2009 - Snow-patches Surviving On Scottish Mountains

[firefly]

Stewfox, if you want to read a bit more about the snow patches in Scotland then my Wiki page is a good place to start.

Norrance is correct with his assessment of 1976. That year, the the lasting winter snows arrived in the first week in September. Incredibly early. Had they not, the snow at Garbh Choire Mor (Braeriach) would have vanished. In this picture from the 2nd October 1976 you can see the 'old' snow at the bottom, with the new, whiter snow on the top from the falls a month or so previously. Interestingly, the 'old' snow in that photograph dates from 1959, which was the last time it melted completely.

Different things affect how late the snow lasts, but the most important factor is the depth of the snow that falls over the winter. It hardly needs to be said that it will take far longer to melt snow of 50ft depth than it will to melt 30ft of depth. By-the-way, these figures are not at all unusual. In my opinion, Observatory Gully of Ben Nevis and Garbh Choire Mor's depths in March-April will exceed 75ft in snowy winters.

Most snow that survives will typically be against shady cliffs facing NE or N. This affords protection from summer sun in some instances, but it is not the only factor. Temperature and rainfall also play a part. It's a complicated business!

TWS, I'm not sure what the 1967 winter was like (well before I was born), but I will ask Adam Watson.

Cheers!

[Terminal Moraine]

Although the 1967 winter was on the mild side it was not exceptionally mild and certainly not mild enough to have a severely detrimental effect on high level snow cover. December 1966 was on the mild side and rather wet, Jan' 1967 was fairly mild and rather dry, Glasgow recorded 85mm, 72% of average and the mean temp' was 1.3c above average.

By February there was a definite north/south split developing; it was milder than average, +1.5c at Glasgow, +1.3c at Stornoway, but also wet with 107mm (132%) at Glasgow and 107mm ( 152% ) at Stornoway.

The winter was also characterised by frequent winds from a westerly source.

March was very wet in the Highlands and the Hebrides, at Stornoway it was the wettest March on record to that point with 202mm ( 348%) and temperatures close to average, a recipe for enormous amounts of snow in the mountains I would have thought.

April saw a return to rather dry weather with temp's about average, so not much thawing, and this was followed by a cold and wet May with mean max' temp's widely 2 or 3c below average and rainfall around 150% of average in northern Britain so proabably a good top up of snow at high levels.

Braemar recorded 53 mornings with snow lying during the 1966/67 season ( October-May )

[firefly]

Well done, TM! I'm not sure where you get your figures from, but if the March and May figures are correct then that would explain why so much snow fell. The patches that remained in 1967 were the biggest to survive in 1938-2009. At Alltan na Beinne on Beinn a' Bhuird, men skied on 780 m of snow in late August 1967; an incredible amount!

As for 1951, this photograph of the Garbh Choire Mor from the 20th April shows the mind-boggling amount of snow present. Adam Watson told me that this is the most amount of snow he had ever seen there.

Edited December 7, 2009 by firefly

[JRMcLeod]

Well done, TM! I'm not sure where you get your figures from, but if the March and May figures are correct then that would explain why so much snow fell. The patches that remained in 1967 were the biggest to survive in 1938-2009. At Alltan na Beinne on Beinn a' Bhuird, men skied on 780 m of snow in late August 1967; an incredible amount!

As for 1951, this photograph of the Garbh Choire Mor from the 20th April shows the mind-boggling amount of snow present. Adam Watson told me that this is the most amount of snow he had ever seen there.

How deep do you guess that snow was? Do you happen to know what the deepest snow recorded in the mountains is?

[firefly]

No records exist (that I am aware of) which give the maximum depth of snow for the Scottish mountains. However, from photographs I have studied of Garbh Choire Mor, and from being there at first hand, I would say that the snow in the photograph from 1951 is in the region of 20-25m deep. Observatory Gully on Ben Nevis will, I believe, carry as much snow as this during snowy winters.

This is only speculative, but I believe these figures will be fairly accurate.

[Methuselah]

Well done, TM! I'm not sure where you get your figures from, but if the March and May figures are correct then that would explain why so much snow fell. The patches that remained in 1967 were the biggest to survive in 1938-2009. At Alltan na Beinne on Beinn a' Bhuird, men skied on 780 m of snow in late August 1967; an incredible amount!

Now, that's what I call deep! How high was Ben Nevis that year?? :lol:

Sorry firefly...I know what you mean...

[firefly]

Ah, yes. Perhaps I should've made that clearer. 780m of descent was ski-ed in August 1967.

[JRMcLeod]

20-25 mtrs...that would be a crazy sight if cut straight through the middle!!!

[firefly]

20-25 mtrs...that would be a crazy sight if cut straight through the middle!!!

Indeed. However, you don't have to imagine too hard to see it. Below is a picture from the 22nd August 2008 at Ben Nevis, where myself and Blair Fyffe are shown beside the existing snow at Observatory Gully. We estimated the depth at 10m.

[Terminal Moraine]

Well done, TM! I'm not sure where you get your figures from, but if the March and May figures are correct then that would explain why so much snow fell.

Thanks Firefly. All monthly data came from the Met' Office's 'Daily Weather Report Monthly Summary' and the Braemar snow data from the Met' Office's 'Snow survey of Great Britian' so about as trustworthy as it gets.

