With CairnGorm Mountain officially closing for the season with the end of regular lift served snowsports at close of play on Sunday 6th June it’s time to total up this year’s fantasy lift league!

The results of the Fantasy Lift League for the 2010 season can be found by visiting the thread in the forum. The actual lift league can be found in the forum thread.

If you want to just see the nice graph of the snow making model, jump to the foot of this post!

For the 2010 competition a new extra was added, in the form of virtual snowmaking for the Sheiling Trainer Tow using ‘virtual’ Ratnik Sky Giant IV guns with AA nozles. The specs of these guns are as follows (with AA nozzles):

Start-up Temperature: -1.3c Wetbulb
Flow Rate (AA Nozzles): 2.72lps (at lowest quoted water pressure on gun specification).

Obviously not all the water that comes out of a gun will convert to snow and not all of the snow will land were you want it, so to keep calculations simple and to some extent account for these factors the following two assumptions will be used:

• Only machine made snow is counted. The calculation ignores natural snow inputs.
• A snow density of 0.5kg/l will be used, a so called ‘technical snow density’ value of 0.4kg/l is used for packed piste snow, so this figure gives a pessimistic conversion factor that we’ll use to account for the fact not all the water lands as snow, nor does all the snow go where it’s wanted.
• Snowmaking aims to provide a run that is 300m long, by 20m wide (inc uptrack) at a minimum average depth of 30cm for the Sheiling Tow to be counted as ‘Open’.

Snow loss from thaw conditions was calculated using a basic degree day ablation model, adjusted to use the average temperature returned from the database where the the AWS (Automatic Weather Station) recorded data every 5 minutes - rather than calculate an approximate average based on the Tmin and Tmax (Maxium Daily Temperature).

At it’s most basic a degree day ablation model is:

M = D_f*(Tmax -Tm)/2

Where M is the melt rate (water equivalent in mm day ^-1),  D_f is the degree day factor (mm °c ^-1 day ^-1), Tmax is the max daily temperature (°c ) and Tm is critical temperatre for melt to occur (°c).

Within Day Temperature variation

An important aspect of Scotland’s climate is the variation of temperature within the day where the free air temperature may lie above 0°c for part of the day and fall below 0°c for the rest. Thus it is often the case that snow fall and snow melt will occur within the same day and similarly with a snow making system it is possible that there maybe at least some albation during the same day as when snow making was in progress.

This scenario could occur due to afternoon daytime maxima climbing above 0°c or due to a change in weather systems, such as a warm front sweeping in possibly overnight.

Thus applying a degree day ablation model on a full day basis increases the scope for considerable error in modelling as noted by (Dunn, 2000). Dunn, introduced an extra factor F_m (fraction of the day where T > Tm). Thus:

M = F_m*D_f*(Tmax -Tm)/2

However, both the average temperature and the F_m value used by Dunn et. al. was an approximation derived from daily temperature values and day length.

Adaption for use with AWS data

With the availability of AWS data sampled at 5 minute intervals throughout the day with weather stations situated at the foot of the Sheiling Trainer Tow and at the SSC Hut at the same elevation as the top of the Sheiling Tow, it is possible to accurately calculate the actual F_m value and to derive from SQL queries an actual rather than guestimated average temperatre for the period where T > Tm.

Calibrating a Degree Day Model for the Cairngorms?

Work previously done by Dunn et. al. as part of research into modelling catchment dynamics in the upper Dee catchment provides values to calibrate the degree day model. Though these have been used for the Sheiling ‘virtual snow making’ calculations, a couple of notes of caution:

• The snow density of machine groomed on-piste snow will be substantially higher than natural snow for the majority of the snow season.
• Machine made snow is naturally denser and more thaw resistant due to crystal structure than fresh natural snow.
• Thus ideally the Degree Day Factor should be re-calibrated specifically for modeling machine made and on-piste snow on CairnGorm Mountain.

The values provided by Dunn et. al. are as follows:

Degree Day Factor (D_f): 9.5 mm °c ^-1 day ^-1

Critical Melt Temperature (Tm) +1.8°c

Modelling Accumulated Depth

For the ‘fantasy lift league’ to keep the modelling as simple as possible natural snow inputs were not considered and the model was based soley on the accumulation and ablation of machine made snow, using a uniform snow density of 500gl-1 for both freshly made snow added and for the actual snow depth loss calculated from the mm of meltwater equivilent from the degree day ablation model.

Combining the modelled daily snow making hours with the daily ablation rate it was possible to calculate the new snow made and total up an accumulated depth of machine made snow for each scenario (based on number of guns). When the accumulated depth exceed 120cm for any scenario only 1/4 of the available snowmaking hours were used beyond that point.

