This is a 38-second time-lapse video sequence of the storm that developed over Washington, D.C. on August 21 that caused a 51 minute rain delay at Nationals Park. The video sequence was shot in Reston and Fairfax, Va., and shows the storm maturing from cumulus clouds into a slow-moving drencher that delayed the Nationals game. (Kevin Ambrose)

Isolated “pop-up” thunderstorms are hard to forecast and often impact small areas with heavy rain. The storm Tuesday evening developed over Alexandria and Washington and seemed to remain almost stationary. Most areas outside of the District remained dry while it poured over Nationals Park in Southeast D.C.

I knew conditions Tuesday evening were favorable for a storm or two, so when I saw cumulus clouds building to the east of Reston I started my video camera. The clouds grew upward but remained almost stationary.

The weather conditions remained calm and dry over most of the area while the storm over Washington put on a colorful show in the sky for those of us located in the western suburbs. At sunset, the clouds seemed to glow.

The storm ultimately produced a 51-minute rain delay at Nationals Park. The rain was localized, but heavy. Despite the rain delay, the Nationals beat the Braves.

Keep reading for photos of the storm.

A storm begins to take shape near Washington, D.C. at 7:10 PM. This photo was taken from Reston, VA.