Intense atmospheric river with heavy rain, strong winds to hit Tri-Cities
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- Atmospheric river will cross the Cascades, bringing warm temperatures and heavy rain.
- National Weather Service issues wind advisory for the region; gusts up to 43 mph.
- Yakima River forecast to rise to action level, approaching flood stage.
The Tri-Cities can expect wind, heavy rain and high water in the Yakima River early this week after an atmospheric river crosses the Cascade Mountains.
An atmospheric river is a flowing column of condensed water vapor in the atmosphere, in this case bringing warm air and moisture from the subtropical Pacific Ocean.
Many atmospheric rivers that move into Washington state drop most of their moisture before hitting Eastern Washington, but this one is expected to be strong enough to cross the Cascade Mountains.
Monday a 60% chance of rain is forecast for the Tri-Cities, with less than a tenth of an inch of rain expected.
Then will come the wind ahead of the worst of the weather system.
The National Weather Service has issued a wind advisory for the Tri-Cities, from 7 p.m. Monday to 7 a.m. Tuesday. The advisory covers most of Eastern Washington.
Gusts of up to 43 mph are forecast for the Tri-Cities.
Tuesday the Tri-Cities is expected to see its heaviest rain of the week, said Matt Callihan, lead meteorologist for the National Weather Service region that includes most of the Mid-Columbia.
Between a tenth to a quarter of an inch is possible.
It is expected to be the second heavy rainfall of the month, after 0.24 inch was recorded on Thursday, Dec. 4, in the Tri-Cities. Normal rainfall for December is about 1 inch total for the month.
More rain is expected through Thursday, with the chance of rain dropping from 90% Tuesday night to 40% Thursday.
Nighttime lows are forecast in the 40s all week, with Wednesday night the warmest. A low of 49 is forecast, which is warmer than the usual average daily high temperature in December in the Tri-Cities.
Highs could be as warm as the 60s, with 61 degrees forecast for Monday and 60 for Wednesday. Temperatures will start to cool some on Thursday, with highs through Saturday in the mid 50s.
Normal highs for the Tri-Cities in December are about 41 degrees and normal lows are about 27.
The combination of warm weather and rain in the Cascade Mountains will melt snow, and rivers will rise, Callihan said.
The Yakima River is forecast to rise to what the weather service calls the “action” level of 11 feet at Kiona Wednesday night, up from about 5 feet Sunday afternoon. The gauge near Benton City is the closest one to the Tri-Cities.
The river is expected to get as high as 12.4 feet there, close to the flood stage of 13 feet, on Friday.
Water will be running fast, Callihan said.
As the river just upstream from the Tri-Cities rises, people should use caution along the river banks and be prepared to move livestock out of pastures along the river.