UK Weather - Spring 2018

[Simon Culling]

Despite the meteorological spring starting on 1st March, you would not guess it from the weather. A lot happened in the first three days of March, but suffice to say, it snowed in most places and it was very cold. I will try to flesh out a few details in the coming days as there were quite a few notable events. Here in Hythe we were not too badly affected with a 5cm snowfall during Thursday 1st March causing inconvenience rather than chaos, but it did make driving fun for those not used to the snow. The attached photos are from the late afternoon and evening of Thursday and give a general impression of one of the lesser affected areas.

For the country as a whole, the snow provided a lot of inconvenience for travellers and the working economy as transport was disrupted. It did not help the farmers either, as this is the start of lambing time. Following the start of the thaw, many households have no water (burst pipes) and the shops look like a war is on - my local supermarkets had no bread, eggs or milk yesterday and precious little meat and fruit/vegetables. Here in the UK we tend to panic when a few snowflakes fall and it can take weeks to get over it!

The CET for March was -0.5*C (-5.0*C) up to the 4th and the EWR was 11mm also up to the 4th, which is 15% of the monthly average of 74mm.

[Simon Culling]

The first two days of March saw snow falling over most of the UK/Eire with some heavy falls in places. Synoptically, this came from a low pressure (around 975mb) approaching from the south and bumping into (and slowing down) the high pressure to our north east over Scandinavia with the snow falling from the leading warm front which was orientated roughly east-west. Snowfall was variable with the heaviest prompting two 'red weather warnings' from the Met Office for an area of SW England and for central Scotland - the highest level depths reported were in the 50-60cm range, but the strong (and gusty) ENE wind made these measurements difficult and piled up some massive drifts. There was also a significant snow event in the eastern half of Eire, including Dublin. The BBC had numerous stories on the snow and the rather silly "beast from the east", but this is fairly representative of the date:

http://www.bbc.co.uk/news/uk-43236763

[Simon Culling]

The cold spell in the south was thankfully quite short in duration and the temperature gradually lifted through 3rd/4th March to be back to near normal by the 5th with rain or showers at times. However, the cold weather hung on in the north of the UK for much of the past week with further snow at times - indeed yesterday (Thurs 8th) 5-10cm of very wet snow accumulated quickly in the morning rush hour in a swathe from Merseyside to Yorkshire causing the usual problems on the roads.

It has become progressively milder in the last couple of days in the south of the UK and we will see a push of even milder air across the whole country from the south over the weekend with the maximum temperature in the south possibly pushing 15/16*C if there is any sunshine on Saturday - this would be the warmest day of the year so far.

I will fill in some further details on the worst of the weather in the first few days of March when I get a chance. There were some massive snow drifts and even a spell of freezing rain in the south.

[Simon Culling]

The main snowfall of the cold spell occurred during 1st/2nd March as a low approached from the south and milder air butted up against the cold easterly flow. The low originated over Portugal (where it was named 'Emma') and drifted north to be over the Brest Peninsula by 12:00 on Tuesday 2nd March with its attendant fronts pushing north into southern England. The main energy was on the western side so the heaviest snow fell in south west England and southern and central Wales where approx. 30cm fell, although with a lot of drifting, it is difficult to get reliable figures. The highest official measurement was at St Athan, which is an RAF airfield on the south coast of Wales - a figure of over 50cm was reported on both the 2nd and 3rd of March. A lot of these snow measurements are now done by automatic means, but some of the picture from south wales (particularly further inland in the 'Valleys') do show a lot of snow. As mentioned in a previous post, the snow was very powdery due to the sub zero temperatures so drifting in the stiff wind (averaging 20-30mph) was considerable. The tweet below contains a picture from Rhoose on 2nd March - this is very close to St Athan.

https://twitter.com/scooby_scott1/statu ... 9831500800

[Simon Culling]

It was indeed much milder in the UK this weekend with 15*C reached on both days in the far south. With an area of low pressure lurking to our south west and only moving slowly north it has also been wet at times with periods of rain and/or showers. Today (Sunday 11th March) a 'plume' like set-up existed over southern England as an upper trough approached from the SW and we saw a few clusters of elevated storms develop as the upper lapse rates increased in late afternoon. These storms occurred over central southern and SE England and lasted into the evening in eastern parts.

The attached link gives an idea of the change in the weather over the last week with a comparison of maximum temperatures on Friday 2nd and Saturday 10th March - some show a difference of 16*C.

https://twitter.com/stormbell/status/972526035102203905

The CET for March was 3.1*C (-1.8*C) up to the 10th and the EWR was 40mm up to the 9th, which is 54% of the monthly average.

