Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/11/22 10:30:22 #Date/time of acquisition
WS=    7.59   #Wind speed (knots)
WD=   44.45   #Wind direction (degrees) (0-360)
T =    3.98   #Temperature (degrees celsius)
RH=   15.64   #Relative humidity
BP=  616.64   #Barometric pressure (millibars)