A weather enthusiast who gets excited by extreme weather, but who has little or no knowledge of the science of meteorology.
Weenies often inhabit Internet message boards and issue "wishcasts", which are forecasts based on the author's desire for extreme weather. They try to justify their wishcasts with anecdotes and pseudoscience.
While professional forecasters examine computer models to make forecasts, weenies often treat the forecasters themselves as data sources upon which to form their wishcasts.
When an extreme weather event isn't going to plan, weenies will often react by issueing "bittercasts", which greatly overestimate the extent to which the supposed extreme weather has weakened.
Weenies are very self-absorbed and emotional, and become morbidly distraught when a forecasted extreme weather event doesn't pan out in their backyard. Even if the forecast was generally correct for surrounding areas, weenies will angrily denounce the forecasters.
Some made-up weenie quotes illustrating the terms:
"I have a term paper due tomorrow that I haven't started yet, I think we'll get 3 feet of snow though, just look at the storm swirl on the satellite."
"When DT and LC and JB agree on a forecast, watch out!"
"Well, we're getting dry slotted and it's hardly snowing. The storm's a bust. We'll end up with 1/4 inch."
(Later, weenie still gets a respectable 18 inches)
"We only got 18 inches instead of 36. WORST FORECAST EVER"