Thirty-Five

Meteolux has issued a yellow heat warning for the entire country from 12pm Thursday through 11.59pm Friday, with temperatures forecast to reach between 31C and 33C on Thursday before climbing to 33C to 35C on Friday. The alert level is expected to be raised to orange on Friday, meaning significant heat stress risk.[1]

Thirty-five degrees does not sound extreme by Mediterranean standards. Madrid, Athens, and Nicosia routinely see 40C in summer, and they survive. But Luxembourg is not built for heat. The houses are thick-walled and insulated for winter, which means they trap heat in summer with remarkable efficiency. Air conditioning is rare in private homes. Public transport is air-conditioned, which makes the tram a viable refuge if your apartment has turned into an oven. The old city center, carved into the gorge, at least offers shade from the cliffs and tree cover along the Alzette.[2]

Meteolux's new warning system now factors in humidity and wind to estimate perceived temperature rather than just the raw reading. This is a meaningful improvement. Thirty-three degrees with 60% humidity feels like thirty-eight. The body cannot cool itself efficiently when the air is already saturated, and that is when heat exhaustion becomes a real risk, particularly for elderly people, children, and anyone doing physical work outdoors.

The standard advice applies, and it applies doubly here because Luxembourg's infrastructure is not adapted to sustained heat:

• Close windows and shutters during the day. Open them only at night when the outside temperature drops below indoor temperature. This is counterintuitive but essential. A shuttered house in Luxembourg can stay below 25C even when it is 35C outside. An open house will hit 30C within two hours and stay there.
• Drink water before you feel thirsty. By the time thirst registers, you are already mildly dehydrated.
• Avoid strenuous activity between noon and 4pm. If you must exercise, do it before 8am or after 8pm.
• Check on neighbours, especially older ones who may not have internet access to see the warning.
• Public swimming pools in Luxembourg City (Coque, Les Thermes in Strassen) are air-conditioned and have pools. The municipal outdoor pool in Belair is unheated and will feel like bathwater, but at least it is wet.

The forecast suggests Friday will be the peak. If you can work from home, work from home. If you cannot, the tram is your friend. And if you are tempted to dismiss a yellow alert as mild, remember that Meteolux expects to upgrade it to orange within 24 hours. This is the first serious heat event of the summer, and it is arriving before the end of June. Last year's heat wave peaked in July. Climate does not wait for the calendar.

The full warning details and hourly forecasts are available on meteolux.lu.[3]