Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2008/05/13 14:45:14 #Date/time of acquisition
WS=    1.39   #Wind speed (knots)
WD=  315.54   #Wind direction (degrees) (0-360)
T =    4.78   #Temperature (degrees celsius)
RH=   33.25   #Relative humidity
BP=  613.32   #Barometric pressure (millibars)