Where the accumulated machine made snow depth in any scenario exceeded 200cm at midnight no snow would be made that day or following days until one started with a depth below the 200cm threshold.

The graph below shows the modelled accumulated machine made snow depth from 4th November 2009 till 20th May 2010 (Series numbers correspond to number of Ratnik Sky Giant IV Snow Guns used in the model):

Accumulated Machine Made Snow - Modelled Depth

The graph shows some interesting implications of different numbers of guns in the scenario outlined above given the target depth constraints specified.  While the 2 gun scenario significantly out performs the 1 gun scenario, giving 31 days more cover > 30cm than 1 gun, there is only a small difference between 2,3 guns (3 extra days) and 4 guns (10 extra days over 2 guns). While the 5 gun scenario gives a further 20 day jump over the 4 gun scenario, as can be seen on the graph, keeping the snow depth above the 30cm mark through the milder period in the 1st half of May while all other scenarios see snow depth fall below 30cm or reach 0.

Some further thoughts…

The Degree Day Factor (D_f): 9.5 mm °c ^-1 day ^-1 used may be overly pessimistic in terms of a managed snowsports scenario, a D_f of 3 - 4 mm °c ^-1 day ^-1 would be commonly used within an Alpine Set Up.

However a degree day model does not try to be accurate day to day, but to average out conditions experienced so that it is accurate over a longer time period. Basically such a model does not take account of the difference between a calm, dry day with +7°c and a day with driving rain, storm force winds and +7°c where the snow melt as we know only too well in Scotland would be markedly higher.  The D_f must account for both scenarios.

On the flip side, it is likely the snow making modeling was over optimistic in terms of the % of water pumped through a gun that is actually converted to snow which lands where it is supposed to. Much work is needed to advance the calibration of such modeling for real use in snow making research in the Scottish Highlands.

REFERENCES:

S.M Dunn, S.J. Langan, R.J.E. Colohan “The impact of variable snow pack accumulation on a major Scottish water resource” - The Scienece of the the Total Environment 265 p181-194 (2000)

Just some short clips of spring snow fun on the middle slopes of CairnGorm Mountain on the final day of spring, a scorcher as summer arrived a day early! Despite it being warm in shorts and t-shirt, the spring snow mid-mountain was near perfect, loose crunchy granular spring snow, Coire Cas was just a delight to cruise down creating your own pleasently cooling breeze.

A 4 1/2 minute video of the full top to middle run via the Traverse and Coire Cas is also available at http://www.youtube.com/watch?v=9ksyIq6DeRU .

Video from CairnGorm Mountain on Sunday 16th May 2010, mostly Ptarmigan Terrain Park and at the end descends of Coronation Wall / Headwall.

The Gorm Session from TheMotherlodeProject on Vimeo.

Those who were following the blog late autumn and early winter will remember the snow making videos from Heavenly, California that I posted. By late January the Heavenly Snowmaking crew had met their target base depths that should ensure key links and low level trails last the season and the main winter snowmaking operations were stood down on 31st January.

The Snowmakers Episode IV: Looks back at their winter.

It is said that a picture speaks a thousand words, so here are a couple of thousand words (with a few more overlain) which show a naturally made case for the West Wall Chairlift.

Access to the WWP last week

The top photo was taken from the Laogh Mor Return bridge at the foot of the lower Ciste Gully on Wednesday 17th March, the day before the forecast storm force winds brought a significant thaw.

No Access to the WWP this week

As of the weekend no on snow route from the Ciste Gully, East Wall or the natural fall line of the West Wall (indicated by black arrows) back to the West Wall Poma remains.

All available routes involve crossing heather and uphill traverses to minimise this. The solid red line indicates a common route, while the dashed lines indicate the variations being attempted. All involve leaving the Ciste Gully at a height that misses out a substantial part of the run, compared to the Chairlift Boadwalk (purple line).

For now it remains easier to ski out the Ciste Gully to the car park, but this is a very low level run (below 2000ft) and can’t be expected to last far into spring.

Despite the faff of reaching the West Wall Poma  a significant proportion of the runs are lost, this puts of people off using the area, limiting terrain for more advanced riders. Plus the Poma itself deters intermediates and families from utilising some of the best blue graded terrain on the mountain.

Sign the E-petition to reinstate the Ciste Chairlifts: www.savetheciste.com

The Webcam pages for the Glencoe, CairnGorm, Loch Morlich and Aviemore Winterhighland Webcams has had a small upgrade that makes it much easier to view the older images.

