Author Topic: Windspeed versus Windgust Statistics  (Read 2730 times)

JAG

  • Gentle Breeze
  • **
  • Posts: 22
    • Weather Station: Tajika One
  • Station Details: Davis Vantage Vue
Windspeed versus Windgust Statistics
« on: April 12, 2013, 09:39:20 AM »
I've come across a little issue with wind speed and wind gust statistics. It seems that the MAX values for wind speed are the same as wind gust MAX values.

For example, here are some statistics from my monthly statistics page:

Statistic                             This Month                   Last Month
Avg Wind Speed (m/s):     1.8                               1.7
Max Wind Speed (m/s):     19 (3 Apr 2013 09:05)     13 (26 Mar 2013 00:40)
Avg Wind Gust (m/s):     2.9                               2.7
Max Wind Gust (m/s):     19 (3 Apr 2013 09:05)     13 (26 Mar 2013 00:40)

Conceptually, MAX wind speed and wind gust seems correct. But on the other hand, the AVG wind speed and wind gust values are different. In fact, it looks like Weather Cat maintains these pieces of data separately, as can be seen in the RAW data that Weather Cat logs.

So, which way should it be? Are these separate measurable traits of wind, or one in the same? If one in the same, I wouldn't expect AVG wind speed and wind gust to be different. If separate, I wouldn't expect MAX wind speed and wind gust to be the same.

I hope this makes sense. Is there an explanation on just what WIND GUST means? Wind observed outside the 1st standard deviation?

WCDev

  • WeatherCat Developer
  • Administrator
  • Storm
  • *****
  • Posts: 2809
    • CW9739
    • ISCOTLAN25
    • Trixology
  • Station Details: Main Station: Vantage Pro-2, 24hr fars, solar, soil/leaf station, extra temp stations, no U.V. WeatherLink IP.
Re: Windspeed versus Windgust Statistics
« Reply #1 on: April 12, 2013, 06:36:34 PM »
Hi JAG,
It depends on what variable you're using with the STAT$ tag - there are three: AVERAGEWINDSPEED, WINDGUST and WINDSPEED.

If you use AVERAGEWINDSPEED or WINDGUST it'll pull the data from either the average windspeed or gust records (both are recorded). If you use just plain WINDSPEED then it depends on the operation - if it's MAX then it'll pull the data from the gust data, everything else will come from the average data.

Cheers,
Stu.

JAG

  • Gentle Breeze
  • **
  • Posts: 22
    • Weather Station: Tajika One
  • Station Details: Davis Vantage Vue
Re: Windspeed versus Windgust Statistics
« Reply #2 on: April 17, 2013, 08:23:23 AM »
Stu,

Thanks for the reply.

I actually tired to look up the meaning of the STAT called AVERAGEWINDSPEED, but couldn't find any definition. And the example templates don't use AVERAGEWINDSPEED either. Some addition documentation on this STAT would be appreciated.

I've tried using AVERAGEWINDSPEED vs WINDSPEED vs WINDGUST, both AVERAGE and MAX values. There are some differences in rounding, which are irritating, but other than that the values still seem "confusing".

I wrote a quick PERL script to parse the data from last month (attached), calculating averages for wind speed and wind gust. My values (sum of speeds / number of samples) doesn't come out to those which WeatherCat generate for LASTMONTH. Even the MAX values for wind speed and wind gust are different.

./calc_stats.pl
===> NEW WG MAX (211801): 1.61 > 0
===> NEW WG MAX (211802): 3.22 > 1.61
===> NEW WS MAX (211804): 1.61 > 0
===> NEW WG MAX (211809): 6.44 > 3.22
===> NEW WG MAX (211902): 8.05 > 6.44
===> NEW WG MAX (212015): 9.66 > 8.05
===> NEW WS MAX (212345): 6.44 > 1.61
===> NEW WG MAX (212345): 14.48 > 9.66
===> NEW WS MAX (220215): 8.05 > 6.44
===> NEW WS MAX (220245): 11.27 > 8.05
===> NEW WG MAX (220245): 19.31 > 14.48
===> NEW WG MAX (220345): 22.53 > 19.31
===> NEW WG MAX (221415): 24.14 > 22.53
===> NEW WS MAX (230738): 12.87 > 11.27
===> NEW WG MAX (230911): 25.75 > 24.14
===> NEW WS MAX (230918): 14.48 > 12.87
===> NEW WG MAX (230919): 28.97 > 25.75
===> NEW WS MAX (230921): 16.09 > 14.48
===> NEW WS MAX (252123): 17.70 > 16.09
===> NEW WG MAX (252123): 32.19 > 28.97
===> NEW WS MAX (252130): 19.31 > 17.70
===> NEW WG MAX (252158): 33.80 > 32.19
===> NEW WS MAX (252159): 20.92 > 19.31
===> NEW WG MAX (252204): 35.41 > 33.80
===> NEW WG MAX (260017): 37.01 > 35.41
===> NEW WS MAX (260018): 22.53 > 20.92
===> NEW WS MAX (260020): 24.14 > 22.53
===> NEW WG MAX (260025): 41.84 > 37.01
===> NEW WS MAX (260033): 25.75 > 24.14
===> NEW WG MAX (260039): 46.67 > 41.84
===> NEW WG MAX (260040): 48.28 > 46.67


