South East & East Anglia Regional Discussion ~ December 5th 2012>

[Coast]

[Guenhwyvar]

I don't understand these maps and how it all works....H and L ? Does that mean we have Helicopters and landing spots?

We are in a low it seems?

[NO LONGER POSTING]

new warning needs to be put in place for those showers on the east coast...Half an inch has already fallen in some places up north..

[NO LONGER POSTING]

I don't understand these maps and how it all works....H and L ? Does that mean we have Helicopters and landing spots?

We are in a low it seems?

H = High Pressure...Usually means Summer = Boiling hot Winter = FREEZING!! (if the right set up occurs)

L = Low pressure... Usually rain,sleet and snow..Depending on how tight the isobars are (the lines on the graph) shows wind speed.

Tight bars = Strong winds

Spaced bars = Light winds

Black thick lines with no arrows or half circles = Troughs

Black thick lines with arrows and half circles = occluded front

Black thick lines with half circles = Cold front

Black thick lines with arrows = Warm front

Crash course I think that's right

Edited December 5, 2012 by Surrey

[Coast]

I don't understand these maps and how it all works....H and L ?

It's your fronts you have to worry about!!! :lol:

[Floatylight]

new warning needs to be put in place for those showers on the east coast...Half an inch has already fallen in some places up north..

is it me or are they swinging inland more?

[NO LONGER POSTING]

is it me or are they swinging inland more?

Showers of the coast rarely make it inland because the cold land kills them. The sea is "warm" so helps pep up showers. UNLESS! You get a thames streamer and then it's game on for us in the south east!

[gottolovethisweather]

Heavy wet snow has arrived, on a biting NNW wind!!!

That must be, just the icing on the Beccles cake.

[Kent Snow]

A cold day with a maximum of 2C. Generally overcast but some of this mornings Snow still remains.

[Floatylight]

Showers of the coast rarely make it inland because the cold land kills them. The sea is "warm" so helps pep up showers. UNLESS! You get a thames streamer and then it's game on for us in the south east!

well that ppn was out in the n sea earlier ,now its covering half of ea?

[gottolovethisweather]

I had my first snow shower this morning on my milk round was heavy and lasted 10 mins or so :0)

All that bottled up cold further East will soon be heading our way to produce yet more fun on your milk round.

[Methuselah]

That must be, just the icing on the Beccles cake.

Oh dear!

[Buzzit]

It's your fronts you have to worry about!!!

Y Fronts ? couldn't resist

[Mrsf16]

Are we talking about game on for Fri still or is it now on tomoro?

[Coast]

So why can't we be more certain about snow coming??? Liam Dutton can tell us why in this excellent blog post from a couple of hours ago:

Why is snow so challenging to forecast in the UK?

As predicted, some parts of the UK had their first snow of the winter season overnight and this morning, leading to problems with ice and travel delays. Amounts of snow varied hugely, with some places having a covering, some just falling snow, and others rain or sleet. If you ask any weather forecaster who works in the UK, they will tell you that it can be very challenging to forecast snow here. The conditions are often marginal, which means that, sometimes, predictions can go wrong.

I thought I’d take a little time to journey through and explain the variety of factors than can determine whether or not snow falls, which will hopefully show how complicated it can be.

Temperature of the air

Temperature is probably one of the most crucial factors when determining whether or not snow is likely to fall. As a general rule of thumb, snow in the UK tends to fall when the temperature is 2C or less. It may sound odd that snow can fall when the temperature is above freezing, but you have to remember that the temperature of the air even a few tens of metres above the surface is colder than at ground level. As a result of this, snowflakes can easily remain intact down to the surface, although they do start to melt. This is why snow that falls with a temperature above freezing tends to be fluffy and wet, as partially melted snowflakes stick together.

Snow that falls with a temperature of 0C or below doesn’t experience any melting. Therefore, it is drier and more powdery – like the snow that is great for skiing. When the temperature is in the range of 2-4C, sleet or rain is likely. However, if rain falls for long enough, the temperature of the air will start to fall. This is because water from rain drops will start to evaporate and cool the air – just like the process of evaporating sweat on your skin cools you down in summer.

If this evaporative cooling continues for long enough, the rain can eventually turn to snow. So as you can see, the temperature is crucial as to what falls from the sky, with even half a degree making a huge difference.

Altitude

The height of a location above sea-level is another highly influential factor on the likelihood of snow. In most cases, the higher up a hill or mountain you go, the colder it gets – roughly by 1C for each 100 metres. This is why snow is always more likely over hills and mountains than lower down. What you may be surprised to know is by how much the chance of snow increases with altitude.

