Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 230402 AAA
AFDPQR

Area Forecast Discussion...Updated
National Weather Service Portland OR
901 PM PDT Mon Oct 22 2018

Updated Aviation section.

.SYNOPSIS...A weak front approaching the coast Tuesday afternoon
will likely end this period of dry and mild October weather.
Following a chance of mainly light rain Tuesday afternoon and night,
a stronger and wetter system will affect the area Thursday. High
pressure moves over the area for Friday and Saturday, before another
Pacific system approaches late Saturday and Sunday.

&&

.SHORT TERM...Tonight through Thursday...The large upper ridge that
had positioned itself over the PacNW the better part of the past two
weeks is moving eastward into the Plains, opening the door for
fall-like Pacific weather systems to begin affecting the area. The
first such system provides more of a glancing blow as the main energy
lifts northward into western Canada and southeast Alaska. With the
surface low in the Gulf of Alaska, a weakening north-to-south
oriented cold front along the WA-OR coast moves onshore Tuesday
evening. This will introduce a chance of light rain along and ahead
of the front Tuesday afternoon and Tuesday night.

A weak, low amplitude ridge then moves over Wednesday, for mostly
cloudy but dry conditions. After that, a much more vigorous system
with a long fetch of southwesterly flow brings an atmospheric river
to southwest Canada for Wednesday, sagging southward and affecting
northwest Oregon on Thursday. While the brunt of the moisture and
dynamic forcing appear to remain north of the area, the prefrontal
warm conveyor belt will bring a period of decent rain potential
Thursday. Right now, ensembles remain wide-ranging in terms of
Portland and Willamette Valley QPF, with a fairly even distribution
of members from 0.10" to a little over 1". The model consensus is in
the 0.25 to 0.75" window for most valley locations, with the
heaviest amounts north and over higher terrain. The weather turns
more showery in the post-frontal and cooler airmass Thursday night.
DRB

.LONG TERM...Thursday night through Monday...Post-frontal showers and
relatively cool temperature begin the extended period Thursday night
and Friday. The ensemble consensus brings a transitory ridge axis
over the area late Friday and early Saturday. Saturday should remain
mostly dry under this ridge, but the longer October nights and late
week rainfall may make for a widespread foggy start to the weekend.
Another Pacific system, albeit not as wet, follows a similar storm
track as those earlier in the week, moving toward western Canada
early Sunday. This will bring a warm front northward through the area
Sunday, for overcast conditions and a chance of rain. Most ensemble
members are consistent with the idea of the upper shortwave moving
into southwest BC Sunday night and Monday, for another period of rain
turning to showers across southwest WA/northwest OR. This system does
not appear particularly strong or wet at this time. Temperatures in
general will be close to normal during the extended period. DRB

&&

.AVIATION...VFR conditions will continue in the interior through
late tonight under mostly clear skies and light winds. Expect
another repeat of LIFR fog/low stratus across the area after 09Z
tonight with conditions gradually improving late Tuesday morning.
Increasing mid and high clouds move into the area Tuesday along with
rain chances as a weak front moves across the region.

KPDX AND APPROACHES...VFR under clear skies and light winds through
tonight. Fog/low stratus will impact the terminal after 11Z tonight,
with conditions gradually improving to VFR late Tuesday morning.
Increasing mid clouds on Tuesday with some chance of rain as a front
moves across the area.    Cullen

&&

.MARINE...Conditions remain rather calm this afternoon. However,
things will be a little more active over the next several days.
Models continue to show winds increasing early Tuesday morning as
a decaying cold front moves across the waters. Winds turn
southerly ahead of this system Monday evening, and gradually
increase going into Tuesday. Expect advisory gusts around 25 to
30 kt to develop across the waters on Tuesday so decided to issue
a Small Craft Advisory for winds for all waters starting at 6 AM
Tuesday.

Will see a bit of a break between systems on Wednesday. Another,
slightly stronger front looks to move across the waters on
Thursday, with gusts up closer to 30 kt ahead of the front.
There is still a lot of disagreement behind this system Friday
going into the weekend, with models suggesting another front
moving across the waters late Saturday or Sunday, but exact
timing and strength of this system is uncertain. We`ll have to
wait for later runs to increase confidence.

Seas are generally around 5 to 6 ft this afternoon and will build
to around 8 to 9 ft with the front Tuesday afternoon. Seas stay
up around 8 to 9 feet on Wednesday, then build to 13 to 15 feet
with Thursday`s front. Seas look to gradually fall below 10 ft
going into the weekend. /64

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds from 6 AM to 7 PM PDT Tuesday
     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 CWA or forecast area.


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