Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/07/03 15:27:03 #Date/time of acquisition
WS=    5.81   #Wind speed (knots)
WD=  244.67   #Wind direction (degrees) (0-360)
T =    5.81   #Temperature (degrees celsius)
RH=   58.36   #Relative humidity
BP=  617.78   #Barometric pressure (millibars)