Exeter coldest overnight

Figure 1

Coldest low-level station in the UK was Exeter airport last night, with a 18-06 minimum of -3.7°C (fig 1). The BBC were woefully out in last nights forecast for what is a notorious cold spot (fig 2).

Figure 2 – Courtesy of the BBC

Curious thermograph for Exeter airport though (fig 3), all I can see from the hourly SYNOPs is that the wind must have freshened up at 05 UTC otherwise the frost might have been more severe.

Figure 3

The house that Jack built

This is the purpose-designed house that Jack built.
This is the Cray XC40 supercomputer that cost £97 million, has 1.6 petabytes of memory and runs over 16 trillion calculations per second that sits in the purpose-designed house that Jack built
This is the sophisticated NWP model, that runs on the Cray XC40 supercomputer, that sits in the purpose-built house that Jack built
This is the last night’s forecast produced by the sophisticated NWP model, that runs on the supercomputer, that sits in the purpose-built house that Jack built.
These are the actual temperatures for 04 UTC close to the house that Jack built.

In my reworking of the old nursery rhyme, Jack is of course synonymous with the Met Office, if you’ve not already guessed! What I’m trying to say I suppose is this:

You may have the fastest and the most accurate forecast model in the world, but if you can’t visualise what the model is telling you, then you may be just wasting your time.

These NWP  models generate so much highly detailed forecast data, a lot of which forecasters can’t possibly assimilate, and getting the salient facts about the weather across to the public, such as the overnight minimum temperatures seems to elude them. Compare the forecast temperatures in the graphic from the BBC with the actual temperatures at 04 UTC this morning, and you will notice that they are around 3°C too high in most of Devon. It makes no difference that the Cray XC40 supercomputer is located just 2.26 km to the west of the airport, and even though the mesoscale output from the model may have correctly forecast the temperature at 04 UTC, the BBC graphics are still wrong.

Some may argue that the temperature that the BBC show are for “towns and cities”, but that to me is just a clever get out on their part. There is a problem forecasting extreme temperatures, especially overnight minimum temperatures which has never successfully been resolved, in fact I would say that little effort has ever been expended either by the Met Office, or the company that provides the BBC graphics in doing so. Let’s hope that Meteogroup, in these days of 4K television, come up with an improved way of displaying extreme temperatures which more accurately reflects what the model is  forecasting when they finally take over the service next March.

Graphics speak with forked tongue Kemosabe

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).

Figure 2

BBC Weather and how they visualise forecast temperature extremes

Figure 1 – Courtesy of the BBC

I might be wrong, but in the good old days when the BBC weather presenters used magnetic weather symbols (fig 1), they displayed the extreme temperatures for that day or the coming night, rather than for a fixed time as they do now, which although arguably more accurate, can be misleading at times, as it was last night.

Figure 2 – Courtesy of the BBC

When Ben Rich presented the BBC forecast in the evening (fig 2), he did mention that there may well be a touch of frost in sheltered southern areas, but the graphics he used belied this because the model was displaying much higher spot temperatures at 0500 BST, so graphically at least we got a misleading picture.

Every Autumn I get on my high horse about this one, I know it will seem small and petty to most people, but I specialise in that kind of thing. I do realise that forecasting and visualising extreme temperatures for an island nation like ours is never going to be easy, but why make it harder for yourself by refusing to use a chart of extreme temperatures rather than for just a single fixed time?

There was a good ground frost in places overnight, especially in the south (fig 3).

Figure 3

As you can see there were three places that recorded a slight air frost overnight (fig 4), the coldest of which was Hurn near Bournemouth with a minimum temperature of -0.5°C.

Figure 4

BBC News: It’s official, this morning’s blood-red sun was caused by Saharan dust

Figure 1 – Courtesy of BBC News

It’s official! This morning’s blood-red sun was caused by Saharan dust, so says Simon King the BBC weather presenter.

Was the October storm of 1987 the result of ex-hurricane Floyd?

Figure 1 – Image courtesy of NOAA & Wikipedia

With the 30th anniversary of the ‘great’ storm of October 1987 now just a few days away, I thought it was about time that I looked into the rumours that ex-hurricane Floyd had something to do with it. After looking at some surface pressure charts for the Atlantic from the 12th to the 15th , I can now see how this speculation came about, and also better understand that Floyd was the hurricane that Michael Fish was referring to in his now infamous forecast when he said:

“Earlier on today, apparently, a woman rang the BBC and said she heard there was a hurricane on the way… well, if you’re watching, don’t worry, there isn’t!”

In the prologue to the book ‘Storm Force‘ which he co-authored, Michael Fish does explain that he was talking about hurricane Floyd and:

“…my remark had NOTHING to do with the storm”

He goes on to add that the infamous forecast:

“…was NOT made the evening before and NO woman rang the BBC

Looking at the video on YouTube of the now infamous forecast, it’s not entirely clear to me at what time it was broadcast. It could have been from late the evening before (14th), but it seems more likely it was the broadcast after the midday news on the 15th, because rolling 24 hour news from the BBC started much later than 1987 as far as I remember. Michael Fish reminds us in his prologue is at pains to explain that it was Bill Giles who was the duty forecaster that evening (15th), and it was he who uttered the immortal line:

“…it will be a bit breezy up the channel”

As Michael Fish reminds us:

He kept quiet about this  until he had collected his OBE and retired!

