509
FXUS66 KPQR 100449
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
949 PM PDT Sun Jun 9 2024

UPDATED AVIATION DISCUSSION

.SYNOPSIS...
Generally pleasant and benign weather is on tap for the
next few days. The weak upper trough responsible for areas of drizzle
along the coast earlier today will move east across the Cascades
tonight. High pressure will follow with warm temperatures and plenty
of sunshine for Monday. Another weak system may clip mainly the north
coast with drizzle or light rain Tuesday, then high pressure brings a
return to warmer and drier weather Wednesday and Thursday.
Temperatures may dip below normal next weekend as most forecast
models bring an upper trough onshore - potentially strong enough to
bring more widespread rain to the region.

&&

.SHORT TERM...Now through Tuesday Night...
Now through Wednesday...A weak upper trough deepened
the marine layer enough for some measurable drizzle along the coast
north of Manzanita this morning. The ASOS at Astoria airport reported
the most precip with 0.05". Based on area webcams and the latest
reports, it appears the drizzle has mostly come to an end. The marine
layer should become shallower as the upper trough moves east of the
Cascades and higher pressure in the mid-levels assists subsidence.
The coast should see stratus either persist or return overnight, but
the inland intrusion should be considerably less robust Monday
morning. Any morning clouds inland will quickly give way to sunshine
and a warm afternoon. With 850 mb temps likely to reach +10 to +12
deg C by Monday afternoon, most of our interior lowlands should climb
into the 80s. NBM probabilistic guidance tends to agree with general
40-70% chances of reaching 80 deg F in the Willamette and Hood River
Valleys Monday afternoon. A greater northerly component to the
low-level flow should lead to drier conditions as well.

The NE Pacific remains more active than usual for June, and this will
continue to be the case Monday night/early Tuesday as another upper
trough moves into British Columbia, pushing the tail end of its cold
front into the Pac NW. This looks like a similar situation as today,
where mainly north coastal zones may get brushed with some drizzle or
light rain. PoPs remain low, except perhaps in the Willapa Hills
where most guidance has a little QPF Tuesday morning. High pressure
quickly returns Tuesday afternoon, drying things out and leading to a
fairly seasonable and pleasant day Wednesday.  Weagle


.LONG TERM...Wednesday through Saturday...
Thursday through Sunday...By Thursday, ensemble members
agree on shortwave ridging over the region, supporting drier
and warmer conditions. Our forecast undercuts NBM MinRH both
Wednesday and Thursday as northerly flow should cause dewpoints to
dip well into the 40s or possibly even the 30s as temperatures warm
up under the upper ridge. Essentially, our forecast used a MOS blend
for dewpoints then calculated the MinRH for both days. By Friday, the
upper ridge begins to shift eastward as another trough near the Gulf
of Alaska dips southward toward the Pacific Northwest. By Saturday,
most ensemble members (65%) 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 along with
potentially below average temperatures. For now, the NBM`s 15-45%
chance of PoPs across northwest Oregon and southwest Washington at
the end of the week look reasonable.  -Alviz/Weagle

&&

.AVIATION...VFR conditions prevail across the interior valley with
little to no cloud cover across the area. KONP and KAST are under
MVFR CIGs with a marine stratus deck that has redeveloped around
1400-2000 ft. The deck is expected to lower through the night with
a period of IFR CIGs expected after 9Z. Periods of light drizzle
will also be possible at KAST Monday morning, similar to what was
observed Sunday morning.

Models still show a chance for an MVFR stratus deck to develop
near the mouth of the Columbia River Gorge and backbuild into KTTD
and KPDX around 10z Monday. Probabilities for this to occur have
increased to nearly 50% and forecast confidence has increased from
low to medium. As such, have decided to include broken cigs
around 2200 ft at KTTD and KPDX beginning at 10z.

PDX AND APPROACHES...VFR conditions to start the night. However,
probabilities for MVFR cigs around 2000 ft have increased,
peaking near 50% towards 12z Monday. This stratus deck will
likely develop over/near KTTD first before quickly backbuilding
westward towards KPDX. Expect northwest surface winds around 5 kt.
-Batz/TK

&&

.MARINE...
Buoy observations from early Sunday afternoon showed
significant wave heights at 9 to 10 ft with a dominant wave period
around 13 seconds. This is a foot or two higher than what the
latest model guidance suggests. As such, the forecast has been
updated to increase wave heights for the rest of Sunday afternoon
through Sunday evening to better reflect observations. These
observations also meet criteria for a marginal small craft
advisory. In addition, northerly winds were gusting up to 20 kt.
Therefore have decided to issue a small craft advisory for the
inner and outer waters through 11 PM Sunday. Seas should fall back
below 10 ft thereafter as high pressure strengthens and northerly
winds weaken. High pressure will strengthen even more Monday
morning, bringing seas down to 4 to 6 ft.

Still expecting a weak cool front to move eastward over the
coastal waters early Tuesday morning, bringing a brief shift to
southerly winds. This front looks to be weak, only producing wind
gusts up to 15-20 kt. That said, westerly swell will increase
behind the frontal passage Tuesday afternoon/evening, likely
pushing seas back up to 9 to 10 ft and producing marginal small
craft advisory conditions.

Small craft advisory conditions become even more likely on
Wednesday as a thermal trough deepens along the south Oregon coast
and helps increase northerly winds over the waters. Currently
expecting wind gusts up to 25-30 kt on Wednesday (95% chance). In
fact, cannot completely rule out marginal gale force gusts up to
35 kt over the southern waters (40-60% chance).  -TK

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for
     PZZ251>253-271>273.
&&

$$

www.weather.gov/portland

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