If you examine the forecast chart for tomorrow and next Sunday, you might be forgiven for thinking there is something of a weekly cycle going on here (fig 1), both days are northerly, in fact next Sunday is a cyclonic northerly worthy of any cold spell in winter worth it’s salt. And if you look back over the last two weeks (fig 2), you’ll notice that both the 29th of October and the 5th of November had northerly tendencies too.
Figure 2 – Courtesy of the Met Office
Of course it’s all just chance, but just out of scientific curiosity, I’ll be keeping a close eye on the weather pattern for next Sunday, just to see if we can manage four successive northerly Sunday’s.
- 29th October [N]
- 5th November [N/NW]
- 12th November [N] (forecast T+24 but odds on)
- 19th November [CN] (forecast T+192)
Well a distinct centre never formed on the low as it crossed the UK, and it behaved just as the models had forecast it would. Overnight rainfall was generally in the range of 16-32 mm in the wettest areas in the west (fig 1), but there’s still more rain to come through the rest of today, and in the very same areas, as ex-tropical storm Rina scoots by on her way to le continent during the evening. Looking a little further ahead, Sunday night looks likely to be frosty down here in the southwest of England as the northwesterly eventually dies down.
Figure 1 – Data courtesy of the NHC (approximate GFS positions from the 00 UTC 10 November model run)
I wondered what was holding up the cold front clearance on Saturday across southwestern parts of England (fig 2), but then I noticed on the Berlin Meteorological Institutes website, that the second shallow low the follows behind the low that tracks WNW- ESE across Ireland, Wales and the southeast of England during Saturday morning, was labeled ex-tropical storm Rina (fig 1). The Met Office of course are having none of that because it wouldn’t be correct would it.
Will Rina be the finale of the Atlantic hurricane season?
The last advisory on Rina highlighted what had been yet another rather unusual tropical cyclone in 2017 (fig 3):
Figure 3 – Courtesy of the NHC
Rina lives on in Europe
Interestingly, that rather shallow low which was Rina was when it crosses the UK is forecast to develop into quite a deep low of 991 hPa by 12 UTC on Sunday, as it tracks southeast across the Alps into the northern Adriatic, and quite a significant feature in that part of Europe (fig 4).
Figure 4 – Courtesy of the Met Office
Yellow Warning for rain?
Even more interestingly, so far the Met Office haven’t issued any yellow warnings for heavy rain in southwestern parts during Saturday. I just wondered if the tropical origins of the air might even enhance the rainfall in theses parts.
The BBC news report that a temporary weather station has been installed on the summit of Ben Nevis this Autumn, this is 113 years after the original weather observatory which commenced observations in 1884 closed in 1904.
The AWS looks suspiciously like a Vaisala Weatherhawk (Vaisala WXT536) something I’ve always wanted to replace my aging Vantage Pro with, but something we simply can’t afford my wife says. It stands just a few metres from the summit cairn on what looks like a six metre mast with two huge solar panels bolted on it to provide the power. It looks like the whole thing is a publicity stunt funded by the NCAS and Leeds University to help get a permanent weather station for Britain’s highest mountain. I’ve hunted around on their site, but can’t find any of the data that its reporting. In all honesty it will be little different from the readings that we see from the SIESAWS stations on nearby Aonach Mor (1130* M) or Cairngorm (1237* M) to the east, but then again 108 metres does equates to being 354 feet higher I suppose.
Powering the AWS
The big problem is getting mains power up to the top of the Ben would be very difficult. Even if they dug up the entire tourist route and paved it at the same time, burying the mains cable under it as they did it. No one would want to put pylons up it and scar the whole mountain, the objection let alone the cost would be enormous. Solar power from solar cells might be the best answer, but the Ben is so often cloud covered, and in winter the amount of sunlight those panel would receive would be very small indeed. I shouldn’t think that the transmitter or the sensors would require that much power, but the heating of the anemometer to keep it free of riming would be enormous, and this would be required for at least 75% of the year at a guess. That’s probably why the weather station is being removed in December, I doubt that the temporary structure they have in place at the moment is up to seeing a winter out at 1345 M, the force of wind on those two solar panels must be enormous, and I suspect that if they didn’t take it down it would be blown down anyway.
