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S'COOL: Comparisons for Big Timber, March 1997

We have satellite data for two of the days in March when the Big Timber weather girls made their observations.

March 11, 1997
	Big Timber	CERES/AVHRR	Agree?
Cloud Fraction	Overcast 95-100%	100 %	Yes
Cloud Height	Low	6.5 km	No, but *
Cloud Opacity	Variable	Thick Optical Depth = 40	Yes

*This is an excellent example of the difficulties involved in comparing surface-based and satellite-based observations. Judging from the optical depth, this is a very thick cloud. It is very likely that the cloud base is in the "Low" altitude range and the cloud top is in the "High" range. Thus, the difference in cloud heights reported here is simply a matter of the perspective of the two observations. The additional perspective from ground observers in S'COOL can help us obtain better estimates of cloud thickness. See satellite images.

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March 12, 1997
	Big Timber	CERES/AVHRR	Agree?
Cloud Fraction	Mostly Cloudy 50-95%	100 %	Maybe*
Cloud Height	Low/Mid	2. km	Yes
Cloud Opacity	Variable (Low) Thick (mid)	Thick	Yes

*This is an example of another difficult aspect of comparing surface and satellite observations. The difference in cloud amount is due to the difference in the areas considered. The area seen by the surface observer is a function of several things such as surface elevation, atmospheric haziness, the cloud height, and whether the observer's view of the horizon is blocked by buildings or trees. The satellite observer must try and match the viewing area seen from the surface. In this case, we were probably using too small of an area and missed some clear sky seen from Big Timber. See satellite images.

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