[stewfox]

Indeed. However, you don't have to imagine too hard to see it. Below is a picture from the 22nd August 2008 at Ben Nevis, where myself and Blair Fyffe are shown beside the existing snow at Observatory Gully. We estimated the depth at 10m.

Its been a cold and snowy winter up there so far and I'm sure many more heavy snow falls to come.

Obvioulsy snow patch survival depends on the seasons ahead but I guess you start on a optimistic note for 2010 ?

[firefly]

Whoops! Must put this thread on 'tracking' mode...

Let me give you the answer that my good friend and colleague Adam Watson gave in another thread on Winterhighland:

"Of course none of us can be sure about anything until the main spring thaw has exposed the locations and sizes of snow wreaths. That's an exciting sight every year, but I think will be more anticipated in 2010 than usual <...> but since mid December I've thought 2010 is unlikely to be a top year for autumn snowbeds. Firefly and I agreed this when he came to Deeside and the Mearns in late December.

First, a long snowy winter is not necessarily conducive to unusually many late snowbeds. This is particularly the case if most snowfall comes on north winds, or easterly such as this winter (predominantly NE and SE, though there has been some substantial snowfall and drifting from NW and other directions). Firefly makes this point well. Most long-lying snowbeds face NE, to a lesser extent E or SE. The deepest corries and other holes face these directions, associated with glaciers in the last glaciation occurring on these aspects and forming these corries and holes. Deep holes that face NE are shaded from the sun for much of the day, and crucially in the afternoon, when the sun has warmed air to its maximum for the day. Although many hollows and some corries face W or SW or NW, they are fewer and usually much shallower. Their topography affords little shade from sun during the warm part of the day, and snow depth cannot be massive because the hollow is too shallow.

In 1996 most snowfalls came from SE and there were huge wreaths in June and July on NW-facing slopes, but the deep NE-facing holes had less than usual, and in the end no patches survived. One of the last patches was at the March Burn on Ben Macdui, huge in July, but of course it faces west and melted rapidly in warm sunshine in afternoons. Braemar had 60 days with snow in 1958-59, well above its winter average, and it was a snowy winter in Glen Esk of Angus, but I recall extremely rapid loss of snow by sublimation in Glen Esk, and in the end no snowbeds survived in Scotland, the first time I'd seen this.

I think Doug makes a very good point about the lack of wind this winter. Although much drifting occurred with the recent storm, earlier snowfalls were marked by little wind and remarkably uniform undrifted powder. Although much of the earlier snowfalls were later shifted by wind, this is not like an initial storm, because much of the blowing snow has been lost by sublimation.

As Firefly points out, a top year for autumn snowbeds ideally requires deep Atlantic depressions with heavy precipitation on gales from SW or nearby such as S and W and NW, when much of the precipitation on lowland is rain or sleet. This is especially so for Lochaber, but important everywhere. We may of course yet see it in March or April or May, but the long-range forecast of a strong anticyclone till at least 20 March is good for skiers and climbers, but not for long-lying snow patches!

The Met Office say this is the coldest snowiest winter in Scotland since 1962-63, and that accords with my experience in NE Scotland. The snowfalls of 62-63 came on predominantly SE winds. Have a look at Firefly's archive of snow-patch photos, search for 1963, and you should see my photos of Garbh Choire Mor in late September, with 4 smallish patches. In the end, only three of them survived."

The thread this was taken from in WH is

here.

[Norrance]

Would 2001 be a quite good example of a poor year for snow retention despite heavy snowfalls in February and March? The reason being that the winds were mostly strong from the North East thus loading the SW facing slopes that are first to melt in the sun.

2000 perhaps being an example of a not particularly snowy Winter that had a large number of retentions due to SW winds?

There must still be a good chance of further snowfalls this year that can pack the NE facing gullies with snow though the short term forecast is not particularly favourable.

[Thundery wintry showers]

I read the corresponding article in Weather- I recall that only two patches survived in 2001, and indeed judging by the article the reasons were much the same as in 1996. The westerly-dominated 1999/2000 season did indeed lead to very high snow patch survivals- 41 in total if I remember rightly.

The 1958/59 season certainly looks like it was conducive to low patch survivals- certainly from looking through the synoptic charts for that winter, the impression is one of frequent heavy snowfalls from northerly winds in January, and often-dry weather elsewhere in the season with not many cool zonal spells, and then of course there was the long hot summer with high temperatures persisting well into October.

I was wondering about 2010 survivals potentially being low, since unlike last winter (mid-late Jan 2009) we haven't had any marked spells of cool zonal weather over northern Scotland.

[stewfox]

Whoops! Must put this thread on 'tracking' mode...

..... etc

Great read and useful insight

[stewfox]

When does one start counting 'snow patches' ? end of June ?

Cant find the 2010 thread yet

[Guest]

When does one start counting 'snow patches' ? end of June ?

Cant find the 2010 thread yet

I think Mondy started one...maybe the mods can do some magic mod weaving of threads?! :lol:

Here: http://forum.netweather.tv/topic/62495-surviving-snow-patches/

Edited May 10, 2010 by CatchMyDrift