Highest Wind Speed > Highest Wind Gust

[BCJKiwi]

I noticed the Highest Wind Speed > Highest Wind Gust (61kph vs 60 kph - 3 1/2 months apart)
I guess this may be the result of the calculation methods/averaging mechanisms but do find it a little suprising.
Might I have a spurious reading?

[peterh]

.... and I posted this in entirely the wrong thread

[steve]

You wouldn't normally expect that to happen, because the average is calculated from the individual 3-second speeds (on a Davis) and the highest gust is just the highest of those 3-second readings. However, things start getting tricky when data from the logger is used, and it wouldn't surprise me to see slightly odd things happening in that case; the gust and the average tend to be very close with Davis stations, when using logger data, and things like your station logger interval come into the equation. The fact that the speed is slightly higher than the gust may come down to differences in conversion to kph and rounding between the Davis DLL and Cumulus.

Do you have Cumulus calculating the average? What is your station logger interval? Did either or both of those readings come at a time when Cumulus wasn't running, so the data came from the logger? Or just after starting Cumulus up? I realise that some of these questions may be hard to answer so long afterwards.

The entries from the monthly logs around the times of the two records might also be informative.

[William Grimsley]

.... and I posted this in entirely the wrong thread

... and no he didn't.

[BCJKiwi]

Do you have Cumulus calculating the average? What is your station logger interval? Did either or both of those readings come at a time when Cumulus wasn't running, so the data came from the logger? Or just after starting Cumulus up? I realise that some of these questions may be hard to answer so long afterwards.

The entries from the monthly logs around the times of the two records might also be informative.

Steve,
Cumulus was only intalled 12 days before the Highest Speed was logged. I do not have any backups from that date but it is very likely that the data was from the logger as initially I was working with a wifi connection via the lan to the Davis console which was giving problems (now use a serial connection).
However the monthly log for the Gust data shows the a gap at the time. Data at 9:00,9:05,...9:35,9:40 then a break until 17:40! so yes, issues with the wifi connection. Highest speed is reported at 9:15 in the middle of the gap.
The Gust data looks good as there are consistent readings either side of the time in the monthly log
The current settings (see below) should mean the VantageVue is providing all the data but I cannot guarantee that is the way it was when first set up.

I was curious and as usual you have pin pointed the issue immediately! I will reset the alltime speed a little lower just to remove the seeming anomaly but it is a bit academic as I would expect these values to be overwritten this coming winter as the station came on line after the middle of last winter.
We are well into summer right now with the driest January in Auckland since the 1940s!

Thanks

[steve]

It makes sense to have the station supply the average speed, as you are doing, as it's a 10-minute average anyway. But note that the logger data doesn't contain the average speed, so Cumulus has to take over when using logger data, and do the best it can from the small number of samples available. So you will often see odd effects where the gust speed and average speed are quite close when using logger data.

I notice this myself - even though I don't usually rely on logger data - when we have a storm which results in the power going off. The resulting graph when the power is restored and Cumulus catches up looks strange as there is apparently a sudden jump in the average wind speed during the period the power was off. It's quite frustrating as the difference is actually artificial.