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From: animal@ihlpa.UUCP (D. Starr)
Newsgroups: net.cycle
Subject: Re: Anticipating \Black Ice/
Message-ID: <2230@ihlpa.UUCP>
Date: Fri, 7-Nov-86 14:49:58 EST
Article-I.D.: ihlpa.2230
Posted: Fri Nov  7 14:49:58 1986
Date-Received: Sat, 8-Nov-86 07:10:16 EST
References: <376@cord.UUCP> <11700008@clio> <2222@orca.TEK.COM>
Organization: AT&T Bell Labs, Naperville, IL
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Here in the midwest, we generally only get the kind of "black ice"
that's being discussed under special weather conditions.  The daytime
highs have to be warm enough to melt large amounts of snow, then it
has to get cold enough overnight for the humidity to condense out and
freeze on the pavement.  This situation can usually be predicted by
the heavy fog overnight and in the morning.  This is particularly
annoying because it comes in what seems like "good" weather--usually
a semi-warm (35 and rising) morning, often low fog that looks like it'll
burn away by mid-morning--then you walk down the drive and fall down
on that thin layer of ice.  Nasty stuff.

Luckily, that kind of ice is fairly uncommon here.  Generally, pavement
lubrication is supplied by rain or snow, and gives ample warning.  I
follow some fairly simple rules for winter riding:

1.  Sunny and *below freezing* for a couple days usually means dry
pavement and near-summertime riding safety.  Be careful, though, of
the reduced traction caused by salt film on the roads (salt is a bit
slippery) and the fact that your tires never warm up.

2.  Above freezing for several days is usually safe regardless of
sun or cloud conditions.  The pavement is warm enough that snow will
not stick unless it is incredibly heavy.  I have ridden under 
conditions of snowfall and warm pavement, and while it is slightly
more slippery than rain, it is negotiable with sufficient care.  I
generally don't go out if it's snowing, but will ride within a 2-hour
radius of home under threatening conditions.

3.  Cloudy and very cold (under 20 degrees) is usually OK.  Most snowfall
comes between 20 degrees and freezing; below 20 there usually isn't enough
water in the clouds to produce more than a flurry.  Flurries are not bad
if the pavement is cold; if it warms up enough for car tires to melt it
you can have problems.  This is particularly bad at intersections, where
the catalytic converters throw off a lot of heat.  

4.  Steady temperatures right around freezing are NO WAY.  This iis especially
true if there is lots of half-melted snow on the ground and temperatures
are rising slowly.  This is the perfect circumstance for the formation of
"black ice."

5.  I will not ride in sleet or freezing rain under any circumstances.  If
this means I have to stop somewhere I will do that.

6.  I cheat a little.  I used to carry a business card from Sandman's Cycle
Rescue Service; now I have an old trailer parked at home and can use it to
fetch the bike if I am stranded by foul weather.

One more note--there is another material that I have heard referred to
as "black ice."  This is dirty frozen water.  Because of the dirt in it,
it looks like pavement, and it is found under virtually all winter weather
conditions.  Fortunately, it usually occurs only in small lumps and is
more of an annoyance, like tar strips, than a major hazard.