Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/22 18:19:28 #Date/time of acquisition
WS=   14.03   #Wind speed (knots)
WD=   37.90   #Wind direction (degrees) (0-360)
T =   -0.39   #Temperature (degrees celsius)
RH=    9.96   #Relative humidity
BP=  615.80   #Barometric pressure (millibars)