Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/22 23:22:12 #Date/time of acquisition
WS=   13.55   #Wind speed (knots)
WD=   32.34   #Wind direction (degrees) (0-360)
T =   -0.45   #Temperature (degrees celsius)
RH=    9.72   #Relative humidity
BP=  616.05   #Barometric pressure (millibars)