Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/23 09:56:15 #Date/time of acquisition
WS=    8.77   #Wind speed (knots)
WD=   40.87   #Wind direction (degrees) (0-360)
T =    6.78   #Temperature (degrees celsius)
RH=    7.06   #Relative humidity
BP=  617.04   #Barometric pressure (millibars)