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.