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The Outer Planet Atmospheres Legacy (OPAL) program with Hubble was started in 2014 with the goal of studying time-domain phenomena in Jupiter, Uranus, and Neptune, with Saturn added in 2018 once the Cassini spacecraft was de-orbited. Once a year, the OPAL program images each of our four outer planets, producing pairs of global maps in multiple filters, which are made available at the MAST archive. The OPAL team (Simon, Wong, and Orton) have used the data to discover new dark spots on Neptune, discover a UV-dark oval in Jupiter's southern polar haze cap, measure changes in Jupiter's Great Red Spot over time, detect fine-scale waves, chronicle shifts in haze and cloud layers on all four planets, measure jet streams, and study the structure and evolution of convective storms. The data have also provided a valuable resource enhancing the science return from the Juno and New Horizons spacecraft missions, also supplementing observations from a growing list of observatories including JWST, Kepler, Spitzer, VLA, Keck, ALMA, IRTF, VLT, and Gemini.