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Bill O
02-19-2007, 04:05 PM
Anybody ski or see the East Snowfields recently?

Just curious on the conditions. It looks like many rocks still exposed on the webcam view, but its hard to tell.

KD Talbot
02-19-2007, 05:07 PM
Haven' been up so I don't REALLY know, but from the looks of Jim's photo today, it looks unskiable, for me, anyway. It may be filled in more out of sight over the edge.
KDT

Bill O
02-19-2007, 05:21 PM
Haven' been up so I don't REALLY know, but from the looks of Jim's photo today, it looks unskiable, for me, anyway. It may be filled in more out of sight over the edge.
KDT

It looks grim from that photo, but I'm not sure it tells the entire story. If there is skiable snow it would be beyond the rollover, out of site.

KD Talbot
02-19-2007, 07:03 PM
Warmer weather headed our way this week, so after shift change I'm guessing Neil will check it out for us.

I'm getting off subject, but I skied at Gunstock today, windchills were -22, balmy by MW standards! Now does that increase if I'm skiing at 30mph, or is it pretty constant? How fast can a 200lb guy ski if he's not holding back? Hard for me to judge how fast I'm going. It feels faster than 30, but I know it probably isn't.
KDT

Bill O
02-19-2007, 08:32 PM
If there's a 15mph wind and you add another 30 on top of that it's going to have a huge effect on windchill.

I've never been good at guessing how fast I can ski, but 30mph is pretty easy to hit.

KD Talbot
02-19-2007, 09:10 PM
I suppose speed brings a lot of things into factor. Steepness of the slope weight, etc. The temp was around +5 but a -22 windchill, wouldn't that be faster than 15mph? More like 40mph on the chart I got from MWO. So say I was skiing 45mph with a -22 windchill, how cold would it "Feel Like"? Would that be like an 85mph wind? It's off my little chart. I don't suppose it matters much whether it's -22 or -50. It's brutal in my book. I'm curious because I wasn't cold and I want to sort of rate my equipment.
KDT

Brad
02-20-2007, 05:28 AM
When my son goes windsurfing he wears a wrist GPS. It tells him how far he sailed and the max speed he got to. That would do the trick for you too ...

Patrad Fischroy
02-20-2007, 08:21 AM
It is my impression that the GPS will underestimate your speed on the slope. I am pretty sure that it will only give you your horizontal velocity, not the velocity along the slope. And if it is calculating the distance along the slope the vertical measurements on the GPS are considerably less accurate than the horizontal ones. I seem to recall they are on the order of 3-5 times less accurate.

KD Talbot
02-20-2007, 04:11 PM
I appreciate the input, but for now I'll be content to estimate my speed. I don't carry GPS, a compass and a flashlight are my hi-tech gadgets for hiking. (I will never own a cell phone if I can avoid it.) I'm basically looking for a wind chill chart that goes over 50mph and an answer to the question, if I'm skiing 45mph and there is a 40mph wind, does this equal 85mph, and if it does, then what is the windchill besides damn cold?
KDT

Bill O
02-20-2007, 04:22 PM
if I'm skiing 45mph and there is a 40mph wind, does this equal 85mph, and if it does, then what is the windchill besides damn cold?
KDT

Yes, with many caveats:

Assuming you are skiing directly into that wind.

Assuming its really blowing 45mph. Which it probably isn't from 0-6 feet from the ground. It might be blowing 45mph at the summit on top of a tower, but not on the ski slope.

Assuming you can get going 45mph in a 40mph wind. That would give you an airspeed of 85mph. That's faster than downhill racers go, and they have the best technology in the world, the best form, and skin tight suits.

There's a calculator towards the bottom of this page. (http://www.weather.gov/os/windchill/index.shtml)

Above 60mph you only get small gains for large increases in wind speed.

KD Talbot
02-20-2007, 08:02 PM
Alright, now that's what I'm looking for. If I'm skiing directly into that wind I'm sure I'm not going anywhere near 40mph, am I? Hard to say. And the wind isn't blowing 40mph at ground level, either, is it? So, I'm probably not dealing with wind chills any worse than what is posted, unless I'm getting up good speed and heading straight into the wind. Correct?

When I'm skiing straight into the wind it feels as though I'm barely moving. I'd say 20-25 tops. If the winds blowing 20-25 at ground level then I'm only talking 40-50mph airspeed. With a 5 degree airtemp then it's like -20-25 windchill.

Am I in the right neighborhood?
KDT

Bill O
02-20-2007, 08:04 PM
With a 5 degree airtemp then it's like -20-25 windchill.

