I'd thought I'd read that it was the cold, humidity controlled environment that was aiding the spread.
But who knows, at various times I've read that hot+humid, cold+dry and cold+humid all aid spread. Seems hot+dry seems to be the one missing.
Humidity of the air is important, as that means that when the air is too dry that the droplets get smaller and the virus can then "float" and then travel further. Airborne spread rather than droplet spread. Droplets will tend to fall and thus not travel far. Whereas airborne (floating) can travel very long distance due to wind, stray currents etc As they are floating they can stay in the air for long periods thus increasing exposure time as it means that the transmitter and transmittee do not have to be there at the same time, whereas with droplet spread (ignoring fomite transmission which can also be time lagged) they do.
So with HVAC for facilities that have cases, it is important that:
1/ the the humidity is controlled so that droplets are not aerosolised
2/ that airflow is controlled so that air cannot float around, but is instead drawn out of the room. It is also why you do not want to have open windows or fans (or room AC that can act like fans) as these can interfere with the airflow patterns.
In terms of climate winter does not necessarily mean the air is more humid. And summers do not necessarily mean that the air is more humid. It varies by location. Melbourne tends to be more humid in the colder months, drier in summer.
Whereas Sydney is the opposite.
With abattoir workers it was long exposure times together. plus the close traditional working proximity of such workers. So this has been changed now.
ie See
Managing the risk of COVID-19 exposure: abattoirs and meat processing industry | COVID Safe | NSW Government
And proximity and exposure duration is not juts a factor abattoir workers, spread through household contacts is so prevalent, and is one reason why household spread is so common.
Colder times mean that people can be indoors more.
However I think the biggest factor for number of cases is more other issues such as unknown community spread, people not presenting for testing etc.
ie Taiwan now has a surge on, and it is always quite humid there.
The mean minimum and maximum temperatures over the year.
Show in Fahrenheit