Some rainstorms last an hour or two, but some are all day events. If one of those one or two hour ones, wait a bit. Usually the forecast would tell you what kind of rain to expect.

If you have a smartphone, have coverege and have a data plan, the radar loop will give you an idea of if the rain should move out quickly or not.

If it is a one pot meal and only sprinkling, keep your lighter dry (in your pocket) and go ahead and cook in the rain, you won't melt. But any water drops on the stove burner head can put the flame out so be ready to relight it with your dry lighter quickly.

I also recommend against cooking under vestibule. But have done it but I only do it in a tent where the flame will be at least a foot and a half away from tent fabric, where if I knock the pot off the stove the contents of the pot land on the grass and not in my tent and not on me (avoid burns). And have enough ventilation to make sure no carbon monoxide can build up. Also, I never use a liquid fuel stove under a vestibule as they can spout big flames when not quite hot enough, I only use a butane mix type of stove under vestibule.

In the photo I am cooking in a vestibule, I am sitting inside my tent while doing so. I am more inclined to heat water on my stove in the morning for coffee and hot cereal or some other add hot water to dried food type of meal than I am to actually cook a meal, under the vestibule, so the meal in the photo was quite rare for me. Before you run out and buy one of those bear creek chili envelopes, I only use one third of one for a single meal.