Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/07 10:21:00 #Date/time of acquisition
WS=    0.00   #Wind speed (knots)
WD=   29.16   #Wind direction (degrees) (0-360)
T =    6.33   #Temperature (degrees celsius)
RH=   15.97   #Relative humidity
BP=  618.72   #Barometric pressure (millibars)