Answers on a postcard please

Figure 1

The two vortices (or should that be the two vortexes) in this mornings 09 UTC visible satellite image caught my eye (fig 1), because funnily enough they do resemble a pair of eyes. I can see that the one to the southwest of Ireland is connected to the surface low (Gabi) which looks to have a minimum central pressure of around 982 hPa (fig 2).

Figure 2

The more prominent of the two which is sat in the Celtic sea has me stumped though. You would have thought that it was connected to some upper level feature because the clouds spiralling around it look a lot thicker extending to medium or upper levels, but it’s certainly not at the 700 hPa level (fig 3). Answers on a postcard please to the usual address.

Figure 3 – Courtesy of weatheronline.co.uk

The sheltering effect of Dartmoor

The sheltering effect of Dartmoor seems to have had a long reach if you look at the estimated 24 hour rainfall totals for yesterday from the weather radar network. Conversely the funneling effect of the Bristol Channel, and the resultant large rainfall totals across south Wales, with a finger of higher totals extending northeast towards the Wash was also evident (fig 1).

Figure 1

You would have expected the upper winds to be from around 220° which they were from the 2317 UTC ascent from Camborne (fig 2).

Figure 2

Great expectations of the impending cold snap has everyone in a spin

It’s interesting to see how this impending cold snap has got many people excited about it, even those that don’t usually give a hoot about the weather most of the time, it’s almost like the announcement of a very early Christmas. I saw a good example of this in a tweet from Weather Outlook (fig 1) saying how the ‘thickness’ would fall below 500 dam in NE Scotland – really?

Figure 1 – Courtesy of Twitter & The Weather Outlook

Just to check that I hadn’t just entered the Twilight Zone I looked at one of the few sites that does include a 1000-500 hPa partial thickness forecast chart these days from NOAA (fig 2).

Figure 2 – Courtesy of NOAA

As you can see 1000-500 hPa thicknesses for next Wednesday are expected to be below 528 dam (the old blue or snow line) across most of the country except the west of Ireland and NW Scotland, and the 510 dam (the old brown line) has just about engulfed Belgium. To put this cold spell into some kind of perspective here is the thickness chart from the 13th January 1987, in what I reckon was the coldest couple of days in the British Isles of the whole 2oth century (fig 3).

Figure 3 – Courtesy of the Met Office RAF Binbrook and plotted by yours truly!

I have seen in the last few days people displaying forecast sequences of 850 hPa temperature charts on social media – which I also like to do – and people on Facebook and Twitter thinking that the -15°C isotherm at 5000 feet is the forecast surface temperature!


So in the scheme of things a good cold snap, even very cold for a day or so, but not record breakingly cold. One thing that would make this cold spell memorable though is the length of time it persists into March – which at the moment is still up in the air!

I always had trouble getting an ice bulb going…

Figure 1 – Courtesy of Twitter

When I was an observer the biggest problem I had in winter was getting an ice bulb going when the temperature got close to freezing. Judging by the look of this Stevenson screen (fig 1) they wouldn’t be having that problem at the moment at Izaña in the Canary Islands. It’s not quite as cold as it has been recently (fig 2), but the rime seems to be building up in the northeasterly.

Figure 2

I don’t suppose they are getting very much astronomy done at the moment at the observatory, but that’s at 2,390 metres (7,841 feet) whilst Mount Teide itself rises up to 3,718 metres (12,198 ft), and is the highest point in Spain, as well as being the highest in any island of the Atlantic which of course includes us.

Looking at the very nearby upper air ascent from Guimar (WMO 60018) for midnight (fig 3).

Figure 3 – Courtesy of OpenStreetMap

it looks like Izaña is sat in an inversion with a sub-zero freezing layer that’s not quite been captured by the radiosonde ascent by the looks of it (fig 4). Although I will say at this point that my sonde application does need a good-looking at!

Figure 4

You can see from the special points that the temperature is well above freezing at the 779 hPa level, and remains above freezing till around 11,000 feet and just below the summit of Teide it goes sub-zero again (fig 5).

Figure 5

Finally to finish, here’s a satellite image from yesterday of the Canary Islands, I think you can just about pick out Tenerife with some snow cover or is that cloud (fig 6)?

Figure 6 – 2 February 2018 – courtesy of NASA Worldview.

