CHAMONIX VALLEY AND MONT-BLANC AREA WEATHER FORECAST


Natsume Sôseki
Ask the breeze
Which leaf
First to fall will be
ISSUED AT 20:00 ON SATURDAY SEPTEMBER 16, 2017
VALID FROM : SATURDAY SEPTEMBER 16 -- UNTIL : FRIDAY SEPTEMBER 22 2017

GENERAL SYNOPSIS
Large altitude cold drop whirling between France, the British Isles and Denmark. It will be slowly drifting southeast and finally moving away over Italy while filling by Tuesday. • Altitude stream, currently southwest unstable, will be veering west by the end of the night, then will drive a disturbance over the area on Sunday afternoon and during the following night, causing moderate precipitation in the boundary layer between the polar air high up and the humidity rising and coming in from the Mediterranean, meaning precisely over the Alps. • Instability will persist in the body of the cold air mass on Monday and Tuesday, triggering some showers in a gloomy atmosphere. • More pleasant high pressure weather is expected to setting up for several days from Wednesday.
SATURDAY EVENING SEPTEMBER 16 - AND OVERNIGHT
Cloud passings - probably dry - unseasonably cold
SKY CONDITION : cloudy from the west - clear spells more frequent at times towards the middle of the night - high cloud coming in from the southwest towards the end of the night.
PRECIPITATION : probably none.
WIND - ground level : SW light or calm.
WIND - mid mountain : SW light.
WIND - high mountain : SW -> WSW light to moderate.
TEMPERATURE : low +3°C.
ISOTHERM 0°C : 2200 -> 2000 m.
ISOTHERM -10°C : 3700 -> 3500 m.
Same kind of weather in the Upper Aosta Valley and the bordering Valais.
TOMORROW - SUNDAY SEPTEMBER 17
Cold morning with thickening hazy skies - showers coming in from the west later
SKY CONDITION : high cloud thickening over the morning hours - becoming mostly cloudy, then overcast in the afternoon. Period of sunshine close to 20%.
PRECIPITATION : scattered showers in the afternoon - becoming frequent towards the evening - rain-snow limit towards 1800 m.
WIND - ground level : SW light.
WIND - mid mountain : SW light -> moderate.
WIND - high mountain : WSW light to moderate - W moderate to strong at times.
TEMPERATURE : low +3°C - high +12°C.
ISOTHERM 0°C : 2000 m.
ISOTHERM -10°C : 3500 -> 3600 m.
Same kind of weather in the Upper Aosta Valley and the bordering Valais.
SUNDAY TO MONDAY NIGHT - SEPTEMBER 17 TO 18
Disturbance crossing over - moderate precipitation at times - cold - windy high up
SKY CONDITION  : overcast or mostly cloudy.
PRECIPITATION : light to moderate - moderate at times towards the middle of the night - rain-snow limit dropping towards 1600 m - expected snowfall towards 2000 m : 15-20 cm, locally windblown.
WIND - aloft : W moderate - moderate to strong at times.
TEMPERATURE : low +3°C.
Uncertain.
MONDAY SEPTEMBER 18
Gloomy ‑ much cooler than seasonal average ‑ light and scattered precipitation
SKY CONDITION : overcast or mostly cloudy. Period of sunshine close to 15%.
PRECIPITATION : light and scattered - rain-snow limit towards 1600 m.
WIND - aloft : W moderate -> NNW light to moderate.
TEMPERATURE : low +4 °C - high +10°C.
Incertain.
TUESDAY SEPTEMBER 19
Gloomy ‑ colder than seasonal average ‑ light and scattered precipitation
SKY CONDITION : overcast or mostly cloudy. Period of sunshine close to 0%.
PRECIPITATION : light and scattered - rain-snow limit towards 1700 m.
WIND - aloft : NNW light to moderate - NW moderate at times.
TEMPERATURE : low +3°C - high +9°C.
Very uncertain.
EXTENDED OUTLOOK UNTIL FRIDAY SEPTEMBER 22

Wednesday : fairly sunny ‑ getting milder ‑ cloudy at times in the afternoon ‑ fairly strong bise wind high up. Thursday : fair weather ‑ cold in the morning ‑ mild in the afternoon. Friday : fairly sunny - altitude stream backing southwest - still chilly in the morning - almost warm in the afternoon.

Forecast reliability : fairly good until Sunday ‑ poor thereafter.

ReportsAs a reminder, today in Chamonix, the sun rises at 07:20:15 and goes down at 19:29:47.
45.55 N 6.51 E - Altitude 1040 m
September 21 07:00
Temperature -1°C
Relative humidity 92%
Wind 0 km/h
Sea level pressure 1019 hpa - rising slowly
Pressure at 1042 m 903 mb
Precipitation last 6h 0.0 mm
Skies clear
Visibility 120000 m
Altitude 3845 m
September 21 07:00
Temperature -6°C
Wind NNE 35 km/h
Altitude 2250 m
September 21 06:00
Snow depth 3 cm
Wind 10 km/h
Gusts 15 km/h
Temperature +6°C