"Norman" wrote in message ...

It's been snowing in Tideswell all day with the temp between -2 and -4 and
with
a Force 3-5 wind. The snow has no liquid water content and the action of the
wind has broken it up into a very fine powder which has drifted very readily
in
the wind this afternoon and evening. There's now nothing that can be
described
as a 'level depth' anywhere. Some areas have been blown almost completely
bare
while in others it's getting close to a metre deep. This evening I've
guesstimated 15cm but, come daylight tomorrow, I suspect that I might
increase
that a bit. Nevertheless, there'll still be quite a bit of a guess in there.

The rainfall equivalent is an even more difficult matter. In a situation
like
this the rain gauge is irrelevant. Also, there's no representative bit of
snow
on the ground that I can 'capture' and melt. About the best I can think of
is
to use whatever I decide as a representative depth of fresh snow and use a
10:1
ratio. Does anyone know if there's an 'official' way of dealing with
this....
Ken?...Bernard?

Hi, Norman,

For depth I do as you do and take an average / general / sensible depth of
several readings to the nearest cm. Some days this is only a rough
approximation as I don't think there is an answer! This throws the Met O AWS
snow depth instrument out of the window in my opinion and there is no
substitute for a human observer for snow depths. There is then the issue of
the fresh fall. I use a board placed on top of the snow, but where should it
be placed to obtain a further sensible reading for fresh falls. The Met O do
not ask for a fresh fall measurement any more incidentally.

As you say the rainfall equivalent is even harder. To use the inverted
funnel method you need to be sure that you are only capturing the snow since
the last reading, so you need a "fresh falls board". Where should it be
placed? You must be sure none falls out when you bring the funnel upright!
The Met O way used to be to do this three times and take an average - a
long, laborious practice in an average Copley winter.

In practice I normally just melt the snow that is in the gauge funnel. I
assume that the Met O (and Environment Agency) have placed the rain gauge in
the most suitable place to best record precipitation and go from there. I
also place the fresh falls board close to the gauge.

A couple of days ago I had a fresh fall of 2cm but nothing in the funnel as
the snow had sublimated! I entered "Trace" in the obs as I knew there had
been precipitation.

Incidentally, I use two funnels and bottles here in Copley. I bring one set
in with the snow and melted snow at the obs time and replace them with the
spare set. The next time there is snow to melt I replace with the original
funnel and bottle and so on.

AWS gauges now being used by the Met O record only the snow that melts from
the funnel so I suppose that is now the way. I know the Environment Agency
record in that way from their Copley logger gauge and some of our wettest
winter days are then the sunny, dry ones when the snow is melting from the
gauge! All our worries and efforts could be in vain.

Personally I would not use the "ratio method" as this alters so much with
different types of snow. I usually write a note at the end of the month such
as "precipitation totals unreliable in snow and wind". I do smile sometimes
when I see snow depths reported in millimetres!

Best wishes,
Ken
Copley