Sacramento, prepare to get soaked!

“Bomb cyclone”: that ominous phrase definitely grabs a gardener’s attention. So does another: “atmospheric river.”

Sacramento can expect to get a taste of both this week, according to the National Weather Service, as an unstable weather system sweeps over Northern California.

“Bomb cyclone” sounds like it should be an exploding tornado, but it refers to a weather phenomenon: bombogenesis. Meteorologists use that term when atmospheric pressure drops 24 millibars or more in less than 24 hours. It’s a sure sign of a rapidly developing and intense storm system.

Sitting off the Oregon coast, this strong, low-pressure storm system is pulling a plume of moisture across the Pacific into Northern California and southwest Oregon, says the weather service. That’s the atmospheric river – a long, continuous chain of rain. Think of it as a river in the sky – with all the water falling in its path.

This atmospheric river – the first of our rainy season – is expected to deliver at least three days of stormy weather. Starting Wednesday, rainy conditions will stretch through Friday and possibly Saturday and Sunday, too.

How much rain? Some areas such as Eureka and Humboldt County could see up to 12 inches – as well as flooding and mudslides. The Sacramento Valley is expected to receive 2 to 6 inches; the farther north, the wetter.

Downtown Sacramento’s forecast calls for 3 to 4 inches, spread over five days, says the weather service. The heaviest rain is expected Friday morning. Because we’ve had so little rain so far, this deluge will mostly soak into the ground. Creeks will fill but not flood.

This is also a cold storm; snow levels in the Sierra are expected to drop to as low as 3,500 feet on Wednesday morning. Sierra ski resorts are expecting 10 to 20 inches of fresh snow – just in time for Thanksgiving skiers.

Before the rain really hits, make sure your gutters are cleared of leaves and other debris. Avoid piling leaves in the street or blocking storm drains. Watch out for falling limbs or leaning trees.

Definitely shut off the sprinklers and other irrigation. This storm will deliver plenty of moisture.

This deep soaking will refresh plants’ moisture reserves as well as soften soil. Be patient; if you have something to transplant, wait until next week.