How do we get snow?

TURRICAN

Hello people. I was wondering could somebody explain in not so technical terms the factors which snow reaches the ground.
I know it has to be cold and moist.
Cheers Dave.

omen80

TURRICAN wrote: »

Hello people. I was wondering could somebody explain in not so technical terms the factors which snow reaches the ground.
I know it has to be cold and moist.
Cheers Dave.

Google it and look up a website where you know the information is correct. You will just get a lot of conflicting answers on here from amateur meteorologists.

TURRICAN

omen80 wrote: »

Google it and look up a website where you know the information is correct. You will just get a lot of conflicting answers on here from amateur meteorologists.

I was going to do that but I thought then it would be good to have this info here on the forum where we could all use it.

thetonynator

I know there is a thread on iwo about it, and it was linked here before, but i can't find it at the moment, i'm on mobile, will look again tomorrow.

DOCARCH

Snowbie (formerly of this parish) has a pretty good guide here:

http://www.irelandsweather.com/forum/weather-faq/a-guide-on-how-to-forecast-snow-in-ireland/

BEASTERLY

TURRICAN wrote: »

Hello people. I was wondering could somebody explain in not so technical terms the factors which snow reaches the ground.
I know it has to be cold and moist.
Cheers Dave.

The first ingredient needed is a cold air-mass. For us in wexford an easterly is best.

The colder the air mass the better, because the bigger difference between upper air temps and sea temps the more vigorous sea convection will be.

When the showers or fronts reach us we ideally want the temps to be below 0c and dewpoint has to be below zero. Dewpoint is proportinal to both temperature and humidity. The lower the humidity the lower the dewpoint in relation to temperature so moist damp air is not really what we want.

Sea convectoion showers rarely get very far inland. The east coast streamers of late nov/early dec were exceptions though. 6th of jan 2010 or pre christmas 2010 were more like the norm.

I think it was the 7th of december 2010 brought alot of snow here due to a weakening stalling front from the north. Although the precipitation setup was different the rules for getting it to the ground still apply.

Any more questions, just ask.:)

darkman2

TURRICAN wrote: »

Hello people. I was wondering could somebody explain in not so technical terms the factors which snow reaches the ground.
I know it has to be cold and moist.
Cheers Dave.

The factors which make snow reach the ground? It's very simple actually. We can devide the atmosphere into layers. Every 200m, or there abouts, on average as you go up the temperature falls by around 1c. Once the temperature is at 0c or below at the point of origin precipitation is likely to start out as small molecules of water vapor which freeze instantly forming small ice crystals which accumlate and merge creating a snow flake on it's journey to the surface. Temperatures rise as it falls and so it turns to rain or sleet on most occasions. However under a very cold airmass temperatures can be far lower at point of origin and through the atmosphere to the ground. So, for example, if it is -20c at the point of origin of a snowflake in the clouds then it is highly likely to be well below freezing at ground level and so the flakes can fall intact to the surface. If the surface is freezing it will settle.

Another crucial factor is the time it takes to travel from the cloud to the surface. It might supprise some but windy conditions are actually detremental to whether snow reaches the ground due to cross winds which drag and toss snowflakes horizontally which increases greatly the distance travelled from the cloud to the ground. Thus in windy conditions it's preferable that the air be colder.

In Spring in Ireland snow is not likely to be of the purest type (the type you cannot make a snowball out of) when it reaches the ground because temperatures are higher and there is more strength in the Sun. So whilst we still get snowflakes they are often notably bigger and wetter (because on the way down they melt slightly and merge with other flakes) with the crystals deformed then what we get in January typically. This is the stuff snowballs can be made from.

Another way snow can reach the surface in temperatures that might be thought to be too high (say 5 or 6c) are down-draughts from showers. Basically cold unstable air plunging to the ground bringing the good stuff with it. This tends only to occur in heavy and prolonged showers esspecially thunderstorms.

I know it seems very simple but that's basically it!

fizzycyst

Thanks for that detailed explanation Beasterly and DM2. I now why we are very unlikely to get snow when the upper air temps are -4 or above, cheers.

Mobhi1

darkman2 wrote: »

In Spring in Ireland snow is not likely to be of the purest type (the type you cannot make a snowball out of) when it reaches the ground because temperatures are higher and there is more strength in the Sun. So whilst we still get snowflakes they are often notably bigger and wetter (because on the way down they melt slightly and merge with other flakes) with the crystals deformed then what we get in January typically. This is the stuff snowballs can be made from.

My son wasn't too impressed with the snow we got just before Christmas - it wasn't very sticky and he couldn't make snowballs or build anything with it. Must have been the purer kind. He also noticed that when we went skiing/snowboarding in the Alps last year - it was great for snowboarding but not much good for sticking together for snowballs or building anything.

Su Campu

http://www.irishweatheronline.com/irishweather/the-physics-of-snow-accumulation.html

TURRICAN

thanks a million for the replies ,they were a nice read and im all the wiser now.
me thinks il try my luck on the forecasting section now.:D