Lacrosse - what is a wind gust?

[sunray24]

Lacrosse supplies only one wind speed reading.

In my records section the highest wind gust and highest wind speed occured at exactly the same time yet the gust is 21.6 and the speed is 27.8
Investigation shows that it is the same reading (the gust is multiplied by 1.29 my pole height correction giving the speed reading 27.8)

The correction wasnt applied to the gust but was applied to the speed.
Even though it was one and the same reading.
I have read that gusts dont get the correction in the wiki.

What I dont understand is how a gust can also be a speed at the same time?

Scott

[sunray24]

Am I correct in thinking then that with my Lacrosse in effect because it supplies only one reading that there is no such thing as a wind gust.
That a wind gust is just a peak wind speed, during the past 10 minutes. That is why the correction was applied to the gust beacuse it wasnt really a true gust just the highest wind speed.

Scott

[steve]

Gusts are a bit of a strange thing anyway; there isn't really a universal definition, as far as I'm aware. And the weather stations which Cumulus supports all have their own idea of what a gust is - or in some cases, as with the La Crosse they don't bother.

Cumulus looks for two wind readings from a station, a 'short term' reading, and a longer term reading, and tries to do something sensible with them. The 'short term' reading is displayed as 'Latest', and the longer term reading as 'average' (ignoring the complication of the option to have Cumulus calculate an average). Cumulus takes the highest value of the 'short term' value over the previous 10 minutes and calls that the 'Gust'.

With La Crosse only supplying one wind value, Cumulus uses that as both the short term and the longer term reading; it applies the gust calibration value to one and the speed calibration value to the other, just as it would for other stations.

[sunray24]

Thanks Steve

Understand that now - makes sense
Great program by the way

Scott

[wd40]

. . . the gust is multiplied by 1.29 my pole height correction giving the speed reading . . .

Scott

Is this a Lacrosse correction factor? I was not aware of a correction factor for height. A google search left me empty handed.

Randy

[daj]

Is this a Lacrosse correction factor?

No

I was not aware of a correction factor for height. A google search left me empty handed.

http://wiki.sandaysoft.com/a/Wind_measurement

[wd40]

David, thanks for the link. Should have known that. I keep thinking I have read every page of the wiki; obviously I have not.

Randy

[wd40]

David I went to the wiki to find the anemometer height page again thinking I could straight to the page without using the link in your post. I was surprised to find it in the "Terminology" section. I wonder if the article would be better served in a section like "Setup".

[sunray24]

With La Crosse only supplying one wind value, Cumulus uses that as both the short term and the longer term reading; it applies the gust calibration value to one and the speed calibration value to the other, just as it would for other stations.

I want to apply a multiplier to both the gust and the speed per above (in Lacrosse they are one and the same).
I put the gust multiplier in the ini file but it isnt being applied to the gust.

In the cumulus console I see the latest wind speed which becomes a gust (because it was higher than the previous gust) but it doesnt apply the calibration.
That is - the latest and the new gust are the same figure.

Scott

[steve]

I put the gust multiplier in the ini file but it isnt being applied to the gust.

It's easier to use the calibration screen in Cumulus. If you edit the cumulus.ini file, you have to do it with Cumulus stopped, and it takes effect the next time you start Cumulus.

[sunray24]

It's easier to use the calibration screen in Cumulus. If you edit the cumulus.ini file, you have to do it with Cumulus stopped, and it takes effect the next time you start Cumulus.

Steve have done that but the calibration isnt being applied to the gust.
Looking at the console the latest wind speed (which is say higher than the previous gust thus overwriting it) but when shown in the gust section is exactly the same speed as shown on the latest speed. ie no calibration applied

Scott

[steve]

but when shown in the gust section is exactly the same speed as shown on the latest speed. ie no calibration applied

The gust multiplier is applied to the 'latest' value as it is read; and hence to the 'gust' value (being the recent peak of the 'latest' values). But basically, 'latest' and 'gust' always deal in the same set of values. When a gust multiplier is applied, the 'latest' value displayed should reflect that, when compared to the console.

[sunray24]

I understand now thanks Steve
The multiplier is applied to the raw wind speed reading from the Lacrosse console BEFORE it gets displayed as 'latest' on the Cumulus display.

Thanks again
Scott

[steve]

Yes; I suppose the 'gust' multiplier should really be called a 'latest' multiplier. Or I should try again to get some better terminology that works for all stations; not easy.