Hardy Tropicals UK

Here is a link to wunderground's interactive maps showing most of the UK. Complete with REAL TIME weatherstation temps. You can see cold fronts (if there are any at the time

UK REAL TIME temps

SE England

SW England

Wales & West Midlands

East Midland & East Anglia

Northern England & IoM

Southern Scotland

Northern Scotland

Thanks for the links - handy to see the temperatures plummeting at present !

Thank god I dont live near annandale -5

I was just watching the news, and there was snow falling in central London (for certain). Strange given it's 5C there.

stephenprudence wrote:I was just watching the news, and there was snow falling in central London (for certain). Strange given it's 5C there.

We nearly always get snow showers in April when the temps are 7 or 8C at ground level, but it is obviously a lot colder up in the cloud. It won't settle at 5C unless the ground is frozen.

Yes Dave true enough but the reason for that is the heavy, convective nature of the showers and the effect it has on the dewpoint. This was really light snow, similar to that of a period of stratus induced light snow. London rarely gets snow even in optimal conditions, because the density of building traps moisture, and therefore keeps the dewpoints up. I'm pretty sure the dew point was above freezing by a degree or so, so it's a meteorological mystery indeed!

stephenprudence wrote:Yes Dave true enough but the reason for that is the heavy, convective nature of the showers and the effect it has on the dewpoint. This was really light snow, similar to that of a period of stratus induced light snow. London rarely gets snow even in optimal conditions, because the density of building traps moisture, and therefore keeps the dewpoints up. I'm pretty sure the dew point was above freezing by a degree or so, so it's a meteorological mystery indeed!

Most of that goes right over my head. Can you explain in a bit more detail how you think the dew point can affect the potential for snow. surely, as Dave suggested, if the the conditions are right for precipitation and the air is cold enough, it will snow regardless of what conditions are on the ground.

Simon, believe it or not it takes a particular set of perfect conditions to make a snowflake. Many people think it just snows when it is cold, but this is not the case surprisingly.

For snow to occur, you have to have 3 minimum things in place

- A minimum temperature of -5C at 850 metres above sea level, if this is not achieved the flakes are likely to melt as they fall towards ground.

- Thickness levels of 528 decameters, when the air is thinner it is warmer, when it is thicker it is colder, but signals that it is right for snow is when the decameter levels of air thickness in below 528dca

- If the levels above are satisfied the dewpoint must be at or below 0C. In potential snow situations, this is known as the frost point.

If it is 1 degC and the dewpoint is 1 degC, but the minimum requirements are met, it will rain because the frost point is not reached and the air will be saturated.

If however the temperature at 850 metres above sea level is -10C, the thickness levels are 510dca and it is 1 degC and the dewpoint also of 1 degC it may snow.

However, ocassionally you have a situation whereby the temperature and dewpoint are both below 0C, yet it still rains (freezing rain), this is because temperatures at 850 metres are above -4C. This is commonly referred to as an inversion which is caused the ground temperature is lower than the temperature at 850 metres.

I hope that's a little bit clearer than mud

That's really interesting stuff Stephen but surely all those requirements only need to be bet at altitude, where the clouds are. You were talking about humidity trapped around buildings keeping the dew point up, presumably around ground level. I wouldn't have thought that would affect the chances of snow if conditions were met at altitude.

Well that's the suggestion Simon, at 850m it will be -5C and provided the air has moderate lapse rather (the temperature difference between height contours) then you are looking at definite snow to around 350m where it will be 0C (as you lose 1C every 100m you go up on average). which means providing the dewpoint is below 0C (it needs to be because if there is saturation, there is nowhere for the warmth to go, it is trapped in the moisture and essentially will melt falling snow flakes)

Of course the minimum requirements will always be borderline, but at the minimum requirements sea level connditions:

temperature: 3.5C
dewpoint: 0C
Weather: wet snow (60% pure ice crystals, 40% melting ice crystals) (not settling)

It is vital to the formation of snow. Of course though cities can alter the conditions at ground level, but these minimum requirements are those that are expected in rural areas (standard Met-office measuring sites)

Development conditions for snow is fairly complexed and is part of Atmsopheric sciences

On my way back home from work in Central London it was already -1C at 1600

MarkD wrote:On my way back home from work in Central London it was already -1C at 1600

I got home at 1700 to see it was already -4 and i've hit my coldest so far now -8 at 2200, i'm dreading getting up tomorrow

grub wrote:

MarkD wrote:On my way back home from work in Central London it was already -1C at 1600

I got home at 1700 to see it was already -4 and i've hit my coldest so far now -8 at 2200, i'm dreading getting up tomorrow

Are you up yet

Dave Brown wrote:

grub wrote:

MarkD wrote:On my way back home from work in Central London it was already -1C at 1600

I got home at 1700 to see it was already -4 and i've hit my coldest so far now -8 at 2200, i'm dreading getting up tomorrow

Are you up yet

Yes Dave , got off lightly I fancy only got down to -9 here whereas Benson got down to -12

Time for some serious record lows with all that snow for your folks in the UK...

Alexander