June 5, 2023

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Winds aloft, pressure altitude, mountains/hills and “real” wind vs Windy.com ? : meteorology

2 min read


I have some questions about winds aloft.

  1. If I look at winds aloft on Windy.com, using the ECMWF model, often times the windspeed at 600m is less than the windspeed at 100m. Is this correct or is there some kind of systematic error in the ECMWF wind model ?

Also, If I compare windspeed at 6000′ ABL, ~ 600m AGL locally from my local aviation weather website with Windy.com, the values don’t agree. For example, right now Calgary aviation weather (https://flightplanning.navcanada.ca/cgi-bin/Fore-obs/fd.cgi) is showing 14 knots (7.2m/s) whereas Windy.com is showing 3m/s.

Why the discrepancy ?

2) All the weather modelling systems use pressure altitude instead of actual altitude for altitudes greater than 100m or so. How does this compare to actual AGL and ASL when you are in the middle of a continent ?

3) When I look at wind patterns on Windy.com, it generally shows increased windspeed over elevated terrain, ie mountain tops, etc. I theorize that this is due to the wind on the windward side of the mountains being pushed up in order to cross the mountain tops. Likewise, the wind speed on the lee side of the mountain is reduced as well because the “compressed” wind at the peaks can now decompress and thus reduce its speed. Is this correct thinking ?

Or is the increase in windspeed displayed in Windy.com over mountains due to an actual increase in the elevation the measurement is done at ?

For example, if I select 600m for my reference height in Windy.com and if my mountain top is at 1000m, is Windy.com showing the wind at 1600m relative to the local terrain or 600m relative to the local terrain ?

4) Alberta and BC are separated by the Rocky mountain range. BC is heavily forested and has very low average windspeeds. Alberta, has much higher windspeeds. On a day when the wind is coming out of the west, ie from BC, how can BC have low windspeed and yet as soon as the air gets over the Rockies, Alberta has much higher wind speed ?

Is the wind energy in BC being carried higher aloft and then coming down when the air crosses the Rockies ?

Thanks in advance.


2022-09-08 21:30:41

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