Quick reads. Lasting takeaways.
High pressure is sitting over Chamonix and Zermatt: no precipitation forecast through Sunday, and the valley climbs from 10 to 21 degrees by Saturday. Up at 2,500 metres it is a different story, 4.6 degrees this morning and near freezing at dawn on Saturday. That is a 17-degree gap between trailhead and ridge. Pack for both. A merino base layer and a windproof shell cover it without a midlayer you will carry unused.
Merino base layers ↗Chamonix is heading into a dry spell. After a few showers today, Friday and Saturday stay dry in the valley, and highs climb from 16 °C today to almost 20 °C on Saturday. Nights hold at around 9 to 10 °C. That makes Saturday the day for a long outing. Just remember that the forecast is for the valley floor at about 1,000 metres. On the ridges it will feel far cooler, so a warm layer belongs in the pack.
Zermatt sits at 20.3 °C today. By Friday the high is 12.2 °C, with nights down to 6.7 °C at 1,600 metres. That is an eight-degree slide in three days, and the freezing level drops with it. Chamonix takes 5 mm of rain first. Pack the fleece now. Anyone walking up mid-week wants a midlayer they would have left at home last weekend.
Fleece jackets ↗Two warm days, then a hard turn. Chamonix peaks at 23C on Tuesday with the freezing level near 4,700 metres, so high routes stay dry and clear. Wednesday brings thunderstorms, 15 mm of rain and a freezing level collapsing to roughly 2,750 metres by evening. Above 3,000 metres that means fresh snow on rock overnight. Take the big day on Tuesday.
Jackets ↗Tromsø takes 8mm of rain today, with drizzle since dawn and wind running at 29 km/h off the fjord. Tomorrow the high drops to 11°C, and by Tuesday morning it is down to 6. The season has turned up there. Wind is what pushes water through seams and strips warmth off a damp base layer, so a shell that seals at the hood and cuffs does more for you here than a high waterproof rating on its own.
Waterproof jackets ↗Zermatt sat at 6°C at half past six this morning and climbs to 19°C by afternoon. Chamonix runs warmer, 11°C to 20°C. Both valleys stay dry through Monday. A 13-degree swing means the layer you start in is not the layer you walk in, and a merino base with a windproof shell covers both ends without a midlayer you carry unused.
Merino base layers ↗No rain is forecast for Chamonix through Sunday, and valley highs climb from 19 to 21°C. Zermatt looks just as settled once this morning's fog lifts. The catch is the start of the day. On Saturday Zermatt sits near 7°C at dawn and passes 20°C by the afternoon. That is a 13-degree swing. Start in a light fleece, stuff it in your pack once the sun clears the ridge, and you won't carry a heavy jacket all day for nothing.
Fleeces ↗Today's showers clear overnight. Thursday and Friday come up dry in both Chamonix and Zermatt, with valley highs of 18 and 17 degrees. The mornings stay cold: 10 degrees in Chamonix, under 8 in Zermatt, and colder again as soon as you gain height. That gap between dawn and afternoon is the whole trick of September. Pack for both. A warm layer you can stow by nine, and reach for again on the descent, beats a midlayer you carry all day.
Merino base layers ↗Chamonix takes 32 millimetres of rain today, then two dry days follow. Thursday and Friday top out near 18 degrees in the valley and fall to 10 overnight. Trails will still be running water on Thursday morning. Give the ground a day. Granite slabs and polished limestone stay greasy long after the path beside them looks dry, so the south-facing routes above Argentiere are the safer bet before the weekend.
Hiking boots ↗Chamonix reaches 28.5°C this afternoon with barely a drop of rain. Tomorrow the valley falls to 20°C and takes around 30 mm, most of it in thunderstorms. Zermatt follows the same pattern, 23.8°C down to 15.3°C. That is an eight-degree swing overnight. If you are on a hut route, plan Wednesday's descent for the morning: fog is forecast from first light. Source: Open-Meteo, 8 September.
