'Atmospheric river' could dump rain on Portland metro area

Photo by Mike Warner

PORTLAND, Ore. – KATU meteorologist Rhonda Shelby says the Portland metro area could be in the path of an “atmospheric river” by the end of the week.

Monday marked the last dry day for a while. Rain is expected to begin falling in southwest Washington and northwest Oregon Tuesday.

Tuesday should remain mostly dry, but the precipitation will grow heavier as the week goes on, leading to what forecasters call an “atmospheric river.”

According to the National Oceanic and Atmospheric Administration, an atmospheric river is a relatively long, narrow region in the atmosphere that is carrying water vapor outside of the tropics.

NOAA says it’s like a river in the sky.

They say these columns of vapor carry an amount of water roughly equivalent to the average flow of water at the mouth of the Mississippi River.

When an atmospheric river reaches land, it will release the water in the form of rain or snow. This can sometimes lead to extreme rainfall or even flooding.

Rhonda Shelby says the heavy rain will begin in Washington Wednesday as a strong jet stream pushes remnants of a typhoon into western Washington.

She said there’s a chance of urban street flooding and expects up to 2 inches of rain will fall between Wednesday night and Friday.

The Portland Bureau of Transportation provides three sandbag locations if flooding becomes a concern.

  • SE 88th Avenue just south of Holgate Boulevard in the parking lot at Lents Park. Enter parking lot at the bottom of the hill, and follow one-way traffic to the sand pile at the exit on the east side of SE 88th;
  • SE 111th Avenue and Harold Street at the southeast corner of the intersection; and
  • SW 42nd Avenue and Vermont Street in the lower parking lot of Gabriel Park; enter Gabriel Park from Vermont.

City crews keep the sites stocked with sand and sand bags. No shovels are provided, so the public must bring their own.

There are more than 58,000 storm drains in Portland.

A PBOT spokesperson says crews have been actively clearing and unclogging drains and underground pipes. They say they can't do it alone. Where it's safe, they ask Portlanders to clear drains.

When clearing a storm drain, please keep these tips in mind:

  • If possible, clear the drain before it starts raining.
  • Clear about 10 feet on both sides of the drain.
  • Clear from the sidewalk, not the street. Wear reflective clothing so vehicles can see you.
  • Always wear gloves and be careful of sharp objects!
  • Use a rake, shovel, or broom - not your hands.
  • Watch out for traffic. Don’t clear drains that are in the middle of a street.
  • Be careful of standing water to avoid slipping or stepping on sharp objects.
  • If children are helping, make sure adults are supervising.
  • Don’t try to lift storm drain grates. They are very heavy.
  • Let our crews handle garbage or any hazards in the catch basin. Clear surface debris only.

If the drain is still clogged after you’ve removed the surface debris, call PBOT's Maintenance Dispatchers at 503-823-1700 or email pdxroads@portlandoregon.gov to report it.

Utility companies say they too have been working to throughout the year to prevent power outages and service interruptions.

Certified arborists like Damien Carre of Oregon Tree Care recommends homeowners inspect their trees before bad weather moves in. If a tree is older, shows signs of cracking or dead limbs, or hasn't been pruned in a few years, call a trained professional.

"You get gravity pushing down on them, plus the extra elements, and if it hasn't been pruned like this one, it will eventually have an issue," Carre said as crews felled limbs suspended 30 feet above in a 70-year-old elm tree.

"The rain will make the foliage heavier... the soil is going to be a lot more saturated and potentially cause some heaving in larger trees."

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