A tale of too lows

Figure 1 – Courtesy of the Met Office

It seems to me to be a tale of two lows, tonight’s rather interestingly, some may say bizarrely, hasn’t attracted any warnings for heavy rain so far from the Met Office (fig 1), but they have already issued an early warning for the possibilities of heavy rain for the low that will affect southeast England later on Sunday. Depending on what NWP model you look at the accumulations for Friday don’t look particularly that heavy (fig 2), but I wouldn’t have thought it would have hurt to have issued a blanket yellow warning for southern and central areas for 15 to 25 mm locally 40 mm, but what do I know. I suppose they still have time to do it but it’s cutting it a bit fine.

Figure 2 – Courtesy of www.wxcharts.eu

Tomorrow’s low

Figure 1 – GFS (1) ECMWF (2) UKMO (3)

It’s interesting to see how the three main NWP models handle tomorrows low and the heavy rain it introduces across the country (fig 1). The Met Office take the main thrust of the rain north into Ireland, whilst the GFS and the ECMWF are in no doubt that the action will be centred much further east over southwest Wales. I think the UKMO model looks out of step with the other models on this one, time will tell.

One of the tricks of the trade as a weather presenter when you want to be as vague as possible about the timing of rainfall events like this, is to leave of the exact time in the graphics, so it’s good to see that Aidan McGivern has picked this one up and is now ready to move on to the next chapter (fig 2).

Figure 2 – BBC (1) Met Office (2)

As well as this cyclonic development on Friday another low threatens to spoil the weather in the southeast of England during Sunday. It’s amazing just how the weather likes to dish out bad weather in as fair a manner as possible isn’t it?

Another cold end to a month looms

Figure 1 – Courtesy of www.wxcharts.eu

It seems that we have been caught in a cycle of cold end to months recently. First there was February, then March and now April. That’s according to the latest run of the GFS model, which indicates that the end of April and beginning of May will be changeable and often cyclonic, with winds in the east or northeast, the anomalous warm start to spring of last week will have retreated to the continent, but even here the warm air will be gradually pushed back further east.

Figure 2 – Courtesy of the Met Office

The overnight thunderstorms

Figure 1 – Courtesy of Blitzortung

Here are a few graphics to show the extent of this early thundery spell across the country, the severity and extent of which caught both the ECMWF and the UKMO NWP models out yesterday. As far as I can see most of the lightning was from unstable medium level cloud rather than the more traditional cumulonimbus (fig 1). The rainfall from the thunderstorms looks to have been concentrated in a swathe SSW-NNE through Hampshire, where my estimates from weather radar suggest that as much as 32-40 mm fell in the wettest areas (fig 2).

Figure 2
Figure 3 – None of the rain gauges where in the right places, where was Southampton Weather Centre when you needed it?

I won’t go on about just how poor or late the warnings were for yesterdays thunderstorms from the Met Office, or just how divorced the NWP graphics used by either themselves or the BBC was from reality, the following screen shots will have to suffice (fig 4).

Figure 4 – Courtesy of the Met Office (1&2), Blitzortung (3) and the BBC (4).

“Just some of these western coasts may stay a little murky…”

Image 1 – Courtesy of the BBC (upper) and the Met Office (lower)

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”.

Figure 2

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.

Addendum
Figure 3 – Courtesy of the BBC

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.

Frontolysis and the front that refuses to die…

Figure 1 – Courtesy of the Met Office

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!

Figure 2

Nowcasting and the problem of forecasting low cloud

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.

Figure 1 – Met Office forecast – Visible Satellite – BBC forecast

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.

A lot of hot air over next weeks warmth

Figure 1 – Courtesy of the BBC

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.

Figure 2 – Courtesy of www.wxcharts.eu

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!

Met Office make it three in a row

Figure 1 Courtesy of  BBC/ITV/Actual

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…