There are rain, sun, sand, and hail in the forecast for today... but don't worry, your pokemon will probably be fine.
I've seen so many weather teams lately that I've decided to look into just what makes them work... or fail as so often seems to be the case. I think in analysis I'll start with sun as I see the fewest of these.
Sun teams tend to have an interesting dynamic of fire and grass pokemon because of all the Chlorophyll abilities in grass. Looking at the dynamics, the best boost that sunny day teams received was Ninetails getting Drought as a dream world ability. Now the question, what makes a sunny day team work?
For a sunny day team to work, you first have to get the sun out. This means either Ninetails or a pokemon who can use the move sunny day. Among the list of sunny day pokemon, a few stand out at least in my mind:
The reason these pokemon stick out is because they are good defensive pokemon that can play a second role on the team dynamic. One of my favorites is Venusaur, as he can have the dream world ability Chlorophyll, be bulky enough to easily switch in, and has a lot of power potential with moves like power whip. Nidoking and Nidoqueen are just bulky with a good movepool for aiding the team. Clefable, blissey and suicune are all very bulky, and can help against on opponent who's fire type is looking to grab that free boost for a fireblast. Forretress can spike and spin, and can easily switch in. Spiking can bring 2hko pokemon down to a ohko. Crobat and Gliscor can be good stall breakers against defensive pokemon. Celebi is a good counter to most rain dance users, so it can also be a useful addition.
Once you decide who your team you will rely on for bringing out the sun, you have to decide on a couple sweepers. My suggestion is to make sure you have one fast, powerful fire user (choice scarf shandera or heatran are always good choices) that can take advantage of the sun, but will also be useful if the sun gets taken away. You'll want to probably have two Chlorophyll sweepers as well... but here's the hard part. I personally am a fan of mixed sweepers for these positions because it means that skram/bliss or simaler switching defense strategies can't force you to switch and either para or damage your sweepers. Having a pokemon like Venusaur who can sweep both types if specd right and has sunny day can really free up extra spaces on your team... but be careful! You need to make sure your sunny day user isn't a frail sweeper or you may never get the sun to shine in the first place.
That is the core of a sun team. The rest of your team should be complimentary. If you have too many pokemon relying on the sun completely, you ignore two facts:
1) Any all-sun team has considerable weakness to other weather (especially auto-weather).
2) There is no way a team of 6 sun-based pokemon can have coverage against the entire OU defensive meta... and if it does most of the time it's far too weak to kill it in less than 3 hits or requires switches.
The best fix? Look at your sweeping strong types. Grass and fire will obviously already be there, but often you will have 1-3 more types you can hit well. Find what elements that you are missing (commonly ground or water)
To illustrate I will make a team following my own advise. To start I want to find two sun bringing pokemon. Looking at what commonly gives these teams problems my choices are Suicune and Ninetails. I like ninetails because semi-perma sun is almost indispensable against defense-swap teams who will try to outlast your sun. I like suicune because it's unexpected to run sunny day, and can tank out many other tpyes of weather like sandstorm and rain. My sweepers are both Chlorophyll sweepers and mixed: venusaur and shiftry. Venusaur is my main sweeper because he can use sleep powder to take out any major counters, and has Swords Dance to boost his attack, allowing him to focus on special and use a sleep turn to buff. I like shiftry because it can switch in on any psychic pokemon that threaten venusaur for free, and use the extra turn gained to use nasty plot... which also allows me to just boost one of his two stats and have the other boost by move. My fire user is already on the team in ninetails, but she requires some extra care... I would use high hp and special defense ninetails with choice specs (allowing her to live through a hit and switch in, and then with still decent speed use specs and sun boost to deal heavy damage). This leaves two spots, and not much left to cover. I personally prefer to have a backup defensive pokemon to stop rain and sandstorm, so I throw in Nattoorei here as it almost conpletely stops rain, and gives sandstorm teams a hard time. This gives the team a huge fire weakness, so as my last pokemon I need something that can help remedy that. I chose bulky ddance gyarados because it takes fire well, and after a dance can wreck what's left of a team that's already devistated trying to stop the sun.
Next, i'll look at rain.
Rain teams seem to be almost a gimmick these days. Sometimes they get a 6-0 sweep, and sometimes the same team gets stopped 0-6. Why does this happen?