***** STATISTICS *****
Wind Speed Count  : 13974
Wind Speed Total  : 87776.7900000122
Wind Speed Average: 6.28143623872994
Wind Speed Max    : 25.75
Wind Gust Count   : 13974
Wind Gust Total   : 135113.380000003
Wind Gust Average : 9.66891226563637
Wind Gust Max     : 48.28

I'm still baffled in the difference in values. Does WeatherCat eliminate or extrapolate samples? Does WeatherCat use the HRS data for monthly calculations?

WCDev

  • WeatherCat Developer
  • Administrator
  • Storm
  • *****
  • Posts: 2809
    • CW9739
    • ISCOTLAN25
    • Trixology
  • Station Details: Main Station: Vantage Pro-2, 24hr fars, solar, soil/leaf station, extra temp stations, no U.V. WeatherLink IP.
Re: Windspeed versus Windgust Statistics
« Reply #3 on: April 18, 2013, 04:49:19 PM »
Hi Jag,
Sorry for the delay in answering, am working my nuts off to get the first 1.2 dev release out.

WeatherCat stores windspeed as kilometres per hour, so to convert from your results to m/s you need to multiply by 0.2777r. For example, if we take your average windspeed of 6.28143623872994 and multiply it by 0.27777777 we get 1.74484339476164, which is what the tag is reporting for last month.

Hope this helps,
Stu.

[Edit: I've raised a bug against the manual, currently it says something like 'the WINDSPEED tag is context sensitive, see notes below', sadly the notes don't mention it.]

JAG

  • Gentle Breeze
  • **
  • Posts: 22
    • Weather Station: Tajika One
  • Station Details: Davis Vantage Vue
Re: Windspeed versus Windgust Statistics
« Reply #4 on: April 23, 2013, 07:47:35 AM »
Stu,

I've tried the following STAT tags to get the MAX wind speed versus MAX wind gust.

STAT$AVERAGEWINDSPEED:MAX:LASTMONTH$ returns 13.41
STAT$WINDSPEED:MAX:LASTMONTH$ returns 13
STAT$WINDGUST:MAX:LASTMONTH$ returns 13

The PERL script now returns the following statistics.
Wind Speed Count  : 14764
Wind Speed Total  : 92825.7500000121
Wind Speed Average: 1.74647322960162
Wind Speed Max    : 7.152777835 at 260033
Wind Gust Count   : 14764
Wind Gust Total   : 146072.55
Wind Gust Average : 2.74828695867915
Wind Gust Max     : 13.4111112184 at 260040
Found 37 Gaps, filling 790 Samples
(Thanks for the tip on stored wind speed values.)

From your early post, AVERAGEWINDSPEED:MAX should return the MAX for W: (wind) in the stored data. It doesn't. Is this an bug?

FYI, I attached the data samples to an earlier post.

WCDev

  • WeatherCat Developer
  • Administrator
  • Storm
  • *****
  • Posts: 2809
    • CW9739
    • ISCOTLAN25
    • Trixology
  • Station Details: Main Station: Vantage Pro-2, 24hr fars, solar, soil/leaf station, extra temp stations, no U.V. WeatherLink IP.
Re: Windspeed versus Windgust Statistics
« Reply #5 on: April 24, 2013, 05:06:18 PM »
Thanks I'll take a look at it - sure looks like it's gone for the gust data to me.

Cheers,
Stu.