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Posted
  • Location: Kippax (Leeds) 63m
  • Location: Kippax (Leeds) 63m
10 minutes ago, Kasim Awan said:

The falling of the snow line tomorrow within the colder sector is enhanced by both diabatic cooling of the air (precipitation directly cooling the air) and evaporative cooling.

This can be seen clearly in the high resolution output with 850hpa temperatures which suggest a colder air mass to the east. Yet when freezing lines are viewed it is clear that these are lower within the main area of precipitation, as a result of various forms of precipitation lead heat transfer.

image.thumb.png.0129cd2c8038f854ce1885c12db36f22.png

image.thumb.png.6f2ecd465d71f9d979fac476a66c73bf.png

Again sounding very technical but no sense is made what so ever 

The colours on the map you show are exactly the same over yorkshire where there is the CHANCE of low lying snow, to the colours in say east anglia where it is guaranteed to be rain! So how do those charts prove your point?? 

Edited by Harsh Climate
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Posted
  • Location: Rotherham, East Dene
  • Location: Rotherham, East Dene
2 minutes ago, Harsh Climate said:

Again sounding very technical but no sense is made what so ever 

The colours on the map you show are exactly the same over yorkshire where there is the CHANCE of low lying snow, to the colours in say east anglia where it is guaranteed to be rain! So how do those charts prove your point?? 

The precipitation is heavier in south yorkshire at this time

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7 minutes ago, Harsh Climate said:

Again sounding very technical but no sense is made what so ever 

The colours on the map you show are exactly the same over yorkshire where there is the CHANCE of low lying snow, as the colours in east anglia and just north east london where it is guaranteed to be rain! So how doesthose charts prove your point?? 

Hi mate it's basically showing how the upper atmosphere would suggest colder surface temps out to the east but the surface profile is in fact colder out west where the precipitation is. Also, heavy precipitation isn't a requirement for evaporative or other precipitation lead cooling pal This can occur in lighter precip just to slower rates which is why it's "dynamic" > 10 hours of 0.5mm may be more effective than 1 hour of 4mm.

Regarding the south east, the snow will follow the heavy precip in the cold area, this is forecast to be south on this model. So this more southerly track can't be discounted. Bottom line is every low level area in the Midlands and East of England has a certain % chance of falling within the high ppn area for lower levels this is the best forecast which can be given.

Edited by Kasim Awan
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Posted
  • Location: Rotherham, East Dene
  • Location: Rotherham, East Dene
5 minutes ago, The PIT said:

I never look in detail until closer to the time. Pity we can't get soundings as to what the atmosphere is really like during the day.

Got to admit I feel a tit when I get it wrong.

I know i would like to see these soundings as well ans even the met get it wrong. 

You have to trust your thinking and bravely put a forecast out and if its wrong its wrong.

If im wrong tomorrow ill put my hands up and disect its not a matter of who is right or wrong theres more important things in life to worry about

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Posted
  • Location: Kippax (Leeds) 63m
  • Location: Kippax (Leeds) 63m
4 minutes ago, Scott Ingham said:

The problem you have is your looking at 850s and these only need to be round -1 in this event which was mentioned yesterday.

The most important thing is wet bulb temperatures and strength of precipitation

The way your forecasting works most of the time but snowforecasting is a lot more technical than how you are looking at it.

I hope it does snow just so you can see this set up with your own eyes.

Id be happy to explain in private chat why after the event

That chart shows me in 850s of at least -3 850s on all 3 charts which is 3 times more than needed im this set up

Some good points made there. I agree it can snow with uppers close to or just below 0 but I've seen it first hand many years ago, it took hours of very heavy rain to turn the tide, tomorrow it certainly isn't going to match that intensity. I'll pull a total out of a hat and I think below 80m around say sheffield might get a couple of cm albeit bit wet, nothing to right home about but hey its something.

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Posted
  • Location: Sheffield South Yorkshire 160M Powering the Sheffield Shield
  • Weather Preferences: Any Extreme
  • Location: Sheffield South Yorkshire 160M Powering the Sheffield Shield

Of course the real fun is when the met office forecast heavy snow and everyone on net weather know they are talking rubbish. Remember the freezing rain was it last year and they kept on with the snow forecast all day despite being total rubbish. I think Scotland managed a short spell of snow before that turned to freezing rain.

