Didn't realize how fast a storm could develop until I was coming back on a flight the other day. Was supposed to be perfect weather, with maybe a few scattered clouds ~7,000 ft. The skies were clear and calm, but then about half way back I started to see cumulus clouds ahead. They looked like they were far apart and high, so I figured they were the 7,000 scattered I was expecting and wasn't worried. Shortly after I got under them, though, I started feeling updrafts... it was so bumpy, and occasionally I was actually gaining/losing hundreds of feet at a time. I was having a hard time staying under the Bravo, so thankfully they ended up clearing me into it, which alleviated a lot of my stress.
When I got back on the ground, I had a text from one of the pilots I met with at my destination asking if I got back OK... she said she had seen some "interesting looking cumulus" over in my direction and was worried. Out of curiosity, I looked at the METAR and TAF and they were still reporting scattered at 7,000 (the clouds were not scattered and were much lower) and nothing about rain or a storm. The winds, which were supposed to be calm, were gusting to 16 kts. I went ahead and filed a PIREP, and the rain started falling on my way home. It only stormed for a few minutes and then the skies cleared back up... go figure. Definitely crazy how fast it just popped up like that, and it hadn't even been on the forecast.
Here's a picture I took from my car before leaving the airport (can actually see a little Cessna entering in the pattern... top right). Less than an hour earlier, I had been in clear skies.
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Definitely time to start on my instrument rating!