Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/21 22:37:44 #Date/time of acquisition
WS=    0.00   #Wind speed (knots)
WD=  332.98   #Wind direction (degrees) (0-360)
T =   -0.84   #Temperature (degrees celsius)
RH=   12.49   #Relative humidity
BP=  616.41   #Barometric pressure (millibars)