QUESTION:
What are the weather conditions on Mars?
 
ANSWER from Bob Haberle on March 24, 1997:
As on Earth, weather conditions on Mars depend on location and season. In
general, Mars is cooler, breezier, and much much drier than Earth.
Warmest temperatures probably occur in the southern subtropical
latitudes during late summer and may get up to the freezing point 
(32F) at midday. Coolest temperatures  occur in the winter polar
regions where it remains close to a whopping 190F BELOW ZERO for 
months at a time!

Because of the cold temperatures (and low surface pressures, ~7 mb), 
the atmosphere cannot hold much water so clouds tend to be thinner 
and almost certainly do not produce rain. On the other hand, such dry
conditions allow dust particles to remain in the atmosphere for a
long time. These dust particles are lifted off the surface by
hurricane force winds. Occasionally the entire planet is engulfed by
a dust storm and surface features can be completely obscured.

We hope to learn more about Martian meteorology from the forthcoming
Pathfinder and Mars Global Surveyor (MGS) missions. Pathfinder is a 
lander that carries, among other things, a met package to monitor
temperature, pressure, and wind. MGS is an orbiter that will map the 
entire planet daily for one Mars year (687 Earth days).