Eastbourneguy

Evening all, some absolute filth available on the 18Z ensembles for between Christmas and New Year, not for the faint hearted. Can't wait to be told off by the family on Christmas day while I'm glued to my phone watching the latest runs rolling out!

That's an Atlantic front trying to push in but failing to for a day or two!

Convergence line. Winds backing due to friction over southern East Anglia, meeting the air following roughly the isobars, not subject to as much friction over the sea north of Kent and forced to rise.

Pollution then but it is really a very strange one! If the sub-surface levels are really warm, they would be radiating heat out as well, which would impede settling anywhere. I did think the depth of this cold would be enough, but the weather always is a little git!

In this case, I would guess that the problem isn't that it's pure water not able to freeze, because the ground is a surface that pure water should be able to freeze on at 0C. (conduction from the ground surface below might also be hindering this). It could be that as this snow has come from Europe, it's fairly polluted and has lowered the freezing point of the water that way.

This is true. Water doesn't freeze homogeneously in the atmosphere until as low as -37C without cloud condensation nuclei in the atmosphere or a surface haha.

I would say it has to warm ground temperatures just below the surface, because if it was sublimation everything wouldn't be as wet! Not 100% on this though.

Instability comes from the difference in temperature between the two layers (warmer air rising). If both were the same temperature you have negative buoyancy (neutral really). The 850s are around -10 to -12 currently, and no air parcel is rising to 500 hPa via convection.

Brilliant post!

I'm struggling to understand this. You mean the 500 hPa temps are -28c? You want a large negative difference between the two and to be honest, you would use a lower down height than 500 hPa because no convective cloud top in winter will be that high. Obviously a colder 500 hPa level implies also cold lower down at 700 hPa ish, but not always! Edit: The post on the next page with the Herstmonceux tephigram illustrates this perfectly, big chonky inversions. To be honest, it's probably why 850s have become so widely used in winter, because it's roughly where cloud tops from convective easterlies will be, so you can have a rough guide to instability.

I definitely expected tonight to be convective cell looking like the stuff up north. Looking very bandy, the warning area is going to get absolutely pasted.

My incredibly lucky girlfriend has somehow managed to get more than my folks back in Eastbourne near Manchester. A very thin streamer hitting her. She's already had about 5 snowfalls this winter!

The Met Office amber warning area looks pretty obvious now haha!

Come on convection, do your worst!

To lighten the mood, dew points on the GFS aren't widely expected to be below freezing yet. They fall to below freezing around 6am Which actually coincides with the band ever so slightly nudging further west (forecasted anyway) Also, it hasn't been that cold in the south east, so it was always going to take a bit of time for the transition. The Met Office warnings won't mention rain to begin because most people aren't like us, looking out the window at 4am haha. By the time they look out the window things will likely look much different!