Saturday night’s low

Figure 1 – Courtesy of www.wxcharts.eu

I wonder if Met Éireann will end up naming the low that runs across Northern Ireland later on Saturday? It looks like the Met Office are more concerned about the snow from it over SE Scotland and NE England. This low is not hanging about though, so I can’t see that being a big problem. The latest GFS run does have the low undergoing rapid cyclogenesis, deepening by 30 hPa by the time we get to 06 UTC on Sunday morning (fig 1), and more markedly than do the UKMO in their latest forecast charts (fig 2).

UKMO Chief Forecaster’s assessment

Rain and hill snow, accompanied by some strong winds, is expected through Saturday evening, clearing eastwards overnight. Above around 200 metres, 2-5 cm of snow may accumulate although there is a small chance of 5-10 cm falling over the Southern Uplands. As skies clear from the west overnight into Sunday morning, ice is expected to form on any untreated surfaces“.

Figure 2 – Courtesy of the Met Office

Interesting night ahead as low Friederike scoots eastward

Figure 1 – Courtesy of www.wxcharts.eu

The Met Office have a veritable smorgasbord of warnings in place at the moment that should just about cover any meteorological eventuality, as the deepening low Friederike tracks across Ireland and northern England on latitude 54° north later tonight. Friederike may not be as intense a feature as it was at T+66 (when I said it was a sure-fired be to get named Fionn oops!) but it still exceeds the criteria for explosive cyclogenesis, because at midnight it was 1010 hPa west of Nova Scotia and just 24 hours later according to the latest GFS run it should be 983 hPa and still deepening (fig 1).

The Met Office are still playing it cool and have issued a yellow warning for strong winds, choosing to the old 50-60 mph gust ploy with a small chance of gusts to 70 mph (fig 2). Those winds combined with snow on higher ground might make the cross Pennine routes a little bit tricky overnight! They don’t start the warning till after midnight 0005 UTC (why don’t they ever use 0000 UTC?) which seems a little bit late to me. The W’SW gradient is already cranking up across west Wales and the southwest by 21 UTC. All I can think is that the UKMO model might be slower than the GFS is with Friederike. It looks like the strongest gusts may well come as the winds veer northwesterly as the low transits east.

Figure 2 – Courtesy of the Met Office

The latest on a possible Fionn

Image 1 – Courtesy of www.wxcharts.eu
Figure 2 – Courtesy of www.wxcharts.eu
Figure 3 – Courtesy of www.wxcharts.eu (Latest)

The latest 00 UTC GFS run (fig 3) has a very similar solution to yesterday’s 12 UTC run (fig 2) and a less intense depression across the Irish Sea than in earlier runs and less tight gradient over northern England (fig 1). It will be interesting to see which weather service names this one first, or even if this low is christened at all. The latest forecast chart I can find from big brother shows little change from the earlier T+72, with the culprit low just of the Ayrshire coast (fig 4) at 00 UTC on Thursday.

Figure 4 – Courtesy of the Met Office

Storm Fionn

Image 1 – Courtesy of www.wxcharts.eu

The GFS (fig 1) and the UKMO models (fig 2) are in broad agreement about the position and intensity of storm Fionn at 00 UTC on Thursday. I say storm Fionn because this must be a sure-fire bet now, and probably the weather community’s worst kept secret. I wonder if Met Éireann will nip it and name it before the UKMO does because it looks like so far this season they seem to be taking it in turns.

Figure 2 – Courtesy of UKMO

From the limited NWP data that I can access from the Met Office it seems the track in this T+72 is much further north than in the earlier run. They’ve also shortened the 1000 km bent back occlusion they had in that run, and it with this feature that the strongest gusts occur in storm Fionn. If the GFS is to believed, the strongest winds will be in a swathe across Northern Ireland and northern England. A rough calculation makes the speed the lows moving eastward at around 50 knots, so it’ll be all over by dawn on Thursday. I see the Met Office have an early warning of strong winds in place for Thursday for the whole country south of 56° north, but no word yet about whether it will be named Fionn. Isn’t NWP just wonderful and a marvel of science, allowing us to speculate about severe gales from a low that doesn’t even exist yet.

This weeks explosive cyclogenesis

Figure 1

Another cyclogenetic episode this week as it looks quite likely that storm Fionn will rush eastward across central Scotland from the Atlantic at around 60 knots if the latest forecast from the GFS is correct. If I’ve done my calculations right, the low will have moved 2,678 km and deepened by 36 hPa in the 24 hours ending  at 06 UTC on Thursday – so it’s not hanging around!

