I recall fondly traveling through the Alps with the Traveling Joneses and Buf and MA. Each day we'd see how gorgeous and sunny it was in the morning, how there wasn't a cloud in the sky, and off we'd go without raingear of any kind.
It rained every day in the Alps--typically brief squalls, but in Salzburg we really got dumped on. Five days in a row we saw blue cloudless skies and someone would say "should we bring umbrellas?" and we'd say "nah, look at the sky!" We continually got soaked because of plain stubborness, because we refused to acknowledge how quickly the weather can change in the mountains.
Lesson re-learned today, but instead of the lovely Alps I'm in Baltimore. When I left for class at 7:50am it was COLD, like high 30s, overcast, and windy, and I grudgingly wore my winter coat. When I left class an hour later it was sunny and WARM. I walked home, changed into my running gear, and about a half mile into a 6-mile run an astonishing wind began blowing, a dark line of smudge covered the blue sky, and it started snowing. I'm not talking flurries, I'm talking white-out conditions, pellet-like flakes blowing so fast they were parallel to the ground. The baseball hat I wore to protect my eyes from the sun was now needed to keep blinding snow out of my eyes. There was slush on the sidewalks and the roads, and my hands and legs were bitterly cold in the wind and wet. Traffic slowed to a standstill. Then, once I got two miles out, the sun came out again and it was almost HOT. That's when the hail started, then it rained, then it was HOT again, then it got COLD.