Temperature drop @altitude w/windchill?

[PiLFy 3]

Evening All,
I'm scratching my head @the moment. Something doesn't seem to add up. Some crazy guys N gals @my DZ were jumping this weekend. It was about 32 degrees (& a bit windy) Fahrenheit on the ground. I checked a couple of charts @the engineer's toolbox:

http://www.engineeringtoolbox.com/air-altitude-temperature-d_461.html

http://www.engineeringtoolbox.com/wind-chill-effect-d_112.html

According to these charts. The temperature @14K' was about -20 Fahrenheit. Add windchill @120MPH, & it would be >-100degrees fahrenheit (?!). That can't be right. What am I missing, here?
Thanks.

[quade 4]

There's nothing inconsistent there.

Jump out of an airplane when it's 32°f on the ground and I can pretty much guarantee you'll find the experience to be f'in' cold.

The fortunate things about it is you can pretty much dress for it and you're only exposed to that wind chill for about a minute. You'll be f'in' cold by the time you land and even with two pairs of gloves on your fingers might hurt like hell, but you probably won't die from the cold weather jump.

quade -
The World's Most Boring Skydiver

[PiLFy 3]

Would there not have been frostbite of the face & fingers on most jumpers? They weren't shaking uncontrollable when they landed. I heartily concur w/the fuqqin cold part. I just don't see how it could have been more than -100 degrees fahrenheit without any frostbite.

[quade 4]

There's just not enough time in that temperature for frostbite to take hold. You'll absolutely feel cold, but the tiny pieces of skin you might have to leave exposed won't lose enough heat to freeze solid.

Few people make those kinds of jumps with an open face helmet and without wearing a balaclava or something to cover their skin.

quade -
The World's Most Boring Skydiver

[missbrz 0]

Frostbite occurs in stages. They probably could have had the first stage of frostbite and not even known it. It's relatively easy to recover from that. Plus they were only in that weather for a minute. It probably wasn't long enough for frostbite to set in.

[billvon 2,998]

>I just don't see how it could have been more than -100 degrees
> fahrenheit without any frostbite.

I've jumped at -34F at exit altitude. During that jump we had serious icing problems, and a lot of people took their helmets off so they could still (kinda) see. No frostbite. What saves us, usually, is that we're in that temperature for such a short time.

Keep in mind that for true frostbite to occur the following has to happen:

Capillaries constrict to save heat; this removes the heat source for the skin

Epidermis freezes (it's all dead anyway)

Dermis starts to freeze

Ice crystals grow large enough to rupture cell membranes

All that takes a little time, which is why we are _usually_ OK for a minute at a time.

[LouDiamond 1]

This might help you out.
Wind chill chart with frostbite exposure times

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[PiLFy 3]

Oh, those sick, glorious MFrs!!

I gotta buy 'em some beer for that. That's truly obscene. Thank You for clarifying that, everyone.

[theplummeter 15]

It's also not uncommon (especially this time of year) to have a temperature inversion or non standard temp lapse rates. Yesterday I took off at 34 degrees and climbed into 44 at 11000 feet.

[SansSuit 1]

I want to throw something out there. As someone who regularly exposes his entire body to excessive wind chills , it has been my observation that adrenalin might have some physiological effect on the cold on the body.

Example: A few years ago, I made 2 jumps under almost identical winter conditions, including same altitude. One jump I was nekkid, the other I was wearing my normal jumping gear. I felt much colder on the clothed jump. Even my fingers, which have a tendency to freeze up when cold, indicated I was colder on that jump. (Same gloves, both jumps). I felt the cold on the nekkid jump but it didn't reach me. I'm sure there are other factors that could have affected things but the difference was so drastic that I noted it.

I know that the jumping rush is greater for me when nekkid. I believe that translates into some sort of additional protection.

Peace,
-Dawson.
http://www.SansSuit.com
The Society for the Advancement of Naked Skydiving

[AggieDave 6]

Quote

There's just not enough time in that temperature for frostbite to take hold. You'll absolutely feel cold, but the tiny pieces of skin you might have to leave exposed won't lose enough heat to freeze solid.

Few people make those kinds of jumps with an open face helmet and without wearing a balaclava or something to cover their skin.

Actually, yes there is enough time in that temperature for frostbite to take hold. Frostbite happens in stages and damage is done even in the early stages.

Here is a list of times/temp/wind speed. So depending on your canopy and opening altitude, you can start getting up to the danger times.

http://www.survivaltopics.com/images/windchill-chart.gif

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

[davelepka 4]

Quote

According to these charts. The temperature @14K' was about -20 Fahrenheit. Add windchill @120MPH, & it would be >-100degrees fahrenheit (?!). That can't be right. What am I missing, here?
Thanks

Yes, it's very cold. However, keep in mind that as soon as you leave the plane, you gain 3 degrees for every 1000ft you fall, so by the time you open less than a minute later, it's 25 or 30 degrees warmer than when you exited. On top of that, opening a parachute takes the wind down from 100+ mph to something in the 20 or 30 mph range.

