Numerical Weather Prediction
A method of weather forecasting that employs :
A set of equations that describe the flow of fluids, which is translated into computer code, combined with parameterizations of other processes, then applied on a specific domain, and integrated, based on initial conditions and conditions at the domains boundaries
The ECMWF model being used for the BBC forecast by MeteoGroup is not really handling the sea fog that’s rolling into west of Cornwall and along the north coast of Devon too well this morning (fig 1). The UKMO model has at least captured something in the way of cloud across the southwest, what exactly it is in looking at the graphics is a little bit harder to work out, is it cirrus, or stratus or just sea fog? Alex Deakin doesn’t seem overly concerned about it though, he says that’ll it be “just some of these western coasts that may stay a little murky”.
I’ve been watching this fog and low stratus as it rolls in across the southwest and it’s moving quite smartly to say there’s very little gradient (fig 2). I just wonder how much further east it will progress during the rest of the day as well as how far inland it’ll make it.
In the national forecast just after the main BBC news the graphics looked very similar to the ones used during the morning, but in the regional forecast at 1.40 pm it appeared as if they had updated the model which gave a much more realistic fit with the satellite image (fig 3). Ben Rich was too busy demonstrating how proficient he is with the count-up method (you know the one – “temperatures reaching 24 or 25 quite widely, and maybe even a 26 or 27 and possibly a 28 or 29 in one or two spots”) to even be bothered to show any detail of low cloud in the southwest.
Another classic series of forecast charts from the Met Office this morning with another front that refuses to die (fig 1). The front in question tried to cross the country yesterday as a cold front, and at the moment is returning northward as a warm front pushed northward by continental air. It’s set to make another attempt to introduce cooler Atlantic air on Thursday and Friday as it undergoes frontolysis. This front seems likely to become a real fly in the ointment in the next few days, forecast to be sprawled through the heart of an anticylcone by Saturday and spoil the first decent spell of weather we’ve had this spring.
I must admit that models seem to have handled the clearance northward of the cloud from that frontal system extremely well (fig 2) from what I could see looking through the Velux windows in our attic bedroom this morning!
All sorts of problems in forecasting the exact position and the extent of low cloud across the country this morning. This is nothing new of course and must be the bane of most NWP models in slack situations like this. Both the UKMO and the ECMWF models (if that’s the one MeteoGroup are currently using) have a poor grasp of low cloud at 09 UTC as you can see by this mornings visible satellite image, and don’t forget these graphics are probably from the 06 UTC model run so the forecast’s are no more than three hours in the future (fig 1). In the 1980’s the word nowcasting was coined to describe these short-term forecasts, but it looks like low cloud in situations like this are proving difficult to keep track of.
You may have noticed that I’m fixated at the moment in examining and comparing the forecast output from the UKMO and the ECMWF models, by grabbing screen shots of the MeteoGroup forecast on BBC 1, and the Met Office video forecast from their website. Why do I do this? Perhaps it’s out of sheer frustration, knowing that although we indirectly pay for both of these institutions, we see output from either model in any detail except by snatching screen shots. I’m so glad that MeteoGroup did win the BBC contract because it does help in highlighting the differences and shortcomings of both models.
Yes it’s official, it looks likely that Thursday and Friday of next week may well be on the warm side for April (fig 2). But there’s nothing unusual about warm days in Spring, and someone should tell the media to cool down and not get so excited (fig 1), because after all spring did spring over six weeks ago according to their definition.
The hype you get these days from the NWP soothsayers is getting to almost biblical proportions. In the winter they are the same people who’ll tell you with great delight that the cold snap that hasn’t even started yet, will only last a couple of days. Well two can play at that game, because it saddens me to report that it looks likely that this weeks warmth may also be fleeting!