I wrote an article earlier this week about the fact that there are two weather stations on Cairngorm, one owned and run by Heriot-Watt university and the other by the Met Office. Wouldn’t it be sensible if Heriot-Watt and NCAS collaborate with one another and move the existing one on Cairngorm (the one that pops up out of a protective can twice every hour) and relocate it to the old observatory ruins on top of Ben Nevis? Of course this doesn’t get round the crucial power problem, which short of installing some kind of small nuclear power cell might always be the problem. They must have power on Cairngorm to run both weather stations, but because it’s close by the ski slopes there is power to the Ptarmigan restaurant at the top of the funicular railway less than a kilometre away. It must have been a tough job but someone must have buried an armored power cable right to the rocky top of Cairngorm to provide power for those weather stations, and did a pretty good job of disguising it because I never saw any sign of them – that maybe the way to go on Ben Nevis?
Addendum:- After a little investigation the prices for the Weatherhawk don’t look as expensive as they were a just a few years ago.
The latest run of the GFS model (fig 1) has sided with the UKMO model (fig 2) and decided not intensify the low that runs across Central England on Saturday. It still looks a thoroughly wet day though, especially across the west of Wales and the southwest of England though, with a westerly gale along the English Channel, if this latest forecast is correct (fig 1). Sunday looks a windy day with strong northwesterly winds particularly down the east coast of England and Scotland, with wintry showers down to quite low levels in the northeast of Scotland I would fancy.
Figure 2 – Courtesy of the Met Office.
I wonder if the enhanced troughing in the GFS solution will be justified, the Met Office have little troughing on the cold front in their solution.
Figure 1 – Courtesy of OGIMET
The latest GFS model run is looking very windy across southern areas early on Saturday. The GFS model has been running a shallow low across northern areas for the last five days or so but never made a lot of it. The latest midnight run though has deepened the feature more than those previous runs, and I should imagine it’s now a candidate to be added to the “one we will be keeping a close eye on” category.
There are still a good many places that haven’t seen an air frost this Autumn (fig 1), but only a few who have escaped a ground frost (fig 2). I notice that there is a spurious -9.8°C in those SYNOP figures from Cork so ignore that. Tibbenham in Norfolk is also an incomplete record which I haven’t filtered out. I’m a little suspicious of the two ground frosts for Jersey airport, but they do in fact check out. How an island can have ground frosts, and stations on the mainland can’t, looks very suspicious, all that I can think is not all of the French stations report minimum temperatures at 06 UTC.
The earliest air frost I see was reported by Redesdale Camp on the 19th of September, I don’t seem to collate the earliest ground frost for some reason, perhaps I was having a bad day when I wrote this app.
Figure 1 – Courtesy of the BBC
There are numerous problems that I see with this approach to forecasting the overnight minimum temperature that David Braine uses quite regularly in the weather forecast on BBC southwest, and last night’s forecast he gave was a case in point (fig 1):
- The colour contoured temperatures are invariably at odds with the individual spot values.
- You never know the exact location of any of the spot values, for instance is the 8 for Sennen or the 1 for Sherborne?
- Are the temperatures from two separate models, and why are they usually so different and misleading?
- I know that we live on a peninsula down here in the southwest, but why are 6 out of the 8 spot values at coastal site?
I have a theory that the colour contours show the minimum temperature for the overnight period, and the spot values are the forecast temperature, in this case for 05 UTC even though the minimum will occur close to dawn. If what I believe is the case the solution looks simple.
- Never combine the extreme colour contoured temperatures for a period with spot values for a fixed time.
- Instead of using spot values for a fixed time pick out temperatures for towns and cities from the colour contoured value.
- Use slightly higher resolution data and finer contours to highlight the differences between valleys and moorland. In Anticyclonic situations the valleys will be much colder that the hills.
- Zoom in a lot more, and pan from west to east, at least 75% of the area in the forecast for the southwest is the open sea!
Here for the record are last nights minimum temperatures from 1800 to 0600 UTC (fig 2).
Running rainfall totals for the last 12 months are still a little low across southern areas of England and Wales (fig 1), although there has been a recent sharp upturn from the anomalies of earlier this year. The running total for southwest England and Wales for instance had dropped to 82% of the long-term average in late June, but have now bounced back up to 94.3% (fig 2). This data is from the gridded daily regional series maintained by the Met Office that extends back to 1931.
I don’t know how long it will persist for, but there’s some interesting line convection (squall line) associated with the cold front that’s just clearing the extreme west of Wales and Cornwall first thing this morning.