Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/22 11:00:27 #Date/time of acquisition
WS=    7.35   #Wind speed (knots)
WD=   63.06   #Wind direction (degrees) (0-360)
T =    4.59   #Temperature (degrees celsius)
RH=   18.54   #Relative humidity
BP=  616.49   #Barometric pressure (millibars)