754 
FXUS66 KPQR 210443 AAA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR 
943 PM PDT Fri Sep 20 2019

Aviation discussion updated.

.SYNOPSIS... High pressure briefly returns to SW Washington and NW
Oregon tonight and will result in less clouds and slightly warmer
temps Saturday, especially in the afternoon. Clouds will be on the
increase again Saturday night ahead of a cold front that will spread
more rain across the forecast area Sunday. After what may be the
coolest night so far this season Sunday night, dry and mild weather
is likely Monday. Additional frontal systems may bring more wet
weather later in the week.

&&

.SHORT TERM...Tonight through Monday...Shower chances will continue
to wane this evening as higher pressure starts to build into SW
Washington and NW Oregon. Despite some lingering cloud cover valley
fog will be possible tonight/Saturday morning as ground moisture
remains high. Morning fog/low clouds should give way to at least some
sun Saturday afternoon, potentially allowing temperatures to break
into the 70s for the inland valleys. Unfortunately, these sunbreaks
will likely be short-lived as mid and high clouds will return by
Saturday evening ahead of the next frontal system.

Guidance continues to show a stronger and slightly better organized
frontal system approaching the coast late Saturday night and moving
onshore before dawn Sunday. This will spread rain across the Pacific
Northwest, but rainfall amounts remain modest at best with up to 0.50
inches possible along the coast and in the higher terrain and between
0.10 to 0.25 inches possible in the interior lowlands. Rain looks to
then quickly transition to showers by Sunday afternoon. Models
continue to show a brief period of some weak instability over the
forecast area Sunday afternoon/evening as the upper level cold pool
moves over the region. This could result in some isolated
thunderstorms, but any convection should quickly come to an end
Sunday evening.

Transient high pressure then returns late Sunday into Monday. This
will likely result in at least some patchy valley fog developing
across the region Sunday night/Monday morning. Monday should then be
a near repeat of Saturday, albeit with slightly cooler temperatures
despite sunbreaks during the afternoon hours. /64

.LONG TERM...Monday night through Friday...A flat ridge over the 
Pacific Northwest will persist through Thursday. The zonal onshore 
flow of this pattern will keep skies mostly overcast and temperatures
mild in the upper 60s for highs. While conditions will 
generally be dry through Thursday, there is a chance for isolated 
scattered rain showers throughout the forecast area on Tuesday. On 
Friday, a digging long-wave trough will advance towards the west 
coast. A front along the leading edge of the trough is expected to 
bring stratiform precipitation to much of the area on Friday. What 
makes this trough slightly different in comparison to the troughs in 
the past few weeks is that it is slow moving; almost stationary in 
nature. 

At this time, while fairly consistent with the overall trough 
progression, there is a slight difference in the trough position. 
The ECMWF is keeping the low, which is anchored in the center of the 
trough, to the west more-so over western Washington. In comparison, 
the GFS is pushing the low eastward over southeast Oregon/southwest 
Idaho. Ultimately this will have an impact on precipitation timing 
both in arrival and duration, as well as any convective activity 
that may be accompanying the system. -Muessle

&&

.AVIATION...As a surface ridge of high pressure builds into western 
Oregon tonight, expect clouds and patchy fog to redevelop overnight 
and continue into Saturday morning. Along the coast expect flight 
conditions to lower into MVFR to IFR range around 06Z, with the 
lower conditions generally more widespread on the central part of 
the coast. Over the interior, TAF sites should see a wide range of 
conditions varying from VFR to IFR developing around 12Z. Conditions 
are likely to improve to VFR in the 18Z-20Z time period Saturday.

KPDX AND APPROACHES...Expect CIG to lower to MVFR around 12Z, but 
there is a small chance (less than 15 percent) of IFR conditions to 
develop with low clouds and fog. Conditions are likely to improve to 
VFR around 18Z Saturday. Bowen

&&

.MARINE...Winds 15 kt or less over the waters expected to continue 
through Saturday. Winds switching to the south by Saturday night 
will strengthen some overnight, gusting to 20 kt by Saturday 
morning. A cold front will move east across the coastal waters on 
Sunday, and is expected to reach the coast between noon and 3 PM. 
Winds switch to the northwest behind the front, with gusts peaking 
around 25 kt Sunday afternoon and evening, strongest over the outer 
waters beyond 20 nm. Stronger northwest winds return mid to late 
next week.

Seas will remain in the range of 4 to 6 ft through Saturday evening. 
The cold front Sunday will boost seas into the 8 to 10 ft range 
through Sunday night. A west to northwest fetch developing in the 
northeast Pacific will bring building seas to above 10 ft around mid 
week. 

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.

&&

$$

Interact with us via social media: 
www.facebook.com/NWSPortland 
www.twitter.com/NWSPortland

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.