Dave Cornwell wrote:

Dave Cornwell wrote:
Norman wrote:
Scott W wrote:

Of interest to contributors in the Home Counties I have published a snow
survey / winter index on my blog for my area in east London. It is
inspired by the old Snow Survey of Great Britain which ceased
publication after the 1991/92 season.

Further to Dave Cornwell's comment a few weeks back that people mostly
remember a winter through the amount of days with snow lying I decided
to use the data I produced for my winter forecast and try to find out
what snow cover has been like in my area going back to 1946/47 - the
first year of the original snow survey. I then divided the snow lying
days by the winter mean to give the index. I realise there is the work
of Bonacina to consider but as this is national I wanted to look more
indepth

Not surprisingly the 62/63 season came out a long way ahead of the
rest - mostly through the sheer sustained depth of the cold. There's
also one or two surprises - strange how the memory can fool you.

It is a work in progress and I would welcome any input.

http://wp.me/p2VSmb-8M

Using the mean temp in deg C gives a highly non-linear index as the temp
approaches 0 deg C. For example, for the same snow depth the index
calculated with a mean temp of +0.1 is double the index calculated with a
mean temp of +0.2 deg C, which is certainly not the sort of result you
are looking for. A mean temp of 0 deg C would give an index of infinity
then as mean temps dropped below 0 deg C the index would be a decreasing
negative value. Using a mean temp in deg K would be a much more valid
approach.

---------------------------------
Hi Norman - indeed I have been helping Scott with this and have suggested
Fahrenheit or adding a constant to the means to get a more proportional
index and I think Scott will do that when time permits. Most interesting
though and a good approach I think as it takes away some of those more
subjective memories. Dave
-----------------------------------------
In deg F, with (Snow Lying/Mean deg F) x 100 it comes out something like
this:- 1 1962-63 0.2 32.3 213
2 1946-47 1.3 34.3 168
3 1981-82 3.7 38.7 74
4 1954-55 4.4 39.9 68
5 1984-85 3.6 38.4 68
6 1978-79 2.9 37.2 64
7 1952-53 3.8 38.8 64
8 1985-86 4.1 39.4 55
9 1955-56 3.8 38.8 51
10 2009-10 3.3 37.9 50


Nevertheless I agree deg K would be better. I don't think Scott's intention
is to get an index that has quantitative meaning, more a general ranking
which it seems to do better than anything else I've seen.

I agree that the approach is interesting. As you say, the absolute index values
don't have any meaning. The indices enable winters to be compared but deg K is
certainly the way to go.

If snow depth could be incorporated into the calculation of the index that
would add another relevant factor. Currently there is the so-call Eden Winter
Snow Index (EWSI). The monthly (or seasonal) value is calculated as the sum of
the daily 0900 snow depths (cm). It would then be a matter of deciding what
were appropriate weighting factors to be applied to Scott's index and the EWSI
before adding them. All good stuff.

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.