Weather values are instantaneous:
#CFHT/GEMINI Weather Tower Data
2009/07/04 06:39:06 #Date/time of acquisition
WS=   -0.11   #Wind speed (knots)
WD=  268.50   #Wind direction (degrees) (0-360)
T =    2.86   #Temperature (degrees celsius)
RH=   14.77   #Relative humidity
BP=  617.29   #Barometric pressure (millibars)