/Recm2402.gif


Loughborough, EM.

Knowledge is power, ignorance is weakness.

Duane.
Osprey
31 December 2013 08:15:22

Thank you all for the extra info on Dam


Very much appreciated


Nobody likes a smartass, especially another smartass...
If it ain't broke, don't fix it!
GIBBY
31 December 2013 08:21:35

Good morning. Here is the latest report on the midnight outputs of the NWP for the final day of 2013.


All models show a continuing very unsettled period between now and the end of next weekend with details slightly different between the models but  all saying the same message of Low pressure over or to the NW of the UK with a strong to gale West or SW flow over all areas. The wet and very windy spell is going to persist through the first week of 2014 with strong winds and heavy rain alternating with brief drier and more showery interludes. Temperatures will remain close to average largely offset for much of the time by the strength of the wind.


GFS then moves into next week showing very little change with the rest of it's run typifed by continuing very strong West winds and further spells of rain with some colder periods over the North with wintry showers at times over the hills. There seems only a small chance of much in the way of anything more than very short dry interludes between the rain bands.


UKMO closes it's run next Monday with an intense depression under 950mbs just off Northern Ireland with gale or severe gale force WSW winds over the UK with showers or longer spells of rain rushing through on the breeze through the day in very average temperatures for early January.


GEM is also reluctant to show anything other than more of the same towards the end of it's run with the chance of a rather colder and less windy period later next week when wintry showers might occur almost anywhere for a time.


NAVGEM too shows frequent Lows crashing across the Atlantic and into the UK bringing repeated bands of wind and rain, heavy at times across all areas in average temperatures.


ECM today shows a slight change towards the middle of next week with a pause in the Atlantic bandwagon allowing for a quieter couple of days with a few wintry showers in colder air before I'm afraid the next system over the NW Atlantic regains supremacy with fronts crossing East over the UK by the end of the week returning wind and rain to all areas as well as returning temperatures to average values.


The GFS Ensembles paint all too familiar a picture again this morning with an Atlantic bias throughout carrying forward the very unsettled, wet and often windy period to which we have become accustomed right out to the far end when there are quite a few members showing an Anticyclonic end to the run biased towards the South of the UK.


The Jet Stream remains very strong crashing over the Atlantic and into the UK or Northern France for the next week to 10 days before the High pressure based bias in the ensembles pushes the flow further North across towards Iceland at the end of the run.


In Summary it seems my innitial encouraging thoughts towards a break in the pattern to something more wintry last night was a tad premature as any such thoughts from this morning's output have been largely dwarfed or removed as the seemingly immovable train of Atlantic weather systems remain. There does seem some indication of a slow down of intensity of the wet and windy period later in the outputs as High pressure does show more of a hand but not necessarily in the right place for cold weather to become established.


Martin G
Kilmersdon Radstock Bath Somerset



Look up my New Facebook Weather Page  for all the latest up to the minute weather stories as they happen
Whether Idle
31 December 2013 08:36:27


 


In Summary it seems my innitial encouraging thoughts towards a break in the pattern to something more wintry last night was a tad premature as any such thoughts from this morning's output have been largely dwarfed or removed as the seemingly immovable train of Atlantic weather systems remain. There does seem some indication of a slow down of intensity of the wet and windy period later in the outputs as High pressure does show more of a hand but not necessarily in the right place for cold weather to become established.


Originally Posted by: GIBBY 


The Atlantic is too powerful at the moment. 


Dover, 5m asl. Half a mile from the south coast.
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