Hi Pat,
All the snow reports that I have seen quote depths in centimetres. When I
lived in South Africa I never saw any snow reports. Somehow I suspect
that
Oz is the same.
Regards (tongue in cheek)
Martin
-----Original Message-----
From: owner-u...@colostate.edu [mailto:owner-u...@colostate.edu] On Behalf
Of Pat Naughtin
Sent: 16 February 2011 23:52
To: U.S. Metric Association
Subject: [USMA:49874] Re: Snow ratios
On 2011/02/17, at 09:34 , James R. Frysinger wrote:
John Steele points out that my mental math needs some WD-40 to get
loosened back up.
Make those figures 0.7 mm/cm, etc.
Thanks again, John.
Jim
Dear Jim,
Drat -- those pesky centimetres strike again -- this is the same error I
made in this month's Metrication matters newsletter that started this
thread.
Sliding the decimal point back and forth clearly needs a squirt of your
WD-40.
Cheers,
Pat Naughtin LCAMS
Geelong, Australia
On 2011-02-16 1444, James R. Frysinger wrote:
Interesting. The data in this article jibe well with the sparse data I
collected. I had stated here earlier that my observations were averaging
in the order of 7 mm/cm to 8 mm/cm of rain to snow. The annual data
given on page 11 of this report (13 cm of snow to 1 cm water equivalent)
work out to 7.7 mm/cm. Their data set is much larger than mine, making
their inferences much more robust. Also, the locations are widely
separated. Yet, we came out to about the same conclusions!
Jim
On 2011-02-16 0300, 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 <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
<http://www.metricationmatters.com/>for more metrication information,
contact Pat at pat.naugh...@metricationmatters.com
<mailto:pat.naugh...@metricationmatters.com>or to get the free
'/Metrication matters/' newsletter go to:
http://www.metricationmatters.com/newsletter to subscribe.
--
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 pat.naugh...@metricationmatters.com or to get
the free 'Metrication matters' newsletter go to:
http://www.metricationmatters.com/newsletter to subscribe.
