27/11/2019: Today's Updates... Morning Snow Falling At Lower Elevations Than Expected...
Further precipitation is expected tonight and tomorrow. The snow/rain limit looks like being between 1350m and 1500m, so a marginal event for the village, however, any heavier precipitation would see that rain/snow limit come down at times and so a covering of snow is possible at 1200m - though it will be a very wet covering as the 0c isotherm will be some distance above the village. There is a good chance of some very useful snowfall for most of the ski area.
Here is the latest Arome chart for the potential snowfall up to Friday morning... chart from www.meteociel.fr
Thereafter, Friday may also see further precipitation, with the snow/rain limit coming down just a touch, which is promising, followed by a dry and mostly fine Saturday. For Sunday, which should be the first day of our daily forecast updates, there is the chance of another period of snow.
In summary - an interesting few days which should be good for most of the ski area, though the lowest areas may miss out on the heavier accumulations.
After this morning's excitement, the weather has been drier, milder and windier with one or two showers coming through. The snow/rain limit has risen higher - up to above 1700m by the looks of it, but there hasn't been much additional precipitation. A quick trip was made up to the Col du Saix, where there was a fresh wet covering of about 5cm of snow and reports from Plaine Dranse suggested up to 7cm of fresh, with deeper accumulations above 1800m.
Tomorrow is looking interesting in terms of the potential for snowfall, though at the moment snow/rain limits may be near to, or a little bit above the village - at perhaps around 1400m, however, there is the potential for much of the ski area to benefit. More on this on an evening update, once some of the 12z model runs have come out.
Photos from this afternoon...
As the heavier precipitation has now moved away, the evaporative cooling effect has now passed - so we have light rain falling in the village. However, this morning's period of snow has deposited some accumulations to lower elevations much earlier than expected in this unsettled period, which is good news for the ski area.There will be a look at the forecast for the next few days on a post during the day, but first a look at what happened this morning... photo a few mins ago...
Normally, snow can fall approximately 300m below the position of the 0c isotherm, or freezing level as it is also known. The models last night (and this morning) were suggesting the 0c isotherm wound be between 1900m and 2200m early this morning.
Using the 300m rule, the lowest elevations that snow would have been expected to fall, would have been somewhere between 1600m and 1900m.
However, when the precipitation is very heavy and there is not much mixing up aloft - ie the wind above the area falls light, snow can fall to much lower elevations.
This process is all to do with thermodynamics... when liquid water evaporates, the air around it is cooled (eg like sweat cooling the human body). When you have heavy rain falling, with snow falling higher up and melting, as all this falls, it evaporates and cools the air due to those thermodynamic processes. Normally, the cooler air would mix with warmer air in the vicinity, offsetting this process of cooling - but - if there is not much wind, the cooling process continues, eventually allowing the snow to reach much lower elevations than expected.
There is a detailed scientific explanation of this (in French) on the Meteo Suisse website.
As this effect has now passed, snow/rain limits will be higher again during the day
We have a bonus situation in Chatel this morning, with snow falling to much lower elevations than expected. This is very good news indeed at the moment... more to follow...
Bonjour from Chatel, where there are some unexpected wet flakes of snow mixed in with the rain at the moment at our location at close to 1200m. This is potentially due to an effect known as evaporative cooling, which can occur in periods of heavy precipitation... more on this during the morning.