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Posted
  • Location: Rotherham, East Dene
  • Location: Rotherham, East Dene
5 minutes ago, Harsh Climate said:

Some good points made there. I agree it can snow with uppers close to or just below 0 but I've seen it first hand many years ago, it took hours of very heavy rain to turn the tide, tomorrow it certainly isn't going to match that intensity. I'll pull a total out of a hat and I think below 80m around say sheffield might get a couple of cm albeit bit wet, nothing to right home about but hey its something.

If you start at 2.5C (which is where I expect Rotherham to be tomorrow), 93% humidity gives you a wb of 1.78C. So after an hour @ 2mm/hour about 1.78C. The next hour has a temp of 1.78C > 1.23C which is less of a jump because the evaporative cooling has increased the environmental humidity to 95% which decreases the latent heat transfer, and the next hour even less from 1.23C to 0.8C. So it might take 2.5 hours for you, at 2mm/hour. Obvs if you get 4mm/hour 1.25 hours will be enough.

We have 4 hours of more than 2mm/hour so at my latitude 69metres id suggest around 4cm

Some equations done with @Kasim Awan last night

Near the coast at sea level you need 4 hours so places like hull wont see anything

Also i agree on 2cm for sheffield.

Im not forecasting a pasting but i cant sit back and say lower ground wont see anything because its not strictly true.

Some low level areas will get snow

Edited by Scott Ingham
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3 minutes ago, Scott Ingham said:

If you start at 2.5C (which is where I expect Rotherham to be tomorrow), 93% humidity gives you a wb of 1.78C. So after an hour @ 2mm/hour about 1.78C. The next hour has a temp of 1.78C > 1.23C which is less of a jump because the evaporative cooling has increased the environmental humidity to 95% which decreases the latent heat transfer, and the next hour even less from 1.23C to 0.8C. So it might take 2.5 hours for you, at 2mm/hour. Obvs if you get 4mm/hour 1.25 hours will be enough.

We have 4 hours of more than 2mm/hour so at my latitude 69metres id suggest around 4cm

Some equations done with @Kasim Awan last night

Near the coast at sea level you need 4 hours so places like hull wont see anything

Thanks for reposting my message sent last night haha

Yes, the wet bulb is basically the effective evaporative cooling temperature. It has several functions, including the temperature which would result from evaporative cooling and it itself is a function of the humidity which drives evaporative cooling. but when you run the equations through most areas require 1-3 hours of 2-3mm/hour rainfall with starting adiabatic temperatures of 2C.

Euro4 for tomorrow is out btw. It is clearly forecasting this thermodynamic gradient.

 

image.thumb.png.77c8f3eb48287c32a36bdf8e35bb6307.png

Edited by Kasim Awan
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Posted
  • Location: Garforth, Leeds 86m asl
  • Weather Preferences: Heat, Snow, Thunder
  • Location: Garforth, Leeds 86m asl

Yeah so I personally am not that confident of seeing lying snow in my locations (Garforth - home and Cleckheaton - work) but would think I'll see something falling. Everything just seems a bit marginal with the dew points and likely precipitation intensity. I reckon Pennine parts plus the far northeast of the region will do well, east of the A1 on the low ground may struggle. Of course, as we found out last Friday, anything is possible really so I'll definitely be keeping an eye on the radar and this forum! Good luck everyone, pictures please if you get lucky! 

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Posted
  • Location: Rotherham, East Dene
  • Location: Rotherham, East Dene
1 minute ago, Kasim Awan said:

Thanks for reposting my message sent last night haha

Yes, the wet bulb is basically the effective evaporative cooling temperature. It has several functions, but when you run the equations through most areas require 1-3 hours of 2-3mm/hour rainfall with starting adiabatic temperatures of 2C.

Euro4 for tomorrow is out btw. It is clearly forecasting this thermodynamic gradient.

 

image.thumb.png.77c8f3eb48287c32a36bdf8e35bb6307.png

Your welcome helps people to understand for sure!