Am I in the right neighborhood?
KDT

Seems about right.

Steve M
02-20-2007, 10:59 PM
Here is a wind chill formula I found online, hopefully this will help you.

Wind chill temperature = 35.74 + 0.6215T - 35.75V (**0.16) + 0.4275TV(**0.16)

T is the temp. in degrees F.
V is wind speed in statute miles.

Note: In the formula, ** means the following term is an exponent (i.e. 10**(0.5 ) means 10 to the 0.5 power, or the square root of V), - means to subtract, + means to add. A letter next to a number means to multiply that quantity represented by the letter by the number. The standard rules of algebra apply.

rockin rex
02-21-2007, 07:06 AM
CUT YOUR SPEED BEFORE YOU JUMP!!!!!!!!!!!!!!!! (l.o.l.) Wind speed, ski speed and Temp is neat to figure out but what about speed, distance off ground when jumping and how much pressure is on the leg if you don't land it?? My son was at Stratton on Monday and he said temps were rather chilly willy there. Great idea to figure wind speed and speed skiing to actual temps that you are in on the mountain.

hobbes
02-21-2007, 12:32 PM
MWO's wind chill page, with handy chart, is at http://www.mountwashington.org/weather/wind-chill.php

Brad
02-21-2007, 06:17 PM
It is my impression that the GPS will underestimate your speed on the slope. I am pretty sure that it will only give you your horizontal velocity, not the velocity along the slope. And if it is calculating the distance along the slope the vertical measurements on the GPS are considerably less accurate than the horizontal ones. I seem to recall they are on the order of 3-5 times less accurate.
I do not think it is a question of GPSs being inaccurate. They just record the location - and elevation. It is a question of what software does to calculate distance and speed off the data. If it assumes flat surface - roads - water - then it will not be accurate. However, if it uses elevation in the calculation, then it should be accurate.

Patrad Fischroy
02-22-2007, 09:41 AM
Accuracy using a GPS is a relative term. Here is some data that I have picked up over the years as a mapper and with some dabbling in survey work. You may feel that I am quibbling, but in the case of steep terrain the effects of this are somewhat more severe than on flat land.
Most handheld consumer GPS units have an average accuracy of about 1-5m under optimal conditions, that is, clear sky, widespread satellite coverage, and minimal solar activity. The satellites used for our GPS system only extend to a latitude of 55 degrees North and South. When skiing, you are generally on a North facing slope. The chances of having a good constellation of satellites are not so good as most of the satellites will be blocked by the mountain. Plus, due to the geometry of the satellite, (their designed positioning was optimized for horizontal positioning) vertical measurements have an accuracy that is on the order of 1.5 to 2 times worse than the horizontal or 1.5-10m.

Bill O
02-22-2007, 12:03 PM
So...does anybody know about snow conditions on the East Snowfields?

Patrad Fischroy
02-22-2007, 12:07 PM
Sorry for the sidetrack:o

Bill O
02-22-2007, 12:14 PM
So...does anybody know about snow conditions on the East Snowfields?

Looking at the zooms things seem to be filling in nicely. Certainly big improvements over last week in the east fields on in Tucks.

As for GPS...the kind we have access to is not really to be used for elevation, unless it has a built in barometer. Unless you have more information than me, and you might, I think the GPS satellites go over 55 degrees in latitude. They are polar orbiting satellites, meaning they go over the poles, and complete an orbit every 90 minutes or so.

They are great fun for measuring speed when sea kayaking, but probably not for skiing.

Patrad Fischroy
02-22-2007, 12:59 PM
Face it, as much as you can geek out on anemometers and their response times and accuracies, I get the same way on geospatial measurements :)

as to the satellite orbits

http://www.gmat.unsw.edu.au/snap/gps/gps_survey/chap2/222sats.htm

The applicable text is

"The Block II satellite series have been deployed in six orbital planes at 60 intervals about the equator, with each containing 3 or 4 of the primary satellites equally spaced in the orbital plane (Table below). The orbital planes are at an inclination of 55 relative to the equatorial plane. According to deployment plans there are to be 3 active spare satellites spread evenly in addition to the primary 21 satellite configuration. However, the reality is that satellites are launched at predefined intervals, and if the constellation health is maintained, often more than the minimum 24 satellites are available. For example, at the time of publication of these notes (September 1999) there are 27 satellites transmitting signals that users can track."

And I do appreciate your knowledge on the instrumentation used in meteorology. And most particularly, your willingness to share it.