BULLETIN FROM FRIDAY DECEMBER1, 2023 AT 10:10 AM

FRIDAY, DECEMBER1 TO WEDNESDAY, DECEMBER 6

GENERAL SITUATION AND EVOLUTION

BAD WEATHER – Persistence of a large low-pressure system centered on the Baltic States, bringing very unstable maritime polar air from the Barents Sea and Spitsbergen to SW Portugal. – Minimum 999 hpa in the SE margin of this flow, to the immediate S of Brittany this morning, shifting towards Aquitaine as it fills in, but accelerating a very wet and disturbed reverse flow from Madeira towards Belarus, and concerning the immediate NW of the Alpine arc where the pressure field has continued to collapse [ Chamonix, 1001 – Sion, 1003 – Innsbruck, 999 ]. Shifting to the E, the influx of polar air forms a trough that will keep the disturbed flow colder than usual on Saturday.

FRIDAY DECEMBER1

Bad weather – snow in the upper valley this evening – strong gale in the mountains

Cloud cover: overcast, ceiling in the valley – cloud cover blocked against the mountains – sunshine: 0%.

Near-continuous, moderate precipitation – rain-snow limit dropping towards 1600 m – quantity expected towards 1800 m: 25-30 cm, windy and packed

NEXT NIGHT

Bad weather – in the valley, rain turns to snow showers – strong wind at higher altitudes

Cloud cover : overcast – ceilings generally below 1800 m – a few patches of fog at the bottom of the valley – iso 0°C falling towards 900 m

Precipitation evolving into showers, but nevertheless frequent – rain-snow limit falling towards 600 m – quantity expected around 1600 m: 10-25 cm, blown away

Wind aloft: very irregular SW – strong -> moderate – jumping NNW shortly before dawn

Minimum valley temperature: -4°C

SATURDAY DECEMBER 2

Gloomy – continued cooling – snow showers – windy in the mountains

Cloudiness : very cloudy to overcast – fleeting sunny spells not impossible in the afternoon – sunshine : 15%.

Showers becoming scattered or even isolated in the afternoon – rain-snow limit below 600 m at daybreak – amount expected around 1000 m: 5-15 cm

Wind aloft: moderate NNW -> moderate to strong

Valley temperatures :

min, -6°C

max, -1°C

SUNDAY DECEMBER 3

Sunny – biting cold under clear skies at dawn – easing on the adrets in the afternoon – windy at higher altitudes

Cloud cover: slight risk of low clouds in the early morning – otherwise clear or partly cloudy – sunshine: 85%.

No precipitation

Wind aloft: predominantly NW – moderate to strong

Valley temperatures: minimum falling – maximum stationary

CHANGE UNTIL WEDNESDAY DECEMBER 6

MONDAY: thaw – a disturbance arrives from the W, covering the upper sky during the morning – snow showers in the upper valley in the afternoon – WSW wind in the mountains

TUESDAY: disturbance partly blocked against the high mountains – still very cloudy with snow showers – clearing possible in the evening

WEDNESDAY: very uncertain: becoming cloudy to very cloudy as the hours go by – probably no precipitation – stationary temperatures – temporarily windy in the morning

During these three days: 30 to 50 cm of additional snow around 1500 m

Forecast reliability :
fairly good until Sunday – mediocre thereafter.