Noob question about met.ie forecasts

smacl · 10-06-2011 02:49PM #1

Just looking at the forecasts for this Sunday from met.ie for Wicklow and from the main forecasts I get the following;

We can see 50kph winds predicted for Wicklow at mid-day. However if you go to the wind section of their 5 day forecast, you see maximum winds over coastal of Wicklow of 17 knots (31.5kph) with the rest at 11 knots (20kph). I'd copy the chart, but there are explicit warnings not to do so on the bottom of the page. The scale on this chart also seems screwy with the first range in white being knots - 0, rather than 0-6. If this was the error, our coastal max would be 22 knots (40kph) which is still a long way of the 50kph predicted elsewhere on the same site.

Any reason for this major inconsistency, and is the 5 day chart reliable enough to look 2 days ahead? Looking at the surrounding data on Saturday and Monday, wind speeds are lower, so I'm wondering where the 50kph value is coming from and is it meant to represent an extreme or typical value for the time and geographical area?

Anyone willing to predict how windy it is actually going to be in Wicklow on Sunday? Reason for asking is it is the day of the Wicklow 200 cycle which I'm doing.

stevenmu · 10-06-2011 03:49PM

Wind speeds increase dramatically with altitude.

I was told a rule-of-thumb formula before which I can't seem to remember or find on line at the moment, but I remember being amazed at how quickly wind speed increased over quite small altitude changes. A 20kph-30kph difference between coastal Wicklow and higher up into the mountains seems quite believable.

http://en.wikipedia.org/wiki/Wind_gradient

edit: there's also the hill effect, hills/mountains speed up air passing over them.

smacl · 10-06-2011 03:58PM

Thanks Stevnmu, this also has been my experience cycling in the mountains in Wicklow, and what I'd expect. The met chart however, from my reading of it as a novice, has the wind speed much higher on the coast.

Noob question about met.ie forecasts

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