Monday, 27 December 2010

BBC Weather, part 4

So it is over. on the 3rd I finally (*) received a response from BBC Complaints that explains the discrepancy I have seen in the BBC Weather system on-line. The previous installments of the saga can be found in part 1, part 2 and part 3.

I reproduce the relevant part of the email below (I emailed them to as for permission, but after two weeks have had no reply). I have included it as I believe that it may be of interest to others.

As for the thinking behind the forecasts they are sent to us from the Met Office via two different feeds, and each feed drives what weather symbol is shown.

Daily Weather Symbol
The daily weather symbol indicates the most representative weather type for the whole of the relevant day or night. This could either be the predominant weather type - that is the weather that lasts for the longest period of time, or alternatively, the most significant weather type.

So if a day is forecast to be predominantly sunny with the possibility of a brief shower, then we are likely to see a sunny symbol rather than shower symbol. However, a thunderstorm symbol may appear if a thunderstorm is expected in an otherwise largely dry day. For the purposes of the forecast the day covers the period from 0600 to 1800 UTC and the night from 1800 to 0600 UTC on the following day.

Three Hourly Weather Symbol:
The weather symbol that appears for each three hourly timestep indicates the weather that is expected at or near the relevant location, around the time indicated.

For example if a shower symbol appeared for Exeter at 1500, we're saying there is a chance of a shower in the Exeter area at, or close to 1500 (there could be one a short distance away and it may actually occur at 1430). As the three-hourly forecast is 24 hours from the point when it is viewed, depending on the time at which you are viewing the forecast the most representative weather symbol for the day might not have appeared.

I think that this explains the observed problems.

It has been an interesting little diversion, and shows the problems there can be in delivering the weather forecast, yet alone forecasting it in the first place.



(*) I received the email in the morning. At first, when viewed in MS Live Mail application, it showed as being empty. Only in the evening, after a couple of glasses of wine, did I dig further. I noticed that the size of the mail was 7K, which was much bigger than I would expect for normal email headers. So I dug into the system and retrieved the plain text of the email as a file. It showed a large section like this:
PEZPTlQgZmFjZT0iVGFob21hLCBWZXJkYW5hLCBBcmlhbCIgc2l6ZT0yPgo8UCBjbGFzcz1Nc29O
This was obviously some form of encoding, and a few lines above was:
Content-Transfer-Encoding: base64
So the email had been encoded in base64. This is often used when you need to transmit binary data - for instance images or audio - over email, which is text-only. I went onto an on-line decoder and retrieved the base text of the message. I have no idea if the problem was with the BBC mail system, a corruption during sending or Live Mail's inability to decipher it.

2 comments:

Alan Sloman said...

Interesting stuff - about a week ago as I clicked on the detailed BBC forecast I was asked to fill in a questionnaire about the Forecasting service. I mentioned in fair detail the problems that you and I have both observed but have yet to hear back from them.
I still do not think that the explanation they have given you explains the problem though.

Maverickapollo said...

Base64 is used to encode binary data as text for attachments. That could be a attachment by the BBC mail system for archive or something, or even a signiture image.

Live Mail has several issues, Base64 decoding being one of them.