So you actual exposure time to -100 wind chill is very brief, on the order of seconds. From there, the air temp will steadily increase and the wind chill gets cut considerably when you open. Even with that in mind, it's cold as shit.

[MikeJD 0]

Quote

One jump I was nekkid, the other I was wearing my normal jumping gear.... Same gloves, both jumps.

Cheater!!

[wayneflorida 0]

Some points:

1. Those formulas are for standard laspe rates. very seldom are things standard.

Current temp here his about 61
Mobile winds aloft forecast says 35 at 12,000.
Not standard lapse rate.

2. Wind chill effect does not increase directly proportionally as the wind speed increases.

3. Air is less dense at 13.5K so wind chill effect would be less than same conditions on the ground.
There is no wind chill in space.
Good site that gives winds aloft with temps.
Change for your location

http://www.usairnet.com/cgi-bin/Winds/Aloft.cgi?location=MOB&Submit=Get+Forecast&hour=06&course=azimuth

[PiLFy 3]

Good points, & good site. Thank You

[PiLFy 3]

"you gain 3 degrees for every 1000ft you fall"

Wow, almost balmy, but I'm still not doing it...

Somehow, when facing 100 below zero (give or take). Thirty degrees doesn't sound like much. I've already frozen enough times in life. I like my comfort. I can wait another month.

[PiLFy 3]

El linko esta rota.

[PiLFy 3]

It's a free country, Jeff. Adrenalin or perversion, whatever works for you. Merely thinking of my scrotum in a -100* wind blast is enough to give me PTSD. If I'm not willing to do it wearing 10#s of insulated clothing. I'm certainly not willing to do it in the buff.

[PiLFy 3]

Thanks again for all the info, everyone.

[billvon 2,998]

>3. Air is less dense at 13.5K so wind chill effect would be less than same
>conditions on the ground.

Ah, but the planes fly faster. It all washes out. (In other words, 100 KIAS on the ground feels the same as 100 KIAS at 13.5K, assuming the same temperature.)

[PiLFy 3]

Dunno. I stumbled onto a tract explaining that colder air @altitude is drier. "The combination of low temperatures, low absolute humidity, & high winds at altitude poses a serious risk of cold-related disorders, such as hypothermia & windchill injuries." They were talking about Everest, but the effect would still be the same. Albeit less pronounced.

http://books.google.com/books?id=zQGKmbg18J8C&pg=PA281&lpg=PA281&dq=windchill+decreases+with+altitude?&source=bl&ots=y5eayy-Tyu&sig=TjIRyPe05BC1sWPTm-L8UaDiEa0&hl=en&ei=Z2-STajBMsS3tgeo0phl&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCIQ6AEwAw#v=onepage&q=windchill%20decreases%20with%20altitude%3F&f=false

[SansSuit 1]

Quote

Quote

One jump I was nekkid, the other I was wearing my normal jumping gear.... Same gloves, both jumps.

Cheater!!

Safety gear.

Peace,
-Dawson.
http://www.SansSuit.com
The Society for the Advancement of Naked Skydiving

[theonlyski 8]

Quote

Quote

Quote

One jump I was nekkid, the other I was wearing my normal jumping gear.... Same gloves, both jumps.

Cheater!!

Safety gear.

So you wore a condom too?

"I may be a dirty pirate hooker...but I'm not about to go stand on the corner." iluvtofly
DPH -7, TDS 578, Muff 5153, SCR 14890
I'm an asshole, and I approve this message

[kawisixer01 0]

I'm not too convinced on the accuracy of those charts. Having spent a lot of time jumping cessna 182's, I tend to glance at the thermometer on the wing a lot. Typically I've seen a 1-3 degree/1000' drop. A couple weeks ago I jumped it was like 35-40 on the ground and around 25 at 11k. And the wind chill charts i've seen show that the wind chill effect drops off quite a bit in the speeds above like 40mph. It is not a perfectly linear relationship. Having jumped in the winter, i've learned the main thing is to just make sure you don't have exposed skin. The only thing that gets real cold is your fingers under canopy.

[quade 4]

Quote

I'm not too convinced on the accuracy of those charts. Having spent a lot of time jumping cessna 182's, I tend to glance at the thermometer on the wing a lot. Typically I've seen a 1-3 degree/1000' drop. A couple weeks ago I jumped it was like 35-40 on the ground and around 25 at 11k. And the wind chill charts i've seen show that the wind chill effect drops off quite a bit in the speeds above like 40mph. It is not a perfectly linear relationship. Having jumped in the winter, i've learned the main thing is to just make sure you don't have exposed skin. The only thing that gets real cold is your fingers under canopy.

The outside air temperature gage (OAT) is a dry bulb temperature. Wet a cotton ball and wrap it around a thermometer, stick it out in the wind and you'll get a VERY different indication.

quade -
The World's Most Boring Skydiver