Mt d'Arbois - 12/04/21

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Mt Blanc Valley Weather - 3 Day Forecast

High 1031 west of Brittany, extending southeast, while alitude polar air thalweg, Norwegian Sea to Northern Spain, is drifting east; resulting cold front encounters mediterranean humidity along its eastern flank, thus triggering snowfall above 1000m over Northwestern Alps, embedded in moderate south-southwest stream early this morning. That snowy spell is expected to ending on the rear of the front towards the middle of the day while altitude stream will veer northwest and rising pressure field will allow for some sunny outbreaks. Improving further on Tuesday. Fair weather then expected to ruling Wednesday to Friday.
Gloomy morning with snow flurries - some sunny outbreaks later, mainly high up
SKY CONDITION : overcast this, changeable ceiling 1500-1800m - becoming mostly cloudy with fleeting sunny spells as of the middle of the day - earlier outbreaks high up. Period of sunshine close to 20%.
PRECIPITATION : more and more light and scattered over morning hours - rain-snow limit towards 800m, dropping - expected snowfall towards 1800m: 10-15cm.
WIND - ground level : SW very light -> calm -> NE light.
WIND - mid mountain : calm -> NNE light -> light to moderate.
WIND - high mountain : SSW moderate to strong -> SW -> WNW light.
TEMPERATURE : low 0C - high +6C.
ISOTHERM 0C : 1300 -> 1200 m.
ISOTHERM -10C : 3300 -> 2700 m.
Clearing skies - cold snap by dawn - some low cloud patches - windy high up
SKY CONDITION : becoming clear or partly cloudy towards the middle of the night - earlier high up - some low stratus cloud patches likely - iso 0C dropping towards 900m.
WIND - aloft : WNW light -> NNW moderate - occasionally moderate to strong.
Fairly sunny - unseasonably cold - wind keeps blowing noticeably high up
SKY CONDITION : clear or partly cloudy - some low stratus cloud in the valley at first, possibly - some cumulus cloud in the median altitude range. Period of sunshine close to 75%.
WIND - aloft : NNW -> NW moderate - occasionally moderate to strong.
TEMPERATURE : low -5 C - high +9C.
Fair weather, bitter cold in the morning - getting noticeably milder later
SKY CONDITION : clear or partly cloudy - cumulus cloud growing above median altitude range slopes in the afternoon. Period of sunshine close to 80%.
WIND - aloft : NW moderate to strong -> WNW moderate.
TEMPERATURE : dropping lows - rising highs.

Thursday: fair yet cold in the morning, getting mild in the afternoon - some cumulus cloud above median altitude slopes in the afternoon - strong northwest high up in the afternoon. Friday: mainly sunny on the whole - still fairly cold in the morning - afternoon cumulus cloud getting somewhat more bulky than previously - altitude stream backing southwest, mostly light. Saturday: uncertain - sunny morning, yet fairly cold - locally mostly cloudy in the afternoon with cumulus cloud spreading while getting bulky, thus keeping quite cool temperatures.

Forecast reliability : fairly good until Thursday.