CHAMONIX VALLEY AND MONT-BLANC AREA WEATHER FORECAST
ISSUED AT 09:15 SATURDAY AUGUST 17
VALID FROM : SATURDAY AUGUST 17 ‑‑ UNTIL : THURSDAY AUGUST 22 2019
Higher than the lark
Resting in the sky
Of the mountain pass
Azorean High has been withdrawing over the Atlantic. Pressure field remains however fairly high over the Mediterranean, going along with an altitude anticyclonic spur that is drifting east. • Low 979 hpa getting close to Scotland makes altitude flow backing west to southwest, fairly strong. • Cold front of that low is waving west‑east, almost stationary, over Northern France and drives high cloud passings over our Region this Saturday. • Loose foehn gradient will dry atmosphere further overnight and on Sunday morning north of the Alps. • While getting lower south as well, pressure field should trigger prefrontal rainy‑thundery deterioration by Sunday evening; however outlook becomes very uncertain at this stage.
TODAY - SATURDAY AUGUST 17
SKY CONDITION : clear or partly cloudy ‑ high cloud patches crossing over at times, quite frequently in the morning, then getting scarce. Period of sunshine close to 80%.
PRECIPITATION : none.
WIND - ground level : SW light ‑ early afternoon thermal light to moderate.
WIND - mid mountain : WSW light to moderate ‑ occasionally moderate.
WIND - high mountain : WNW ‑> W moderate to strong.
TEMPERATURE : low +8°C - high +27°C.
ISOTHERM 0°C : 4300 ‑> 4400 m.
ISOTHERM -10°C : 6200 ‑> 6500 m.
SKY CONDITION : partly cloudy, then clear ‑ good radiation condition regarding snow surface re‑freezing, yet iso 0°C close to 4500 m.
PRECIPITATION : none.
WIND - aloft : W moderate to strong ‑> WSW moderate.
TEMPERATURE : low +10°C - temperature inversion toward 1700 m.
SUNDAY AUGUST 18
SKY CONDITION : clear or partly cloudy ‑ becoming cloudy towards the evening. Period of sunshine close to 85%.
PRECIPITATION : none until the end of the day ‑ pre‑frontal thundery shower likely in the first part of the following night ‑ rain‑snow limit towards 3900 m.
WIND - aloft : WSW moderate ‑> SW moderate to strong ‑ foehn puffs in the upper valley.
TEMPERATURE : low +10 °C - high +30°C - temperature inversion toward 1300 m early in the morning.
MONDAY AUGUST 19
SKY CONDITION : cloudy to mostly cloudy ‑ some sunny spells, lasting longer towards the middle of the day. Period of sunshine close to 35%.
PRECIPITATION : scattered shower in the morning ‑ more frequent with possible thunderstorm in the afternoon ‑ rain‑snow limit towards 3800 m, dropping.
WIND - aloft : SW moderate to strong ‑ occasionally strong.
TEMPERATURE : noticeably dropping highs.
EXTENDED OUTLOOK UNTIL THURSDAY AUGUST 22 2019
Tuesday : unsettled ‑ cooler ‑ frequent shower ‑ southwest begins to decreasing in the evening. Wednesday : improving ‑ fairly sunny after early morning low cloud dispelling ‑ warm in the afternoon. Thursday : somewhat sultry and unstable ‑ often cloudy, especially in the afternoon with some shower risk moreover. • Very uncertain outlook for the three days.
Forecast reliability : fairly good until Sunday ‑ poor thereafter.