Apparently there is actually an abbreviation for weather intelligence - "Wx."
One of the things I love about blogging is the level playing field. I get to engage life-long professionals in politics and national security as, if not equals, at least something like possible-future-equals. I get a bit of a thrill when an established blogger notices me (the weakness of the human ego). One example of this that is the first-ever comment on my blog (which is still quite young) was from Nicholas Gvosdev, the editor of the National Interest. More recently, the intelligence blog "Kent's Imperative" (a riff on Kant's Imperative and Sherman Kent) noticed my post on the National Intelligence Estimate on Climate Change. Woo, validation! Kent's Imperative categorizes the climate change NIE as weather intelligence.
Probably the most fascinating example of weather intelligence is during the Normandy landings. The weather patterns in the Atlantic and Western Europe were generally unfavorable to landings, because the Allies needed the light of the full moon as well as clear skies in order for their aircraft to find their drop zones, as well as for the tide to be at its highest possible point. This confluence was rare. The weather patterns in that region meant that weather moved from the Atlantic eastwards to France. Allied domination of the seas meant that they would have advance warning of the weather, compared to the Germans who didn't know what was beyond the horizon from the French coastline.
The days before the June landings were cloudy and unfavorable for an amphibious assault in France. The Germans assumed that this weather would continue for the next several days, and thus the Germans assumed that the Allies would be unable to attack for several days and lowered their readiness. Rommel took the occasion to visit his wife in Germany for her birthday, and many division commanders, etc were also away. The Allies, however, knew that there was a gap in the clouds that would arrive on June 6, and thus they executed their attack on June 6. The Allies' superiority in Wx gave them a direct decision advantage over the Germans that they were able to leverage by achieving total surprise (or as close as they could have achieved in the broader picture).
It seems to me that weather intelligence is not easily classified into HUMINT, GEOINT, MASINT, OSINT, or any of the other stovepipes. If Wx was collected by individuals on the ground ("Brr I'm cold"), it would be HUMINT. If Wx was collected via satellite, it might be GEOINT, if it was collected by measuring barometric pressure, it might be MASINT, or if it was collected by reading the newspaper's weather forecasts, it would be open source intelligence. Given these requirements, as well as that Wx would only really be useful to a limited set of consumers (soldiers on the ground, pilots, or people trying to predict environmental disasters) Wx must be a massive headache to manage. The IC apparently decided it would fit in the Air Force, in the Air Force Weather Agency, although that agency is only ten years old.
That's another great thing about blogs (and the interblag in general) - it can get me off on tangents, and I end up learning by accident.