Low Carola is deepening very quickly at the moment, and the curl of cloud she is spinning up makes an impressive site in the latest satellite imagery to the southwest of Ireland (fig 1), as do the plotted observations and barograph from the weather buoy 62029 better known as ‘K1’ (figs 2 & 3).
As far as I can see Carola easily breaks the barrier for rapid cyclogenesis of 24 hPa in 24 hours, the pressure there has fallen by 37.4 hPa in 12 hours, in fact I don’t think I have ever seen sustained pressure falls like that on a chart from an extra tropical low.
No doubt the French will have claimed this low and come up with their own name for it, but I noticed it didn’t even get a mention in the BBC forecast at 12.58 pm from Sarah Keith-Lucas.
An area of heavy rain has developed in the last hour over northeast Scotland (fig 1). It doesn’t get much more intense that 16-32 mm per hour, well actually it does, the pixels turn white with intensities of 32 mm per hour and higher. According to the UKMO analysis it looks like it’s a very active bent back occlusion that’s behind it (fig 2).
I did notice that the rain never even got a mention in the BBC weather at 12.58 pm, although we did get Sarah Keith-Lucas showing us a couple of nice pictures, one by Geoff of Histon in Cambrideshire, and the other by Alan in Topsham in Devon!
I thought that I would take a retrospective look back (excuse the tautology) at the last two cold snaps that we’ve had, and some of the snow depths that were reported by various AWS around the country. The graphs show accumulated and fresh snow depths that I’ve gleaned from SYNOP reports which in the UK helpfully include hourly snow depths (NWS please take note). The blue bar chart in the graph represents fresh snow, that is the difference in snow depth between each hour, red bars indicate snow melt, and the light blue bar series is the hourly snow depth. Bars that span more than an hour are because I’m missing those observations.
From the recent cold spell that started last weekend (17th March) I’ve included the chart for Dunkeswell in Devon (fig 1) and High Wycombe in Buckinghamshire (fig 2).
As you can see the snow on the higher ground of Devon (Dunkeswell 252 m amsl) will do well to survive much longer than four days, all though the deeper drifts on the moors will last longer. You can see why the heavy snow on the morning of the 18th at High Wycombe caught the Met Office out, with the bulk of the 27 cm falling in just two hours (fig 2).
The snow came quite late to St Athan in south Wales (fig 3), but when it did come overnight on the 1st and 2nd of March, it did it in style and put down 56 cm before it had finished. That amount of snow took a whole week before it thawed away completely.
The snow at Wittering in Cambrigeshire started on the evening of the 26th and came in a couple of batches, with a maximum depth of 37 cm by the 3rd of March (fig 4).
Scotland also had a lot of snow, as these next two graphs testify. The first is from Bishopton in Glasgow, where a maximum depth of 46 cm was reached on the morning of the 2nd of March (fig 5).
Finally here’s the snow graph for Drumalbin a weather station on a low hill in south Lanarkshire, where 55 cm or more of snow had accumulated by the 1st of March (fig 6).
I’m sure these laser measured snow depths are very accurate, but in both snow events the wind was strong and there was a lot of severe drifting going on, so how representative these depths are is open to question.
Quite a mild start to the day with Trawsgoed already close to 13°C at 09 UTC. The mild conditions won’t be around for long as a cold front is already starting to bring a dramatic clearance into the southwest (fig 1). That will go some way in making up for yesterday. Next week looks rather cold and cyclonic according to the Met Office (figure 2).
82 hours of sub-zero hourly temperatures came to an abrupt end at around 01 UTC this morning, as the wind veered southeasterly and the rain came, to put an end to the longest such spell since at least 2010 down here in Devon.
March has certainly come in like a lion this year, well a lion is a beast after all. Nowhere across the country seems to have escaped the snow and freezing temperatures, and at 09 UTC this morning 49 cm of snow is being reported at St Athan in south Wales and 46 cm at Bishopton, Glasgow (fig 1). From what I can see from the chart almost every SYNOP station is also reporting an hourly gust of 25 knots or more, on another day of fresh to strong easterly winds, and although not as cold as the last two days, it’s still subzero in many places.
I would say at this point that not all SYNOP stations have snow depth sensors, and some that do aren’t reporting a depth at the moment, probably as a result of severe drifting, which could also be affecting the snow depths from the stations that are reporting one!
Spare a thought for the hill sheep farmers and their livestock, they must be going through a particular frigid time at the moment. Just imagine how much snow must have fallen on higher ground and the intense cold if conditions are like this on Great Dun Fell (fig 2).
It’s turning out to be quite a wet February 2018 more especially in western areas. The wettest place in the SYNOP observations is Capel Curig as usual with 6.55″ of rain up until this morning (fig 1). There are still some drier spots around though, notably in eastern Ireland, the Vale of York and the southeast of Scotland, although I only have a 79% record for Edinburgh Gogarbank.
The heavy snowfalls of the last couple of days over western Russia and central Asia have put our overnight warning for of just 1 to 3 centimetres into perspective. The above chart are the reported snowfall depths at 06 UTC this morning overlaid with contoured MSLP (fig 1). As you can see from the inset table one of the observing stations close to Moscow (WMO #27612 Dolgoprudny) is reporting 53 cm of level snow (~21″). Dolgoprudny,I’m reliably informed by Wikipedia, lies 20 km north of the city of Moscow.
Russia has a terrific SYNOP observing network, but they only report a snow depth once a day, and for some strange reason, probably to do with time zones, eastern Russia report it at 03 UTC, and western Russia stations at 06 UTC. Without some kind of bespoke SYNOP snowfall application that scans all observations for the latest reported snow depth in all observation for a selected day (now there’s an idea), I can’t extend the chart any further eastward.
The primroses are out down here in Devon, well they’ve been out a while, but I just noticed the first bee of the year in the garden this morning. It’s not that surprising because it’s very mild, with Exeter airport the warmest station in the British Isles at 10 UTC with a temperature of 12.6°C under cloudy skies (fig 1). Being in the lee of Dartmoor, that SC sheet could well break up a little bit, and if it does, we might see a maximum of 14°C.
We’re into the fourth week of January tomorrow so I thought that I’d take a quick peek at how much precipitation we’ve so far this month across the British Isles. As you can see from the plotted chart of accumulation (fig 1) it’s been a month of considerable contrasts even for January. The wettest place is western Ireland with Valentia topping the WMO block #03 table with 168.4 mm (6.62″) of rain far. In contrast, parts of sheltered Caithness and Aberdeenshire haven’t seen very much precipitation so far , with Kinloss the driest SYNOP station with just 7.2 mm, admittedly I don’t have a 100% complete record for 03066 this month.
I am a slightly dubious about the accumulations that I’ve calculated for places such as Loch Glascarnoch and Tulloch Bridge. I have 95% reception for the SYNOP reports, but because it’s been quite a snowy January over Scotland I’m not sure how well the AWS that the Met Office use cope with precipitation in the form of snow because the accumulations do look low. I would have thought that the gauges were heated somehow.