Author

Topic: Reading and Writing on Weather Maps  part 6 of 5

cbassani

posted April 08, 2020 07:58 PM
Hi. I was trying to calculate the wind velocity based on the definition:
V = (40/(D*sin(Lat)))*0.8
V = (40/(1.7*sin(48.5)))*0.8
On my calculator, using the above order of operations, I get 19.19. On my computer, following the same order of operations, I get 15.13 (the same as the video).
I am struggling to understand the difference between the two, because I would typically use my phone's calculator for these functions. If I do, I will be incorrect (according to the video). I'm stumped! Any thoughts?


cbassani

posted April 08, 2020 08:22 PM
Here's an excel version of the same calculation attached  Velocity is calculated at 19.19.
In the video, the reported wind observation was 20 kts and was also pointed in the opposite direction as would have expected based on wind direction from High to Low.
Thanks for any guidance you can provide.


David Burch

posted April 08, 2020 09:24 PM
You can include an image but not a file.
Your formula is right. surface wind = 0.8 *40/[D*sin(Lat)]
Be sure the angle is set for degrees if using degrees. Some apps like Excel require radians, so you would use sin(48.5*pi()/180) or sin (deg(48.5))
From: Starpath, Seattle, WA


cbassani

posted April 09, 2020 12:28 PM
I think that helps! What I learned is that both Excel and the calculator on my phone require me to convert degrees of Latitude into Radians as you suggested. Thank you!
The image I've uploaded is a screen capture of the spreadsheet that I've been working on to understand the calculation.


