Azzy brought up a bunch of dragon feats- specifically, legendary dragons have a few decent feats. One we can go at a baseline of 7-C (causes light earthquakes, small volcanoes, the works). That said, we have a storm feat and a blizzard feat. Let'sa go.
White Dragon's Blizzard Ballad
Because Zelda Songs are the theme of the day. So, a White Dragon can generate a blizzard around its lair for 6 miles. Namely, this happens when it rests. So it should scale to their potency, since this hinges on an action they take.
|“||The region containing a legendary white dragon's lair is warped by the dragon's magic, which creates one or more of the following effects: Freezing precipitation falls within 6 miles of the dragon's lair, sometimes forming blizzard conditions when the dragon is at rest.||„|
|~ Azzy's Sources|
We can assume the height of the blizzard to be at least up to low-cloud level, so 2000m. Radius of 6 miles means its volume would be 5.86e11 m^3 of air affected. Mass of air is 1.225 kg/m^3, so mass should be 7.179e11 kg.
Baseline "severe blizzard" is -12 C. Assuming it starts at average temperature, that'd be a heat change of 28 C (16 C being standard). Specific heat of air should be 1012 J/(kg x K).
Just so you can check me, plug in values here. We get 2.034 x 10^16 Joules, Small City level+
Blue Dragon's Stormy Sonnet
Like I said, Zelda names.
|“||''The region containing a legendary blue dragon's lair is warped by the dragon's magic, which creates one or more of the following effects: Thunderstorms rage within 6 miles of the lair.||„|
|~ Azzy's Sources|
So, the quote implies it is a relatively severe thunderstorm, though it isn't anything devastating as it doesn't damage PCs when approaching. I'm gonna say Moderate as a low-end, and Heavy Instability as a high-end (more likely). This is CAPE method, by the by.
So, six mile radius. We can get volume of a cylinder with 6 miles and a height of 9144 meters (30000 feet). Convert miles to 9656.1 m and do our volume calc for a cylinder to get 2.679e12 m^3 as our volume. Density of a cloud is 1.003 kg/m^3, per this wiki's standards, so let's get a mass of 2.687e12 kg.
Low-end instability value is 2500 J/kg, high-end is 4000 J/kg, netting us values of the following:
6.718e15 Joules, Small City level
1.075e16 Joules, Small City level
Not bad as a supporting feat.
White Dragon's Winter Wonderland: 4.86 Megatons of TNT, Small City level+
Blue Dragon's Bustling Barrage (Low-End): 1.61 Megatons of TNT, Small City level
Blue Dragon's Bustling Barrage (High-End): 2.57 Megatons of TNT, Small City level