Wind speed estimates...

[GNR]

I've been noticing in both the trail conditions and the trip report section some estimates of wind speeds between 40mph and 70mph...now, I am not disputing the claims here, but how does one know the speed of the wind one is in? Has anyone here ever had a device to scientifically measure the wind speeds they are experiencing on a hike? How is this done?

 

[Waumbek]

The Beaufort Wind Scale (land version) is a rough guide. My guess is that at 40 mph, you feel resistance walking; at 60 mph, it gets quite difficult to move upright against the wind. I don't know how to estimate 70 mph; I think I'd be crawling by then. Since I've never actually measured my perception of wind speed against an actual anemometer, I could be off; I've measured against what is generally being reported elsewhere (tv, radio, etc.).

 

[cbcbd]

Kestrel makes anemometers. Basically it uses a fan to measure wind speed.

 

[Mike P.]

I've been hiking with a friend you has an anemometer. What we thought was 60 -65 MPH he could only get meausured at 47 MPH. Overall, I'd say many people over estimate but some people here spend a lot of time out in 40+ winds & may be better than others guessing.

All day in 40 MPH winds is still pretty tough

 

[dug]

I agree. We were convinced once that we were in 60-70MPH winds. I got home and checked all applicable weather in the area, and reports were 20MPH, with gusts close to 40MPH. Embarassing....I guess I'm just a wussie.

I now use a different scale:

-Calm
-Breezy
-Windy
-Friggin' Windy
-F$%&* Windy!!!

 

[DougPaul]

Just a quick note on the physics: the force due to wind is proportional to the density and proportional to the square of the speed. (For the equation minded: force=1/2 * rho * v*v * S, whre rho is the density of the air, v is the velocity, and S is the equivalent area of the object) So it will diminish at lower pressures, but increase rapidly with wind speed.

As a calibration point, a 16 mph wind speed at sea level produces a dynamic pressure of about 1 lb/sq-ft. A standing person might have an effective area of about 5 sq-ft, so a 64mph wind would produce a force of about 80 lbs.

Doug

 

[sapblatt]

As a calibration point, a 16 mph wind speed at sea level produces a dynamic pressure of about 1 lb/sq-ft. A standing person might have an effective area of about 5 sq-ft, so a 64mph wind would produce a force of about 80 lbs.

Doug

That is frightening - especially to those of us who take up more than 5 sf!

I reported a guess on Osceola of 40-50 mph...
looking at the Beaufort Scale I was not too far off - we saw entire trees swaying - from pretty low down on the trunk - that is a Gale and is 34-40 mph. I am dissapointed - I usually exagerrate a lot more than that!

 

[Kevin Rooney]

My estimates are close to what Waumbek suggested - when the winds reach 35-40mph they begin to rock you around, it's getting difficult to stand up and you stumble frequently. In wind speeds of 60+mph it's very difficult to stand up, forward progress is difficult, and you've being knocked down frequently.

Another difficult situation to hike in is where the winds aren't too bad - maybe 20-25, but there's an occasional much higher gust of 45-50mph. I've found the need to constantly be ready for that occasional odd gust to be very tiring.

 

[DougPaul]

Another difficult situation to hike in is where the winds aren't too bad - maybe 20-25, but there's an occasional much higher gust of 45-50mph. I've found the need to constantly be ready for that occasional odd gust to be very tiring.

Highly changeable winds of any form are difficult--I was once leaning into a steady wind when it suddenly stopped. I fell into pushup position...

Doug

 

[bill bowden]

Estimates of wind speed

As the posters have observed estimates of wind speed vary dramatically. Here's my own scale (somewhat verified by a friend's anemometer from the Nature Company)

20-25mph sounds really loud but no impact on your mobility
40-45mph pushes you around and care is needed in placing your feet
50-60 mph progress is difficult into the wind and foot placement very difficult cross or downwind
70 mph - upwards dig in your crampons, lean on your ice axe and wait for the gust to subside before trying to move

As for stories of summitting in 100 mph winds, those guys are either very, very strong or make poor estimates of wind velocity (or possibly both)

 

[Orsonab]

Anemometer blowout (groan) sale....

Saw this in the catalogue I got today for anybody who's really interested:
http://www.sierratradingpost.com/eu...=mode+matchallany&track=true&sid=10E9E0B6FA51

 

[Ed Poyer]

My experiences are similar to Kevin's. For me, gusts at 40-45 has cause me to lose footing, stumble etc. I knew it was 40-45 because I had a wind guage. I've asked people to estimate the wind at various times, then check it against the wind guage reading. Their estimates are generally very much over stated. A common dynamic is for folks to think they've been exposed to much higher winds than they in fact were, then they go out & get clobbered.

As far as Beaufort scale is concerned, the wind in the tree tops can be very different from what you are actually experiencing on the ground. If you doubt this, just climb a short observation tower, & feel the change in the breeze.

