Alright, so I've seen a lot of storm feats that should be applicable, but they're too generic to deserve an individual calculation, so in order to avoid using estimates, I'm going to use this blog as a way to have a source to quote for the AP of these kinds of feats.
Keep in mind that this is all working under the assumption that the storm covers the horizon, and that the person is at a sea-level location (normally this last part is assumed even if they're in a regular city scenery, but the results vary greatly if they're high in the air or on top of a tower or mountain, for example.), and the person is average in height. A few centimeters don't make a significant difference, but if you're willing to actually use the observer's official height, you can go right ahead.
Average male human height = 1.7 m
Distance to horizon = 4700 m
Low Instability (For when there are just clouds) = ((pi * 4700^2 * 8000) * 1.003) * 1000 J = 556847800503615.42588442169370923 J = 133.089 kilotons, or Large Town Level
Medium Instability (For when there's just rain) = ((pi * 4700^2 * 8000) * 1.003) * 2500 J = 1392119501259038.5647110542342731 J = 332.724 kilotons, or Large Town Level
High Instability (For when there's rain and lightning) = ((pi * 4700^2 * 8000) * 1.003) * 4000 J = 2227391202014461.7035376867748369 J = 532.359 kilotons, or Large Town Level
Extreme Instability (1990 Plainfield Tornado; basically use this when there are additional things like really big tornados apart from rain and lightning) = ((pi * 4700^2 * 8000) * 1.003) * 8000 J = 4454782404028923.4070753735496739 J = 1.064718 megatons, or Small City Level
So yeah, if you're too lazy to calc a storm, or just don't know how to do it, use this as the bare minimum.