Area Forecast Discussion
Issued by NWS Portland, OR

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665
FXUS66 KPQR 160538
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1038 PM PDT Sun Sep 15 2019

Updated the aviation discussion

.SYNOPSIS...Wet and cooler weather is expected to continue through
Wednesday as a couple of moisture laden fronts move across the
region. There is a slight chance for thunderstorms with the
post-frontal showers Sunday evening, Monday and Wednesday. The shower
activity will wane near the end of the week with a day or two of
drier weather. Yet another system will move into the region early
next week.

&&

.SHORT TERM...Tonight through Wednesday...An early season cold front
will continue to move through the region this afternoon with steady
rain falling over the region.  Rainfall amounts over the past 12
hours ranged from around 0.75 to about 1.15 inches along the
Coast/Coast Range, 0.3 to 0.75 inch in the valley and around 0.75
inches in the Cascades and foothills.  Rain will continue for the
next several hours, especially in the Cascades until the front pushes
east of the area.

The attendant cool, upper level trough will move into the region this
evening and remain over the area through Monday bringing additional
showers. The cold air aloft associated with the upper level trough
will help destabilize the atmosphere bringing a chance of
thunderstorms over the coastal waters and coast later this evening
into the overnight hours. There will also be a chance of
thunderstorms over most of the interior Monday afternoon and evening
as the upper level trough and instability transits the area. Snow
levels will also lower to about 6500 feet.

Another strong and moist front will bring another round of moderate
to heavy rain on Tuesday followed by another cool upper trough
Tuesday night and Wednesday. The upper level jet dynamics support
widespread heavy rain, and expect an additional 0.75 to 1.5 inches of
rain Tuesday morning through Tuesday evening. Winds will be breezy
with the front passage on Tuesday with gusts of 40 mph possible along
the coast and 30 mph along the valley.

Another cool upper level trough follows the front for continued
showers and possibly isolated thunderstorms Tuesday night and
Wednesday. /tw

.LONG TERM...Wednesday night through Sunday...The shower activity
will slowly wane Thursday as the upper level trough departs the area
and a weak upper level ridge transits the region. Cannot rule out
that some stray showers will continue Thursday into Friday as weak
disturbances move through the upper level flow.  There remains quite
a bit of uncertainty in the weather towards the end of the week and
into next weekend.  At this juncture, looks like late Friday and
Saturday could be fairly dry, then another upper level trough
approaches the region on Sunday bringing a chance of showers. /tw

&&

.AVIATION...A slow-moving front has finally moved into the
Cascades and will push east of the region later tonight.
Conditions have improved behind the front, with mainly VFR currently
being observed across the region. However, scattered post-frontal
showers are bringing occasional MVFR cigs. Expect the predominant
VFR conditions with occasional MVFR in showers to continue through
much of the night. Shower activity is expected to pick up over the
coastal waters and right along the coast late tonight into Mon
morning. There will be potential for thunderstorms at the coastal
TAF sites through the next 24 hrs, with the best chances appearing
to be around 12Z-18Z Mon. The shower activity will likely taper off
over the interior lowlands late tonight, with cigs potentially
settling into an MVFR deck by early Mon morning. The interior will
become more unstable Mon afternoon, and the thunder threat will
likely shift more toward the interior by 21Z Mon. Thunderstorm
activity should taper off by 03Z.

KPDX AND APPROACHES...Expect mainly VFR conditions through 12Z Mon,
with brief MVFR possible under passing showers. Think cigs may
settle toward MVFR by 12Z and remain through late morning.
Showers will pick up over the valley Mon afternoon. Expect mainly
VFR conditions Mon afternoon and evening, with the potential for
some heavier showers or even a thunderstorm or two to bring brief
MVFR or IFR conditions. Pyle

&&

.MARINE...A broad and weak surface low pressure will drop
southward across the waters through Monday. This should bring
relatively benign winds, though cold air aloft will probably
result in some squally showers and thunderstorms tonight and
Monday. Expect seas to stay in the 7 to 9 ft range through Monday
evening.

Forecast models continue to trend stronger with the next front,
which will impact the coastal waters later Monday night and
Tuesday. Gales look like a good possibility, so have issued a
Gale Watch for all zones starting 12Z Tuesday. It looks like the
strongest winds would be brief, lasting about 6 hours during the
day Tuesday. Seas will be steep and wind-driven with the front,
peaking at 10-11 ft.

Winds settle Tuesday night into Wednesday with broad low pressure
over the waters, but seas stay in the 8 to 10 ft range with NW
swell. High pressure returns to the waters late in the week.
Bowen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Gale Watch from late Monday night through Tuesday afternoon for
     Coastal Waters from Cape Shoalwater WA 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.



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