CHAMONIX VALLEY AND MONT-BLANC AREA WEATHER FORECAST


Matsuo Bashō
On a mountain path
This wild violet puts
An innocent spell on you
ISSUED AT 08:55 FRIDAY SEPTEMBER 25
VALID FROM : FRIDAY SEPTEMBER 25 ‑‑ UNTIL : WEDNESDAY SEPTEMBER 30 2020

GENERAL SYNOPSIS
Low 988 Southern North Sea, fed with maritime polar air by a Greenland Sea originated thalweg. • Resulting cold front reached our Region towards 05:30 this morning, going along with showers and wind gusts. It’s now digging towards the Mediterranean, followed by active and windy tail. • That disturbance on the whole will be then drifting east and filling, thus loosening Bise gradient before Saturday afternoon. Polar air income high up will simultaneously result in a cut‑off focused between Tyrol and Adriatic Sea by Sunday, which should keep unstable and cold condition over the Alpine Range until Monday, with mostly light to moderate winds high up, and some scattered showers at times (rain‑snow limit towards 1800‑2000).
TODAY - FRIDAY SEPTEMBER 25
Unsettled and cold ‑ fairly heavy precipitation, occasionally ‑ windy high up
SKY CONDITION : mostly cloudy to overcast ‑ ceiling often drop below 1500 m ‑ possible fleeting sunny outbreak, late morning or early afternoon. Period of sunshine close to 15%.
PRECIPITATION : moderate early in the morning ‑ becoming intermittent and light until mid‑afternoon ‑ heavy shower resuming upon secondary occlusion crossing, mid‑afternoon and evening ‑ rain‑snow limit towards 1800 dropping towards 1400 m in the evening ‑ expected snowfall towards 2000 m : 20‑25 cm, windblown.
WIND - ground level : SW light ‑ moderate gusts at times.
WIND - mid mountain : SW ‑> WNW moderate ‑ occasionally moderate to strong.
WIND - high mountain : WSW strong ‑> WNW moderate ‑> NW moderate to strong.
TEMPERATURE : low +3°C - high +7°C.
ISOTHERM 0°C : 2100 ‑> 1700 m.
ISOTHERM -10°C : 3700 ‑> 3100 m.
OVERNIGHT
Bad weather ‑ sustained and windblown snowfall in the median altitude range
SKY CONDITION : mostly cloudy to overcast ‑ ceiling often below 1500 m ‑ iso 0°C dropping towards 1500 m.
PRECIPITATION : continuous and moderate ‑ somewhat more sustained at first and towards the latter part ‑ rain‑snow limit dropping towards 1200 m ‑ expected snowfall towards 2000 m : 20‑25 cm, windblown.
WIND - aloft : NW ‑> NNW moderate to strong.
TEMPERATURE : low +2°C.
SATURDAY SEPTEMBER 26
Still unsettled and much colder than seasonable ‑ snow in the upper valley
SKY CONDITION : mostly cloudy to overcast ‑ thick cloud stuck against north and northwest slopes of the high massifs. Period of sunshine close to 0%.
PRECIPITATION : wintry shower, locally fairly heavy ‑ rain‑snow limit dropping towards 1100 m at times ‑ expected snowfall towards 1500 m : 10‑20 cm.
WIND - aloft : NNW moderate to strong ‑> NNE light to moderate.
TEMPERATURE : low +2 °C - high +5°C.
SUNDAY SEPTEMBER 27
Improving somewhat, though freezing ‑ often mainly cloudy ‑ Bise getting up later
SKY CONDITION : often mostly cloudy ‑ frosty cloud stuck against northern slopes ‑ fleeting sunny spells towards the middle of the day. Period of sunshine close to 20%.
PRECIPITATION : afternoon shower risk ‑ rain‑snow limit towards 1200 m.
WIND - aloft : NNW moderate ‑ noticeable Bise in the median altitude range.
TEMPERATURE : dropping lows ‑ slightly rising highs.
EXTENDED OUTLOOK UNTIL WEDNESDAY SEPTEMBER 30 2020

Monday : Bise wind dropping in the afternoon ‑ getting milder ‑ frequent yet light shower ‑ fleeting sunny spells. Tuesday : getting further mild ‑ sunny spells and cloud crossings in westerly stream. Wednesday : uncertain ‑ fairly sunny in the morning ‑ westerly streams becomes unstable ‑ cumulus cloud growing in the afternoon ‑ seasonable temperature.

Forecast reliability : Fairly good until Saturday.

ReportsAs a reminder, today in Chamonix, the sun rises at 07:25:39 and goes down at 19:21:26.
45.55 N 6.51 E - Altitude 1020 m
September 25 - 08:00
Temperature +6°C
Relative humidity 91%
Wind 5 km/h
Sea level pressure 1005 hpa - falling
Pressure at 1042 m 885 mb
Precipitation last 6h 9.8 mm
Skies overcast - ceiling towards 1500 m
Visibility 3000 m
Altitude 3845 m
September 25 - 07:00
Temperature -12°C
Wind WSW 45/70 km/h
Altitude 2250 m
September 25 - 07:00
Snow depth 3 cm
Wind SSW 21 km/h
Gusts 33 km/h
Temperature -2.6°C