My estimates of the 24 hour precipitation totals up to 06 UTC this morning may appear to have been a little high for Liscombe (fig 1 & 2), but at this resolution, you only need to be a pixel or two out to make a big difference – well that’s my excuse anyway.
But apart from yesterday being such a cold and miserable day in east Devon and west Somerset, the wet snow that fell for much of the afternoon made it rather unusual too. Here are the plotted observations for Dunkeswell in Devon (fig 3), the snow started here at 13 UTC, perversely the warmest time of the day, and lasted until 17 UTC, before milder air from the northwest lifted temperatures and turned it to rain.
Full marks to the Met Office about yesterdays warning for heavy rain in this part of the world, especially Exmoor (fig 4).
I think the widespread nature of the wet snow falling across lower lying parts east Devon and west Somerset yesterday afternoon caught them out though. The photo of the snow at Christ Cross above Silverton yesterday afternoon is rather appropriate taken as it was on Good Friday (fig 5)
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.
A melting snowman must be one of the saddest sights to any of you snow lovers out there, and especially so to any of you in southwest England, where we only see snow lying every six or seven years or so. This particular snowman was created on Sunday by children and adults alike, but looks to be in a pretty terminal state late this morning, and will be lucky to see the afternoon out! I’ve been watching it as its slumped over from my study winter, and it seemed to be calling me to go up and take its photo for posterity, which I’ve duly done!
A slightly premature press release from the Met Office regarding the latest cold spell and today’s snow (fig 1). Maybe it would have been better waiting for tomorrow to release it, in light of the fact that it’s still snowing across large parts of Devon and Cornwall (fig 2).
We’ve had around 5 cm of fresh snow this morning here in mid-Devon to add to the 5 cm or so that we got overnight, in a spell of moderate snow that’s now moving away W’NW across Devon. There’s an interesting convergence line that’s pluming a line of showers northwest across the Channel from the Cherbourg peninsula towards Devon. At the moment that looks like it might keep the snow falling in this part of the world for the rest of the afternoon, as the latest models suggest it will. I saw this type of convergence happen in an easterly from Cherbourg that affected Guernsey in the last cold spell, but this is a new direction for me.
Automatic weather stations now make up nearly all the network of observing sites in the UK, and they all have an inerrant problem when it comes to reporting precipitation totals in very cold weather, and that is they can’t!
Precipitation from AWS
Have a look at the 12 hourly totals [18-06] from 06 UTC this morning from across the country (fig 2) and you’ll see that almost all stations are reporting no more than a ‘trace’ of precipitation. These accumulations are obviously incorrect because most of the precipitation that’s fallen in the form of snow will still be stuck, frozen in the funnel of the gauge. Some AWS sites do have snow depth sensors, but these are not the answer, and can be easily fooled as we have seen this winter, by drifting when the wind is strong enough to lift any snow that has fallen.
Here’s are my estimates from the radar network of the precipitation that has fallen since 06 UTC on Saturday morning (fig 3). If this is anything to go by then, the deepest of the snow looks to have fallen across Norfolk and Suffolk in some kind of convergence zone, with precipitation totals as high as 16-24 mm. I estimate that there was around 6.9 mm from around High Wycombe, which I realise is not enough to account for the 27 cm of snow there at the moment. In my defence I offer the “spoking” that’s evident from the Chenies radar. Chenies lies not so many miles E’NE of High Wycombe, and I did speculate last year that the “spoking” that occurs there at times is caused by the radar being blocked by some of the large trees that surround the site.
I don’t know enough about why this is such a problem in the 21st century, you would have thought that it would be easy enough to detect when temperatures are close or below freezing and turn on heating elements inside the gauge to melt any snow that it catches. For all I know this might be already happening, because the SYNOP format is not how AWS report their readings these days, and much more detailed one minute or even more frequent observations from all the sensors are being taken and transmitted back to Exeter, which may include the water equivalent of any snow that has fallen, who knows…
Heavy snow at High Wycombe caused the Met Office to issue a very early (or should that be very late?) amber snow alert for London and the southeast of England at 0407 UTC this Sunday morning. The 27 cm of snow that fell there must have caused severe problems especially on Wycombe hill I imagine. It’s not the first time that High Wycombe has caught the Met Office out with snow this winter, it did it on the 11th of December 2017, and again on the 21st of January 2018.
The Met Office have just issued a plethora of weather warnings for the coming weekend for snow (fig 1). I’m not going to get in the thinking of how 5 to 10 cm of snow equates to an amber warning for severe weather, and ask how other countries cope with snow and we can’t, because it’s simply not worth it.
I’ve just done the weekly shopping with my wife at our local Tesco’s in Cullompton this morning, and it’s already quite obvious that panic buying in preparation for the snow that’s forecast for this weekend has begun. It got me to thinking about just how effective weather warnings issued by the Met Office, especially for snow, are. Do they actually save the lives of people who listen to them? Or do they just cause panic buying at every supermarket in the country?
Hearing the warning
It’s no doubt that they are very effective, especially in how they get their message across by means of a mix of social media, smart phone apps and 24 hour rolling television news. This usually has little effect if the warning concerns either rain or wind, but as soon as amber or red warnings for snow is issued, the whole nation seems to go into melt down mode, and panic buying starts in earnest, with most people hoping that they’ll end up being snowed in for days, and due to health and safety concerns of course, won’t be able to venture out until a thaw has set in.
Heeding the warning
So at least panic buying does suggest that people are hearing them, but does this mean that they are being heeded for safety on the roads? Will people drive more carefully or not attempt to drive at all? I don’t know if any study into the effectiveness of weather warnings has ever been undertaken, but I would be fascinated to read the conclusions of it, if ever there was.
The climate team at the Met Office have been working overtime and have produced a report detailing the events of the recent cold spell which as you know started on Sunday the 25th of February and lasted to following Saturday the 3rd of March 2018.
I’m not certain if the snow depths in this chart (fig 3) are particularly accurate from what I saw locally here in our part of Devon – 0 cm really? They would have been better using the snow depths reported from their WOW network, which for some reason known unto themselves you can’t plot on a chart.
I did say last Sunday in the article return of the easterlies that it was still in the land of science fiction, well the models look to have been spot on even at T+168. The Met Office have a discrete centre of 1002 hPa on the low that seems to form on the northern edge of a warm trough that’s moving westward across France for 12 UTC on Sunday (fig 1). None of the other models, apart from the French ARPEGE seem to have pressure as low as that across the Channel on Sunday (fig 2), although it’s difficult to synchronise the validity time. It’s still 72 hours away, and we are now close to the vernal equinox, but this situation has the potential to cause a lot of disruption, especially if snow falls in the overnight period.
Today’s 06 UTC (Friday) from the GFS has a similar feel to it at T+42 (fig 3).