Still cant believe I slept through that one.
For me it has to be the January 2004 snowstorm, watching light rain turn to horizontal snow in a matter of seconds, with visibility reducing to nothing just as quick. It was amazing as it hit, big black clouds hanging overhead, I was dissapointed that the previous nights snow was melting to nothing, then this squall line creeps up behind me while I'm watching from my South facing window.
Summer of 2007 too, never seen so much rain.