Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/21 10:05:50 #Date/time of acquisition
WS=    5.63   #Wind speed (knots)
WD=   38.34   #Wind direction (degrees) (0-360)
T =    1.54   #Temperature (degrees celsius)
RH=   30.93   #Relative humidity
BP=  617.29   #Barometric pressure (millibars)