Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/23 23:13:57 #Date/time of acquisition
WS=   15.77   #Wind speed (knots)
WD=   69.33   #Wind direction (degrees) (0-360)
T =    1.44   #Temperature (degrees celsius)
RH=    7.98   #Relative humidity
BP=  617.08   #Barometric pressure (millibars)