After reviewing this article and looking into the website I can say that this claim is not completely false but it is misleading. The cold does not make you skinnier, but working out during winter comes with some benefits. The article is titled, “How winter weather impacts your weight loss journey” and although it is related to the cold and contribution to weight loss, that's not exactly what it's claiming. A quote from this article says, “Research shared by the National Institutes of Health has shown that cold weather can activate “brown fat” in our bodies, a type of fat that burns calories to generate heat. This means that exercising in the cold can potentially boost fat burn, making winter workouts even more effective.” This means that when you workout in cold weather your body will want to produce heat to keep you warm and with that activates brown fat.
As stated, Tim Harris the journalist of this article got this information from the National Institute of Health. A trusted government source that came out with an article on brown fat back in 2019. Found here: https://www.nih.gov/news-events/nih-research-matters/how-brown-fat-improves-metabolism
In this article Harris Wein, a director at the Nation Institute of health wrote about an experiment led by Dr. Shingo Kajimura at the University of California, where they proved that colder temperatures activate more brown fat than normal temperatures. This experiment consisted of men being put in these 2 different settings and exercising while tracking their blood levels of glucose, fats, and amino acids. Linkedin to Harris Wein: https://www.linkedin.com/in/harrison-wein-5628a36/
Overall this claim seems to be used to seek attention towards the article. After looking at the website that published this piece, The Weather Channel, something that stood out to me was the footnote that said “The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.”
Although it's a very interesting topic I feel it's important to mention that this piece might have been written for the purpose to entertain.