The Tower ATC decides on the active RWY and they are aware of the wind since they have to give the wind everytime someone lands or takes off however it is not always a simple procedure to change the RWY as the sequence has to be considered. Acft that are planing on a downwind are usually high as they plan to loose the hight on the downwind where as acft on a straight in approach (Again a sore point) would be lower so if we swing the RWY the traffic inside 75NM will be too high most of the time. It isn't always a quick thing to change the RWY and can take 30min sometimes as the sequence is planned as such. Acft on the Taxi are also considered as all the taxiways ae unidirectional meaning one can't just do a 180 on them. However one can still backtrack if really neccecary.
Other factors that are used in selecting a RWY (there are actually 11 in the ATC book in total) are how many taxiways one has to use. use of navaids (ILS etc),airspace restrictions. So if the wind is less than 10kts sometimes we will prefer to use a downwind RWY instead as the facilities are better that serve it. With the VIR incident the TWR ATC had considered a RWY change but due to restrictions from a Radar vectoring point of view it the change was delayed.
Also the ATC will usually contact the met people to see the predicted trend before swinging but although they try they are not always 100% correct.
With a thunder storm as well the wind will change very rapidly and then once the cell has moved change again so this further complicates the change as one can't always plan for it.