On 11/02/2013 10:37, John Hall wrote:
In article ,
Dave Cornwell writes:
Or for the youngsters who like online stuff similar here based on
RH:-
http://www.sciencebits.com/SnowProbCalc

(plus a link to the theoretical equations)
Presumably using dry-bulb and dewpoint, or dry-bulb and RH, or dry-bulb
and wet-bulb are all alternative ways of doing what's effectively the
same calculation. (Wet-bulb temperatures seem to have rather gone out of
fashion for some reason. It's surprising, since if the wet-bulb is below
0C you know at once that anything frozen isn't going to melt.)

I have one of those two-a-penny electronic weather stations. It gives
me the air temperature, relative humidity and dewpoint.

To apply Will's formula is a simple matter of noting two readings,
adding them together, and seeing from Will's list what the snow
probability is. And the consensus of opinion here seems to be that this
works well enough for most practical purposes.

Unless you actually have a psychrometer or a properly exposed wet-bulb
thermometer, how easy is it to obtain the wet-bulb temperature without
solving what I believe is a fairly complex equation or resorting to
tables or even one of those special slide rules?

Need I say more?

[P.S. Will's formula is also a lot more accurate than the "Precipitype"
predictions you see, some of which seem to rely mostly on the 850hPa
temperature (= -3C rain; -4C or -5C sleet; = -5C snow) regardless of
the temperature and humidity structure below.]

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- Yokel -

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