Generally, Mars - 50 percent farther from the sun than Earth - is bitter cold. Its atmosphere is paper thin (1 percent as dense as Earth) and, at times, windy and dusty.
There is no rain on Mars because the low temperatures and pressures mean water can only exist as vapor or ice (although it may have have rained in the geologic past say scientists).
Snow occasionally forms in the upper atmosphere but does not reach the ground writes Universe Today.
Storms consist of just wind and clouds (composed mostly of ice cystals that have evaporated from Mars’ polar ice cap), and sometimes dust.
NASA provides a lot of the basics about Martian weather on its Quest educational website. I’ll excerpt some highlights in italics below:
The temperature on Mars may reach a high of about 70 degrees Fahrenheit (20 degrees Celsius) at noon, at the equator in the summer, or a low of about -225 degrees Fahrenheit (-153 degrees Celsius) at the poles. ... In the mid-latitudes, the average temperature would be about -50 degrees Celsius with a nighttime minimum of -60 degrees Celsius and a summer midday maximum of about 0 degrees Celsius.
On Mars, the air is saturated (100% humidity) at night, but undersaturated during the day.
Wind and dust storms
Occasionally, winds on Mars are strong enough to create dust storms that cover much of the planet. After such storms, it can be months before all of the dust settles. The maximum wind speeds recorded by the Viking Landers in the 1970’s were about 30 meters per second (60 miles an hour) with an average of 10 m/s (20 mph)
The average air pressure on Earth is 29.92 inches of mercury (or 1,013 millibars). This is more than 100 times Mars’ average of 0.224 inches of mercury (7.5 millibars).
Weather cleared out for landing of Curiosity
As noted above, dust storms are common on Mars but, according to NASA, were “taken into account when Curiosity’s landing system was designed and tested.”
Malin Space Science Systems (MSSS), which provides weekly Martian weather reports, noted the presence of dust storms on Mars last week, but away from Gale Crater, where the rover landed.
As is typical for this time of year, the weather on Mars was dominated by sporadic, local dust storms in the southern mid-latitudes this past week. Local dust storms lasting 1-2 days were observed in Sirenum, Aonia, and Noachis, while dustier conditions persisted in both the Hellas basin and the Valles Marineris canyon system throughout the week. . . . With the Mars Science Laboratory Curiosity rover set to land in Gale Crater next week, weather conditions at Gale were benign, with the skies being dominated by diffuse water ice clouds
NASA said a dust storm formed southwest of Gale Crater around July 31 but transformed into “an inactive dust cloud on Aug. 2.”
Martian weather was perfect for the touch down of Curiosity NASA said.
The atmosphere is clear and seasonal around Gale Crater, in agreement with the computer models used to simulate Curiosity’s landing. . . . Dust activity is picking up on the other side of the planet, as shown by the dust clouds marked on the left side of the map. None of these dust clouds will arrive at Gale Crater before Curiosity does.
Curiosity will take Martian weather readings
The Curiosity rover will do its part to advance our understanding of the weather on Mars.
Sensors aboard the rover exposed to the Martian elements will measure wind speed, wind direction, air temperature, humidity, and ground temperature.
Using an instrument called the Radiation Assessment Detector, the rover will measure the intensity of solar and galactic cosmic rays and particles.
“These particles are natural radiation that could be harmful to astronauts on a Mars mission or to any microbes near the surface of Mars,” NASA says.