[Simon Culling]

One of the features of the cold spell was the drifting of the snow. As I have already explained, the snow was very powdery as it fell at temperatures well below freezing and this resulted in some very large drifts building up even when snow was not falling. Because of all this drifting of the snow, many roads became blocked simply because they filled up with snow. Here in the UK many rural roads are bounded on both sides by hedges and the wind scoured the fields of snow and deposited it in the roadways. The links below give some idea of the scale of the drifts:

http://www.bbc.co.uk/news/uk-england-devon-43271227

https://twitter.com/BethyPea/status/969927727129268224

[Richard]

That drifting of snow is amazing.

And i see southern UK might be in for another very cold easterly wind soon, even getting down in to the top of Africa

[Simon Culling]

Yes indeed Richard, we are due for another spell of cold weather here in the UK, but thankfully it appears that it will be short lived. The cold air will filter westwards overnight Friday and into Saturday introducing cold and windy weather with an increasing risk of snow showers. The worst of the cold will be felt on Sunday when much of inland England + Wales will see a maximum of around 0*C and frequent snow showers. Unusually, the high over Scandinavia will decline Sunday and move away to the SW and this will cut off the direct feed of cold air - this is quite an unusual way for this type of weather pattern to end.

Until the arrival of the cold air we will continue to enjoy mild weather - today (Thurs 15th March) the temperature reached 14/15*C in a few places in-between the rain and showers and we will see temperatures close to this on Friday with plenty of heavy showers and a few thunderstorms. Then comes the dramatic change to much colder weather overnight into Saturday.

The CET for March was 4.2*C (-0.9*C) up to the 14th and the EWR was 55mm up to the 13th, which is 74% of the monthly average.

EDIT: The temperature reached a high of 15.9*C at Porthmadog (NW Wales) on Thursday 15th March. This is the highest temperature so far this year and would have been influenced by a foehn effect over the Welsh mountains in the SSE wind.

[NZstorm]

Parts of London had high's today of -1C today with freash E/snow showers. Exceptional weather for mid March.

[Simon Culling]

Indeed NZstorm, today was a lot colder than yesterday with afternoon temperatures over much of England + Wales at least 10*C lower, and with a stiff (20mph) ENE breeze to boot. The table below gives an idea of the changes of temperatures at 15:00 on the two days - from Friday to Saturday - and it certainly felt a lot colder.

I have also attached a temperature trace for London Heathrow for the last 6 days which gives a good indication of the dramatic temperature fall over the last day or so. On Friday, Heathrow reported a temperature of 7.5*C at midnight, but this had fallen to 2.6*C by 06:00 on Saturday morning and to 0.4*C by 09:00. The temperature then hovered around this level until 15:00 when the hourly temp finally fell below freezing (to -0.1^C).

[Simon Culling]

Sunday 18th March was indeed a very cold and windy day across most of England + Wales with quite a few places recording an 'ice day'. The lowest maximums for 09:00 to 09:00 I could find were:

-3.1*C at Tredegar Bryn Bach Park
-2.7*C at Liscombe (on Exmoor, Somerset)
-2.1*C at Dunkeswell (south Devon)
-1.5*C at Little Rissington (Gloucestershire)
-1.4*C at High Wycombe (Bucks)
-0.7*C at Kenley (Surrey - southern suburb of London).

An area of snow moved west across the southern half of England and was heavy in the south west and particularly so on the eastern slopes of Dartmoor, with 20-30cm reported here. Even coastal parts of Devon had 10cm+.

Here in Hythe we had a couple of falls, but only 4cm recorded as the maximum depth. The mild weather of the last two weeks has warmed the ground so light snow struggled to settle on the roads here.

http://www.bbc.co.uk/news/uk-43445768

[Simon Culling]

Yesterday (Mon 19th March) was another very cold day for mid-March with a few of the higher sites having another 'ice day'. For example, Okehampton on Dartmoor only reached -0.5*C and Wych Cross (at 200m amsl on the Sussex Downs) only saw -0.3*C as an hourly maximum. Kenley, in the southern London suburbs only reached 0.8*C as a daytime maximum. The snow is slowly melting, particularly where the sun shows itself, but on the moors in the SW they still have a full cover of at least 20cm. The photo below was taken yesterday afternoon (Mon 19th) at about 2pm and shows snow on the Hythe Pier which juts out into the Solent estuary. Not often we see snow here! At the time it was cloudy and breezy and only 1*C, so very cold at the end of the pier.

