Turning colder but is there plenty of snow on the way? - November 3, 2016
The weather is about to turn much colder from the north as we see northerly winds set in just in time for the weekend period with snowfall a risk for higher ground.
We’ve had a large number of messages via our Facebook page, website and also via my personal Facebook account asking if lower ground will see any snow, I’ve even had people from the south coast of England, Kent and even Cornwall ask these questions.
Firstly, with constant over-hyped and scaremongering reporting from the tabloids over recent days this colder snap couldn’t have come at a worse time as all it does is just provide fuel for the fire and we see many people actually taking note of these stories when in fact there is colder weather moving in.
What we have to remember is that we’re in the first week of November and as a result there are many contributing factors when it comes to colder spells of weather during this period, in this instance we see a developing area of low pressure pull south-east across the country on Friday and as it does so it will open the gates to colder air flooding down from the north and north-east, sourced from Scandinavia.
When it comes to colder spells of weather and “looking” for snow, we look at a wide variety of variables to get a rough idea if snowfall is supportive and to what levels it may fall, higher ground or lower ground for example. Three of the main factors you look at with cold spells are 850hpa temperatures, 500-1000hpa thickness and freezing level (heights), these 3 variables give us an indication of how cold the upper air will be right down to the surface. As we nearer the time-frame of any colder spell/event we then move on to the high resolution models which give more detail at short range. We then look at dew point temperature, surface temperature, 850hpa temperatures and freezing level at more detail.
Forecasting snowfall to lower levels (general rule of thumb)
500-1000hpa thickness (DAM) SUB-528
Freezing level ideally below 200m, could be slightly higher as during heavier precipitation the freezing level will drop and support snowfall down to lower ground (we call this evaporative cooling). Get 100m or the freezing level down to 0m then that is perfect!
Dew points 0c or below
850hpa temperatures around -5 for inland areas, -7 or lower for coastal areas where temperatures can be influenced by warming of the sea, especially north sea facing coasts.
Wet bulb freezing level low as possible/surface temperatures as close to 0c.
At the moment the temperature of the north sea is still rather warm and as a result this can “modify” any colder air that is originated from Scandinavia, during cold spells in the depth of winter where we see the near continent much colder having sustained longer colder spells we would generally look for upper 850hpa temperatures of around -7 to -8 for snowfall to lower levels across northern and eastern areas, this is of course a general rule of thumb without looking at other contributing factors.
The current cold spell doesn’t have upper 850hpa air temperatures and other variables supportive of snowfall down to lower levels and with a fair bit of modification from the warmer sea, despite it feeling much colder with the risk of overnight frosts and cooler temperatures by day, any snowfall will be restricted to higher ground. So let’s take a look at this weekends weather!
The above image shows sea level pressure and 850hpa temperatures. As you can see the blues and purples represent much colder air and with tightening isobars and winds from the north/north-east it is going to feel notably colder than of late.
Friday sees a wet day across the north with showers and longer spells of rain affecting Northern Ireland, Scotland and the far north of England. The showers will turn increasingly wintry across the mountains of Scotland. Showers will be well scattered across inland areas of England, though for southern areas we see some rain sliding along southern coastal counties edging into south-eastern parts of England by midday.
Saturday & bonfire night
Come Saturday the colder air will be well established across the UK with much cooler temperatures, plenty of showers which will merge together to bring longer spells of rain and of course snow falling increasingly lower across Scotland. At the moment we expect the snowline to be around 200-250m across Scotland, though during heavier precipitation this level may drop so you may see something wintry down to lower levels of Scotland for a time.
Showers will be most frequent across northern, eastern and western areas of the United Kingdom. The above chart shows the precipitation type, pink being snow, green represents sleet/wet snow mix and blue is rain. Even across the highest ground of northern England there may be some wintriness, though the snowline is rather restricted here with the level at around 350m. Snowdonia may also see some snow falling for a time also.
Let’s take a look at Saturday’s temperatures.
Now the all important bonfire night forecast
For many inland areas it will be a dry and very chilly bonfire night, though winds will strengthen with gale force winds expected across eastern counties of Scotland and England in particular, making it feel raw, so do make sure you wrap up well. Showers will continue to affect Northern Ireland, eastern coasts of Scotland and England and western coasts of England and Wales with snow showers continuing over the hills of Scotland.
Please find your minimum temperatures, windchill temperature and wind gusts for Bonfire night below.
To conclude; turning much colder from the north with snow over higher ground of Scotland (though not exclusively) and possibly down to 300-350m for a time across the hills of northern England, showers and longer spells of rain at times, especially across northern, western and eastern areas, with sleet and hail down to lower levels at times during any heavier precipitation. A raw feel to bonfire night is expected with a significant windchill factor locally with gales affecting eastern coastal counties of Scotland and England, showers continuing across coastal areas on bonfire night with a clear & cold night for central/inland areas. You can track any snow over the weekend via our UK Snow radar application for Android by clicking here, or by using our web based snow radar by clicking here.
Sunday will be wet and very windy, especially across eastern areas with east to north-east winds and plenty of showers, I’ll have more on this later, though I’ll leave you a chart for now showing sea level pressure and precipitation for Sunday. Have a fun bonfire night, stay safe and don’t forget to wrap up warm.
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