While not rare to see storm activity in May in California, it is indeed rare to get a full-blown Pineapple Connection storm coming from the moisture-rich direction of Hawai'i in May. It is also a storm approach trajectory that has storms at maximum power as they cross this state. Kind of like the perigee of an orbit or the bottom of a sling shot, the storm has maximum power when heading pole-ward after having rounded the bottom part of its turn as it travels along the arch of an upper air current.
What happens when a storm that belongs in February comes through in May?
Certainly it should be more dynamic, with pronounced convective activity, resulting in heavier rain overall with isolated thunderstorms.
Normally California storms are highly predictable, even when they are powerful. You can expect steady, gentler, shorter rains over the valleys and longer, more drenching rains over mountains. California also is not in a 'cyclogenesis zone", a place where storms suddenly and freshly generate, such as the Great Plains or the Atlantic Shelf (home to the "The Perfect Storm"). This calm zone is made possible in part by the Jet Stream having to go around the Himal Laya then having to cross the vast Pacific Ocean, which helps set the zones up where they are, plus the Pacific is made of cold current along North American coast. That's less storm fuel.
Most May rainstorms come out of the north, basically serene moss-watering Pacific Northwest storms that have strayed a little south. But this is a gangbuster from the southwest direction.
The weather watcher in me is downright enthralled.
In the pic, the valley rainshadow is nicely visible, with a long shadow going across the valley between Fresno and Visalia. High sections of two Coast Ranges, the Santa Lucia and The Diablo Range, reach into the sky to wring out the moisture in the passing air.
UPDATE -- received a long, warm drenching rain 6-9 pm. Outstanding!
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