Northern Oregon Cascades

 Areal Flood Watch  Statement as of 8:21 am PST on December 20, 2014

... Flood Watch remains in effect from 4 PM PST this afternoon
through Monday afternoon for southwest Washington and northwest

The Flood Watch continues for southwest Washington and northwest
Oregon from 4 PM PST this afternoon through Monday afternoon.

A classic atmospheric river type precipitation event is setting up
over the Pacific northwest today... which will continue to impact
the region into early Monday. A very long fetch of moisture with
origins west to the South China Sea is feeding into this
system... bringing the potential for very large rainfall totals
across the region. A deep and moist westerly flow will develop
today and continue through Sunday. With the flow forecasted to
remain perpendicular to the Coast Range and Cascades for an
extended period of time... expect strong orographic enhancement to
lead to the highest rainfall totals over the mountains. The Coast
Range... foothills and Cascades are expected to see in the range of
6 to 12 inches of rain... with locally higher amounts possible.
Lower but still significant totals are expected for the lower
terrain. Projected rainfall along the coast is forecasted to be
around 4 to 8 inches. The interior lowlands should see 1 to 4
inches... with the highest amounts closer to the Cascade foothills.

Given the latest forecasted rainfall totals... it appears that
there is the strong potential for flooding over the weekend on
numerous rivers and tributaries draining the Coast Range and
Cascades. A few rivers may even reach major flood stage. The
Current River stage forecasts indicate that the faster responding
rivers could reach flood stage as early as tonight. There are also likely
to be impacts from Urban and Small Stream flooding and flooding
along low lying pasture land.

In addition to the flooding concerns... excessive rainfall has the
potential to create landslides... debris flows... and excessive runoff
in the vicinity of recent wildfire burn scars. Burn scars from two
large fires this Summer... the 36 pit fire in the Clackamas river
basin near Estacada and the deception complex near Oakridge... will
be particularly vulnerable.

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.

The next update for this watch will be issued by 10 PM Saturday

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