It's a cloudy and overcast day, about 19 degrees, with windspeeds up to 7.5 mph (not counting gusts).
Common wisdom says bumblebees don't fly in the wind, though of course you'd expect them to have some provision to do so, at least to overcome the challenge of being caught out in a breeze.
Of course, above a certain speed, like a canoeist paddling upstream, they wouldn't be able to make progress against the wind.
Unlike an aeroplane, however, Bumblebees do not rely on air-speed over their wings in order to generate lift (which is what gave rise to the popular myth "scientists say bumblebees shouldn't be able to fly; a comparison with the physics of fixed wing flight doesn't work for bumblebees).
It seems our bufftails are a hardy bunch - whilst activity is much reduced today, it hasn't stopped a few hardy ones venturing out to collect pollen and/or find a mate; time is, after all, of the essence as far as both are concerned. The one I've just seen has been out for about 30 minutes and come back with a decent stash of pollen.
And one final nail in the coffin for the concept of "dull days" - cloudy and overcast it may be, but the light inside our nest box has increased to a level where the infra-red camera is occasionally switching to full colour daylight mode. All that white cloud and reflected light is making it bright.
Maybe the brightness of the day is tempting the bees to venture out. Or maybe they just enjoy the thrill of a windy flight.