Thankfully the weather will be warming up this week with temperatures returning to nearer normal and the usual mix of rain/showers and sunny intervals. There are signals in the models for a northerly flow for the Easter weekend, but that is a long way off.

CET for March was 4.2*C (-1.1*C) up to the 19th and the EWR was 72mm up to the 18th, which is 97% of the monthly average.

[Simon Culling]

Returning to the very cold weather at the beginning of March, the far south of England had a rare visitor - a period of freezing rain. This occurred on the evening of Thursday 1st March as the warm front reached the south coast and temporarily introduced some slightly warmer air aloft. The area affected by the freezing rain ran along most of the southern coastal counties of England from Sussex westward to Devon, with the cities of Bournemouth + Exeter reporting half an inch (1cm) of clear ice on most surfaces, even giving a similar crust on top of the snow on the ground. This produced sheet ice on the roads and plenty of prangs between vehicles and a surge in broken bones at Accident + Emergency. The article below (sorry about the journalism of the Sun) has some good photos:

https://www.thesun.co.uk/news/5710181/f ... k-weather/

The rain fell at temperatures between -1*C on the coast and -3*C further inland, so the froze instantly. Here in Hythe, the snow turned to light freezing rain around 10pm, but thankfully we missed most of the precipitation. Even so, on the Friday morning, all exposed surfaces were covered in 1-2mm of clear ice and there was a thin crust of ice on top of the snow.

[Richard]

Freezing rain is a interesting phenomenon alright. I dont recall NZ ever experiencing it before, the closest we come here is when wet snow falls on wet surfaces, sky clears and it freezes. Here one for the panel - has NZ ever had freezing rain?

[Simon Culling]

Richard - freezing rain/drizzle occurs in the UK from time to time but usually consists of a few showers falling on frozen ground from earlier clear skies. Proper freezing rain, which is often seen in the USA, requires a warm layer above the ground (which would be <0*C) to melt the falling snow to rain which then falls through the colder layer near the ground and freezes on the cold ground. The sounding below is for Herstmonceux (close to the south coast of Sussex, so just in the right place) for 00:00GMT on Tuesday 2nd March as the freezing rain was falling and it shows a shallow warm layer between approx. 2500ft and 5000ft above the surface. This looks like a classic set-up for freezing rain. This sounding was taken from a tweet on Dan Holley's Twitter page.

[spwill]

We can get light rain falling onto frozen ground and producing ice but not freezing rain/ice storms like they get in USA. New Zealand has a mild Winter and the likes of Central Otago is only cold by NZ standards

[NZstorm]

When living in London I saw ice pellets. That is rain frozen to ice before it hits the ground.

[NZ Thunderstorm Soc]

......but then, What is graupel?

[Simon Culling]

Ice pellets are formed under the same atmospheric conditions as freezing rain, i.e. you need a shallow warm layer above the boundary layer where the snow falling from above can melt. Ice pellets will form when partially melted snowflakes (from falling through the warmer layer) then refreeze into small translucent ice 'balls' usually <5mm in diameter. During the freezing rain event on 1st/2nd March, ice pellets were also reported in many of the affected areas- indeed we had a couple of spells of them here in Hythe.

Graupel (or snow pellets or soft hail) are a different animal. They are convective in nature and form when super-cooled water droplets collide with falling snowflakes and instantly freeze on its surface - I think this process of growth is called accretion. Graupel is typically 5-10mm in diameter and is soft to touch and will easily crumble between your fingers and will break up when hitting the ground. We often get 'soft hail' in the spring in the UK when the upper atmosphere is still very cold and I would imagine it is fairly common on the south island of New Zealand in the winter.

[Orion]

Freezing rain is a interesting phenomenon alright. I dont recall NZ ever experiencing it before, the closest we come here is when wet snow falls on wet surfaces, sky clears and it freezes. Here one for the panel - has NZ ever had freezing rain?

My own post #190 (from Mayfield) in the General June Weather 2012 thread viewtopic.php?p=119562#p119562 , reads in part:

around 10.30pm we had what I can only describe as slowly-falling ice - faster than snowflakes, slower than hail, no rain with it, and it seemed clear, not white like that graupel stuff.
The temp. had warmed up then from about -1.0 (when I'd been expecting a good frost) to +0.4.

There was some discussion about the topic further down in that thread.

