ECMWF windspeeds

BlueSkyNick

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I've been looking at THIS CHART in an attempt to forecast the weather this coming weekend.

The windspeed scale is bugging me. It starts at 15 m/sec and goes up to 40 m/sec. By my maths, 15m/sec equals 54km/hr which is the bottom end of a Force 7, innit? So the chart isn't a lot of use, at least for working out if its going to be a 3, 4, 5 or 6 in the Solent.

Or am I doing something wrong?

Given that tcm recently chastised me for looking at www.weather.co.uk, where can I get a better forecast for 5 - 7 days ahead?
 

simonjk

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Hi BigNick,

The trick here is to look at the chart title.

The wind speeds shown are for 850mb (about 5000ft), so no, wouldn't be much use for the Solent! /forums/images/graemlins/smile.gif

The isobars are shown on the charts, so you'd need to take a measure from these to work out the forecast surface speeds.

However, always be VERY careful when dealing with model derived winds. As a forecaster, I work out the winds speeds intially using the model forecast, but then amend them using current charts etc...

The forecast on my website at http://www.weatherweb.net/uksail.htm has some model derived winds in the forecasts, so you don't need to do much working out. They are free too.

If you want to know more about forecasting wind speeds from the charts, just ask.

Simon
 

Scillypete

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15m/sec is just under 30 knots of wind so almost bang in the middle of the force 7 range.
Using the ecmwf charts is good for seeing what the weather is likely to do in the forthcoming week but it is only a prediction. From the charts you would have to make your own best guess on the windpeeds based on the isobars on the chart you are viewing where there are no colour codings.
On the day when you actually get out on the water it is always guaranteed that you will have a force six-seven on the nose no matter which direction you wish to go in or where you got your forecast from!!
 

alant

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Re: ECMWF windspeeds (Conversion chart)

4-5m/s=F3
6-8m/s=F4
8-11m/s=F5
11-14m/s=F6
14-17m/s=F7
17-21m/s=F8
21-24m/s=F9
25-28m/s=F10
28m/s+=academic. /forums/images/graemlins/ooo.gif

On this website, anything above a yellow colour is not nice weather.
 

peterb

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[ QUOTE ]
The wind speeds shown are for 850mb (about 5000ft), so no, wouldn't be much use for the Solent! /forums/images/graemlins/smile.gif

[/ QUOTE ]

The Met Office's book "Meteorology for Mariners" suggests "Over the sea, it is found that the surface wind speed usually is about two thirds that of the geostrophic wind." That drops your 30 knots down to 20 knots, near the top of F5.
 
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