Snow
 

Just a couple of pics from upstate NY. This is about 2-3 hours northwest of Cooperstown.

Upstate NY

dont beleive I would get on that roof without some temperary support under it. Good way to die.

Ron

He certainly doesn't have far to fall with all that now under him. I was doing the same thing once while I was home on leave, helping my dad clear snow off the roof on the back part of his house. It was an addition he put on himself but he only had a 3 degree slope on it. So he and I went out there to shovel it off and I slipped on some accumulated ice and fell. Oh, did I mention that it was the 2nd floor roof? Fortunately there was plenty of snow below me and I wasn't hurt. It happened so fast that I didn't even realize it until I hit the snowbank. I looked up to see my dad leaning over the edge saying, "Well, you gonna lay there all day or come up and help me finish." He's not the sympathetic sort.

Lets do some math
It takes 7 to 17 inch of snow to equal 1 inch of water, depending on the temp and the altitude and the amount of moisture.
This snow looks pretty packable (make a snowball) which means the moisture is there. Lets figure 10 inch = 1 inch.
A guy is generally 6 feet , so this snow looks like 5 feet tall. The roof area is not shown , but judging by what is shown, it's a good guess that the roof is at least 30X30.
Soooooooo
Naught goes into Naught , divided by the rotation of the earth and X 3 for Pac not having snow, = 28,125 lbs (for real answer) on that roof, before he climbed up there.
A couple well placed 4x4s would help the piece of mind.

Most of the rooves are designed to withstand a 60-80# deadload. There were a lot of new sounds coming from them.

In the picture, the snow has already compressed. The snow had little moisture because of the low (0-15 deg.) Temps. Not like an April or May snowfall that is loaded with water. Most oft the lake effect snow is that way...poofy. Even on the low end of your estimate, it's still heavy.

Keep in mind, the more he removes, the more concentrated the load becomes too.

Q
I would guess you mean 160-180% of dead load.
That would only be 300 LBs in a 10x10 area. I believe that snow is more than that. If you like I'll figure it. Also if that snow wasn't packable ( moisture) heavy it wouldn't stay up like it did. It would fall like powder. So , It may not be quite 28,000 lbs but , ok , Take off 8,000. That still leaves about 10 times your 60-80 figure.
Bracing is the only way I would get under that roof.
Hears a thought for ya. The roof would not colapse at the ends, it would do what is called a Vee shap collapse, and guess where he is and also guess where all that snow would go when it collapsed. (hint) on top of him.

Ron

Not really a place I want to be

Me Neither! Glad it's been mild here in the lower part of NY State.
I understand clearing off the roof, but with all that much snow where the heck to you put it after a while?

Man glad I don't live in NYC anymore, I don't think I could survive the cold back east anymore. Have been declimateized for that type of environment. Man I get cold here in Northern Ca when it gets 45 degrees at night here. That much snow in NY state unbelievable.