FXUS66 KPQR 202220

311 PM PDT Wed Sep 20 2017

Area Forecast Discussion
National Weather Service Portland OR
310 PM PDT Wed Sep 20 2017

.SYNOPSIS...Showers and early evening thunderstorms will continue
across northwest Oregon and southwest Washington as an upper level
low moves southeast over the area. Cold air aloft will continue to
keep snow levels as low as 5000 feet. Heavy showers are possible
this afternoon and evening but will become lighter after sunset. The
primary upper trough/low will linger over Washington and Oregon
Thursday, then slowly move east by the weekend, with showers slowly
decreasing. High pressure builds in over the weekend and continues
into early next week for some great late September weather in store
for the region, with cool nights with patchy fog but mild sunny days.

.SHORT TERM...Tonight through Saturday...The deformation band that
was over southwest Washington this morning has been moving south all
day as the upper low shifts south. The band crossed the Columbia
River around the time of max heating today resulting in some
thunderstorms and heavy precipitation. Radar indicated rainfall
rates of over 1 inch per hour over short periods in this band with
some gage accumulations near 1/2 inch in the last 3 hours in Clark
County. This band has been slowly moving south and due to the east
to west orientation is expected to produce some heavy rain across
the northern Willamette Valley and the Columbia River Gorge. A flash
flood warning was issued due to a higher potential for debris flows
or flash flooding of creeks and streams below the Eagle Creek Burn
area. That band should continue to weaken as it moves south this
evening and heating and upper level support diminishes. After
tonight the flash flood threat should end for the foreseeable future
as any showers tomorrow should be lighter.

Snow has been reported as low as 4600 feet in the Cascades but most
of the sticking snow on any roads will be above 5000 to 5500 feet.
The snow advisory will continue until 8 pm when snowfall rates
should decline as upslope winds decrease and the atmosphere begins
to slowly stabilize.

Northerly flow aloft will be over the area Thursday and Friday with
precipitation mostly ending over the valleys on Thursday night.
However there could be some showers over the Cascades as moisture
moves south in the northerly flow aloft. Some areas of fog are
expected to develop Friday morning if we get some clearing,
especially with all the moisture around. There is a chance of fog
again Saturday morning with a slow warming trend beginning Saturday
afternoon. Schneider

.LONG TERM...Sunday night through Wednesday...High pressure will
build into the area. Snow levels will continue to rise into early
next week. Weak offshore winds will probably keep the coast mostly
clear. However, temperatures will also start warming back up near
normal into the start of next week. -Bishop

.MARINE...Dropped Small Craft Advisory for the waters within 10
nm of the coast this morning as buoys have been reporting
winds below 20 kt. Seas dropping as well, but still 10 ft at buoy
89, so kept SCA in place for offshore waters. Seas may still come
up a little bit to as high as 11 ft before finally dropping below
10 ft tonight or early Thursday morning.

Quieter marine weather is expected by late this week and into
the weekend as typical summertime northerlies return to the area.


OR...Winter Weather Advisory until 8 PM PDT this evening for
Northern Oregon Cascades.

Flash Flood Watch until 8 pm this evening for Cascades in Lane
County-Central Columbia River Gorge-Northern Oregon
Cascades-Western Columbia River Gorge.

WA...Winter Weather Advisory until 8 PM PDT this afternoon for South
Washington Cascades.

PZ...Small Craft Advisory for winds until 2 PM PDT this afternoon
for Waters from Cape Shoalwater WA to Cascade Head OR from
10 to 60 NM-Waters from Cascade Head to Florence OR from
10 to 60 NM.

Small Craft Advisory for hazardous seas until 5 AM PDT Thursday
for Waters from Cape Shoalwater WA to Cascade Head OR from
10 to 60 NM-Waters from Cascade Head to Florence OR from
10 to 60 NM.

Small Craft Advisory for Rough Columbia River Bar until 1 PM
PDT this afternoon.



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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the forecast area.
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