The weather agency says most of the country will see temperatures of over 30C on Monday.
But the real heat will arrive after Monday, with MeteoSwiss forecasting maximums of 33–37C from Tuesday through to Thursday.
The agency has now issued a level 3 heat alert (significant danger) for many parts of Switzerland. For the Basel region and for central Valais, a level 4 alert (severe danger) has been issued.
Warnung des Bundes: #Hitzewarnung der höchsten Stufe 4 für die Region Basel und das Zentralwallis. Für gewisse Bevölkerungsgruppen können die hohen Temperaturen ein Gesundheitsrisiko darstellen, warnt das @BAG_OFSP_UFSP. #Hitzewelle wird voraussichtlich bis Sonntag andauern. pic.twitter.com/tkQxwrF8RD
— MeteoSchweiz (@meteoschweiz) June 24, 2019
Swiss heat warnings are based on the so-called “heat index” which is calculated by combining temperature and relative humidity.
A level 3 alert equates to a heat index score of 90 or more over at least three days. A level 4 alert means a heat index of 93 or more over at least five days.
The last time Switzerland issued a level 4 alert was in 2015.
Maximums of 39C possible
Some places could even see maximums of 39C – incredibly hot in Switzerland where the hottest temperature ever recorded was 41.5 in Grono in the canton of Graubünden in 2003.
And certain locations could ever experience their hottest day ever as the tweet below shows. The first column (Rang 1) indicates the current records for the cities listed while the final orange column shows the forecast maximum for Wednesday.
Übersicht der bisherigen Top-3 Höchsttemperaturen aus dem Messnetz der #MeteoSchweiz seit Messbeginn. Orange dargestellt die #Prognose für nächsten Mittwoch zum Höhepunkt der #Hitzewelle. Neue #Hitzerekorde sind im Bereich des Möglichen. pic.twitter.com/CufOs8amyS
— MeteoSchweiz (@meteoschweiz) June 22, 2019
Meanwhile, Wednesday night could be warm in Switzerland’s larger cities with minimums above 20C possible.
The hot weather is set to last until next Sunday, MeteoSwiss said.
The Swiss government advice for heatwaves includes avoiding the sun between 11am and 3pm, avoiding strenuous activity where possible, drinking plenty of water and eating light foods.