More Rain and Minor Flooding

WX_FloodWatcg20151216
GEOS Satellite Picture of Looming Storm

GEOS Satellite Picture of Looming Storm

FORECASTS AND CONDITIONS

by: Jim Willhight       Dateline: Albany, OR

After a day with little rain (only 0.01 inch), more tropical moisture is headed our way within hours. It looks like the immediate threat (the first of more storms) will hit central Oregon pushed by the jet stream heavy with tropical moisture.

The rainfall will clear the coast range and arrive in Albany around 4 pm today.  Around one and 1/4 inches of rain should fall the first 24 hours of the storm with another 3/4 of an inch for second 24 hour period.  The National Weather Service predicts 1.92 inches of rainfall over the next two days.    

Below is a graph of the six hour rain projections for the next 48 hours.

6 Hour Projected Rain Totals- Albany, OR

Willamette River at Albany (top) and Harrisburg (bottom). Click to review current river levels

Willamette River at Albany (top) and Harrisburg (bottom). Click to review current river levels

The ground is saturated with rainfall from the previous  storms with areas of standing water that has failed to retreat in spite of the light rainfall in the past few days.

As a result of the soggy ground and new rainfall forecast, some minor flooding is expected from the upcoming storm.  

As a result of the size of the upcoming storm the National Weather Services has issued a  flood watch from 4 am tomorrow (12/17) to 4 am on Friday (12/18).

Note that the two Rivers in the Immediate Albany area, the Willamette and the Santiam are going to crest at close to flood stage. 

The Willamette is projected to crest at just below action state at 21.2 feet in Albany, and upstream in Harrisburg in action state at 12.4 feet (14.0 is minor flood stage). Note that minor flood stage is 25 feet at the Albany gage, the projected crest  about 4 feet below the minor flood stage.

Santiam River at Jefferson

Santiam River at Jefferson

For the Santiam River, at the convergence of the North and South Santiam Rivers in Jefferson, the action stage is 14.0 feet. The crest expected to be slightly below that at 12.4 feet so some minor lowland flooding is expected. Upstream at the Waterloo, Foster and Cascadia South Santiam River gauges the crest will be well below action stage.

As noted in the NWS Flood Watch two rivers in the area, but not directly affecting Albany are the Mary's and the Luckiamute which will both crest above action stages. See river gauge graphs of the two rivers below.

Flood Watch

National Weather Service Portland OR   255 pm pst Tue Dec 15 2015

Flooding possible Thursday and Friday for northwest Oregon and Southwest Washington.

Heavy rain Wednesday night through Thursday will cause sharp rises on area creeks and rivers. Ponding of water and creek flooding is possible as early as Thursday morning...with river flooding possible as early as Thursday afternoon for faster responding rivers.

Marys River (Left) will be again into the action stage, just below flood level. The Luckamute River (right) will crest above minor flood stage. 

Marys River (Left) will be again into the action stage, just below flood level. The Luckamute River (right) will crest above minor flood stage. 

Storm total rainfall will be 3 to 7 inches in the coast range and cascades foothills and 1 to 3 inches in the Willamette Valley and Southwest Washington inland valleys. With saturated soils and rivers still running high from last week`s heavy rain, rivers are likely to rise sharply in response to this week`s predicted rainfall.

Ponding of water on roads and creek flooding is possible as early as Thursday morning. Flooding of faster-responding rivers could begin Thursday afternoon with slower-responding rivers reaching flood stage sometime Friday or early Saturday.

RIVER FLOW & LEVEL

Rivers of concern (rivers in bold are local): 

  • Southwest Washington
    • Grays
    • Lower Cowlitz.
  • Northwest Oregon

Precautionary/preparedness actions

A flood watch means there is a potential for flooding based on Current forecasts.

Landslides and debris flows are possible during this flood event. People...structures and roads located below steep slopes, in canyons and near the mouths of canyons may be at serious risk from rapidly moving landslides.

You should monitor later forecasts and be alert for possible flood warnings. Those living in areas prone to flooding should be prepared to take action should flooding develop.