Upper air

Surface observations describe one level. A sounding describes the whole column — where the moisture sits, where the air is stable or unstable, and how the wind changes with height.

That profile is what separates a day of harmless fair-weather cloud from a day of deep convection and thunderstorms, even when the surface conditions look identical.

Soundings also anchor the models. A global model with no observation over the tropical Atlantic is guessing at the vertical structure it is supposed to be forecasting.

Upper-air observations for the Eastern Caribbean come from a small number of stations across the region, and each one covers a large area of ocean. Their value to Grenada's forecast is out of proportion to their number.