Figure 2 – Courtesy of the Met Office

From the only relevant forecast chart I can find from the Met Office (fig 2), it looks like they track the low further south at 52° rather than 56° north, which I can only imagine would impact even more of the population. The question I have about that particular forecast chart is how come a low that’s only 24 hours old has a bent back occlusion wrapped around the length of that one?

Forecast of -14°C from the Met Office a little on the low side

Figure 1 – Courtesy of Twitter and the Met Office

Yesterday afternoon the Met Office were promising the coldest night since February 2012 (fig 1) when they said on Twitter:-

“Temps in rural parts of Scotland could fall as low as -14 or -15 °C tonight, which would make it the UK’s coldest night since 11 February 2012, almost 6 years ago! High pressure will bring clear & calm conditions and is dragging cold arctic air from the north”

Unfortunately, the low cloud of yesterday evening didn’t finally clear till towards midnight, neither was it ever  perfectly calm, and with only a patchy or thin cover of snow, the air temperature never got down as low as the -14°C that was promised.

In the end after trawling through all climate reports from sites which they like to keep to themselves, they did manage to find a -9.1°C at Dalwhinnie, just down the A9 from Aviemore (fig 2). The model does have problems, the -9°C instead of -15°C is just a symptom, it mishandled the overnight forecast of low cloud, surface wind, and probably the whole pressure field.

Figure 2 – Courtesy of Twitter and the Met Office

For the rest of us poor mortals who have to rely on the kindness of a man in Barcelona and his OGIMET website, here are the coldest spots from the SYNOP reports (fig 3). As you can see the other forecast temperatures outwith the Highlands of Scotland were much more accurate, except for southern areas and across East Anglia, where the strength of the wind prevented an air frost.

Figure 3
How did the BBC do?

The BBC who presumably use the same model data as the Met Office, almost got it almost right with a -10°C minimum (fig 4). I don’t know what they were thinking with a -4°C for the Western Isles and a -3°C for the Northern Isles though.

Figure 4

At one time the Met Office would have been just content in announcing the coldest night for six years after it had happened. But now because of the pressures of social media and to maintain their corporate image, they feel they must announce it before it does. This faux pas is certainly not on the same scale as the barbecue summer forecast was, and probably will go unnoticed by the vast majority of people anyway.

Overnight ice in southwest poorly forecast

Figure 1 – Courtesy of BBC Spotlight (6.55PM)

Here’s the forecast 04 UTC temperatures from the BBC (fig 1) in what constitutes the overnight minimum chart from yesterday evening’s news. As you can see the model colour contoured NWP temperatures have been totally ignored, and labels for much warmer temperatures of “towns and cities” overlaid on top. To me this is totally misleading to any viewer, but the BBC weather presenters continually to do this, ignoring the fact that Exeter airport is one of top UK cold spots, and last night it caught them out again (fig 2), with temperatures dipping to -3.5°C. Even sites closer to the sea such as Plymouth and Culdrose saw a slight touch of frost – their first of the Autumn or Winter.

Figure 2

Unusually the Met Office did respond with a very belated yellow warning of ice for the southwest at 0637 UTC (fig 3), no doubt when they heard about some road accident caused by the rain from yesterday’s showers freezing on roads across Devon and Cornwall.

Figure 3 – Courtesy of the Met Office

There was really no excuse for the lateness of this warning, especially when the Met Office HQ lies just a mile or so west of the airport. They obviously have to follow a process to cover themselves from any possible repercussions from accidents and injuries caused by icy roads and pavements, the only problem is that it came at least 12 hours too late! Temperatures at the airport were already -2°C at 23 UTC yesterday evening so there really was little excuse (fig 4).

Figure 4

They didn’t do too well in the National forecast either, although Darren Bett did say that “cloud might be a bit more unreliable in central areas and that there might be a touch of frost” there (fig 5). I’m not sure if the -3.6° C at Pershore can be regarded as a “touch of frost” though.

Figure 5 courtesy of the BBC (6.30PM)
What went wrong?

I think that the Met Office model, especially across the southwest, just kept producing too much in the way of cloud and showers for much of the night (fig 6) which just didn’t materialise, from looking at the weather radar. I would love to grab some forecast NWP evidence from the UKMO mesoscale model to back that up, but of course that’s on a need-to-know basis, and I don’t need to know!

Figure 6 – Courtesy of BBC Spotlight (6.55PM)