When I lived in Canada, we sometimes would grade our snow as slushy, fluffy,
crunchy, squeaky.
Slushy - 0 to -3.
Fluffy - -3 to -12.
Crunchy - -12 to -25.
Squeaky - anything below -25.
John F-L
----- Original Message -----
From: Pat Naughtin
To: U.S. Metric Association
Sent: Wednesday, February 16, 2011 8:02 PM
Subject: [USMA:49870] Re: Snow ratios
Thanks Scott,
A most interesting reference.
Cheers (and G'day to you too!),
Pat Naughtin
Geelong, Australia
On 2011/02/16, at 20:00 , Scott Hudnall wrote:
As an avid skier, I pay close attention to the temperature of the storm -
as colder storms yield lighter, fluffier powder. Optimal conditions would be a
relatively cold storm at night, with clear skies during the day. (We call this
a blue-bird powder day).
In fact, I am headed to Whistler, British Columbia later this week!
(Whistler is unofficially and affectionately nicknamed "Australia's largest ski
resort" because many of the resort staff are Australian snowboarders!)
Anyway, here is an excellent paper on snow ratios that may help you out:
http://www.meted.ucar.edu/norlat/snowdensity/from_mm_to_cm.pdf
G'day Pat!
Scott Hudnall
Oakland, CA USA
On Feb 09, 2011, at 16:31 , Pat Naughtin wrote:
Thanks Jim,
I will use your data when I correct the other error. I have to say that I
have been uncomfortable with the 10 times approximation between snow and ice as
being too trite. Can I plead ignorance as we in Australia don't see a lot of
snow unless we travel to our few mountains. Our highest mountain, Mount
Kosciusko, is only 2228 metres high somewhat puny by your standards.
Cheers,
Pat Naughtin
Geelong, Australia
On 2011/02/10, at 07:32 , James R. Frysinger wrote:
If anybody is worried about their roofs, please use at least 320
kg/m³ for wet snow on sloped roofs. If you have a flat roof, determine whether
the drain is working, it will be the difference between 320 kg/m³ wet snow and
960 kg/m³ slush.
I believe that those figures assume an accumulation of 80 cm of "snow",
whether it be light and fluffy, wet and dense, slushy, or icy. If 80 cm of snow
falls, then, due to insolation (not insulation!) and warming by air or by
conduction from below, the depth will no longer be 80 cm.
And of course, not all snow accumulations are 80 cm in depth.
Rather than recommending a load estimate figure (that is based on 80 cm
of accumulation of whatever sort -- snow, slush, ice), it might be preferable
to teach the method, which then can be adapted to any given precipitation
amount.
I collect and report daily precipitation data for CoCoRaHS
http://www.cocorahs.org
including snowfalls. For snow I measure the depth of the accumulation,
collect snow from an area of known size, and weigh it to determine the
"rainfall equivalent". Working backwards for this winter for some of our
snowfalls, I observed that the snow:rain ratio might be better stated as
1 cm:0.7 mm
1 cm:0.75 mm
1 cm:1.2 mm (followed rain and freezing rain)
1 cm:0.26 mm (notes indicate unusually light & fluffy snow
with large "flakes")
As you can see, there is quite a bit of variation in those ratios for
my location. Generally, I would tend to characterize our snows as averaging 0.7
mm to 0.8 mm rainfall equivalent in 1 cm of snow from what I have seen the last
4 years. As John suggests, other areas might typically see snow of a different
average density.
This variation is exactly why meteorologists melt (or weigh) fallen and
accumulated snow to determine its actual water content. If one is concerned and
capable enough to estimate roof loading, they probably should do likewise.
By the way, some architects might show maximum snow loadings on the
plans for the structures built from those plans.
Jim
On 2011-02-09 1208, John M. Steele wrote:
I just received Metrication Matters 93, and saw the aircraft hanger
example again. As it is snow season in the US, and people need to
worry
about their roofs, I have to point out two huge errors in the example
as
I don't believe anyone should rely on that example.
80 cm of snow != 8 mm of rain
Even if the 10% rule were true, it would imply 80 cm of snow is 80 mm
of
rain. Doing some Googling on snow load and roof designs, I find the
density of wet, heavy snow is more like 32-33% water density, 320 -
330
kg/m³. The Washington (DC) area is not noted for light, fluffy powder,
and light fluffy powder isn't what collapses roofs. Using the 320
kg/m³
x 0.8 m, the actual roof load was more like 256 kg/m³ if the drainage
system was still working, not the 8 kg/m² of the worked example.
Flat roofs are a particular problem as snow tends to clog drainage and
then you get slush, a mixture of ice and water. Not surprisingly, the
density of slush lies between 920 kg/m³ (ice) and 1000 kg/m³ (water).
The figure above of 320 kg/m³ is for drained (but wet) snow - imagine
snow on a screen so any water melt can drip out.
I can't find the spec for flat roofs, a lot of local codes in the
northern US are 35-40 lb/ft² for sloped roofs. That converts to 170
kg/m². Some extreme snow areas are higher, and I would expect flat
roofs
to be higher.
If anybody is worried about their roofs, please use at least 320 kg/m³
for wet snow on sloped roofs. If you have a flat roof, determine
whether
the drain is working, it will be the difference between 320 kg/m³ wet
snow and 960 kg/m³ slush.
--
James R. Frysinger
632 Stony Point Mountain Road
Doyle, TN 38559-3030
(C) 931.212.0267
(H) 931.657.3107
(F) 931.657.3108
Pat Naughtin LCAMS
Author of the ebook, Metrication Leaders Guide, see
http://metricationmatters.com/MetricationLeadersGuideInfo.html
Hear Pat speak at: http://www.youtube.com/watch?v=_lshRAPvPZY
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
Metric system consultant, writer, and speaker, Pat Naughtin, has helped
thousands of people and hundreds of companies upgrade to the modern metric
system smoothly, quickly, and so economically that they now save thousands each
year when buying, processing, or selling for their businesses. Pat provides
services and resources for many different trades, crafts, and professions for
commercial, industrial and government metrication leaders in Asia, Europe, and
in the USA. Pat's clients include the Australian Government, Google, NASA,
NIST, and the metric associations of Canada, the UK, and the USA. See
http://www.metricationmatters.com for more metrication information, contact Pat
at [email protected] or to get the free 'Metrication matters'
newsletter go to: http://www.metricationmatters.com/newsletter to subscribe.
Pat Naughtin LCAMS
Author of the ebook, Metrication Leaders Guide, see
http://metricationmatters.com/MetricationLeadersGuideInfo.html
Hear Pat speak at: http://www.youtube.com/watch?v=_lshRAPvPZY
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
Metric system consultant, writer, and speaker, Pat Naughtin, has helped
thousands of people and hundreds of companies upgrade to the modern metric
system smoothly, quickly, and so economically that they now save thousands each
year when buying, processing, or selling for their businesses. Pat provides
services and resources for many different trades, crafts, and professions for
commercial, industrial and government metrication leaders in Asia, Europe, and
in the USA. Pat's clients include the Australian Government, Google, NASA,
NIST, and the metric associations of Canada, the UK, and the USA. See
http://www.metricationmatters.com for more metrication information, contact Pat
at [email protected] or to get the free 'Metrication matters'
newsletter go to: http://www.metricationmatters.com/newsletter to subscribe.
