How to Know, When There is Snow!
Posted on January 28, 2019
Despite what The Daily Express might tell you, forecasting snowfall in the UK is a met office nightmare. Forget that twit, Nathan Rao, and your friends who claim to have ‘the best weather apps ever’ as they are talking shit. This is because even the most sophisticated computer models struggle to get snowfall bang on, even on the day of the event.
The UK conditions for snow (especially here in the south) are incredibly marginal, resulting in a history of red faces as cautionary predictions come to nowt. This was especially the case when a newsreader once said to a forecaster “Where’s that nine inches you promised me last night”
Of course, all that a weather forecaster has to do is mention a sleet shower on the peaks of the Isle of MccLintochy and workers in banks, shops and post offices, will join in with dog walkers by saying that we should be braced for arctic conditions. People in Sainsbury’s, Andover, were stocking up tonight.
There are a number of key factors what can be the difference between rain and snow. Luckily for you folks, I have done some studies and indeed, some blatant plagiarising, to show why predicting snow is a forecaster’s nightmare.
Temperature is as you might imagine (if you are still reading) is critical when calculating whether or not snow is on the way. As a general rule of thumb, snow only falls when the temperature is 2C or below.
If it sounds a bit weird that snow can fall when the temperature is above freezing, remember that the temperature of the air, even 20 or 30 metres above the surface, is colder than under your feet.
As a result, snowflakes can remain intact right down to the surface, before they melt. As a consequence, snow that falls with a temperature above freezing is slushy and wet, with partially melted snowflakes sticking together. Great for smashing your workmate in the face with a snowball, not so good for sledging.
For skiing, sledging and breaking your ankle whilst pretending to be young again, you need snow that falls with a temperature of 0C or below. It then falls very powdery and is also very rare down here in Hampshire.
However, it only takes the temperature to rise to 3 centigrade to ruin any hopes for a day off work or school. However, if rain falls for long enough, the temperature of the air will start to fall as the rain drops evaporate and it may well turn to snow. You see, it is very fine margins when it comes to snow. A 0.5c temperature swing can change everything from a winter wonderland into a mud bath.
Hills and Mountains
The height of a location above sea level is a major factor when it comes to snow. The higher up you go, the colder it gets. The temperature drops by about 1C for every 100 metres you climb. That’s why you often see snow on mountain tops. Well, not in Hampshire because there are no mountains.
However, we do have hills and knowing how you all like to be amazed by my blogs, check this out for a mind blowing fact to impress your friends.
If there is a 20% chance of snow at sea-level, this rises to 35% at 100m, 60% at 200m and around 75% at 300m. If you are local to Basingstoke and of a maverick disposition, you can occasionally witness this when rain is falling in Cliddesden whilst a mile away in Farleigh, it snows.
The same can apply coming from Aldermaston in the Kennet Valley up in to Tadley. I know because on my paper round as a child, I was a drowned rat in Aldermaston village and a polar bear by the time I got back to my home in Baughurst. Eeeh it were tough when I were a lad…GLOVES you say!? Never heard of them.
Towns & Cities
Urban areas are always warmer than rural areas during winter. This, of course, is due to the heat generated by manufacturing, transport, houses and bullshit emanating from the banking industry. In places like London where traffic is heavy and bullshit levels are high, this will often be enough for rain to fall instead of snow.
Even smaller provincial towns such as Reading and Basingstoke will occasionally be warm enough to make snow fall as rain. With that in mind, think back to October and The Daily Express headline ‘100 DAYS OF SNOW!’ If you still believe that shit you need a clip around the lughole.
Just in case Dominic Raab is reading, The UK is an island. It is also surrounded by relatively warm water. Not that it feels warm in July when you pop in for a dip at Swanage Beach and spend the next half hour wondering where your testicles are.
The seaside is nearly always cooler in summer but in winter, temperatures in coastal areas are nearly always warmer. Basically, if you see snow in the forecast and you don’t like the look of it, go to Bournemouth for the day. Remember to take a brolly though, as it will be pissing down.
As I said earlier, if rain falls for long enough, a process of ‘evaporative cooling’ will often lower the temperature, resulting in rain turning to snow.
This is only really effective when the air is still, with little, or no wind. Colder air from above descends to the ground more consistently when it is still, whereas as wind unsettle the pattern.
Light rain is generally less likely to turn to snow than heavier rain in this way. This is because there is not so much moisture for ‘evaporative cooling’ to take place. I only learnt that today which is proof that reading broadens the mind. However, this shouldn’t be mistaken with making someone more interesting. I read and learn about Brexit and it makes people hate me.
So, in summary, there a few things to remember when there is snow is in forecast
1/Keep checking the forecast as snow areas change quickly
2/ Stay away from The Daily Express
3/Weather Apps are a waste of time, even the one your mate says his the best one ever.
4/ If someone says it is too cold to snow, tell them to stop being ridiculous and punch them in the face.
5/Carry a shovel just in case you meet Nathan Rao and you want to hit him over the head with it.