Roller Coaster No 2 & the Traditional Early December Mild Spell

After opening weekend it’s back to the weather Roller Coaster this week as the Atlantic really roars in to life unleashing a bought of zonality that comes with one of those dreaded full on South Westerly assaults on Tuesday.

Whether our recently formed early season base is either consolidated or robust enough for the top at CairnGorm to come through remains to be seen, we will just have to wait and see.

However don’t be too despondent to have had a base at all is actually quite good for this stage of the game as early season turns are often on baseless snow and the early part of December is traditionally a mild, wet and often stormy time.

Graphs of the average 850hpa (approx 4500ft) temperature actually show a rising trend for early December as we climb out of a marked November dip, before average temps start to drop off again later in the month as the decline towards thermal mid-winter in the second part of February begins. (see below)

GFS ensemble 850hpa Temperature Chart

Tuesday looks to be the worst day with winds exceeding 100mph in stronger gusts on the tops and Munro Level temperatures nudging painfully close to double figures for a time.

There will however be some snow preceding and following the warm sectors this week, much will depend on timing and exact tracks of the storms. The further North they track unfortunately the wider the mild sector we’re exposed to.

It doesn’t provide much comfort to skiers and boarders but it’s not uncommon to see the Scottish Mountains stripped completely in the first half of December, indeed even in bumper winters like 2001 the big snows of November 2000 were almost completely obliterated in the mild, wet and stormy first half of December. On the Gorm anyway only limited snow in the Top Basin and where it had been packed down by funicular construction traffic on the Traverse held out.

It’s also contrary to increasingly popular belief not a new phenomenon. V A Firsoff wrote in his 1949 book ‘The Cairngorms on foot and ski': “In November and December there may be considerable precipitation at higher levels, as a rule accompanied by high winds, but Old Yule is more often black than white and the heavy snows do not come till the second half of January, sometimes not even then.”

That was very true of the 2001 season as well, January was cold, but largely dry, surface conditions were often decent, but the runs were very narrow, it wasn’t till the tail end of the month and first days of February that the first big snow storms since late November arrived.

Any sliding done in Scotland before Hogmanay is a bonus, snow often comes between Christmas and New Years Day, but even January historically is still early season in Scotland. Spring is King and the best snows often don’t come till March or even into early April. So please don’t put the toys back in the loft at Christmas!

Roller Coaster No 1

After a flat calm blue sky Friday with sub-zero temps from the higher Glens upwards, a low pressure system is marching in, the wind’s already picking up at low levels in the Central Highlands, and blowing a hoolly further North and West. The low is off course complete with the obligatory Friday night warm sector! :(

While the forecast is not good for anyone wanting to get out on Saturday, depending what happens early next week, the situation weatherwise this weekend might longer term be in our favour, at least for the higher parts of CairnGorm which is where the most snow has stuck this week.

Overnight the FL looks to peak about 4500ft (but this could vary depending on exact track), so we’ll get a period of increasingly wet snow preceding a period of rain at most if not all levels before the precipitation gradually turns back to snow. The layer of wet snow, combined with rain will wet and soften the existing snow pack, consolidating it down a bit. A subsequent layer of  wet will be laid down as temps begin to fall and then this freezing up as temperatures gradually fall back during Saturday.

It’s these kind of cycles that are classic base building conditions, it all comes down to the thaw being sufficient to consolidate the snow pack, but short enough to not do too much damage. What comes through the next 24 hours will thus be in better shape to stand up to the coming weeks roller coaster, but we’ll just have to wait and see how much mild and probably more importantly how much rain we get next week.

Sunday looks set to have a Freezing Level between 1500 and 2000ft with a mix of sunny spells and snow showers, but overnight milder air will be sucked in as it gets pushed up and around the area of high pressure to our SW.  We then look set to enter a period of ‘roller coaster’ zonality, the track of the lows will be all important, a bit more to the South and we’ll get re-freezes between the less severe thaws, bit further North and we’ll end up with raging zonality sweeping band of rain after rain across with near double digit Munro level temperatures.

Should we get the latter, we can at least console ourselves that it’s better to have a bout of screaming zonality now than mid Feb.  One last thing, the models have been really struggling with fairly significant ensemble scatter only 2 to 3 days out on some runs, and some of those ensemble members were fairly tasty.  The best solution for Scottish Snowsports isn’t as one might expect long periods of blocked cold conditions, but the Holy Grail of cold Zonality. We managed to get to cool Zonality last winter at times, can we improve up on it?