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Scotland/Alba weather discussion - Jan 2021 onwards


LomondSnowstorm

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Posted
  • Location: Morningside, Edinburgh (98m ASL)
  • Weather Preferences: Snow, and lots of it
  • Location: Morningside, Edinburgh (98m ASL)
5 minutes ago, LomondSnowstorm said:

A small look at the soundings for just before the main front arrives, based on the NMM. This is for Coatbridge at 6am:

image.thumb.png.8a42fb14edb5bac00c59b5b49ae09589.png the precip map:image.thumb.png.a340e9fb563100edd21b5031e39eef6d.png

 

Going through some of the key variables:

Freezing level - check (under 350m)

Wet bulb freezing level - also check (less than 300m from the surface)

Surface temperature - fine enough (around 1-1.5C or so, bearing in mind the surface has a lower pressure than 1000hPa)

Dew point - meh (0.5C or so)
 

Twet - not bad (1C or so)

Uppers - around -6C at this point so fine

 

Overall you'd probably expect it to be snow, but the reason I'd maybe be a little more confident comes from this paper (it's a bit lengthy but a good read, maybe for a time when there's less nowcasting to do!) https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjS3Z_OosnuAhXtVRUIHXBnA_QQFjAAegQIBRAC&url=http%3A%2F%2Fwww.diva-portal.se%2Fsmash%2Fget%2Fdiva2%3A968860%2FFULLTEXT01.pdf&usg=AOvVaw1b5qEOXtTdFZZOiLiyY4UL

 

Basically,the conditions are perfect for the 'melting effect' on latent heat (I think I've described it as evaporative cooling in the past but that's slightly different) whereby the snow melting at higher levels uses up heat energy and causes the temperature to drop to near freezing over a layer of maybe a few hundred metres. I'm sure we've seen this a couple of times or more this winter so far, and it's particularly pronounced with persistent, moderate to heavy precipitation as we're likely to see early tomorrow, and also with a near saturated surface layer as we're likely to have (near 100% humidity). The one caveat to this is primarily areas of low temperature advection, and this is where it might not be enough closer to the coast (I'll post a sounding for Fife and maybe the Lothians if it's different after I've had my tea) or if the easterlies are very strong, and of course if we get the full warm sector at any point it won't be sustainable. However, I just wanted to give a bit of theoretical basis to what we're looking for tomorrow.

Wet-bulbing! This was my favorite phenomenon back in Boston

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Posted
  • Location: Luncarty (4 miles north of Perth 19m ASL)
  • Weather Preferences: Hot Summers Snowy Winters Stormy Autumns
  • Location: Luncarty (4 miles north of Perth 19m ASL)

Yes @LomondSnowstormanother variation on a theme from ECM but all roads lead to snow... A couple of more days at least to establish the severity and likelihood of a mini beast at weekend. 

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Posted
  • Location: Wallyford, East Lothian
  • Location: Wallyford, East Lothian
6 hours ago, mountain shadow said:

If it's a direct Easterly I think you'll be ok as your a good 10 miles or so from the East coast, if it's more Nor Easterly then it's a shorter distance from the sea.

It's probably nigh on impossible to say exactly, you'll just have to wait and see!

Yes, ill expect rain or sleet and if it snows it’ll be a pleasant surprise. We had a few showers this afternoon which were all of snow, albeit of the wet variety. Hopefully bodes well.

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Posted
  • Location: Upper Tweeddale, Scottish Borders 240m ASL
  • Location: Upper Tweeddale, Scottish Borders 240m ASL

Currently 1.5°C and under the frontal edge across Lanarkshire /the western Borders. Radar says precipitation, weather type radar says snow. Outside says its the lightest unidentifiable ppn and is barely reaching the ground.... 

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Posted
  • Location: Perth, Scotland
  • Weather Preferences: SNOW :-D
  • Location: Perth, Scotland
23 minutes ago, edo said:

I'm optimistic Ally... Not so much tomorrow although there is hope but late in week onwards is all snow here if models stick with it 

Thanks @edo it would great to see some significant snow in Perth, as I feel we kinda of missed out in 2018.  

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