As i dissected players teams I started to realize that it was the name that people seemed to follow instead of the spirit, and it was making obvious holes in teams. Many people see rain and instantly think ludicolo, kingdra and kabutops sweeping through whole teams. The problem? This works great against a generally banalced team as you can knock out their one or two decent counters by hitting+sacrificing with one or two of your sweepers and winning with the third... but it's just not a solid gameplan overall as a defensive team that uses SR can switch kill you, or just use the switch causing to deal damage or para. For instance, the minute you send out ludicolo an opponent with blissey can grab a free switch and paralyze what you swap to. When kingdra uses outrage, skarmory comes in and uses whirlwind to put off your team and cause SR/spikes damage... or predicts your switch to a special sweeper and deals large damage with brave bird.
Rain is over used on rain dance teams.
As with the sun team, you can't have a team that entirely uses rain. The best way to run a rain dance team is what I like to call Fake Rain Dance. basically you convince your opponent you have a rain team, beat up their rain counters in turn, and then finish with a swift swimmer. For this strategy you only need two rain involved pokemon. The first i call the Bait, and the second the Clencher. For bait, you need something obviously rain based that starts rain. The easiest is Drizzle politoed as its weak, has hypnosis to annoy the opponent, and gives the opponent an easy choice of switching to a water counter. Then use grass, ground, rock or electric pokemon to eliminate their counters, switch back to politoed, rinse and repeat. On my test teams for this strategy, i often actually never bothered to bring out my swift swimmer because I would kill them with just politoed once their water resistances were all gone.
Many people also overestimate the power of thunder. There are plenty of 120 power moves, and if you don't have the stab or special attack to back it up they'll never be able to ko most common threats. Its a good move to have on a pokemon like jolteon, but only when you don't make the moveset just to spam it. Choice scarf thunder is BEGGING to get swapped in on by something with enough power to KO your other pokemon.
Anyway, no need to make an example team here. Just make sure that you use mixed sweepers whenever possible to prevent the need to switch, and that you stay away from obvious strategies like using rain then immediately switching. Its sometimes best to get only 1 turn in the rain with your swimmer to kill one of your opponent's pokes, then go back to defending.
Next I looked at sandstorm teams.
These teams got a real boost with gen 5 as now they can get a couple pokemon with a speed boost and attack boost, which was the main problem with them before.
I see a ton of different ideas for sandstorm, and many of them work. The main problems I see have mostly to do with three main topics:
1) The Lead
2) Sweeper Choices
3) What to do when it falls apart.
DON'T LEAD WITH A SANDSTORM INVOKER!!!
i mean really people. Hippodon can only defend against maybe 15% of leads, and normally just gets up SR then gets KOd, tricked, taunted, or slept.Tyranitar is a great antilead... because he can take a hard hit and retaliate. Try bringing that back if the opponent brings in hail? yaaaaa....
Sweep based on what you want to do with the team, not based on whats the fastest. Doryuuzu is an amazing pokemon in the sand... but he has a ton of weaknesses and can't even get out without some help. He also has problems since he only has one real stab. You need to make sure you balance your team, and keep your number of actual sweepers and sand reliance down to a minimum.
When you lose the sand (especially to rain) it can make it really hard to recover. Make sure you have a "Recovery Plan" that you can use to get your sand back up even in a harsh environment. If you assume the worst that your opponent can do do stop you and have a backup plan that gets around it reliably then you can always recover.
The last type of weather is Hail.
Hail is the type i've personally seen fail the most. It doesn't give speed or extra damage, so you can't just choose a group of ice pokemon and hope that it works. In fact, there are only three real reasons to use hail.
2) Snow Cloak
3) Ice Body
Now the real key is in how to use these. Blizzard is a no brainer, just a strong stab that is resisted by a decent number of pokemon, but good for stab and better than ice beam. Any pokemon benifits from blizzard, but only if that pokemon was capable before. Snow Cloak is only really useful on a pokemon like froslass who can use thunder wave and substitute. A paralyzed pokemon trying to hit against snow cloak has a 60% chance to hit, so the basic idea is to switch in, twave, and then set up sub while healing from leftovers until you get a sub, then deal damage until the sub is broken. rinse and repeat, using the leftovers healing to keep it up. Ice body is good as a stall tactic on Walrien, but he should be used carefully as he can get Pp stalled and then just take up a spot.
Similar rule for Hail as with Sandstorm: Don't lead with abomasnow. He doesn't make a good lead in most circumstances, and there's no reason why you need to start hail from the start. Hail is a stalling weather, don't rush into it.
Weather is a great tool, but so easy to accidentally misuse. Just make sure you use it in a way that it actually supports, and that you have a recovery plan, and it can easily be a great addition to a team.
Have any questions about pokemon? Go ahead and ask, I'm always looking for new things to look into ^^.