Greater Vancouver Area

 Areal Flood Watch  Statement as of 10:54 am PST on December 19, 2014


... Flood Watch in effect from Saturday afternoon through Monday
afternoon for southwest Washington and northwest Oregon...

The National Weather Service in Portland has issued a Flood Watch
for southwest Washington and northwest Oregon. This watch is in
effect from Saturday afternoon through Monday afternoon.

Confidence continues to increase that a classic atmospheric river
type precipitation event will set up over the Pacific northwest
over the weekend and continue into early Monday. A deep and moist
westerly flow is expected to develop Saturday morning and
strengthen later Saturday and Sunday. A very long fetch of
moisture with origins west to the South China Sea will feed into
this system... bringing the potential for very large rainfall
totals across the region. 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... with 2 to 5 inches expected over the
interior lowlands.

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 reach major flood stage. The Current
River stage forecasts indicate that the faster responding rivers
could reach flood stage as early as Saturday evening. There also
appears to be potential for flooding on some of the main Stem
rivers early next week. In addition to flooding potential on the
main Stem rivers and tributaries... there are 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 6 am Saturday
morning.





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