Figure 1 – Courtesy of the BBC and Twitter
I find it almost impossible to access a BBC weather forecast from the previous day on the BBC iPlayer. If I wasn’t such a trusting person, I would say that it’s to prevent people like me reminding them of a poor forecast. It’s similar in a way to the reluctance of the Met Office to archive the warnings that they issue, presumably this is to prevent any possible future litigation against them. It seems that the BBC presenters accepted the minimum temperatures from the model for Sunday night, even after it got things wrong on Saturday night for the very same reason, too much wind and cloud, particularly in eastern regions. I wonder if in the state-of-the-art graphics engine that MeteoGroup are poised to introduce will allow the presenter to edit these values?
The forecast temperature extremes across the UK are quite important to the Met Office, they are used at a selected number of places as a metric to calculate their annual bonus. If I remember correctly, they get full marks in verification if the forecast is within +/- 2°C of the actual value. Presumably, they will now use the temperatures that they publicise in their National video forecast, rather than the one that will eventually be provided by MeteoGroup for the BBC, from whatever model they choose to use.
Figure 1 – Courtesy of Twitter & BBC Weather
The graphic that the BBC Weather team used in their tweet this morning (fig 1), is of yesterday evenings forecast minimum temperatures for rural places at dawn. If you compare these spot values with the actual minimum temperatures [18-06] from the SYNOPs (fig 2), you’ll see that they’re pretty wide of the mark for many places, but especially so across England, as overnight temperatures were held up in many places by a combination of too much wind and too much cloud. As an example, minimum temperatures in the Vale of York were forecast to be around 2°C, but were actually around 9°C, the ever reliable cold spot of Exeter Airport was forecast to have been 4°C but was over 7°C, southern Scotland was forecast to have been 1°C, but Eskdalemuir could only manage a minimum of 7.3°C.
Initially I did think this cloud and rain was down to one of those magical troughs that suddenly appear in the analysis, and which run parallel with the isobars, but surprisingly, and rarely, the British isles were free of any frontal structures on the midnight analysis (fig 3). It’s quite obvious though, that this week the Met Office mesoscale model has never quite got to grips with the showery northerly airstream left behind in the wake of storm Aileen, and has performed very poorly, both in the handling of convection, and the subsequent forecasting of overnight minimum temperatures, due to the cloud, showers and wind associated with these features.
Figure 3 – Courtesy of Wetterzentrale
I think the person that handles the tweets for BBC Weather ought to be a little more careful, that the graphics used in any tweet are factual, and not as much as 7°C colder than they were in reality. The weather has a way of catching you out if you don’t continuously monitor it, and overly rely on a model that seems to be having one of its heads this week.
I can’t see much wrong with the forecast charts from either the UKMO or the GFS (figs 2 & 3) when compared with the 00 UTC plotted chart for 13th. It may have been that there was not just enough oomph in Aileen to produce more of an impact, or maybe the explosive development started just a little bit too late and further east. Having said that pressure did fall by around 20 hPa across northern England in 10 hours during Tuesday afternoon and Evening.
The GFS model was correct when it had the tightest gradient from storm Sebastian at midnight tonight further south, across most of England and Wales south of 54° north. It’s a subtle change between todays T+24 (fig 1) and yesterdays T+48 from the Met Office (fig 2).
Here’s the latest GFS solution, with the tightest gradient at midnight south of 53° north.
The low being a little further south of course changes the position of the occlusion, and the area that will see the heaviest of the rain. That yellow warning for heavy rain has now been moved south and extended (fig 4).
Figure 4 – Courtesy of the Met Office
The only thing left that they have to do now is to extend the area of strongest winds further south, Oh I nearly forgot, and decide if they should call it Aileen or leave it at Sebastian. In light of recent tropical cyclone activities, and not wanting to cause any mass panic amongst the populace, naming it Aileen seems unlikely now, but what if Sebastian has more fire in its belly than they think?
