wind speed wrong (kph/miles)

[Stefan Pachlina]

Hello,

feb 24 2020, it was a stormy day in austria ... but most weatherstations (weewx-map, wunderground-map) show windspeed like 64kph.
but on this day wind speed was ~103kph

i have the same problem with my weather-site.

http://wetter.pachlina.net/

i configured weewx.config to see kph:

[[[[Groups]]]]

  ....

  group_speed = km_per_hour

  group_speed2 = km_per_hour2

  ....

but what i see are miles and not kph.

cause if i multiplicate the wind-speed with 1,61 i get the right wind-speed of 103 kph

so what is to do to get the right values?

is there something more to do?

i read the manual again and again, but i cant find the solution to see right wind speed.

all other values are ok .. like temperature in celsius.

and this is what i see on many many weatherstation around austria, germany .... with weewx-map, wunderground, ...

hmmmm any idea?

thx

Stefan

[angry tux]

Hi,

I get somewhat similar values on my WH1080 station and Weewx here in Germany, I always thought it was just calculated average instead of real (momentum) values.

But maybe you are right and they are in miles....

Will be interesting what the developers say.

regards

Dieter

[Thomas Keffer]

Hello,

Looking through your website, it looks like the max wind you saw was 63.7 kph. How do you know it was really 103 kph?

It would also be worth looking in your database. Try this:

sqlite3 weewx.sdb

sqlite> select datetime(dateTime,'unixepoch','localtime'), usUnits, windSpeed, windGust from archive where dateTime>=1582491600 and dateTime<=1582502400;

Hopefully, if I got the time zone right, this will print out wind values in your database from 23-feb-2020 2200 to 24-feb-2020 0100 local time.

-tk

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[Stefan Pachlina]

Hello,

in austria was a stormwarning of storm "Sabine" by weather-service https://warnungen.zamg.at ....   but yes, we are talking about wind-gust ~100kph

Heavy roof tiles were dropped from the roof and crashed on the street, etc .... it was a terrible night.
Cause of that ... wind-gust was greater then 63.7 kph ;)

so what i see in dB is frustrating:

2020-02-23 22:01:00|1|13.6453452968298|20.5798650378416
2020-02-23 22:31:00|1|22.8168068897809|39.5938707793257  <-- parts of my roof flew away :D
2020-02-23 23:01:00|1|17.4481464451266|27.2906905936595
2020-02-23 23:31:00|1|9.17146159295115|14.5401220376055
2020-02-24 00:01:00|1|14.5401220376055|25.0537487417202
2020-02-24 00:31:00|1|21.2509475934234|34.8962928902531
2020-02-24 01:01:00|1|19.0140057414841|31.0934917419563

are these values the one directly from my weatherstation? unformatted by weewx?

i found a very interesting section in weewx.conf an in customers guide.

[[Corrections]]

i think i can do something like that in that section:
windSpeed = windSpeed * 1.61

but i dont undestand what my weatherstation is doing with the windspeed hmmmmm

regards
Stefan

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[Thomas Keffer]

According to the database, you saw a max gust of 39.6 mph, or 63.7 kph, which is exactly what was reported on your website. 

It is always possible there is a bug in the driver for the WH1080, but unlikely. A bug this fundamental would have been discovered a long time ago. 

Perhaps Matthew has an opinion...?

-tk

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[mwall]

On Thursday, March 5, 2020 at 5:39:21 PM UTC-5, Thomas Keffer wrote:

According to the database, you saw a max gust of 39.6 mph, or 63.7 kph, which is exactly what was reported on your website. 

It is always possible there is a bug in the driver for the WH1080, but unlikely. A bug this fundamental would have been discovered a long time ago. 

Perhaps Matthew has an opinion...?

stefan, why do you think that your station experienced a maximum gust of 100kph, not 63.7kph?

i am pretty sure we worked out all of the unit conversion issues in the fousb driver a very long time ago.  i don't have recent data (two anemometers are broken right now), but for years i ran a comparison of fousb, acurite, te923, and ws23xx stations, and the fousb wind values correlated with those of the other stations.

the sensors report an integer value that is 10x m/s.  so we divide that by 10 to get fractional m/s.  then we multiply that by 3.6 to get the km/h that is required by METRIC unit system.  in your case, that is then converted to mph when saved to database (since your database is US).

you might test by comparing the following 3 values:

- what you see on your weather station console

- what you see coming out of weewx at the same time

- what you see on a hand-held or nearby anemometer at the same time

m

[Cameron D]

Hello Stephan,

I am still not sure why you think your station was reading 100km/h. I wonder if the following could explain the discrepancy...

If that speed came from official weather reports, then their standard (in many countries) requires that they are measured in open flat areas with the anemometer 10m above ground level.  Wind speed decreases as you get closer to the ground.

Also, the presence of buildings, trees and so on, creates a much more turbulent flow. The wind can have as much energy but lower measured speeds are recorded since vertical components are not normally measured by home instruments.

Cameron.

[Stefan Pachlina]

Hello,

hmm, i will do following.

1) i will buy a hand-held-windmeter to check windspeed at the current position of my weather-sensors ... maybe you are right and the position of the windsensor is not perfect.

2) I will move my weatherstation-outsensors to the top of the roof. (currently its not at the top, 3m lower, but no slipstream from west, north and south)

You should know that I see many kilometers to the mountains.

There is nothing higher in sight (from the west) than my house. So the wind loves my roof :D

i am just wondering why all other stations i checked have the same "problem".

lets see :)

thx for you help ....

[Thomas Keffer]

I live in the Columbia River Gorge, an extremely windy area in the summer. About 5 years ago, I moved the wind sensor from the top of my roof to a 3 meter post in a back field. Wind speeds dropped by half.

Kestrel makes very high quality hand-held meters. Their model 2000 measures wind and temperature and is under $100. Mine is over 20 years old and still functions perfectly.

-tk

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