673 
FXUS66 KPQR 151032
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
332 AM PDT Wed Oct 15 2025

.SYNOPSIS...A ridge of high pressure continues to facilitate 
dry conditions through today and much of Thursday across the 
interior valleys - limited impacts. Beginning later Thursday 
into Friday the pattern become more progressive starting with a 
weak frontal system ushering in chances (30-50%) for light 
showers, more likely near the coast. Then confidence is high 
widespread rain moves overhead for the second half of weekend 
into early next week thanks to an upper-level trough. Lower
forecast confidence by the middle of next week. 

&&

.SHORT TERM...Now through Saturday...Headed through today a 
positively-tilted upper-level ridge continues to slide 
eastward building heights aloft before finally passing overhead
and deamplifying during the day on Thursday. This pattern will
allow portions of the coast-range through the interior valleys 
to begin the day with rather cool temperatures, especially for 
spots like the Hood River Valley, wind-sheltered coast 
range/Cascade valleys, and portions of the central/southern 
Willamette Valley. Frost Advisories and a Freeze Warning (Upper 
Hood River Valley) continue through 9 AM this morning. 

While an offshore component to the wind is present to start to 
day, more seasonable onshore north-northwesterly flow returns 
this afternoon. There remains some uncertainty as to just how 
low temperatures will drop again Wednesday night into Thursday 
morning with most ensemble model guidance showing a slight 
warming trend in the mean albeit with a larger spread - 
dewpoints trend higher as well. Whether we see frost at our 
more prone areas which have been impacted the last couple of 
nights may come down to two main factors: the proliferation of 
mid to high cloud cover this evening and tonight in addition to 
any clouds associated with a weak marine surge Thursday 
morning, and whether winds can stay light enough to allow the 
near surface boundary layer to decouple. It would be a fairly safe
bet (60-80% chance) for yet another night of temperatures in 
the low to mid 30s across the Upper Hood River Valley, Cascade 
valleys, higher coast range valleys (think Vernonia area), and 
more protected areas in the central/Southern Willamette Valley
tonight, but locations which have been on the fringe (mid to
upper 30s) the last two nights may be just a hair too warm for
impacts tonight. Once the current round of frost/freeze 
products expire this (Wednesday) morning be on the lookout for 
the potential of additional frost advisory issuance tonight 
into Thursday morning.

Then later on Thursday into Friday morning a weak/decaying 
trough and accompanying frontal system attempt to swing into the
region from the northwest ushering in a few rain showers, most 
likely along the coast and across the higher terrain of the 
north Oregon Coast Range, Willapa Hills, and Washington/North 
Oregon Cascades. The immediate shorelines of Willapa Bay, Long 
Beach Peninsula, and coastal Clatsop County, as well as upstream
in the Columbia Estuary to Cathlamet/Wauna, may see a 20-40% 
chance of 0.25" of rain or more, while chances of a wetting rain
elsewhere and inland along the I-5 corridor is less than a 5% 
chance. At least the added cloud cover and westerly flow 
drastically lowers the threat for frost concerns for most 
locations sunrise Friday morning. 

Behind this weak disturbance, a quickly moving transient ridge 
of high pressure aloft shifts overhead on Saturday while the 
flow aloft turns northwesterly to southerly in the afternoon 
hours. Expect a bump in high temperatures and prevailing dry 
weather through most of the day across the I-5 corridor 
Portland/Vancouver metro southward. However, a frontal system 
will be lurking just off the coast by the afternoon hours. 
There's some uncertainty as to how quickly the rainfall 
associated with this front shifts into southwestern Washington 
and western Oregon during the afternoon/evening hours Saturday 
which is responsible for the ~15-30% PoPs Portland northward 
through Cowlitz County during this period. The ECMWF based 
solutions in particular are bit faster bringing in precipitation
compared to the GFS and Canadian; something to watch. -99

.LONG TERM...Saturday night through Wednesday...There remains 
good consensus between deterministic and ensemble modeling 
systems that a trough over the northeastern Pacific digs 
overhead, bringing a return to wetter weather across the Pacific
Northwest. At this lead time, there is high confidence in the 
occurrence of rain in the Saturday night/Sunday time period 
while the main mode of uncertainty is the amplitude of the 
trough and progression thereafter. Around 40-45% of global 
ensemble members favor a deeper trough and a resultant wetter 
outcome in addition to a slower progression eastward on Monday,
while the other 55-60% favor a less amplified and quicker 
moving trough and thus a drier scenario overall (we'll still get
some rain). The amplitude of the trough will also heavily 
modulate snow levels with the former deeper trough scenario more
favorable for a period of Cascade pass level snowfall late 
Sunday into Monday. Beyond this point ensemble models suggest 
some sort of ridge feature attempts to build into the region 
around Tuesday followed by another trough Wednesday/Thursday. 
Although, uncertainty abounds regarding the exact amplitude and
longitudinal placement of these two features helping to drive 
lower forecast confidence late in the forecast period. -99

&&

.AVIATION...VFR conditions generally prevail today with minimal
impacts. Cooler temperatures to start this morning will 
increase chances for frost formation within the interior valleys
potentially impacting Willamette Valley terminals from KUAO 
southward. Freezing temperatures expected around K4S2 in Hood 
River. Easterly flow aloft to start the day likely turns more 
onshore and gains a northerly component in the afternoon before 
switching a light southerly overnight - winds likely remain 5-10
knots or less. However, late in the forecast period there is a 
growing chance (30-50% after 06-08z Fri) for fog and/or low 
stratus formation along the coast around KONP to KAST. That 
said, confidence is low in the exact timing of any degraded 
conditions. 

KPDX AND APPROACHES...VFR through the next 24 hours. Light winds
remain variable near the surface into the sunrise hours this (Wed)
morning but more predominate east winds aloft around 2000-3000ft 
AGL will exist with gusts up to 20-25 kt; these wind speeds may
be impactful for flow into the terminal. Fortunately these 
east winds a couple thousand feet above the surface will 
rapidly drop-off 14-17z Wed. -99

&&

.MARINE...High pressure remains in place the next couple of days
with winds continuing the decrease into Wednesday morning. Expect
north to northwest winds to persist through Thursday morning while
seas hold around 4-6 ft with a dominate period of 14-15 seconds. 
Our next time-period of concern arises on Friday into Saturday 
with the onset of a frontal passage. Will see a quick surge of a 
northwesterly fresh swell and elevated winds, in addition to a 
nearly an 80% chance based on the GEFS WAVE models for seas of 10
ft. The pattern remains rather active through the latter half of
the weekend into early next week as another, albeit stronger,
frontal system progresses into the coast waters. Conditions will 
quickly amplify as a result with a 40-60% chance of seas greater 
than 15 ft late Sunday into early Monday. -99/27

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Frost Advisory until 9 AM PDT this morning for ORZ104-115>118.

     Freeze Warning until 9 AM PDT this morning for ORZ121.

WA...Frost Advisory until 9 AM PDT this morning for WAZ204.

PZ...None.

&&

$$

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