By Paul Homewood
There was a discussion about the merits of using sustained wind speeds rather than gusts on the Ophelia thread the other day.
Doug Holman gave this particularly relevant comment:
Some people measure speed (velocity for the purists) in mph while others use kph or knots. What matters is that comparisons are made using the same units. We would rightly object if we were caught doing 48 in a 30 limit and it turned out that the speed camera had been inadvertently set to kilometres instead of miles.
Conventionally, we measure wind in terms of a mean speed but “warmunists” (a term borrowed from Ian Magness, above) seem to think that they can win their battle against capitalism by replacing mean with maximum gust speeds. A gust is (by definition) at least 10 knots (11 mph) more than the mean speed but a maximum gust could be much higher, and depends on numerous factors, such as the local topography and wind direction. That’s why mean speeds are used in overall risk assessment, such as in the shipping forecast.
If we stick to the Beaufort scale, we know that there’s risk of trees falling when the mean speed reaches between 55 and 63 mph, or “force 10”. Of course, the gusts will be higher. But which would you consider more dangerous: a “force 8” gale (between 39 and 46 mph) with a single freak gust of 80mph or a proper “force 10” storm with widespread gusts of the same speed?
Frankly, I blame the car manufacturers for replacing “air conditioning” with “climate control.” It led some of our “professional” politicians to imagine that this could work for the entire world. If their understanding of meteorology is this risible, are we not entitled to know what, if anything, we can safely entrust them to do?
This has been a particular bugbear of mine for some time, and, with Storm Brian heading our way, it is a good time to revisit it.
The real problem that I find is that the UK Met Office rarely seems to offer any assessment of mean wind speeds, either on their forecast or after the event. Instead they concentrate on gusts, as their latest missive above about Brian highlights.
A good example of this came in their news release about Ophelia on Tuesday, which stated:
Ex-Hurricane Ophelia has moved out over the North Sea after bringing gusts of over 90mph to parts of the UK.
There have been widespread impacts across Northern Ireland, western Wales, north west England and south west Scotland. Travel disruption, fallen trees and power cuts have all been reported with many properties already having had power restored.
The strongest wind gusts were recorded on the southern edge of the low pressure through the afternoon on Monday (16 October). The tables below outline the top wind gusts recorded in the UK and the Republic of Ireland.
Nowhere in their report was there the slightest mention of sustained or mean wind speeds, although they certainly keep such data.
But matters are even worse because all of the UK sites mentioned are extremely exposed sites, and clearly not representative of most of the country.
For instance, Capel Curig is high up in the wilds of Snowdonia, at an altitude of 216 m.
Aberdaron is not only at the tip of the Llyn Peninsula in N. Wales, but the weather is at the top of the cliffs at a height of 95 m.
Places like Mumbles Head also appear regularly near the top of the wind charts for similar reasons.
Not to be outdone, the BBC now use black logos (denoting gust speeds) at times of windy conditions, rather than the usual grey ones for mean speeds:
This is done supposedly to warn people, but I suspect most would be totally confused.
I suspect the real purpose of all of this is to overhype storms and make them appear much worse then they really are.
What makes this all so unforgiveable is that there is already a well established system for forecasting and reporting winds, the Beaufort Scale.
The fact that this is still used for serious purposes, such as the Shipping Forecasts, suggests that the Met Office’s preoccupation with gusts on exposed headlands is nothing more than a PR exercise, concerned with generating headlines.
via NOT A LOT OF PEOPLE KNOW THAT
October 20, 2017 at 11:06AM
Iowa Climate Science Education 