The culprit as we know was not any of the messengers, but a combination of poor guidance from Bracknell, poor forecast from what now looks a rather crude and unsophisticated NWP model, which itself was due in no small part to a dearth of ship observations from Biscay during the afternoon. Anyway I digress, as I so often do these days, so back to the main point of this blog.

Is there any truth in that speculation, that the October storm was the remains of ex-hurricane Floyd?

Figure 2 – Data courtesy of the NHC

Floyd had just slipped past the southern tip of Florida as a hurricane on the 13th of October 1987, here’s the reanalysis chart for 00 UTC (fig 3).

Figure 3 – Data courtesy of NCEP/NOAA reanalysis

The chart below (fig 4) shows the last position listed in the Hurdat2 archive for ex-hurricane Floyd, and this is how Wikipedia described the demise of Floyd.

Unexpectedly the storm turned sharply northeastward into the southeastern Gulf of Mexico. Based on reports from the Hurricane Hunters, Floyd briefly attained hurricane status on October 12. Around the same time, the nearby cold front spawned a low pressure area that cut off the hurricane’s inflow. While moving through the Florida Keys, Floyd became the only hurricane to affect the United States that year. However, its convection was rapidly decreasing over the center due to the front, and shortly thereafter Floyd weakened to tropical storm status. The circulation became nearly impossible to track on satellite imagery, although surface observations indicated it passed just south of Miami, Florida. The storm underwent extratropical transition as it weakened over the Bahamas, and Floyd was no longer a tropical cyclone by late on October 18*. The circulation dissipated within the cold front early the next day.

Figure 4 – Data courtesy of NCEP/NOAA reanalysis

And below (fig 4) is the position of the embryonic low that became the ‘great storm’ at 00 UTC on Thursday the 15th of October. I’ve measured the approximate distance between the last observed position of ex-hurricane Floyd and the first of the October storm, and its a whopping 2,600 nautical miles, and even if it had been doing over a hundred knots as a surface feature, Floyd just couldn’t have made it. Perhaps at the middle and upper levels if there had been a jet that spanned the Atlantic from the Bahamas to western France which was blowing at 240° and 100 knots, tropical air from Floyd could have been pulled eastward to fuel developments in mid Atlantic. I’m no expert, but I suppose it’s possible that tropical air somehow got entrained into a developing extratropical low, Floyd did rather mysteriously turn to the northeast and lose intensity as the Wikipedia article points out, but I would have to download more reanalysis wind data for 500 hPa and above to check if that could have been the cause, there’s nothing quite like a good conspiracy theory is there?

Figure 5 – Data courtesy of NCEP/NOAA reanalysis

As we now know the rest is history (fig 5) even though the coarse grid of the NCEP reanalysis doesn’t quite get the intensity of the October storm.

Figure 6 – Data courtesy of NCEP/NOAA reanalysis

*This slip may be intentional or not, but I reckon that 18 should be a 14 according to the NHC record.

The weather presenter’s book of dodge’s

Figure 1 – Courtesy of the Watch Forum

When I was a child I use to buy a weekly comic called the Beano out of my pocket-money. One of  my favourite cartoons in it was about a character called Roger the Dodger (fig 1). Wikipedia nicely sums up much better that I can what Roger was about if you are not of that age:

His strip consists solely of Roger’s basic remit to avoid doing chores and homework which usually involves him concocting complex and ultimately disastrous plans, the undoing of which results in him being punished (usually by his long-suffering father). To perform these tasks he enlists the help of his many ‘dodge books’.

Weather Presenters Dodge #1

I sometimes wonder if there is a book of weather presenter’s dodges and what some of them are? A recent Twitter posting from the BBC weather team has led me to believe that I’ve found a dodge worthy of inclusion in their book of dodges. In the next few days, its forecast that the two ex-hurricanes Maria and Lee will merge in mid-Atlantic, and from the remnants of the two, a super low will form and threaten the British Isles with what could be storm Brian. As soon as I think of them actually naming this storm Brian I can’t help but smile, because it immediately brings back memories of Brian Conley’s alter-ego stuntman ‘Dangerous Brian’, anyway I digress. So the thing is, the Met Office ensemble models are split as to exactly which track this low will take and how much it will intensify by, and even if Brian will even happen at all. That’s where dodge #1 is so clever because the gist of it is this – tell the viewer that there are two possibilities and let them decide. Brilliant! It gets you off the hook, because you get it right whatever happens, and this is exactly the dodge that Matt Taylor employed yesterday in his weather for the week ahead video (fig 2).

Figure 2 – Courtesy of BBC Weather and Twitter

I can’t say what the Met Office forecast for later on Sunday looks like, either from their ensemble or deterministic models, because as you know the Met Office like to keep us in the dark about what our model is saying. The GFS model on the other hand has backed off a forecast with an intense low as deep as 946 hPa for 12 UTC on Monday. It now brings the remains of two hurricanes rather quickly eastward as a discrete low at around latitude 50° north, before it’s absorbed into a trough of the dominant parent low south of Iceland during Sunday morning (fig 3).

Figure 3 – Courtesy of NetWeather.TV