German and Belgian power prices for next-day delivery jumped to their highest since 2008. The German spot power price for Tuesday delivery opened at €90.50 ($95.85) per megawatt-hour (MWh), before retreating to €84 per MWh. The price was €20 higher than on Friday for Monday delivery. Belgian prices climbed to €110 per megawatt-hour.

Prices In France, which largely depends on electricity for heating, rose to their highest since November. The French baseload contract opened at €120 per MWh, compared with €85.50 per MWh paid on Friday for Monday delivery.

The strong demand is expected to last through the week, and the French grid operator RTE has warned the supply could be strained as workers at Electricite de France’s (EDF) power plants plan a 24-hour strike on Monday. Six of the company’s 58 nuclear reactors are offline. Two reactors recorded unplanned outages over the weekend and have now restarted and are ramping up output. One more reactor is expected to restart on Tuesday.

RTE said it was ready to use exceptional measures to guarantee electricity supplies this week due to record consumption.

The average temperatures in northwest Europe were seen below minus four degrees centigrade on Monday and are forecast to fall sharply below seasonal levels for most of the week.

According to Germany’s national forecaster Deutscher Wetterdienst, on Tuesday temperatures are to fall as low as minus 20 degrees Celsius in some mountain regions.

Polar air from Scandinavia was said to bring ice and permafrost to some areas in Germany.

Freezing weather has already forced flight cancellations in Frankfurt, led to blackouts in Switzerland and restricted shipping on ice-choked rivers.