I see that the Met Office have just issued a yellow warnings for strong winds for Monday across the southwest of England, but the gradient on Tuesday evening when the next low breezes in looks even tighter in the latest GFS model run, maybe this is storm Aileen, and the first storm of the 2017-18 season?
If anything the Met Office model seems to have the low (981 hPa) a little more intense and deeper than the ~984 hPa of the GFS.
Apologies for the title of this one, but I thought that I would get in before the Daily Express did!
The Met Office online video forecasts are a great idea, but the ’10 Day Trend’ they publish on YouTube hardly lives up to its name as the latest forecast chart they show in it is for next Tuesday, and that’s only 5 days from now (fig 1). They do of course have NWP forecast charts that go beyond T+120, but thankfully, the Americans do generously publish the output from their GFS model, and here’s a look at the output from it for next week (fig 2).
I am still mystified at the disparity between the forecast charts from the GFS (fig 2) and the headline in the Met Office video (fig 1). The chart for next Thursday from the GFS looks quite ominous with a very tight gradient across the whole country, with gales over coasts and hills, and I hardly think that ‘windy at times’ really does it justice.
Because of the Met Office’s refusal to publish forecast charts beyond T+120, the only thing that you do is imagine that their model don’t generate as intense a depression as the GFS model does for next week. I watch with interest to see if there are in fact gales next Wednesday and Thursday, or if the ‘perhaps drier later’ promise in the video, turns out to be correct.
Early tomorrow morning a finger of rain will push up across the southwest of England extending northeast towards Lincolnshire, that’s according to the latest GFS forecast run (fig 1). What exactly this feature is that will introduce this area of rain across the south isn’t that easy to fathom, but according to the T+36 forecast chart from the Met Office it’s an upper cold front (fig 2).
What it does mean that tomorrow looks like being a wet day for a good part of the south and southeast of England, and it won’t be overly warm either, because the dashed line in the chart across west Wales, is the 546 dm thickness line, as a cold trough pushes into western areas. This will come as quite a shock to people in London and the southeast, where temperatures today have been around 26° C, tomorrow in stark contrast they may be more than 12°C lower in places once the rain has set in.
Earlier this week I was spouting on about how ex-hurricane Gert would usher in a change of type and that by the end of next week summer would have made a home back. That was on Thursday, but the latest guidance from the NWP models suggest that once the low (that was the remains of ex-hurricane Gert) has finally struggled to cross the country, which looks like it will take most of the week, things will have changed very little, and mobility will be resumed after just a brief incursion of warm and humid air from the continent for a couple of days at the start of next week. Having said that, I did hear on the BBC weather that the models are having a torrid time on what effect Gert will have on the forecast for later this weekend, but looking at the latest run from the GFS and the UKMO models, their solutions for Monday do look remarkably similar (fig 1 & 2).
Figure 1 – Courtesy of the BBC (Spotlight 6.55 pm on the 17 August 2017)
Today’s showers were a lot sharper than forecast by the Met Office model that was used in the BBC forecast on Spotlight yesterday evening (fig 1), with some white pixels in the weather radar, indicating intensities of >32 mm an hour (fig 2). Thankfully they were moving quickly.
Neither was there any mention in the forecast of any thunderstorms in any of today’s showers over the southwest of England (fig 3).
Figure 3 – Courtesy of Blitzortung
Just checking to see how they did on last nights national forecast, and again no mention of any thunderstorms (and any flashing lightning graphics), or of the intense showers indicated by the weather radar. All Darren Bett seem to be interested in was saying how cool it will be, he must have been out of the country for the last four weeks or so. All I can think is that the new Met Office model is having problem in convective situations like this, I am assuming of course that the BBC are still using Met Office NWP data at the moment!
Figure 4 – Courtesy of the BBC (weather for the week ahead)
Or did they mention this large area of very heavy rain in the afternoon over Wales in earlier forecasts. Is it only me that notices just how poor the weather forecast was?