Jackets ↗Chamonix reads 18.6 degrees this morning with showers already moving through the valley. Tuesday climbs to 28. Wednesday turns hard the other way: around 35 mm of rain forecast for Chamonix, and over on the Zermatt side highs drop to 15 with the freezing level following. A hut walk that feels like high summer on Tuesday will feel like late autumn a day later. Take the shell even if Tuesday tempts you to leave it in the car.
Rain jackets ↗Chamonix sat at 16.7°C at half six this morning under a clear sky and climbs to 27.7°C by afternoon. Zermatt does the same trick from 11.3°C up to 25.7°C. That is a 14-degree swing on a single walk. The dry spell is short: 3.8 mm of rain reaches Chamonix on Monday and 6.8 mm on Tuesday, while Zermatt's afternoon high slides to 19°C. Start early, and pack the layer you will only need on the way down.
Merino layers ↗Chamonix and Zermatt both show zero rainfall today and tomorrow, with highs of 25 and 21 degrees. The catch sits at the other end of the day. Zermatt drops to 13.6 overnight, Chamonix to 17.3, so a ridge walk that starts cold finishes in full sun. Carry a light shell rather than a midlayer. Rain edges back into the Valais on Sunday, which makes the long routes a job for the next two days.
Softshell jackets ↗Zermatt sat at 11 degrees at half six this morning and climbs to nearly 27 by afternoon. Chamonix runs the same pattern, 16 to 28. That is a 16-degree swing on a dry, cloudless day. Pack for both ends: a light base layer you can hike in at dawn, and enough water for an afternoon that feels like July. From Saturday the peaks drop back to around 22 degrees, so this heat is a short window.
Merino base layers ↗Chamonix and Zermatt sit under dry high pressure into the weekend: no rain in the three-day forecast, and Friday reaches 29 degrees in the Chamonix valley. The catch is the morning. Zermatt read 7 degrees at half six against a daytime high of 23. That is a 15-degree swing before lunch, so the light insulated layer you resent carrying at noon is the one you want on a seven o'clock start. Source: Open-Meteo, 3 September.
Jackets ↗A stable high sits over the western Alps for the next three days. In Zermatt that means near 6°C at dawn and 23°C by afternoon, a 17-degree swing before lunch. Chamonix climbs even warmer, up to 27°C on Friday. No rain in the forecast. Start cold, finish hot: a merino base layer plus a light windproof shell covers both ends, without the bulky midlayer you would carry unused all afternoon.
Merino base layers ↗High pressure sits over the western Alps for the next three days. In Zermatt the morning starts near 6°C at 1,600 metres, then Chamonix climbs past 23°C by afternoon. That is a 17-degree swing before lunch. No rain in the forecast. A merino base layer under a packable windproof handles the dawn chill without the bulk you would carry unused once the sun is up.
Merino base layers ↗The first cold nights of the season are back in the Alps. A thunderstorm front clears Chamonix today; behind it the air turns dry and sharp. Days still reach 21 degrees, but valley temperatures in Zermatt drop to 7 by tomorrow morning, and it sits near freezing above 3,000 metres. Pack the warm layer. An alpine start in a summer setup gets cold fast.
Fleece jackets ↗A stable high sits over the western Alps this week. In Chamonix, mornings start near 11°C and afternoons climb past 23°C, with dry skies forecast for the next three days. That is a swing of more than ten degrees. Begin in a light insulating layer, then strip back to merino as the sun gets to work. Zermatt runs cooler, around 9°C at dawn. Pack a windproof shell for the ridgelines and both ends of the day are covered.
Merino base layers ↗Clear skies over the Valais this week, and the numbers tell the shoulder-season story. Mornings in Zermatt sit near 7 degrees, afternoons climb to 20. That is a 13-degree swing between the first hour and the warmest one. Pack a merino base layer and a windproof shell: you start cold and finish warm without a bulky midlayer riding along all afternoon. The gap only widens from here.
Merino base layers ↗
