431
FXUS66 KPQR 102243
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
343 PM PDT Mon Jun 10 2024

.SYNOPSIS...A warm and sunny June afternoon for SW Washington and NW
Oregon as high pressure dominates the region today. The high pressure
will weaken and shift eastward tonight, allowing a decaying cold
front to brush the forecast area Tuesday. Precipitation will be
minimal, though there will likely be areas of drizzle along the
coast. Otherwise, a deeper marine layer and strong onshore flow will
lead to cooler temperatures Tuesday into Wednesday. High pressure
brings a brief warmup Thursday, but below normal temperatures appear
likely for the weekend as an upper trough moves into the Pac NW with
clouds and a few showers.

&&

.SHORT TERM...Now through Thursday...Quiet weather across NW Oregon
and SW Washington this afternoon under high pressure. After a cool
start with many outlying areas in the 40s and lower 50s, temps
climbed rapidly during the midday hours and most of the forecast area
is now as warm or warmer than they were at the same time yesterday.
The warming trend today has been most notable along the coast and in
the Coast Range; for example, the 2 PM temperature at Tidewater RAWS
was 73 deg F - versus 51 deg F at the same time Sunday. This is
likely due to a more northerly component to the low-level flow and a
shallower marine layer, both acting to limit the influence of the
cooler marine air.

A vigorous upper level trough along 140W is causing low pressure to
develop near 46N/133W as of 3 PM; this low will track NE eventually
pushing a weak cold front toward the Pac NW coast. The upper trough
and approaching front will cause the marine layer to rapidly deepen
late tonight; eventually deepening it enough to produce areas of
drizzle along the coast and in our coastal ranges. It does not appear
the moist layer will be deep enough for precipitation to reach the
Willamette Valley, but locations such as Battle Ground near the S WA
Cascade foothills may still see some occasional drizzle. The cold
front actually moves onshore and across the Willamette Valley midday
or early afternoon Tuesday, so there will be at least some degree of
cloudiness for most of the day. One exception to this may be the
Eugene metro, where the front may be slow enough to arrive such that
the first half of the day has plenty of sunshine and temps climb to
the mid 70s before the front arrives Tuesday afternoon.

Strong high pressure will build in behind Tuesday`s frontal system,
first leading to strong west winds through the Columbia Gorge, then a
cool night by June standards Tuesday night throughout the forecast
area. With dewpoints expected to fall deep into the 30s (possibly
even the 20s) and winds calming down overnight, it would not be
surprising if some of our coolest outlying valley locations such as
Timber Jct dip into the upper 30s Wednesday morning. Frost is highly
unlikely, but it will be chilly for the season. The cool start to the
day Wednesday will hold back temps a bit, just like today, but the
air mass will be warming up so afternoon temps should end up
seasonable.

High pressure will persist through Thursday, leading to another cool
night Wednesday night, but probably not quite as cold as Tuesday
night. As the air mass continues to warm Thursday, it appears likely
Thursday afternoon will be a few degrees warmer than mid-June
normals. Based on NBM probabilistic guidance, it appears there is a
40-70% chance of the PDX metro reaching 80 deg F Thursday afternoon,
while chances for the same in Eugene are closer to 20%.  Weagle

.LONG TERM...Friday through Monday...The upper ridge begins to
shift east of the forecast area on Friday as another trough near the
Gulf of Alaska dips southward toward the Pacific Northwest. This will
lead to a cooling trend and return of widespread low PoPs. Saturday,
most ensemble members agree on troughing entering the region with
below-average 500 mb heights. If this scenario pans out, then we
would see increasing chances for widespread precipitation and below
average temperatures. For now, the NBM`s 20-50% chance of PoPs across
northwest Oregon and southwest Washington at the end of the week look
reasonable. Sunday, most ensemble members (85%) continue to show
troughing, but are uncertain of the exact axis location and
magnitude. Meanwhile, the other 10% of members show zonal flow or
weak ridging returning over us, which would lead to a warm-up back to
more seasonable mid-June temperatures. -Alviz/Weagle

&&

.AVIATION...Current satellite shows clear skies and VFR conditions
across the western Oregon and SW Washington this afternoon.
Overnight into Tuesday morning a very weak frontal boundary will
move into the area starting with high clouds streaming into the
region, at least initially. Expect the marine layer and at least
MVFR CIGS to re-develop at the coast later this evening and
overnight as well with chances (around 30-40%) for IFR stratus and
light rain and/or drizzle near KAST after 10-12z. Inland sites likely
stay VFR through Tuesday morning, but will still see cloud cover
increase and CIGS lower. Probabilities for MVFR CIGS then
increase to 20-40% for inland sites after ~20z Tuesday.

PDX AND APPROACHES...Generally VFR cigs/vis with northwesterly
flow through the day. While stratus will reform Tuesday morning,
there is only a 20-30% chance for MVFR CIGs towards the end of the
TAF period after 16-17z Tuesday, increasing to 30-40% after 20z
Tuesday. -Schuldt

&&

.MARINE...High pressure will begin to progress to our east this
evening and overnight ahead of a weak weather disturbance
approaching the Pacific Northwest. On Tuesday, a weak frontal
boundary passes over the waters but will likely not be impactful
as far as wind is concerned (at least initially), decaying as it
reaches the shore. That said, an accompanying westerly swell
arriving on Tuesday will push seas to 10-13 feet at 11-13 seconds
leading to Small Craft Advisory conditions. Following this trough
northerly winds will also increase Tuesday night into Wednesday as
another area of high pressure redevelops over the waters - gusts
between 20-30 knots likely. Come Wednesday evening/night when
winds peak the NBM projects a 70-90% chance for Small Craft
Advisory level wind gusts (>21 knots) with similar probabilities
persisting through Thursday. From there, another trough is
anticipated to move into the region late week into the weekend,
although confidence is low in the exact impact at this time.
-Schuldt

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 5 PM Tuesday to 5 AM PDT Wednesday
     for PZZ210.

     Small Craft Advisory from 11 AM Tuesday to 11 PM PDT Thursday
     for PZZ251-252-272.

     Small Craft Advisory from 5 PM Tuesday to 11 PM PDT Thursday
     for PZZ253-273.

     Small Craft Advisory from 8 AM Tuesday to 11 PM PDT Thursday
     for PZZ271.

&&

$$

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