This post discussed the clouds appearing above Meridiani during the current Summer season and water/ice deposition on the surface:

Space Sciences
Could We Make A "Solar Still" On Mars?
Posted by Robert Clark on 1/4/2006 8:37:27 AM
http://habitablezone.com/space/messages/409580.html

There have been some video posted to the Unmannedspaceflight.com site of these night-time clouds:

http://media.putfile.com/earthrise-oppy-sol-687

http://www.lyle.org/~markoff/op_movie/opp_687L1.gif

Do the fast bright streaks in the second video look like meteorite trails?

I suggested the current deposition of the water/ice at Meridiani may become liquid at some point because of the warm maximum temperatures during the current Summer season. This is supported by the detection of carbonate in dust by the rovers, and also from orbit:

January 09, 2004
Spirit Lowers Front Wheels, Looks Around in Infrared.
"We came looking for carbonates. We have them. We're going to chase them," said Dr. Phil Christensen of Arizona State University, Tempe, leader of the Mini-TES team. Previous infrared readings from Mars orbit have revealed a low concentration of carbonates distributed globally. Christensen has interpreted that as the result of dust interaction with atmospheric water. First indications are that the carbonate concentration near Spirit may be higher than the Mars global average."
http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20040109a.html

On Earth in nature carbonate is produced by iteraction with *liquid* water. There have been some laboratory experiments that attempt to show it can form with water vapor alone but this hasn't been seen in nature. I suspect in fact in these experiments some small amounts of liquid water are involved undetected by the experimenters.
It is quite key then that the HEND instrument on Mars Odyssey shows water/ice deposition occurs on Mars even at near equatorial locations:

47 - EVIDENCE OF THE SEASONAL REDISTRIBUTION OF WATER
IN THE SURFICIAL MARTIAN REGOLITH BASED ON ANALYSIS OF
THE HEND MAPPING DATA.
R.O. Kuzmin, E.V. Zabalueva, I.G. Mitrofanov,
M.L.Litvak, A.V.
Parshukov, V.Yu.Grin'kov, W. Boynton, R.S. Saunders.
"As it well seen from fig.1b,c,d, two distinctive
"hollows" of neutrons flux reduction have been appeared
in the northern hemisphere during northern summer at
Ls=130°-170° and in first half of northern winter at
Ls=270°-330°, being extended from high to low
latitudes. At that, later "hollow" (Ls=270°-330°) is
characterized by much stronger reduction of the
neutrons flux and it traces from northern polar region
up to low latitudes in the southern hemisphere. The
first "hollow" is related with periods of the northern
middle summer, while the second one - with of the
southern middle summer. In both case the residual
polar caps serve as main source of the water in the
Martian atmosphere."
p. 2
http://www.geokhi.ru/~planetology/theses/47_kuzmin_et_al.pdf

This deposition was confirmed by Opportunity by the detection of frost on the rover during the Winter season. But I consider it quite key here that HEND shows the deposition is actually higher during the current southern Summer season. So since maximal temperatures can exceed melting currently, the carbonate may form in the period when temperature is above melting but before it reaches the boiling point in the low atmospheric pressure on Mars.
I therefore propose to search for this liquid water by the rovers. However, I am informed that for technical reasons the rover engineers prefer not to deploy the rover arm in the middle of the night. During the current Summer season, the greatest deposition probably occurs at night because of the colder temperatures. You want to cover the area during the night to preserve this water before it burns off in the daytime.
So some other methods: perhaps the RAT could be applied not in the middle of the night but close to but just before sunrise. I don't know if this would be sufficient to preserve the moisture. Another possibility: move a small rock in the middle of the night to cover a small area. Then uncover the area during the early morning, as soon as light is available.
Another possibility: it may work to use a wheel to cover the area. This would have to be done at night to insure the deposition has already occurred. Then as soon as light comes, move the vehicle to uncover the
area. The problem is this might disturb the area so much to make the moisture no longer visible.
Still another possibility: I remember reading the rover could move all the wheels so that they all dug into the ground at the same time. Then we could do that so that the bottom of the rover clung tightly to the ground. Then move the rover to uncover this area at sunrise. A problem with this is that if the rover bottom is this close to the ground it may be difficult
to extract the rover from this position.
Any others?

Bob Clark