Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/23 15:00:39 #Date/time of acquisition
WS=   15.94   #Wind speed (knots)
WD=   31.88   #Wind direction (degrees) (0-360)
T =    7.30   #Temperature (degrees celsius)
RH=    9.90   #Relative humidity
BP=  615.65   #Barometric pressure (millibars)