Winter in Europe has huge variations in severity. The difference between a cold and a mild winter can make an annual 15% difference in gas consumption in Germany, for example [1]. The difference between running out of gas and not running out of gas falls right between those two weather scenarios.

Winter being generally colder than summer - that's climate, which is different from weather.

[1] https://www.focus.de/finanzen/boerse/konjunktur/studie-skizz...