A ‘lightbox’ pop up has been added that enables viewers to toggle through 6 images from the last hour and/or the last 15 hourly images from each camera. So if you’ve just got in from work to see dusk on the camera you can view an hourly snapshot of the whole day with ease.

Viewing today

The sustained thaw of recent days has been steadily weakening the ice that had kept it’s wintry grip on Loch Morlich for 94 days and alas the overnight gales coupled with rising water levels eventually fractured the weakened ice and within hours the Loch was open and choppy, once the ice fractured the wind and increasing waves accelerated the break up.

^Loch Morlich remains ice bound at dusk on Thursday.

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^But by late morning the Loch was free from the grasp of winter.

Sad in a way that the Loch did not remain frozen for another week to break the 100 day mark and it will seem slightly strange to look down from the ‘Gorm for the first time in three months and not see the white frozen expanse below.

The bit of good news for snowsports though is that the air temperature was back below freezing at the Summit late afternoon and dew points are below 0c and it’s dry, plus the wind is moderating. Snow should be setting up firm higher up and drying out and crunching up lower down - the thaw for now has relented.

Adam Watson reports that by the afternoon snow had stopped thawing and was firming up about 150-200ft above the car park level at Glenshee and at 2600ft the ground was still frozen where snow free. Frozen ground is as good as a base in that any new snow falling sticks straight away, it might almost be the Spring Equinox, but spring can stay on hold just now, we’re hopefully not yet done with winter 2010.

Sheiling AWS down to remove sticking wind vane.

Recently the Sheiling Tow AWS had been reporting an unusually high frequency of suspected anemometer icing when the SSC Hut and Loch Morlich weather stations were not. An inspection of the weather station on my last visit to the mountain showed that the anemometer cups were no longer spinning freely and was sometimes snagging the wind vane housing - giving the anemometer an abnormally high resistance to be overcome before the cups would spin, greatly increasing the threshold wind at which an actual wind speed would be reported.

Two wind vanes sitting in the snow

The anemometer was swapped out on Saturday (13th March) and replaced by a brand new one. This is not permanently installed until it’s determined if the old one is fixable, reason being not wanting to cut the long wind vane cable to the length needed for this installation unnecessarily as it could render the vane useless for other sites.

Unfortunately the long cable being bundled up is picking up electrical interference, which has been giving some nonsense wind speed readings  on Saturday evening. If gust speed or current wind speed is reported far in excess of other recent speeds or those from other AWS’s on the mountain, it is likely to be false. Will try and fix the Sheilings own anemometer and if this is not possible will shorten the cable and permanently install the new one.

Sheiling AWS back in place as skiers head for home on the Carpark Run late Saturday afternoon.

After a trial with a laptop for a camera server a couple of weeks ago it was decided to install a permanent webcam at the top of the Main Basin T-bar, just short of the Summit of Meall a’ Bhuiridh itself. The trial being followed by the ‘big snowstorm’ and resultant road issues  on the planned installation day, meant a longer delay in installing a permanent camera than planned, but this was undertaken today (Friday).

Summit Webcam at Glencoe

The Live Image can be viewed at http://www.winterhighland.info/cams/glencoe .

I’d also like to take this opportunity to say a big thank you to Nigel and the entire fantastic team at the Crianlarich Hotel where I spent Thursday night for their hospitality and friendly service. Their Skier Special provides simply amazing value, £25b&b per night for a single or £40 for a twin/double and if you stay 3 nights you get a 4th on the hotel.

Fantastic breakfasts, will keep you going all day, from the traditional full fry up, to smoked salmon and scrambled eggs, to healthier options of fruit juice, fresh fruit etc. Excellent evening meals too, served in the bar or informal lounge with two massive wood burners at either end. Also have a drying room (much need after Thursday afternoon lugging stuff up the hill in preparation for Friday…)

See www.crianlarich-hotel.co.uk .

GPRS Issues affecting our CairnGorm and Glencoe on mountain cameras

There continues to be intermittent but regular service interruptions to Vodafone’s data service in some rural parts of the Highlands. Glencoe staff report regular occurrences where connections are possible but no data throughput is available - this has caused several spells of down time to the cameras, but not always at the same time. It appears that some of the cameras might be able to intermittently pick up more distant masts.

There is also a recurring issue with the Meall a’ Bhuachaille mast above Glenmore that serves CairnGorm. The root of this problem is thought to be weather related but the word from Vodafone is that engineering staff have not been able to carry out work on some of the high level rural masts due to access issues and depth of snow cover.

Well so says the sign at the door to the Meall Odhar Cafe…

Meall Odhar Cafe Sign.