816
FXUS66 KPQR 141547 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
847 AM PDT Sat Sep 14 2024

Updated public and aviation discussions...

.SYNOPSIS...A fall-like weather pattern will continue over the next
week. Chances for light showers this weekend, however much of the
time will be dry. Dry and mild conditions on Monday will give way to
cool and wet conditions Tuesday into Wednesday as a strong frontal
system brings widespread rain to the area. Trending dry again late in
the week with slightly warmer temps.

&&

.SHORT TERM...Now through Monday night...Radar, satellite and surface
weather observations from Saturday morning depicted mostly cloudy
skies across northwest OR and southwest WA with areas of virga
associated with a weak upper level impulse. The exception to that
was over the Long Beach Peninsula and Willapa Hills where at least
some light rain has reached the ground with passing showers, albeit
not much. Chances for light showers will spread inland late Saturday
morning into the afternoon, but most of the day will be dry,
especially south of Salem. Temps should be very similar to what was
observed on Friday.

Cool, dry and calm conditions Saturday night will give way to another
chance of light showers on Sunday as an elongated upper level low
moves southward down the Washington and Oregon coast towards northern
California. Models continue to suggest precipitation with this low
will be light, spotty and disorganized. As such, most locations will
wind up mainly dry or completely dry on Sunday, especially over the
Willamette Valley and southwest WA. Any showers that do develop over
the area on Sunday will diminish Sunday night, giving way to
widespread dry conditions Monday through Monday night as dry
northeast flow aloft develops on the backside of the aforementioned
low. Monday is shaping up to be the sunniest and warmest day of the
week with high temps most likely in the mid 70s, except 60s at the
coast. That said, cannot rule out temps a bit warmer than that as the
NBM is showing a 10-25% chance for highs near 80 degrees. Monday will
be an excellent day for outdoor activities, especially given the
rapid change to cool and wet weather expected the following day. This
system is discussed below in the long term discussion. -TK


.LONG TERM...Tuesday through Friday...Conditions will deteriorate
quickly on Tuesday as a stronger frontal system brings more
significant moisture into the region. Confidence is very high
widespread rain will occur across all of western WA/OR during that
time as every single ensemble member from the GEFS/GEPS/ENS are
showing QPF and NBM PoPs are over 90%. Despite high confidence for
rainy conditions, confidence is still lower in regards to exact rain
amounts. A large degree of model spread remains for QPF, however
ensemble member clustering is evident between 0.25-0.50 inches for
the lowlands.

The latest NBM probabilities for 24-hr rain amounts over 0.5 inches
have decreased a bit from 70-80% to 50-70%, which makes sense given
less ensemble member clustering evident between 0.5-0.75 inches when
compared to yesterday`s guidance. Despite the decrease, probabilities
are still fairly high, especially for 24-hr rain amounts over 0.25"
as these values range between 70-90%. This means a soaking rain
capable of putting a significant damper on wildfire activity is very
likely to occur regardless of uncertainty on exact rain amounts. This
system will also bring temps around 10-15 degrees below average for
this time of year with highs likely in the low to mid 60s on Tuesday.


Expect post-frontal showers on Wednesday with conditions drying out
Wednesday night into Thursday. From there, temperatures will rebound
to near seasonal averages for interior lowland valleys heading into
next weekend.  -TK

&&

.AVIATION...West to northwest flow aloft, with considerable lower
and mid-level clouds today. Should remain VFR inland, though will
have lower CIGS (3500 to 4500 ft) into the early afternoon from
Cowlitz Valley southward to the south side of the Portland metro.
Along the coast, will maintain MVFR into early afternoon, with
gradually improvement to VFR as the lower clouds break apart.

PDX APPROACHES...Lower VFR this am, then will see the low clouds
break up. VFR continues afterward, with main deck around 5000 to
6000 ft. Not much change tonight, with VFR clouds.   /Rockey

&&

.MARINE...Rather benign weather today as a weakening front on the
waters dissipates as it moves ashore later this morning. Another
weak trough moves to the waters later tonight into early Sunday
morning. Pressure gradients increase Sunday as high pressure
strengthens offshore for gusts to 25 kt mainly over the outer
zones (10-60NM). Lower forecast confidence for gust to 25 kt for
the nearshore zones. Overall seas stay in 3 to 6 ft range today
and tonight, then 6 to 8 ft Sunday, Monday.

Then a front will push across the waters Tuesday as it
elongates/weakens over the coastal waters. Models vary some on the
timing/strength of this system, so will see how things shape up
as get closer in time to next Tue. /mh /Rockey

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 5 PM Sunday to 11 AM PDT Monday for
     PZZ272-273.
&&

www.weather.gov/portland

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