Judging Wind Speeds

[critterdude542]

Hey everyone,
I've been meaning to ask an online community this question for a while.
Without any specific equipment, how do you guys judge wind speeds?
I was one Mount Shasta a few weeks back and a guy came down from the summit claiming 70mph winds. I asked if he could stand up in it and he said yes
and I personally thought his idea was bogus.

My personal judgement has always been
0-25mph: just annoying
25-35mph: getting pretty breezy
35-45mph: gusts of this could start to move you around
45-55mph: getting knocked around a bit, getting difficult to walk
55-65mph: hard to walk, gusts of this could knock you down (I feel like this is where steps become hard to place properly and your ice axe/hands/arms get blown to the side unintentionally
65-75mph: can barely walk forward, gusts of this knock you on your ass!
75+: Go home

Anyone out there got any ways they personally judge it? Am I totally wrong? I guess there is a personal bias on any judgement like this but I thought I would see what others thought

[nartreb]

Search in SP's threads, there's one here somewhere that gives a formula for estimating force of wind on a standing human. As I recall, at my weight and size a steady 95mph would be enough to get me airborne if I leaned into it.

To give an idea how imprecise the numbers are, Wikipedia tells me that the terminal velocity of a falling skydiver is around 120mph - that's in belly-down orientation, and I assume for a standard-weight male. In other words, dive into a vertical wind tunnel blowing upward at ~120mph, and you'll float, immobile, as long as you maintain maximum area facing into the wind.

But getting knocked off your feet requires a lot less wind than staying aloft would require. Gusts add to the challenge, of course. As a rule of thumb, anything above 73 mph (hurricane speed) is going to make walking very interesting.

Here in New England, we have the advantage of a weather station on the top of Mt Washington. Just walk around on the summit, take your best guess, then go inside to see what the actual speed was. Or since the door is closed in winter when the big winds come, check online once you get back.

I generally check the forecast *before* heading up, so I can't recall going past about 60mph. At that speed, it's like crossing a fast stream: you have to pay attention, and you don't want to be carrying anything remotely kite-like (like snowshoes; even hiking poles will drag on you), but you can walk pretty normally once you adjust to leaning a little.

Speaking of the Mt Washington observatory, here's a good video of 86 gusting to the 90s:
http://www.youtube.com/watch?v=czazfwci ... ure=relmfu
That poor guy has no axe, nothing to grab or shelter behind, and is not wearing traction. The same site has videos of folks doing various stuff in steady wind in the 70s, and while they're not exactly graceful, they're pretty much upright.
Example: http://www.youtube.com/watch?feature=en ... C3DUwseZn8

So I think you underestimate humans' ability to handle a good blow. But I share your skepticism regarding uninstrumented estimates. Most people have no way of calibrating their wild guesses about wind speed.

[Deleted User]

I know that gusts around 125 to 132 start ripping shingles off warming hut roofs...we had to lay on our bellies on our skis and pull ourselves over the ridge on the way to the Bensen hut one winter. Gusts around 100 have lifted me with a 55 lb. pack and thrown me down by Glen pass on the PCT. I went by a weather report from Bishop, so really there is no way to just guess. It does seem like I take flight around 100 and I am about 135 lbs. There are some scary night winds around the crest that are definitely hurricane force, you can tell by the trees that only have branches on the east side...

[yetibob3]

Having an accurate Davis weather station and living where there is a lot of gusty wind in the 40-55 MPH range (aargh!) I think Critterdude's assessment is spot on. Hiking the ridges in the local hills is not pleasant in winds gusting in this range; I get knocked around a bit and I'm a big guy. Note that drag forces go as the square of wind velocity; at 70 MPH they are almost twice that at 50 MPH. That will knock you on your ass if hit by a sudden gust; I've seen it happen when rare winds were measured in that range at the local airport. The very rare winds stronger than that are really scary, when concrete roof tiles blow off (at around 80 MPH) and cars get moved around. You don't want to be outside. Once many years ago we were hit by a squall while on a local climb when a gust at the airport was measured at 109 MPH, fortunately I was in a chimney, secure like a chuckawalla lizard. My belayer, at the top of the rock, was picked up clear of the rock and blown like a flag from his anchor. Anyone not tied in would have been blown off and killed. Fortunately this lasted only a matter of seconds. I suspect many claims of strong wind are exaggerated.

[DanTheMan]

Yeah but terminal velocity means that you are hitting that wind speed everywhere around you because you are the one falling through the air. When measuring wind speed on the ground, where exactly are you measuring at? The wind speed is always lower close to the ground, and it's zero at the ground/air interface. Even a weather station 10 feet off the ground might see significantly higher wind speeds than a standing adult. So you can't really compare the two numbers.

[nartreb]

You've got to measure wind speed somewhere. Weather stations have standards for height, so at least they're pretty consistent. (I always thought Mt Washington was cheating because the anemometer was on the roof, but maybe their mast is lower than normal to compensate.) At the ground, the wind speed *approaches* zero in the mathematical sense, but notice in the video how the guy was still swept along the patio after he fell down. I've got some photos of rime formations on the floor of that patio, it's quite obvious that the wind speed less than a centimeter off the ground is not zero.

It should be noted that a mountain or ridgeline will form a half-nozzle, increasing the wind speed at the crest. This effect will diminish with increasing height above the ridge. (The fastest-moving spot should be a little above level with the crest, and slightly downwind.)