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Quote:Quote: The difference between a 1 minute average and an 8 or 10 minute average is actually pretty dramatic. I'm not sure which one would be most 'representative' of the storms potential damage. The issue with surface winds as a ratio of winds aloft is because of turbulence and how well the wind 'mixes' down towards the surface. Also of note, the 'surface isn't defined as the actual surface (but instead 2 or 10 meters above the actual surface). which is why there is often a difference in the wind speeds at the theoretical surface versus the actual surface. Trying to model actual surface condition (as opposed to 2 or 10 meters up) is incredibly difficult, you have all sorts of microscale phenomena to deal with, such as frictional forces and turbulence from objects, which makes the modeling that much more problematic. As far as mixing from the "upper levels" (850mb and lower pressures), There are lots of papers on TC wind mixing exploring that very issue. Since TC winds are not well mixed, some of the questions that is still being answered are: how do the winds aloft mix down to the surface and when can the mixing ratios of winds aloft be applied to determine surface winds? (At least, I don't think there are definitive answers on those...) So in short, they don't actually simply stick with flight level winds, They use surface obs when possible, only resorting to ratio estimates when there isn't any other option. And because of the nature of the winds, that there is a lot of variability in wind speeds even in locations that are relatively close to each other spatially. which can make a wind forecast look bad even though it's representative of the maximum wind speeds in that area instead of every single location in that area. |