Used to find evidence of an "ice-shower" on the grass there in the mornings sometimes.
Also experienced the glaze of clear ice on the road surface and even a gravel driveway, shocking stuff to walk on, as slippery as soapy glass.
Mayfield is at 250m a.s.l.

[Simon Culling]

Hello Orion. I think what you were describing in June 2012 were ice pellets. They are small and spherical ice balls, usually <5mm in diameter and consist of clear ice. They form under the same general synoptic conditions as freezing rain and both of these forms of precipitation are common on the eastern side of the USA. We get them here in the UK from time to time.

Here in the UK (and I would expect inland on the southern island of NZ) we occasionally get a different kind of 'freezing rain' where a front moves in from the west overnight and despite warmer air ahead of the front (and rising air temperatures), a sharp frost is not all lifted and the rain falls onto frozen ground for a while. Whilst this is not a classical set-up for freezing rain, it can provide treacherous conditions underfoot and on the roads for a relatively short period.

Weather-wise here in the UK, it has been much milder since the end of last week's cold spell with the usual mix of showers and drier sunnier days. However, the colder air is set to return tomorrow (Weds 28th March) with cold rain for most of us and then a spell of 'April showers' into the Easter weekend with some frost at night.

CET for March was 4.7*C (-0.8*C) up to the 26th and the EWR was 79mm up to the 25th, which is 106% of the monthly average.

[Simon Culling]

A new record coldest day for March for the whole of the UK was evidently set on 1st March 2018 at Tredegar, Bryn Bach Park in south Wales. The highest temperature was -4.7*C for the 0900-0900 standard period and this beats the previous record of -4.6*C which was set at Cassley (Sutherland) on 1st March 2001. The Tredegar station is at an altitude of 360m.

Eire was also badly affected by the late Feb/early March cold spell with a lot of snow falling on the eastern side of the isle - in counties such as Wexford, Wicklow, Kildare + Dublin. Over 30cm fell in places (which is a lot for this area) and again there was considerable drifting in the strong NE wind. This video shows just how much snow fell on 1st/2nd March in the coastal town of Wexford:

https://twitter.com/StormchaserUKEU/sta ... 9132090368

[Simon Culling]

The weather has been thoroughly miserable here for the last few days with plenty of cold rain and/or showers and not a lot of sunshine. Literally, every time I have ventured out of the house, I have got a drenching. It has finally dried up this (Saturday) afternoon, but it remains cloudy and rather cool - just 7*C here in Hythe. The forecast for the rest of the Easter weekend is not much better either, with rain all day Monday with sleet and snow from the Midlands northward - there could be quite a lot of snow over the hills.

The 'fantasy island' section of the models (10 days ahead) is toying with the idea of a southerly setting in with temperatures getting past 20*C, but I fear it will always remain at this distance as the effects of the SSW in late January on the Northern Hemisphere general circulation will take until the end of the spring to unwind. It could be a cold and wet spring based on this assumption - so let's hope I am wrong as we could do with a bit of warmth.

[Simon Culling]

The wet weather has continued into April with all of the UK enjoying a soggy Bank Holiday Monday - with plenty of wet snow in northern England + southern Scotland. We have a low pressure system to our SW and this is throwing fronts northwards with the cold air remaining on its leading edge and hence the snow. The frontal boundary has become almost stationery over the far north of England and this gave a large temperature differential across the UK today with highs of just 1-2*C in the snowy areas, but up to 14*C in the showery south, although there was precious little sunshine.

The milder theme will now persist this week, particularly over more southern parts, but the showers or longer periods of rain will be with us until later in the week - indeed we could see some very sharp showers and thunderstorms on Tuesday + Wednesday. Later in the week a brief southerly will brush the more SE parts of the UK and we could see 18*C or so on Saturday.

[Simon Culling]

We are entering a break in the rains now for the next few days and it will warm up a bit as we draw in a southerly off the now warming European continent. It certainly won't be summerlike, but it will be an improvement on recent weeks - we have already had at least half the normal rain for April in the first 5 days. Looking forward, the model solutions are rather mixed, but most suggest a return to cooler and more unsettled conditions after the middle of next week.

The final CET for March was 4.9*C (-0.8*C) which means it was colder than January. The final EWR was 117mm, which is 158% of the monthly average - reflecting the very wet second half of the month.

Yesterday was a decent day with mostly clear blue skies so I went for a walk in the New Forest, but unfortunately a veil of cirrus + cirrostratus spread over in the afternoon making the sunshine hazy. The forest is very wet at the moment with plenty of transient pools, which can be seen n the second photo.