Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/07 10:38:03 #Date/time of acquisition
WS=    5.08   #Wind speed (knots)
WD=   49.62   #Wind direction (degrees) (0-360)
T =    7.40   #Temperature (degrees celsius)
RH=   20.18   #Relative humidity
BP=  618.54   #Barometric pressure (millibars)