Snow starting to mount up over higher ground

The incessant band of wintry showers that are feeding into western parts in the fresh or strong west northwesterly airstream means that snow is starting to accumulate quite significantly over higher ground at the moment. There’s 25 cm at Eskdalemuir in the southern uplands with more to come (fig 1).

Figure 1

The freezing level across Scotland is close to the surface this afternoon, at Watnall it’s lower at around 1500 feet, but at Camborne it’s still up around 3200 feet. I notice from the T+15 frame of the 06 UTC GFS model that cold air advection will continue through the evening and night, so we might even see a covering of snow (the purple contours) in the southwest away from windward coasts (fig 2).

Figure 2 – Courtesy of www.wxcharts.eu

Not a peep out of the Met Office about the possibility of a named storm on Thursday. The latest GFS run shows the low deepening very little as it runs quickly across Northern Ireland and northern England. I’m surprised that Met Éireann have not named the storm anyway, because they have a status Orange alert out for severe gales – mean speeds 35-43 knots – with gusts to 65 knots (fig 3), perhaps they’ve been leaned on by the big Chief at Exeter.

Figure 3 – Courtesy of Met Éireann

200 mph jet over UK

Figure 1 – 300 hPa 16 Jan 2018 00 UTC

I notice the max winds in the northwesterly jet across the UK last night were over 170 knots at a number of stations. Here’s the 300 hPa chart for western Europe (fig 1), and here are the special points from the Castor Bay ascent in more detail (fig 2). At 43,425 feet the wind there was blowing 174 knots (200 mph) from 290°, very high, but not exceptionally so. Don’t you just miss the Stornoway ascent?

Figure 2

January sick and tired of you hanging on me…

Figure 1

No, it’s not my attempt to recreate the intro to “Dad’s Army”, it’s the approximate movement northwestward of a sheet of stratus across southern areas of the country this morning (fig 1). Yesterday’s clear skies are fast disappearing as the bank of cloud moves relentlessly northward, and a return to a dull and dreary January day that we know so well.

It’s a great shame that the anticyclone of yesterday didn’t stick around longer. I’ve got a feeling that we’ll be as sick and tired of January by the end of this month as Pilot where back in 1975.

There is a sharp inversion and associated sub-zero layer on this mornings 11 UTC ascent from the Herstmonceux ascent in Sussex (fig 2), at around 3,000 feet. In fact the ‘proper’ freezing level above is at almost 8,000 feet (fig 2). Low level winds are north of east, so maybe the stratus is forming as the result of moister air feeding in from the E’NE, rather than following the flow that I’ve indicated on the satellite image (fig 1).

Figure 2

Erie lake effect snow event

Figure 1 – Courtesy of the NWS

The 165 cm of snow (65.1″) that’s fallen on Erie Pennsylvania during the last few days does put into perspective the recent snowfall we’ve seen in the UK so far in December 2017. Here’s the BBC news report on the snow emergency that’s going on there right now in Erie.

The city of Erie does have a few advantages that we don’t often see in the UK during winter, and that’s copious amounts of very cold arctic air flowing directly from Arctic Canada, and being situated on the southern shores of Lake Erie in a howling northwesterly. These two things combine to produce a lake effect event and masses of snow in this part of the world, which according to the NWS has broken all previous records in Erie (fig 1).

Here’s the chart for 18 UTC on Christmas Day, I’ve inset the six hourly observations from Erie (fig 2). You’ll notice that the SYNOP from Erie International (WMO #72526) does not include snow depths as some other stations report. This is probably to do the severe drifting that must be going on with powdery snow in temperatures that have fallen from 0°C on the 23rd to -10°C today (28th December).

I would just love to know how they can manage to measure over 65″ of snow with any degree of accuracy when coupled with drifting. Perhaps they measure snow depth at regular intervals at a given spot, then clear it way or drop a board on top of the previous accumulation, before measuring it keeping an aggregate depth. That would be difficult to do because even with just a mean speed of 10 knots powdery snow like that would just blow right back in, and what about compaction over time?

Figure 2

The visible satellite image for December 27th shows how the very cold and dry air picks up moisture and instability in the west northwesterly flow of most of the Great Lakes (fig 3). Most lakes look clear of ice, and the comparatively warm lake surface temperatures must just generate continuous bands of snow showers. The lake effect has to affect other lakes other than Erie, I would have thought the eastern shores of lake Michigan would suffer just as badly  as the southern shores of lake Erie, but that never seems to make the news, perhaps it’s because the population is sparser and there are no large cities directly on the eastern shore line of Michigan, or maybe the water temperature is much lower and convection less explosive than over lake Erie.

