Why do wind speeds often jump from 20 knots to 40 knots

Question

Looking at the BBC weather forecasts I've often noticed that strong winds will often be over 40 knots (for the UK at least). Most of the time (nearly always) the wind will jump from 18-22 knots to over 40 from one hour's forecast to the next. I don't often ever see wind speeds in the high 20s or 30s. Why is this the case? I looked at the Weibull distribution but this doesn't seem to apply.

Link to Weibull distrubition please... Also, your term jump needs a timespan - it makes quite a difference if the increase is in 5 minutes or 1 hour. Please [edit] the question. — Jan Doggen, Oct 10 '19 at 11:21

score 7 · Accepted Answer · edited Jul 15 '23 at 11:35

7

This is an (annoying) artefact of BBC weather forecasts, and not an actual feature of the weather.

At low wind speeds, the speed shown is the expected average speed.

At higher wind speeds, the speed shown is the maximum expected gust.

It changes over when the maximum expected gust is 40 mph (not knots). You can tell the difference because average wind speeds have a white background, and gusts have a black background:

There is a little bit of explanation about half way down this page: https://www.bbc.com/weather/about/17185651

edited Jul 15 '23 at 11:35

Philip C

103
2

answered Oct 10 '19 at 17:09

Semidiurnal Simon

5,810
1
21
43

1

Ahh! That makes sense now of course. Thanks. – Calanus Oct 15 '19 at 20:30
@philip C thanks for editing this screenshot in! – Semidiurnal Simon Jul 17 '23 at 12:53
1

@SemidiurnalSimon No problem - I was looking for the answer you gave because I noticed it on the forecast that day :P – Philip C Jul 17 '23 at 12:59

Why do wind speeds often jump from 20 knots to 40 knots

1 Answers1