New -- Boards WINTER forecast contest

M.T. Cranium wrote: »

Ogimet? If not, we will work this out by consensus. Perhaps somebody on the forum can go in and get the answers at source. I will put the word out, who lives within 10-15 miles of Casement? That might be a good start.

Maybe I will come over and pitch my tent. :cool:

Fionagus wrote: »

I just checked Ogimet's data for last January and they do indeed have the snow depths for Casement so that should work fine

http://www.ogimet.com/cgi-bin/gsynres?lang=en&ind=03967&ndays=30&ano=2010&mes=02&day=01&hora=00&ord=REV&Send=Send

[SIZE=-1]AAXX 11001[/SIZE] [SIZE=-1]03967 11465 70906 10021 20009 30080 40197 57014 60011 76062 875//
333 42005 81712 87650=

thetonynator wrote: »

1. DEC IMT will be 4.8
JAN IMT will be 4.9
FEB IMT will be 4.5

2. DEC precip will be 80%
JAN precip will be 110
FEB precip will be 80%

3. Max temp for the three months 13.7
Min temp for the three months -7.8

4. Highest wind gust in knots 55 knots

5. Snowfall in cms at Casement for period 1 Nov to 31 Mar: 17.5cm

OPTIONAL comments _ Great work lads, a lot of effort and time gone into this!!!

M.T. Cranium wrote: »

Update on the contest. I contacted Met Eireann about the verification of snow depths at Casement. So far I haven't heard back. I will wait until 10 November and if I haven't resolved that issue, I will let all contestants know that we are switching the location. You may then adjust your prediction if you wish.

6.7 Measurement of snowfall and snow cover

The authoritative texts on this topic are
WMO (1994) and WMO (1992a), which cover the
hydrological aspects, including the procedures,
for snow surveying on snow courses. The following
is a brief account of some simple and
well-known methods, and a brief review of the
instrumentation.

Snowfall is the depth of freshly fallen snow deposited
over a specified period (generally 24 h). Thus,
snowfall does not include the deposition of drifting
or blowing snow. For the purposes of depth
measurements, the term “snow” should also
include ice pellets, glaze, hail, and sheet ice
formed directly or indirectly from precipitation.
Snow depth usually means the total depth of
snow on the ground at the time of observation.
The water equivalent of a snow cover is the vertical
depth of the water that would be obtained by
melting the snow cover.

6.7.1 Snowfall depth
Direct measurements of the depth of fresh snow on
open ground are taken with a graduated ruler or
scale. A sufficient number of vertical measurements
should be made in places where drifting is considered
absent in order to provide a representative
average. Where the extensive drifting of snow has
occurred, a greater number of measurements are
needed to obtain a representative depth. Special
precautions should be taken so as not to measureany previously fallen snow. This can be done by
sweeping a suitable patch clear beforehand or by
covering the top of the old snow surface with a
piece of suitable material (such as wood with a
slightly rough surface, painted white) and measuring
the depth accumulated on it. On a sloping
surface (to be avoided, if possible) measurements
should still be taken with the measuring rod vertical.
If there is a layer of old snow, it would be
incorrect to calculate the depth of the new snow
from the difference between two consecutive measurements
of total depth of snow since lying snow
tends to become compressed and to suffer
ablation.

6.7.2 Direct measurements of snow
cover depth
Depth measurements of snow cover or snow accumulated
on the ground are taken with a snow
ruler or similar graduated rod which is pushed
down through the snow to the ground surface. It
may be difficult to obtain representative depth
measurements using this method in open areas
since the snow cover drifts and is redistributed
under the effects of the wind, and may have
embedded ice layers that limit penetration with a
ruler. Care should be taken to ensure that the
total depth is measured, including the depth of
any ice layers which may be present. A number of
measurements are taken and averaged at each
observing station.
A number of snow stakes, painted with rings of
alternate colours or another suitable scale,
provide a convenient means of measuring the
total depth of snow on the ground, especially in
remote regions. The depth of snow at the stake
or marker may be observed from distant ground
points or from aircraft by means of binoculars or
telescopes. The stakes should be painted white
to minimize the undue melting of the snow
immediately surrounding them. Aerial snow
depth markers are vertical poles (of variable
length, depending on the maximum snow depth)
with horizontal cross-arms mounted at fixed
heights on the poles and oriented according to
the point of observation.
The development of an inexpensive ultrasonic
ranging device to provide reliable snow depth measurements
at automatic stations has provided a
feasible alternative to the standard observation,
both for snow depth and fresh snowfall (Goodison
and others, 1988). This sensor can be utilized to
control the quality of automatic recording gauge
measurements by providing additional details on
the type, amount and timing of precipitation. It is
capable of an uncertainty of ±2.5 cm.