Figure 3 – Courtesy of NOAA Worldview

Just doing a reality check here on that bit of rambling about the SST of Lakes Michigan and Erie (figs 4 & 5), and it turns out that Lake Michigan is considerably warmer than Lake Erie at the moment, so bang goes the increased convection due to higher SST’s in Erie theory!

Figure 4 – Courtesy of NOAA
Figure 5 – Courtesy of NOAA

So if the difference isn’t so much to do with the surface temperature of the two lakes, it must be that the air has picked up more extra moisture, and is generally just much more unstable over lake Erie that it is over lake Michigan further west. Here’s the 850 hPa upper air chart for yesterday (27 December 12 UTC) and the tephigram from the nearest location to Erie that I can find, which is  Buffalo (figs 6 & 7). It’s good to see that you can still get a good coverage of sonde stations in some parts of the world. End of rambling.

Figure 6 – 850 hPa chart for 12 UTC on the 27 December 2017
Figure 7 – Tephigram for Buffalo at 12 UTC on the 27 December 2017

Another interesting satellite image…

Figure 1 – Courtesy of NOAA Worldview

Another very interesting satellite image today with a good part of eastern Dartmoor stuck up above the low stratus that’s been plaguing much of the country this week. The NOAA visible image (fig 1) shows the island of high moorland up as well over Devon as well as the warming effect of the W’SW foehn over the Welsh mountains, and the clear skies to the lee of the high ground. Not only that, but there’s also the continuation of ship plumes that were visible yesterday of SW Ireland, today they are a number over the Celtic Sea and Cardigan bay. Here’s the flow outlined by streamlines in the 14 UTC plotted chart (fig 2).

Figure 2 – Streamlines

Here’s the 11 UTC Camborne ascent that shows the inversion up well at around 1900 feet (fig 3).

Figure 3

And here’s a bit more detailed look at the special points in the lower layers of the Camborne ascent (fig 4). The ascent was made a couple of hours before the satellite image, although having said that the hole has been there since sun-up. So all that I can imagine is that the air has dried out that bit more en route from Camborne to Dartmoor, and the inversion is a little lower to reveal so much of eastern Dartmoor.

Figure 4

The same foehn effect is producing even high temperatures than the 11°C we are seeing over east Wales at the moment, with parts of the Moray Firth reporting temperatures as high as 14.3°C at 15 UTC (fig 5).

Figure 5

Why did the Met Office ever close Stornoway?

As you go through life you come up with questions that seem so obvious that you wonder why no one has asked them before. One of them is why did the Met Office choose to close the radiosonde station at Stornoway on the Isle of Lewis?

This is the 300 hPa chart for midnight last night across our part of the world, and as you can see Stornoway is conspicuous by its absence (fig 1).

Figure 1

Scotland did have three strategically placed upper air stations for many years, they where:

  • 03005 – Lerwick
  • 03026 – Stornoway
  • 03170 – Shanwell

All but one now remain. Germany on the other hand since unification, has maintained a good coverage of upper air stations which is second to none. You would have thought that the NWP models would have loved to have the latest information from the eastern edge of the North Atlantic Ocean, in fact since Stornoway closed, you could argue that the NWP model initial analysis is a little less accurate in that very important area.

Of course upper wind and temperature nowadays are being gathered by satellite sensors in space and commercial jets that criss-cross the Atlantic, and the requirement for observations made by radiosondes are no longer that important, but if that thought was shared by the rest of the other European weather services, why haven’t they closed many of their upper air stations too?

I can’t pinpoint the exact date when Stornoway did close, but I think the observations swapped to automatic sometime in 2002, which probably marked the end of the radiosondes, although it may well have been earlier.

Recently the weather radar has undergone a refit on Lewis at great expense to someone. It does rather beg the question that if weather radar data is so important in that part of the world why isn’t upper air data as well?

Another possible option that was open to the Met Office was to relocate to RAF Lossiemouth in Moray, and continue from there as they did for many years with the ad hoc launching of boundary layer sondes at Kinloss. This would have provided the military forecasters there with more observational data with which to forecast for military fast jets and helicopter movements to the rigs in that part of the Moray Firth and North Sea, but that didn’t happen either.

I suppose it’ll just have to remain another one of life’s mysteries why anyone in their right minds would ever close Stornoway, known only to the powers that be down here in Exeter.