Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/07/04 02:41:54 #Date/time of acquisition
WS=    4.59   #Wind speed (knots)
WD=  282.43   #Wind direction (degrees) (0-360)
T =    1.80   #Temperature (degrees celsius)
RH=   24.17   #Relative humidity
BP=  616.09   #Barometric pressure (millibars)