I felt it was Spring too, but it's clear from Hawkeye that this scene takes place during the show. I'm all for using weather as evidence, but when the show itself overrides that, it's a different story. We see Eleanor call someone after seeing her daughter was working with Clint. The implication is that it's Val (or someone related her to her) who then uses Yelena's history with Natasha and anger towards Clint as a chip in having her be the one to carry out the mission. Even if this was Val's original introduction, it doesn't mean the scene has to be set before we see her in The Falcon & The Winter Solider. I believe Hawkeye was originally set earlier in the year, but Covid delays turned it into a Christmas show, which is probably another factor why the weather doesn't match. Either way Marvel itself confirming December, just confirms what I've believed since the beginning and that this scene is meant to be during the show. You can even take Yelena's mention of " holiday time" to be literal.