The Met Office make it three in a row, with an 8-5 win over Meteogroup on today’s maximum temperatures. On the strength of the last three days the ECMWF seem to over-estimate afternoon temperatures, although I still can’t manage to get them to agree on when to report them in either of their forecast graphics. Today I had to use the ITV graphics for the Met Office forecast because the Met Office are so darn quick at deleting any evidence in their early morning forecast. I’m going to have to find a better way that this to verify their forecasts…
It’s difficult to pin these two organisations down when it comes to verifying just how accurate their maximum temperature forecasts are. But the Met Office model is already one up after yesterday, so I thought I’d just see how they did today.
Here are the actual temperatures at 1600 BST today which I mark 76% to the Met Office. The forecast for London was really dreadful from both models, obviously they expected the stratus to clear but it didn’t. I can’t understand why MeteoGroup have labels for both Glasgow and Edinburgh, but only one temperature, and for which city it’s for. If anything MeteoGroup should have had the edge because the actual and forecast temperatures are both for 1600 BST, but that didn’t stop the Met Office taking a two nil lead.
It wasn’t only temperature that caught out both the Met Office and MeteoGroup today, there was also an area of heavy rainfall that extended across Humberside into Yorkshire during the afternoon that escaped both models. I watched the rolling news on the BBC news during the afternoon and I think even worse than the poor forecast was that the presenter never seemed to noticed that it was happening at all, let alone bothering mention it or show a real-time weather radar image. It reminded me of the taped forecast given by Michael Fish as the Boscastle flash floods was in progress in 2004. I can’t see why the Met Office have bothered to update their weather radar network when no one seems to look at it. Here’s the BBC forecast for the east Midland’s from yesterday evening (fig 2).
I’ve been trying to compare forecast temperatures from the Met Office and MeteoGroup to see which NWP model was the more accurate. Here are their forecasts for yesterday (fig 1).
As you can see they use a more or less common set of major cities across the UK which helps. On Twitter the Met Office seem to prefer labelling the 1400 temperature rather than the 1600 temperature as the BBC do, so a direct comparison is difficult. It might be a little easier if both of them displayed a much more useful maximum temperature [06-18] for the day, but that would never do would it? I noticed that in their video forecast for today, the Met Office had switched to labelling temperatures at 1500, although I can’t seem to figure out where that 11°C label is for in this mornings (fig 2).
As you know daytime temperatures are notoriously difficult to forecast with variable cloud at anytime of the year, but especially so in spring with breezes of cold seas, and as you can see there were was a large range in forecast temperatures from the two models for yesterday. Here are the actual air temperatures for 1500 BST for comparison purposes (fig 3).
Despite the timing differences I mentioned above, I make it that as far as yesterday goes, the Met Office forecast temperature was closer to the actual temperature (at 1500 BST) than was the MeteoGroup forecast at 60% of the 14 city sites. Of course I need to put in quite a bit of work over a longer period to see which model is the more accurate.
A lovely solar halo this morning here in mid-Devon which is the old weather lore precursor for rain in 6 to 9 hours, so I’m curious about just how fast the rain will spread across the southwest of England this afternoon, so here are the latest forecasts as of 09 UTC this Easter Sunday morning as a reminder.
Well all the models were much too slow in bringing the rain northeast across the southwest peninsula, and the BBC and Met Office forecasts weren’t much better either. If you look at the 15 UTC weather radar the rain had extended as far as Somerset (fig 2), nothing spectacularly wrong perhaps, only out by a couple of hours or so, but the various forecasts that I took a snapshot of (fig 1) were only for six hours ahead and should have been spot on. At least the old weather saying about solar halos still works!
Not a lot going on at the moment weather wise across the British Isles, but hopefully it should brighten up in many places today from the west on the passage of this frontal system (fig 1). I did notice that there’s been another minor SSW event that looks to have occurred just before the equinox (fig 2).
That, along with some wild NWP output, is what probably led to all those stories of a snowy Easter, stories which now seem to have been summarily dropped like a hot potato. Having said that the models do take each successive Atlantic low a little further south into Biscay as the week progresses leaving the country in an easterly, anticyclonic in the north and cyclonic in the south, so it look’s odds on that’ll it will be a cold Easter (fig 3).