6.7.3 Direct measurements of snow
water equivalent
The standard method of measuring water equivalent
is by gravimetric measurement using a snow
tube to obtain a sample core. This method serves as
the basis for snow surveys, a common procedure in
many countries for obtaining a measure of water
equivalent. The method consists of either melting
each sample and measuring its liquid content or by
weighing the frozen sample. A measured quantity
of warm water or a heat source can be used to melt
the sample.
Cylindrical samples of fresh snow may be taken
with a suitable snow sampler and either weighed or
melted. Details of the available instruments and
sampling techniques are described in WMO (1994).
Often a standard raingauge overflow can be used
for this method.
Snowgauges measure snowfall water equivalent
directly. Essentially, any non-recording precipitation
gauges can also be used to measure the water
equivalent of solid precipitation. Snow collected
in these types of gauges should be either weighed
or melted immediately after each observation, as
described in section 6.3.1.2. The recording-weighing
gauge will catch solid forms of precipitation as
well as liquid forms, and record the water equivalent
in the same manner as liquid forms (see
section 6.5.1).
The water equivalent of solid precipitation can also
be estimated using the depth of fresh snowfall. This
measurement is converted to water equivalent by
using an appropriate specific density. Although the
relationship stating that 1 cm of fresh snow equals
the equivalent of 1 mm of water may be used with
caution for long-term average values, it may be
highly inaccurate for a single measurement, as the
specific density ratio of snow may vary between
0.03 and 0.4.
6.7.4 Snow pillows
Snow pillows of various dimensions and materials
are used to measure the weight of the snow that
accumulates on the pillow. The most common
pillows are flat circular containers (with a diameter
of 3.7 m) made of rubberized material and filled
with an antifreeze mixture of methyl alcohol and
water or a methanol-glycol-water solution. The
pillow is installed on the surface of the ground,flush with the ground, or buried under a thin layer
of soil or sand. In order to prevent damage to the
equipment and to preserve the snow cover in its
natural condition, it is recommended that the site
be fenced in. Under normal conditions, snow
pillows can be used for 10 years or more.
Hydrostatic pressure inside the pillow is a measure
of the weight of the snow on the pillow. Measuring
the hydrostatic pressure by means of a float-operated
liquid-level recorder or a pressure transducer
provides a method of continuous measurement of
the water equivalent of the snow cover. Variations
in the accuracy of the measurements may be
induced by temperature changes. In shallow snow
cover, diurnal temperature changes may cause
expansion or contraction of the fluid in the pillow,
thus giving spurious indications of snowfall or
snow melt. In deep mountain areas, diurnal temperature
fluctuations are unimportant, except at the
beginning and end of the snow season. The access
tube to the measurement unit should be installed
in a temperature-controlled shelter or in the ground
to reduce the temperature effects.
In situ and/or telemetry data-acquisition systems
can be installed to provide continuous measurements
of snow water equivalent through the use of
charts or digital recorders.
Snow pillow measurements differ from those taken
with standard snow tubes, especially during the
snow-melt period. They are most reliable when the
snow cover does not contain ice layers, which can
cause “bridging” above the pillows.
A comparison of the water equivalent of snow
determined by a snow pillow with measurements
taken by the standard method of weighing shows
that these may differ by 5 to 10 per cent.

6.7.5 Radioisotope snowgauges
Nuclear gauges measure the total water equivalent
of the snow cover and/or provide a density profile.
They are a non-destructive method of sampling and
are adaptable to in situ recording and/or telemetry
systems. Nearly all systems operate on the
principle that water, snow or ice attenuates radiation.
As with other methods of point measurement,
siting in a representative location is critical for
interpreting and applying point measurements as
areal indices.
The gauges used to measure total water content
consist of a radiation detector and a source, which
is either natural or artificial. One part (for example,
the detector/source) of the system is located
at the base of the snowpack, and the other at a
height greater than the maximum expected snow
depth. As snow accumulates, the count rate
decreases in proportion to the water equivalent
of the snowpack. Systems using an artificial source
of radiation are used at fixed locations to obtain
measurements only for that site. A system using
naturally occurring uranium as a ring source
around a single pole detector has been successfully
used to measure packs of up to 500 mm of
water equivalent, or a depth of 150 cm.
A profiling radioactive snowgauge at a fixed
location provides data on total snow water
equivalent and density and permits an accurate
study of the water movements and density
changes that occur with time in a snowpack
(Armstrong, 1976). A profiling gauge consists of
two parallel vertical access tubes, spaced
approximately 66 cm apart, which extend from a
cement base in the ground to a height above the
maximum expected depth of snow. A gamma ray
source is suspended in one tube, and a scintillation
gamma-ray detector, attached to a photomultiplier
tube, in the other. The source and detector are set
at equal depths within the snow cover and a
measurement is taken. Vertical density profiles of
the snow cover are obtained by taking
measurements at depth increments of about
2 cm. A portable gauge (Young, 1976) which
measures the density of the snow cover by
backscatter, rather than transmission of the
gamma rays, offers a practical alternative to
digging deep snow pits, while instrument
portability makes it possible to assess areal
variations of density and water equivalent.

6.7.6 Natural gamma radiation
The method of gamma radiation snow surveying is
based on the attenuation by snow of gamma radiation
emanating from natural radioactive elements
in the top layer of the soil. The greater the water
equivalent of the snow, the more the radiation is
attenuated. Terrestrial gamma surveys can consist
of a point measurement at a remote location, a
series of point measurements, or a selected traverse
over a region (Loijens, 1975). The method can
also be used on aircraft. The equipment includes
a portable gamma-ray spectrometer that utilizes a
small scintillation crystal to measure the rays in a
wide spectrum and in three spectral windows
(namely, potassium, uranium and thorium emissions).
With this method, measurements ofgamma levels are required at the point, or along
the traverse, prior to snow cover. In order to obtain
absolute estimates of the snow water equivalent, it
is necessary to correct the readings for soil moisture
changes in the upper 10 to 20 cm of soil for
variations in background radiation resulting from
cosmic rays, instrument drift and the washout of
radon gas (which is a source of gamma radiation)
in precipitation with subsequent build-up in the
soil or snow. Also, in order to determine the relationship
between spectrometer count rates and
water equivalent, supplementary snow water
equivalent measurements are initially required.
Snow tube measurements are the common reference
standard.
The natural gamma method can be used for
snowpacks which have up to 300 mm water
equivalent; with appropriate corrections, its
precision is ±20 mm. The advantage of this
method over the use of artificial radiation sources
is the absence of a radiation risk.