Full smiths period

[Catherine]

What is going on I have just had an email saying that there is a Full Smiths Period in our area. What is going on!! I don't really understand the system but I thought this would happen later in the year.

[Geoff]

I was surprised to get that as well but they are essentially just a weather report, it has been over a certain temperature and over a certain humidity. Later in the year when the spores are around it means it is ideal for them to infect things. No idea why they have sent them out so early this year.

[Primrose]

I signed up to a Blight Alert system a couple of years ago but I can't remember whether you have to go and re-register every year or are on the automatic mailing list once you've signed up.

[Tony Hague]

I thought blight spores were usually carried in rain - might explain a lot !

[Colin Miles]

Well here in 'wet wales' - well recently certainly wetter than anything to the west of it, it's very marginal for a Smiths Period particularly as the temperature and humidity don't coincide. Met Office data? Computer error? See definition below.

The Interpretation of Smith Periods.

Smith Periods for blight control are calculated from hourly temperature and relative humidity values. The weather records on which the post coded Smith Periods are based are supplied by the Met Office.

A full Smith Period has occurred if, on each of 2 consecutive days:

the minimum air temperature was at least 10oC, and
there were a minimum of 11 hours with a relative humidity of at least 90%


Within the calculation there is a provision for a 'near miss'. This occurs when the temperature criterion has been satisfied but the number of hours with a high relative humidity totalled only 10 hours on one or both days.