CHAMONIX VALLEY AND MONT-BLANC AREA WEATHER FORECAST
ISSUED AT 09:45 SATURDAY SEPTEMBER 18 2021
VALID FROM : SATURDAY 18 -- UNTIL : THURSDAY SEPTEMBER 23 2021
Evening let it glow
Red my mountain
In a radiant window
Scandinavian high has been recently well spreading, North of Norway (1030) to Alps (1016) and Azores high is located where it belongs to, featuring 1020 in the west fringes of the Bay of Biscaye. • However, low system located towards Greenland Sea infiltrates polar air high up, which reaches Northern Spain, thus setting up an altitude cut-off on the same above mentioned Bay of Biscaye, and which will be crossing over up to the Gulf of Genoa by Sunday evening. This will indeed cause an active rainy spell (15-25 mm) in our Region between Sunday's dawn and late evening, going along with a considerable temperature drop (± 10°C), likely to recalling snow between 2000 and 2200 m in the High Massifs. • Improving hardly thereafter with slow and gradual temperature rise on Monday and Tuesday.
TODAY - SATURDAY SEPTEMBER 18
SKY CONDITION : clear in the morning - in the course of the afternoon, thin high cloud running over from SW, and cumulus cloud growing bulky abover the massifs. Period of sunshine close to 70%.
PRECIPITATION : late afternoon shower slight risk.
WIND - ground level : calm or variable very light.
WIND - mid mountain : Mainly SW - very light.
WIND - high mountain : W or variable very light -> SSW light to moderate.
TEMPERATURE : low +9°C - high +22°C.
ISOTHERM 0°C : 3600 -> 3800 -> 3500 m.
ISOTHERM -10°C : 5400 -> 5100 m.
SKY CONDITION : partly cloudy in the first part of the night - thickening high cloud crossing over from SW later, then overcast towards the end of the night - ceiling dropping towards 2000 m, or locally even lower - iso 0°C dropping considerably towards 2500 m by dawn.
PRECIPITATION : starting up towards the middle of the night - becoming moderate - locally fairly heavy by dawn - rain-snow limit dropping towards 2200 m by dawn - expected snowfall towards 2500 m : 10-20 cm.
WIND - aloft : SSW -> SSE light to moderate - occasionally moderate.
TEMPERATURE : low +8°C.
SUNDAY SEPTEMBER 19
SKY CONDITION : overcast - becoming mostly cloudy towards the evening, with possible sunny spells. Period of sunshine close to 10%.
PRECIPITATION : continuous and fairly heavy by daybreak - turning into shower in the course of the morning - probably dry in the afternoon - lowest rain snow limit towards 2100 m - rising somewhat in the evening - expected snowfall towards 2500 m : 5-15 cm.
WIND - aloft : SSE light to moderate -> NE moderate - occasionally N moderate to strong.
TEMPERATURE : low +7 °C - high +11°C.
MONDAY SEPTEMBER 20
SKY CONDITION : overcast, then mostly cloudy - stratocumulus cloud in the valley, getting broken - possible sunny spells in the afternoon. Period of sunshine close to 20%.
PRECIPITATION : light and scattered shower likely all along the day - rain snow limit rising up towards 2500-2600 m.
WIND - aloft : NW light to moderate -> occasionally moderate at first.
TEMPERATURE : rising slightly.
EXTENDED OUTLOOK UNTIL THURSDAY SEPTEMBER 23 2021
Tuesday : very uncertain - "less worse" than previously - mainly cloudy to overcast, possible low cloud - probably without precipitation . Wednesday : very uncertain - improbing sunny in the median altitude range - persistent low cloud in the valley. Thursday : very uncertain - probably fairly sunny after early morning low cloud dispelling - seasonable temperature.
Forecast reliability : fairly good until Sunday.