Today, I went out for a walk, and got rather exited when I spotted a Vulpix along the way. Nothing too special in the greater scheme perhaps, but, during the past year I spotted perhaps 5 Vulpix in the wild, so not counting raids or eggs. Ofcourse, I caught it immediately, even if it was just for the candy.
A few hundred meters further: another Vulpix. Well, lucky day in the Vulpix department I guess? During my walk, which took just about 1 hour, I spotted 4 Vulpixes total, and also saw one on my radar for a pokestop that wasn’t on my route.
Yes, it was a sunny day, but we’ve had more sunny days during the past year, so why did I spot a lot of Vulpix today? And, if the sun matters so much, why haven’t I seen any Growlithes? They’re roughly as rare as Vulpix around here.
But, something else was odd as well. Yesterday, I went for a pretty similar walk in the same area, and spotted dozens of Eevees. Today: not a single Eevee.
Which brings me to the topic: particular weather definitely boosts the spawn of pokemons with affinity for that weather, but rather than just randomly drawing from a large pool containing all applicable pokemon with that affinity, the pool is downsized to a selection. So, today I might have spotted several Vulpix, but, if we have similar weather tomorrow, and I make the same round, then it’s very possible that I won’t spot a single Vulpix, but run into half a dozen Arcanines instead. Or Magmars. Or Charmanders. However, I doubt I’ll run into both Charmanders and Vulpixes, or both Magmars and Arcanines. Simply because the “daily pool for sunny weather” (I just assume it’s daily, but it’s also possible that it updates every 6-8 hours, or only once a week) may contain a different “rare spawn of the day”.
And that would explain why some rare spawns seem even more rare then others to the avarage player, even if statistics show they should be comparable in rarity: it’s simply because they’ve been hunting for them on the wrong day (perhaps also in the wrong biome or S2 region, or however Niantic decides to distribute these things). If you really want a Charmander, and you spot a Vulpix, then I suspect it’s better to search another day, or drive some 20 miles, and try elsewhere, because Charmander might not be in the spawn pool for the area you’re in at the moment you’re there.
Oh, and someone from the raid group I’m in also posted an image of a Ninetails he caught in roughly the same area I was walking, just about 1km distant. Which I think is just too coincidental for a catch-the-vulpix-day.
The exact size of the “daily pool”, its contents and rotation times would be something for others to figure out, I’m too lazy for that. I’m just saying there is some very obvious structure in these “random” spawns.