The Best skies are visible right before or right after Rain.
Pay attention to it, do you see it? It's different from other skies & clouds. These skies happen unexpectedly and have just more 'drama'. Often you're in the car, driving through these weather changes, it's amazing the spectacle that can be there.
But it moves fast, coming and going in +/-30~40 minutes.
SSU07 Seascape Plein Air Painting "Bright Sky, Clouds & Gray"
Yes, here it's all gone again! I often say to my students on the beach: See this sky, paint it, paint it FAST, it will be gone fast! Happy times at the beach.
And if you wonder if you can finish it within this 30 or 40 min. window, my answer would be, no, you can't.
But you can finish from memory, or from what's left for you to see.
Get the most important stuff in First, is my rule of thumb.