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Posted
  • Location: Beverley, E Yorks, 19m ASL
  • Weather Preferences: Snow, Thunder - not necessarily at the same time!
  • Location: Beverley, E Yorks, 19m ASL

Dewpoint here 0.2°C and temp 1.2°C., dropping slowly. Raining lightly with virtually no wind. Precipitation started for the first half an hour with ice pellets then changed to rain. We shall see what happens but it's cold enough that's for sure. If the DP drops below freezing, there might be  chance but not holding my hopes up much.

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Posted
  • Location: Kippax (Leeds) 63m
  • Location: Kippax (Leeds) 63m
1 minute ago, Scott Ingham said:

If you start at 2.5C (which is where I expect Rotherham to be tomorrow), 93% humidity gives you a wb of 1.78C. So after an hour @ 2mm/hour about 1.78C. The next hour has a temp of 1.78C > 1.23C which is less of a jump because the evaporative cooling has increased the environmental humidity to 95% which decreases the latent heat transfer, and the next hour even less from 1.23C to 0.8C. So it might take 2.5 hours for you, at 2mm/hour. Obvs if you get 4mm/hour 1.25 hours will be enough.

We have 4 hours of more than 2mm/hour so at my latitude 69metres id suggest around 4cm

I see that your looking very deep into the technical side of predicting snow, I respect and admire you for that. But I think too many times people can be drawn into a theory/model of forecasting that other factors aren't fully recognised or used in their anylsis. 

Like on paper if that formula you say is correct I think there are outside factors that could come into play that disrupt what you have said.

1.like changes in strength/direction of wind perhaps bringing in slightly milder pacels of air

2.small changes in precipitation rates like it could be quite heavy, then quite light for a bit.

 

And not just that I think you can look at similar events in the past over the years and you can find patterns of what kind of weather scenario will produce what to a locale.. 

All in all though snow forecasting in the british isles is probably the hardest trait in meteorology so there will be differing oppinions time to time  

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Posted
  • Location: Normanton West Yorks 100ft asl
  • Location: Normanton West Yorks 100ft asl

Met office’s for me today said from 11am Wednesday till 4am Thursday rain

5am Thursday till 12pm sleet

1pm till 4pm light snow 

 

So far today they have been correct 

 

 

Edited by fazzafarrand
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2 minutes ago, Harsh Climate said:

I see that your looking very deep into the technical side of predicting snow, I respect and admire you for that. But I think too many times people can be drawn into a theory/model of forecasting that other factors aren't fully recognised or used in their anylsis. 

Like on paper if that formula you say is correct I think there are outside factors that could come into play that disrupt what you have said.

1.like changes in strength/direction of wind perhaps bringing in slightly milder pacels of air

2.small changes in precipitation rates like it could be quite heavy, then quite light for a bit.

 

And not just that I think you can look at similar events in the past over the years and you can find patterns of what kind of weather scenario will produce what to a locale.. 

All in all though snow forecasting in the british isles is probably the hardest trait in meteorology so there will be differing oppinions time to time  

You're correct with regards to outside factors. However do remember that under the area of heavy precip *if it is well defined* it will follow this temperature drop, because there wont be any "mild parcels" of air which you discuss. Certainly not on the east side of the Pennines in the heavy precip if it is well defined.

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Posted
  • Location: Skirlaugh, East Yorkshire
  • Location: Skirlaugh, East Yorkshire

Definitely a bit of an inversion present at the moment. Conditions on the ground favourable for snow with a temp of 1.2C and dewpoint of -0.6C. Its raining however!

This can be seen on the skew-t charts with the temperature increasing with height up to 850hPa level:

skew0.377654185126634.thumb.png.f7da21523ae776517d17c698111f6675.png

No chance of anything snowy for a while yet.

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Posted
  • Location: Rotherham, East Dene
  • Location: Rotherham, East Dene
2 minutes ago, Harsh Climate said:

I see that your looking very deep into the technical side of predicting snow, I respect and admire you for that. But I think too many times people can be drawn into a theory/model of forecasting that other factors aren't fully recognised or used in their anylsis. 

Like on paper if that formula you say is correct I think there are outside factors that could come into play that disrupt what you have said.

