189 
FXUS66 KPQR 090356 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
856 PM PDT Tue Oct 8 2019

Updated Aviation and Marine discussions.

.SYNOPSIS...An upper level trough over the region will bring
scattered showers and cooler temperatures through early Wednesday. A 
ridge of high pressure will move into the region late Wednesday and 
persist through Friday for dry autumn weather. Another storm system 
is expected to move into the area this weekend.

&&

.SHORT TERM...Tonight through Friday...A broad upper level trough of 
low pressure with scattered showers will continue to move across the 
region through early Wed. The attendant cold front moved through 
earlier today and brought about 0.3 to 0.5 inch of rain in the Coast 
Range and 0.3 to near 0.75 inch in the Cascades and foothills. 

The coldest air associated with the upper level trough remains well
to our north in northern WA and southern BC. There have been a couple
of lightning strikes in the Puget Sound this afternoon, but none in 
southwest WA as of 200 pm.  The northern part of our forecast area 
in southwest WA remains marginally unstable, so will maintain a 
slight chance of thunderstorms in that area through early evening. 
As the cold air moves in later tonight, expect snow levels to drop 
to around 3000-3500 feet, but precip will be tapering so any snow 
accumulation will be light on the order of 1 to 3 inches.

The upper level trough will move eastward into the northern Rockies
on Wed with a ridge of high pressure building over the area in it's 
wake. As the trough moves eastward, thermal low pressure at the 
surface builds northward from northern CA in southwest WA with the 
flow turning offshore Wed afternoon/evening. Expect temperatures to 
be fairly chilly Thursday morning with low temperatures in the low 
to mid 30s throughout the valley. Some light frost is possible Thurs 
morning in outlying valleys 

The ridge of high pressure will dominate the weather pattern from
late Wed through the end of the work week.  This pattern will bring 
pleasant, dry autumn weather with daytime highs in the low 60s. 
Another storm system is expected to move into the region this 
weekend. /tw

.LONG TERM...Friday night through Tuesday...The 12Z operational GFS 
and ECMWF models are in agreement for most of the long-term 
forecast. Both models show a cold front moving onto the coast Friday 
night. Precipitation from this front will dissipate slowly through 
Sunday night. Slight ridging will reduce precipitation on Monday but 
the next system closely follows with another front moving onshore 
late Tuesday. General temperature trend shows afternoon highs around 
60 and over-night lows around 40. -BPhillips

&&

.AVIATION...Showers associated with an upper trough and surface 
front will dissipate through 06Z Wednesday. Winds will continue to 
decrease, going near calm overnight. High pressure building in 
behind the front will clear skies overnight, which may allow some 
fog or low stratus to develop. However, expect light offshore flow 
to begin Wednesday morning, which should return conditions to VFR 
quickly, if not preclude flight restrictions completely.

KPDX AND APPROACHES...There is a chance for some brief MVFR cloud 
development overnight, but confidence is low due to developing 
offshore flow. Bowen

&&

.MARINE...Steep seas will continue overnight, fluctuating in the 9 
to 11 ft range with dominant wave periods also 9 to 11 seconds. 
Extended the Small Craft Advisory for the waters off the central 
coast through 5 AM Wednesday, which now matches that for the waters 
off the northern coast. Winds will continue to weaken overnight and 
then become offshore around 10 to 15 kt Wednesday. 

Thursday through Saturday morning, seas will remain benign in the 4 
to 7 ft range. Saturday afternoon, seas will begin to build as low 
pressure advances towards the West Coast. Bowen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Wednesday for coastal 
     waters from Cape Shoalwater WA to Cascade Head OR out 60 
     NM.

     Small Craft Advisory until 5 AM PDT Wednesday for coastal 
     waters from Cascade Head OR to Florence OR out 60 NM.

&&

$$

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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.