Hi rushingriver,
Great question, and one that makes me realize how much I miss seeing
snow! ( I live in a desert area )
1)Can it actually get too cold to snow?
No. Even at very cold surface temperatures significant snowfall can
occur. It snows at the South Pole, where it can reach ?22 F, and the
South Pole, where today it is ?8 F.
http://eup.k12.mi.us/~nbeelen/northpole/qanda.htm
http://www.arctic.noaa.gov/gallery_np.html
http://www.theweatherprediction.com/habyhints/222/
http://astro.uchicago.edu/cara/vtour/pole/
http://www.phys.unsw.edu.au/southpolediaries/webcam.html
(2) Does a lower temperature have an effect on the probability of snow?
Yes, when it is very cold, less moisture is retained by the air.
Therefore at warmer (relatively) temperatures, you?ll get heavier
snowfalls. ?In extremely cold air, moisture can condense out much
easier (without the lift necessary to produce clouds). In these cases,
crystallization can occur, and the ice crystals can fall from the sky
even when no clouds are present. ?
http://www.madsci.org/posts/archives/feb2000/950482073.Es.r.html
(3) Can it snow if the temperature is above freezing point?
No. Snow may fall from high in the sky, where it is colder, but if the
air near the ground is warmer than 32F, the snow will turn to sleet or
rain, depending on the air temperature. ?If the snow falls through air
with a temperature below freezing, it stays snow. If it falls through
a deep-enough layer of air that's above freezing before it reaches the
ground, it'll melt and become rain. Once it melts, a raindrop can't
turn back into snow, but it can re-freeze into ice. And that's how
sleet is made -- when raindrops fall through a layer of freezing air
that's thick enough for them to re-freeze. Meanwhile, you can get hail
in thunderstorms where there are strong updrafts and down drafts.
Then, precipitation makes multiple trips up and down through freezing
layers of air. That's why hailstones usually have several layers of
ice -- much like the skins of an onion.?
http://www.earthsky.com/2003/es030125.html
http://www.srh.weather.gov/jetstream/synoptic/precip.htm
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fcst/prcp/rs.rxml
Temperature also has an effect on the shape of a snowflake! At 14 ?10
degrees F, and also at 3 to ?8 degrees, you?ll get snowflakes in the
form of 6 sided plates.(Seen on the next link)
http://www.its.caltech.edu/~atomic/snowcrystals/class/class.htm
http://www.school-for-champions.com/science/snow.htm
Pictures of snowflakes:
http://www.its.caltech.edu/~atomic/snowcrystals/photos/photos.htm
There you go rushingriver! Thanks for an interesting question! If any
part of my answer is unclear, please ask for an Answer Clarification
before rating. This will enable me to assist you further, if possible.
Regards,
crabcakes-ga
Search Stategy:
Snow facts
Snow temperatures
Too cold to snow |
Request for Answer Clarification by
rushingriver-ga
on
14 Dec 2003 10:24 PST
Hi crabcakes,
Yes your answer is good and pretty much answers what I was looking
for. Before I give a rating, I'd like to clarify just one thing about
question #2 (Does a lower temperature have an effect on the
probability of snow?)
Let's assume there are 2 scenarios. The first scenario is: cloud cover
comes across to U.S. to my location, and the temperature is, say, 28
degrees farenheit. In the second scenario, the same cloud cover comes
to my location, but the temprature is 0 farenheit. At that point, will
the difference in temperature change the probability that it will snow
at my location?
Contrary to the desert, I live in a snow area, and often wonder if the
temperature will affect snowfall when I see clouds coming.
Thanks!
rushingriver
|
Clarification of Answer by
crabcakes-ga
on
14 Dec 2003 11:03 PST
Hello again rushing river,
Thank you for the clarification! This has been a most interesting topic!
I have found your answer here:
http://www.straightdope.com/mailbag/msnow2cold.html
Near the middle of this very interesting page is this quote
"the heaviest snowfalls almost always occur when the temperature is
not far from freezing, about 24º to 32ºF (-4º to 0ºC)"
As explained, you need temperatures below 32ºF for snow, but the
"warmer" air retains more moisture than the colder air. So, you would
get more precipitation from temps in the range of 24ºF to 32ºF. The
Straight Dope explains it this way
"...If you could turn all the water vapor in a volume of saturated
frigid air into snow, you would get less snow than if you did the same
thing to a volume of saturated chilly air. How much less? A lot less.
At 32ºF (0ºC), a cubic meter of saturated air (strictly speaking,
saturated with respect to ice) contains about 2.7 grams of water
vapor. At 0ºF (-18ºC), it contains six-tenths of a gram (only about a
fifth as much as at freezing)"
Your second scenario " the same cloud cover comes to my location, but
the temprature is 0ºF. At that point, will the difference in
temperature change the probability that it will snow at my location?"
Yes, you will have decreased odds of it snowing at 0ºF than your first
scenario of 28ºF.
Hope this clears things up for you. I'll leave you with this quote
from the same Straight Dope page posted above, "So, to sum up, at
temperatures near freezing, you can expect big honking snow flakes and
lots of them. One those comparatively rare occasions when it snows
near 0 F, you can expect individual snow crystals, but not very many
of them because such cold air can't "hold" as much water vapor. Below
about -40º, you can expect only very small crystals to fall, and very
few of them at that. So the next time somebody tries to tell you it's
too cold to snow, check the thermometer. If it's warmer than forty
below, send them up Fairbanks way, and they'll never doubt you again."
Regards,
crabcakes-ga
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