ZURICH. The hottest summer in Swiss records is not finished. A high pressure system building over western Europe, christened Thomas by the Berlin weather service that names such things, will bring late summer heat back to the lowlands this week, with 30 degree days possible across the north from Friday and no rain in sight.
MeteoSwiss expects Tuesday and Wednesday to reach 24 to 27 degrees north of the Alps and around 29 in the south, under mostly sunny skies with some high cloud. Mornings will bring fog patches along the river valleys, a sign of the lengthening nights, but they will clear quickly. The zero degree line sits near 3,700 metres.
From Thursday the high strengthens. Forecasters expect often cloudless skies and a steady climb toward the heat mark, with widespread 30 degree readings likely from Friday to Monday and up to 32 degrees possible in Basel or Geneva. A shallow disturbance may bring more cloud on Saturday, but no precipitation.
Meteorological autumn began on Monday. The atmosphere, as forecasters put it, has not read the calendar. The lakes, warmed through the record summer, remain at bathing temperature, and lidos in Zurich, Geneva and Lucerne expect their busiest September weekend in years.
The beauty comes with a ledger. Four cantons, Basel Country, Basel City, Valais and Zurich, remain at forest fire danger level 5, the maximum, and most of the rest of the country at level 4. Open fire bans cover the majority of communes, and each additional dry week pushes the first meaningful rain further into the month.
The drought’s second order effects are now arriving faster than its first. The Rhine and the Danube are carrying a fraction of their normal flow, which is why the federal government on Monday opened the compulsory reserves of protein animal feed. Hydropower utilities are watching reservoir levels recover too slowly, and shipping on the Rhine at Basel continues with part loaded barges.
Agriculture is caught between the two halves of the season. The dry forecast is a gift for the grape harvest now beginning in the Valais and along Lake Geneva, where growers expect healthy fruit and high sugar readings. For dairy farms short of roughage, the same sky means another fortnight of buying feed instead of cutting it.
Climatologists note that September heat of this kind is no longer an oddity. The record summer of 2026 was the hottest and driest since measurements began in 1864 and 1901 respectively, and the season’s warmth is bleeding into autumn exactly as the seasonal forecasts said it would. The monthly outlook keeps the probability of below average rain above 70 per cent for the weeks ahead.
There is no meteorological relief in the ten day outlook. Beyond Monday, the high is expected to hold or rebuild, with temperatures easing only gradually toward seasonal norms. For the fire services, the water managers and the farmers, the wait for rain goes on.
The long range models offer one consolation: September can still turn. A single Atlantic front would change the picture within days, and the first autumn storms historically arrive in the second half of the month. Until then, Switzerland gets a final, golden extension of a summer it has already had rather too much of.