1.like changes in strength/direction of wind perhaps bringing in slightly milder pacels of air

2.small changes in precipitation rates like it could be quite heavy, then quite light for a bit.

 

And not just that I think you can look at similar events in the past over the years and you can find patterns of what kind of weather scenario will produce what to a locale.. 

All in all though snow forecasting in the british isles is probably the hardest trait in meteorology so there will be differing oppinions time to time  

Yeah you are right all them factors will come into play thats why some will hit those amounts and others not (the reason for the last sentence on the met warning?) But do you not agree a sweeping statement saying high ground only is a little rediculous when there are strong chamces someone would get some snow at low level?

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3 minutes ago, reef said:

Definitely a bit of an inversion present at the moment. Conditions on the ground favourable for snow with a temp of 1.2C and dewpoint of -0.6C. Its raining however!

This can be seen on the skew-t charts with the temperature increasing with height up to 850hPa level:

skew0.377654185126634.thumb.png.f7da21523ae776517d17c698111f6675.png

No chance of anything snowy for a while yet.

Now:

image.thumb.png.b321b734934c0d65dd19aa87fb3cd758.png

Tomorrow:

image.thumb.png.fd8ee8265c8270e62443c699dc0d738d.png

> Tomorrow it's phased out so snow should follow normal dew point and wet bulb rules

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Posted
  • Location: Kippax (Leeds) 63m
  • Location: Kippax (Leeds) 63m
11 minutes ago, Scott Ingham said:

Yeah you are right all them factors will come into play thats why some will hit those amounts and others not (the reason for the last sentence on the met warning?) But do you not agree a sweeping statement saying high ground only is a little rediculous when there are strong chamces someone would get some snow at low level?

I'm not saying high ground only, I'm saying generally it will be high ground who will fair best tomorrow with lower areas much more marginal especially the further south you are over our region.

Like you I think some low lying areas will see some snow and locally if everything comes into play upto 5cm. Maybe more north/west yorkshire. 

Il stick my neck on the line to be more clear here are my total estimates by the close of play thursday night..

North york moors/high yorkshire dales 10-20cm

North/west yorkshire above 200m+ 3-10cm 

below 150m+ 2-7cm

Below 80m 0-5cm

 

SOUTH YORKSHIRE

High ground above 300m

8-15cm

Above 200m 

2-7cm

below 150m

0-5cm

Below 80m 

0-2cm wet variety.

 

There you go that's what I think, might be right might be wrong.

Edited by Harsh Climate
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Posted
  • Location: Kirkburton, Huddersfield - 162.5mtrs asl.
  • Weather Preferences: Winter synoptics.Hot summers.
  • Location: Kirkburton, Huddersfield - 162.5mtrs asl.
4 minutes ago, Kasim Awan said:

Now:

image.thumb.png.b321b734934c0d65dd19aa87fb3cd758.png

Tomorrow:

image.thumb.png.fd8ee8265c8270e62443c699dc0d738d.png

> Tomorrow it's phased out so snow should follow normal dew point and wet bulb rules

I swear those are probably the only charts i cannot read. Is there one for Kirkburton, i still wont be any wiser  

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Posted
  • Location: Rotherham, East Dene
  • Location: Rotherham, East Dene
3 minutes ago, Harsh Climate said:

I'm not saying high ground only, I'm saying generally it will be high ground who will fair best tomorrow with lower areas much more marginal especially the further south you are over our region.

Like you I think some low lying areas will see some snow and locally if everything comes into play upto 5cm. Maybe more north/west yorkshire. 

Il stick my neck on the line to be more clear here are my total estimates by the close of play thursday night..

North york moors/high yorkshire dales 10-20cm

North/west yorkshire above 200m+ 3-10cm 

below 150m+ 2-7cm

Below 80m 0-5cm

 

SOUTH YORKSHIRE

High ground above 300m

8-15cm

Above 200m 

2-7cm

below 150m

0-5cm

Below 80m 

0-2cm wet variety.

 

There you go that's what I think, might be right might be wrong.

I dont disagree with them figures id maybe add a couple of cm's to the bottom two in south yorkshire

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