Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/23 21:40:30 #Date/time of acquisition
WS=   19.32   #Wind speed (knots)
WD=   53.42   #Wind direction (degrees) (0-360)
T =    2.39   #Temperature (degrees celsius)
RH=    7.79   #Relative humidity
BP=  617.29   #Barometric pressure (millibars)