I've noticed that a patch of modest height scrub can protect more effectively than a large, solid (truck-sized) rock, perhaps because the wind gets broken up by a mass of small objects such as bushes, but is deflected around a solid knob.
Ed

 

[weatherman]

I like DougPaul's calculations and Bill's estimates. So, 60 MPH knocks you over (my 80 lb son knocks me over if I'm not looking) and 80 MPH may lift you off your feet. I was in an 82 MPH gust a few winters ago at Hojo's that I know about, because I was outside and came into the little doorway for shelter, and the anemometer had just measured it. I realized I could not control my body at that speed unless I was really braced for it. It was fun, but as others mention, I doubt I could have climbed anything with any degree of coordination if it were sustained at that speed.

 

[expat]

Quote: "As for stories of summitting in 100 mph winds, those guys are either very, very strong or make poor estimates of wind velocity (or possibly both)"

I summitted Adams once when the winds were reported by MWO to be 70 sustained with gusts to 100. But we had camped near Madison Hut and came up Adams along the Star Lake trail, so we were out of the wind until we actually stepped on the summit. Of course, since Adams is lower than Washington, there could have been a reduced velocity. I do know that it was impossible to stand, even when leaning, on the summit for more than about ten seconds.

 

[TCD]

I was on the West summit of Pitchoff in the adks a few years ago in the wind. A steady west wind was making it difficult to walk, both because the wind was pushing me off balance, and also because the wind would blow my feet around when I picked them up, causing stumbling. At one point, a sudden gust knocked me right down into a sitting position. I estimated 40, gusts to 60, which sounds reasonable based on other posts.

(For a real high end calibration point, remember that skydivers fall, when spread eagled, about 120 mph. So in theory, in a 120 mph wind, you could tie in and fly like a kite. A 120 mph wind would actually blow you away like an autumn leaf.)

 

[Tom Rankin]

I was on the West summit of Pitchoff in the adks a few years ago in the wind. A steady west wind was making it difficult to walk, both because the wind was pushing me off balance, and also because the wind would blow my feet around when I picked them up, causing stumbling. At one point, a sudden gust knocked me right down into a sitting position. I estimated 40, gusts to 60, which sounds reasonable based on other posts.

(For a real high end calibration point, remember that skydivers fall, when spread eagled, about 120 mph. So in theory, in a 120 mph wind, you could tie in and fly like a kite. A 120 mph wind would actually blow you away like an autumn leaf.)

Having sky dived, i can state confidently that I've never felt wind like that!!!

 

[Pete_Hickey]

Just a quick note on the physics: the force due to wind is proportional to the density and proportional to the square of the speed. (For the equation minded: force=1/2 * rho * v*v * S, whre rho is the density of the air, v is the velocity, and S is the equivalent area of the object) So it will diminish at lower pressures, but increase rapidly with wind speed.

The density. As everyone who rides a bicycle at sub-zero temperatures knows (as do pilots), the density increase as the temperature decreases, meaning that there will be more force from a winter wind than from a summer wind.

 

[DougPaul]

An entry level Cessna pilot once compared the air to a river. With that in mind, I'm guessing what Ed said makes sense. A large rock in the river would create an eddy and the intensity of the upstream current that is downstream of said rock would be a matter of how fast the regular current is moving.

Both air and water are fluids flowing by obstacles. There is a parameter called the Reynolds Number which takes into account the properties of the fluid, the speed of flow, and the size of the object. If two systems have the same Reynolds number, the flows are very similar.

At least as important to the hiker is the boundary layer of the airflow. The "bottom" of this layer is against the ground and does not move, the "top" flows at the free stream velocity. There is a relatively smooth transition between the two if the flow is reasonably laminar. Plants and humans know about this--alpine plants are very short to "stay out of the wind" and humans (usually) know enough to duck down to avoid the wind (or even crawl if the wind is strong enough). The boundary layer in air can be up to ~500 ft thick.

Doug

 

[DougPaul]

The density. As everyone who rides a bicycle at sub-zero temperatures knows (as do pilots), the density increase as the temperature decreases, meaning that there will be more force from a winter wind than from a summer wind.

Or you can take your bike up to high altitudes to reduce the wind resistance...

Doug

 

[Waumbek]

Both air and water are fluids flowing by obstacles.

Check out the spiderometer on MWO's Weather Discovery Center page. The WDC (across the street from EMS in No. Conway) is mainly about wind and is geared to kids (and the young at heart of all ages) with different hands-on ways of understanding how wind works. It is explained with lots of analogies to the movement of water. There's a mock up of the Obs weather station room in 1934, year of the Big Wind. You can go into the room, close the door, punch a button, and you experience a modified simulation of what it felt like when the wind roared up to 231 mph. The entire room rocks 'n' rolls.