There are different definitions of weather, some that include solar flares. In Mutant Future, and Gamma World for that matter, weather can include a lot of things falling from the sky. Here are a dozen with suggested damage or other effects.

Orbital Death Ray: When orbital stations get unhappy, they tend to blow the tops off of mountains or carve new valleys. The area of effect is 1 mile in diameter and damage is 40d10, save versus energy attacks for half. The station can attack once per hour and usually does so 1d6 times before getting bored with frying surface dwellers.

Bliss Field: Another orbital station weapon was created to keep people calm and stop riots in their tracks. The area of effect is 5 miles in diameter, all humans or those with human derived brains must save versus stun at -8 or be trapped in a haze of bliss until the field is shut off (usually 1d10 hours later). Robots and androids were used to capture criminals and now it is usually a blood bath of predators.

Hunger Field: This is a weird orbital weapon that only affects plants. The area of effect is 1 mile in diameter and all true plants (no fungi or mutants with photosynthesis) gain the Carnivore mutation for 1d4 days. Most people and animals can't escape the onslaught.

Solar Flare: Weather from the Sun which may or may not cook the planet. 90% of them are all but unnoticed, 9% of them cause a minor distruption in artifacts (a hickup that causes twice as much power used until the flare is done 2d4 hours later), .9% that cause a major disruption in powered tech (they don't work for 2d4 hours) and a .1% chance of a direct hit of a flare. The last one raises the temperature of the entire atmosphere by 1d10 X 1d10 degrees.

Lunar Flare: A source of radiation on the Moon blankets the face of the planet towards it for 1d4 hours. I suggest reading Wisdom from the Wastelands 38 and 41 (Chris' work on radiation) for some ideas.

Razor Rain: Yes, the name comes from the series Defiance. It is just too good of an idea to ignore. Fragments of orbital cities and ships come down and pepper the ground in an area 1d6 miles wide by 1d10 miles long for 1d12 hours. Those within the storm must save versus energy attacks once per hour. Success means no damage. Failure means 1d12 d6's of damage (so roll 1d12 to see how many d6s you need to roll).

Steel Rain: Similar to Razor Rain in appearance, this weather is caused by an attack by an orbital station. The orbs dropped are small robots. Most are smashed on impact, but enough survive to cause chaos. Damage is the same as razor rain and then add 1 Creeping Doom spell per square mile (caster level is up to the ML). The swarm lasts for 1d4 turns and then the robots are destroyed by the local flora and fauna.

Chemical Smog: There are many nasty chemicals in the air in MF and this includes most of them. There are no standard effects because each bank of smog is different. Be creative and try for effects that are more than acid and mutagens.

Hell Hail: This form of hail can be found all year. It is a mixture of water and a freezing agent. When the hail hits the ground, an area of 3' around each strike takes 1d4 points of cold damage. For a storm, this is usually 5d4 points of damage per turn, save versus energy attacks for half. Hell hail storms last for 1d8 turns.

Pollen Fog: These clouds of pollen are used to slay anything that may be harmful to future progeny of the vegetables that released it. A bank of pollen fog is usually 1d3 miles long and 1/2 mile wide. Anyone within it is affected by a class 6 poison. The save is needed every turn and the fog lasts for 2d4 turns.

Blood Fog: Some kaiju use an attack similar to pollen fog. Mechanically it is identical except that it leaves a lot of blood that will draw scavengers and blood feeders from miles around.

Egg Rain: This weather comes from who knows where. It is sort of like steel rain and pollen fog except the result isn't machines or plants, but rather parasite mutations. See Wisdom from the Wastelands 12 for more information. They infest everything that fails its save versus poison.

As you can see, weather can be exciting and terrifying in the wastes. Learn the signs and know when it is a good idea to get under cover. And when cover doesn't mean squat...