It's been said that the main holdback for specialist casters is that they always retain the potential for being a generalised caster. So what if we push the limits of making a caster as focused on blasting as possible? Here's my proposal, tied together with some flavour.
Weathercaller
HP: 6+CON
Key Atrribute: Wis or Cha, as per weathercalling style
Proficiencies: As Wizard, except with Fortitude and Will swapped (so Expert Fortitude to start, Greater Juggernaut at 17, Iron Will at 9) and Trained in 3+Int skills plus weathercalling style
Weathercalling style
Weather Beckoning Style: Charisma, Performance
Weather Predicting Style: Wisdom, Survival
Weather Magic
You cast from the weather spell list. This comprises of the universal elemental spells (RoE 55) plus any spells that have one or more traits of your preferred weather. Unlike the elemental spell list, when casting a spell that requires you to select an elemental trait, you can only select an elemental trait that is of your preferred weather. If you Learn a Spell, you use your weathercalling style skill to do so.
At 1st level, you prepare three 1st rank spells and 3 cantrips from the common spells on your weather spell list or any other weather spells you have access to. Spells you prepare are prepared to your spell collection, and can cast any of the spells in your collection by using a spell slot of an appropriate level.
As you increase in level, the number of spells you can cast and add to your collection grows. At 2nd, you gain an additional 1st rank spell slot, an additional cantrip and can prepare one more spell to your spell collection. At 3rd, you gain 3 2nd rank spell slots and can prepare 3 more spells to your spell collection. At 4th, you gain 1 more 2nd rank slot, 1 more cantrip and can prepare 1 more spell to your spell collection.
Due to your connection with the weather, you begin to lose low level spell slots from 5th level onwards. From then onwards, you have 4 spell slots of your highest rank, 4 spell slots of your 2nd highest rank, 5 cantrips, and a spell collection of 8.
Once you gain 2nd-rank spells, you can heighten any spell in your spell collection to any level you can cast. The only restriction is that you must select at least one spell of your lowest rank for your collection each time you prepare, ensuring that you can use all your spell slots each day.
Preferred Weather
You specialise in calling a single kind of weather. Your preferred weather grants you two traits for your spell list, two domains whose focus spells you gain, and a weather damage type that is used for certain weathercaller class features
Clear Skies Not a cloud can be seen and the moon and stars are visible even by day. Your preferred weather traits are fire and light, your domains are Moon and Star, and your weather damage type is fire with the light trait that counts as silver
Heavy Rain Thick dark clouds gather, rain pours, lightning sparks from clouds. Your preferred weather traits are water and lightning, your domains are Water and Lightning, and your weather damage type is lightning with the water trait
Blizzard Hail and snow falls from the sky as heavy winds batter about. Your preferred weather traits are air and cold, your domains are Air and Cold, and your weather damage type is cold with the air trait
Sandstorm Dust and sand are churned by winds, scouring flesh from bones. Your preferred weather traits are air and earth, your domains are Dust and Earth, and your weather damage type is slashing with the air and earth traits
Weather Aura
You can force your preferred weather to appear in a small area about you, which empowers your spells. Certain weathercaller class feats and class features also use your weather aura. You gain the coalesce weather action
Coalesce Weather 1A
Aura Weathercaller
Requirements: Your weather aura isn't active
Your weather aura activates. It is a 10ft emanation. While it is active, spells with your preferred weather traits gain the following benefits:
If it's a damaging spell with no duration, you gain a status bonus to its damage equal to double the spell's level
Spell attack rolls (but not spell save DCs) benefit from the item bonus of a gate attenuator
Level 3
Lingering Storm 0A
Frequency: Once per turn
Requirement: Your most recent action was to cast a non-cantrip spell with one or more of your preferred weather traits
Some of the energy of your spells lingers on. Choose a creature that took damage from that spell. They take weather damage equal to the rank of that spell next turn.
Level 5
Enemies in your weather aura also gain weakness to your weather traits equal to half your level. As this is a single weakness, it cannot be triggered twice by an effect with both your weather traits.