Mild air & cold snow
21st January 2022
A strange mish-mash of temperatures today due to complicated inversion conditions:
1215hrs – Air temp at 620m beside Lochan a Choire in Coire Ardair:Â +4.0 degrees C.
1250hrs – Air temp at 910m in Coire nan Gamhna (about 1km away from Lochan a Choire): +7.0 degrees C.Â
1300hrs – Air temp at 1185m at Aonach Mor, our nearest mountain weather station: -1.7 degrees C.
A layer of really mild air below summit level but much colder near and above summits.
The Met Office’s weather station at the Cairnwell (Glenshee) at 933m registered +8.0 degrees C. at midday – a similar altitude to the snowpit site in Coire nan Gamhna.
Just to complicate things further:-
1250hrs – Surface snow temperature at 910m in Coire nan Gamhna: -0.4 degrees C. Lower surface temperature almost certainly due to it the snow losing heat directly to the sky as there was no cloud cover. All new and old snow stayed well frozen at all altitudes despite the mild air temperatures at certain altitudes.
(Above) Lochan a Choire below the crags of the Pinnacle Buttress and the Post Face of Coire Ardair. Very lean conditions!
Wild swimming advisory: Lochan a Choire at 620m was +2 degrees C. at midday Friday.
(Above) A lone climber nearing the top of Raeburn’s Gully on firm snow-ice. Very limited winter sport options at Creag Meagaidh. Easy Gully is complete but will soften as temperatures rise and rain sets in on Saturday.
(Above) The view out of Coire nan Gamhna towards the Post Face and the Inner Coire. Scant cover; patches of firm snow-ice here and there with a little thin, soft and cold windslab on some aspects of the coire rim today.
Wild swimming advisory: the water temperature in the wee footbath of a lochan at 815m was +0.8 degrees at lunchtime. You may not need your dookers for this puddle!
(Above) Talus on the steep NW-facing backwall of Coire nan Gamhna. Not used to seeing this coire in what might loosely be called very late spring conditions, so was interested to observe the contrasting colour, rock type and size of the talus up near the coire rim. It was pink/red and of a consistently smaller size and much finer-grained than the prevailing grey blocky stuff.
(Above) Here’s a close up. Genuinely interested. Can any of the earth science types out there identify the rock type for me? (Edit: Rhyolite??)
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22nd January 2022 5:01 pm
There’s a number of leucogranite intrusions around Coire Ardair: a leucogranite is just a normal granite without any of the dark minerals, e.g biotite, you normally find in a typical granite. This example is fine-grained enough that its basically just a rhyolite, although some geologists would tell you a rhyolite has to have been erupted as a lava onto the surface rather than solidified at depth as this likely has. However they are pedants of the highest order and rhyolite would be a perfectly acceptable field term for this.
22nd January 2022 7:27 pm
Excellent, Euan, just the sort of detailed response I was hoping for! Rhyolite will do for me.
Your ‘pedant’ reference made me chuckle. Pedantry crosses the boundaries of many disciplines!
As a group the SAIS used to be quite pedantic about identifying snow crystals until just a few years ago when it occurred to us that the more important issue – on the vast majority of occasions in Scotland – was how well bonded the layers in the snowpack were, not the grain type.
We still look carefully at snow grains of course, because there are occasions when identifying them correctly is paramount to accurately forecasting snow stability. (Usually, it’s when we have persistent weak layers induced by strong temperature gradients, or buried surface hoar. Experience has shown that these persistent weak layers can make for a very complicated picture of stability and occasionally produce big avalanches).
But arguing about whether a melt-form snow grain is actually better described in the typology as a ‘clustered rounded grain’ or ’rounded polycrystal’ is immaterial for most intents and purposes. (Huge pedant potential in just that one example!)
There are other examples and it’s quite a long list! If you have a few spare hours check this out: https://unesdoc.unesco.org/ark:/48223/pf0000186462