If there is a 20 per cent chance of snow at sea-level, this rises to 35 per cent at 100m, 60 per cent at 200m and around 75 per cent at 300m. This shows how a journey that travels over hills can start off as a rainy one, but can easily turn into a snowy one with a relatively small increase in altitude.

Urban heat

Urban areas are renowned for being slightly warmer than rural areas during winter, due to the large amount of heat generated by city life – buildings, industry and transport. In some cases, this urban warmth can be enough to raise the temperature sufficiently to mean that sleet falls rather than snow. However, to complicate things further, there can be temperature fluctuations within cities too.

As an example, a few years ago, I left work after a night shift at BBC Television Centre in Shepherd’s Bush and it was raining outside. By the time I had reached Ealing – just five miles further west into the suburbs, it was snowing heavily, with a covering of snow on the ground. I phoned work to let them know that it was snowing, and they said that it was still raining in Shepherds Bush!

Such differences in precipitation over a short distance are extremely hard for weather computer models to capture, adding to the uncertainty in snow forecasts.

Distance from the coast

The UK is an island surrounded by relatively warm water, which means that in winter, temperatures in coastal areas are kept slightly higher than further inland. Again, with temperature being so crucial in determining what falls from the sky, it means that whilst snow falls inland, a zone of around 5-10 miles from the coast, will see rain or sleet instead.

Wind strength and precipitation intensity

As mentioned earlier, if rain falls for long enough, evaporative cooling can gradually lower the temperature, resulting in it turning to snow. This process is most effective when winds are light, because colder air from aloft descends to the surface more readily, as the air isn’t being mixed up by the wind.

The intensity of the falling precipitation is also influential. Light rain is generally less likely to turn to snow than heavier rain in this way, because less moisture is available for evaporative cooling to take place. All of the above show just how many factors need to be taken into consideration when forecasting snow. It can be a real challenge and illustrate that whilst we get it right most of the time, sometimes, things don’t go as planned.

http://blogs.channel4.com/liam-dutton-on-weather/snow-challenging-forecast-uk/2568

[gottolovethisweather]

On that first chart I'm liking that front following the rain through come early morning. Accordibg to the GFS 12z, it comes through a wee bit later which I'd prefer as I think it could then be a repeat of today with -5 uppers chasing it in behind.

Still touch and go regarding Friday but that's not surprising given today's shenanigans.

[Kent Snow]

H = High Pressure...Usually means Summer = Boiling hot Winter = FREEZING!! (if the right set up occurs)

L = Low pressure... Usually rain,sleet and snow..Depending on how tight the isobars are (the lines on the graph) shows wind speed.

Tight bars = Strong winds

Spaced bars = Light winds

Black thick lines with no arrows or half circles = Troughs

Black thick lines with arrows and half circles = occluded front

Black thick lines with half circles = Cold front

Black thick lines with arrows = Warm front

Crash course I think that's right

Black thick lines with half circles=Warm Front

Black thick lines with arrows = Cold front

[gottolovethisweather]

new warning needs to be put in place for those showers on the east coast...Half an inch has already fallen in some places up north..

Been watching them for a while now. Good to see the snow being shared around, is that stuff settling, I wonder?

[JennyJane1]

Crash course I think that's right

thank you i never understood it

[tef1975]

Heavy snow here in Norwich.

[Coast]

Heavy snow here in Norwich.

Possibly more to come from the NW over the next couple of hours, but unlikely to affect much of the rest of the region other than the coastal fringes of EA looking at the radar animation?

Edited December 5, 2012 by Coast

[Captain Shortwave]

Just had a heavy snow shower here........finally as it's been pretty much rain/sleet all day. Best of all it has settled and we have a dusting

[Coast]

Everywhere I look I keep getting the heavy precipitation along the SE Coast and inland from there, I can't get a grip on the cold that we would need to turn it into something useful just yet:

marginal  [mahr-juh-nl]

Part of Speech:

adjective

Definition: borderline; slight

Synonyms: bordering, insignificant, low, minimal, minor,negligible, on the edge, peripheral,

Edited December 5, 2012 by Coast

[john pike]

H = High Pressure...Usually means Summer = Boiling hot Winter = FREEZING!! (if the right set up occurs)

L = Low pressure... Usually rain,sleet and snow..Depending on how tight the isobars are (the lines on the graph) shows wind speed.

Tight bars = Strong winds

Spaced bars = Light winds

Black thick lines with no arrows or half circles = Troughs

Black thick lines with arrows and half circles = occluded front

Black thick lines with half circles = Cold front

Black thick lines with arrows = Warm front

Crash course I think that's right

what do the squiggily lines on the maps mean

[Coast]

what do the squiggily lines on the maps mean

Someone left it out when the kids were doing crayon drawings for homework?