Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2010/02/09 16:43:32 #Date/time of acquisition
WS=   18.50   #Wind speed (knots)
WD=   59.13   #Wind direction (degrees) (0-360)
T =    7.21   #Temperature (degrees celsius)
RH=   13.01   #Relative humidity
BP=  618.72   #Barometric pressure (millibars)