981
FXUS66 KPQR 172218
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
318 PM PDT Mon Jun 17 2024

.SYNOPSIS...Showers decrease this evening as low pressure exits
the region. Drier conditions return tomorrow, with winds turning
more northerly. Wednesday to Friday, conditions become much
warmer and drier as light easterly winds downslope from the
Cascades. Conditions begin to cool down and become more moist
late this weekend.

&&

.SHORT TERM...Now through Wednesday night...Radar imagery as of
230 PM PDT depicts lingering shower activity across portions of
northwest OR and southwest WA, mainly over the Cascade foothills,
Cascades, and northern Willamette Valley. Based on CAM guidance,
expect lingering showers to decrease through this evening as
low pressure exits the area. Westerly winds will also gradually
ease. Overnight lows will be pretty chilly for mid to late June,
forecast in the 40s for interior valleys and 30s for high
terrain. Tomorrow (Tuesday), expect warmer weather as 500 mb
heights increase. Temps will be near seasonal normals, with
highs forecast in the low to mid 70s for interior valleys and
60s along the coast. Winds will also turn more northerly,
bringing drier air to the region.

Wednesday, we`ll start to see a thermal trough developing east
of the Cascades over central Oregon. This will lead to light
(less than 10 mph) easterly winds downsloping from the Cascades,
but most Willamette Valley winds will be northerly. As a result,
expect much warmer conditions in the Willamette Valley and
lower relative humidities (around 30%). Wednesday afternoon
highs are forecast to climb into the mid 80s for interior
valleys. NBM probabilities for temps greater than 85 degrees
for interior valleys are currently around 60-80%. Meanwhile, the
coast will still remain mild with higher humidity and temps in
the 60s as they maintain a slight onshore component to the
wind.     -Alviz

&&

.LONG TERM...Thursday through Monday...High pressure increases
through the remainder of the weekend, though it is a bit more
convoluted as there is not good vertical continuity. While high
pressure is forming at the surface, a troughing pattern is
developing in the mid levels. However, looking at the jet stream
(around 35,000 ft) there is a very clear ridging pattern.
Because of this overall messy pattern, confidence is a bit lower
than desired for the long term forecast. In a similar realm to
locations in the east, we will be warming up quite a bit but not
nearly as hot. Ultimately, temperatures will be just slightly
above normal. They challenge remains "just how hot will it be?".
Thursday will be the first day of considerable warming with
temperatures forecast in the mid to upper 80s inland, and
cooler along the coast. Friday is slated to be the hottest day
of the week with the NBM showing temperatures into the 90s
around Portland. Now, the NBM has been quite variable increasing
temperatures day by day.

Specifically looking at the greater Portland/Vancouver-Metro
area, the box and whisker plots for temperatures has narrowed
which generally would coincide with more confidence in the
forecast. However, looking at the other long-term ensembles, it
is a bit less clear. Maximum temperatures around Troutdale on
Friday have the highest probability to be around 85-90 Degrees
F, with only an 10% chance of exceeding 90 degrees F. The NBM
deterministic is putting Troutdale right at and slightly above
90 degrees. Given the variability have decided to let the NBM
ride until we get a few more runs to hopefully narrow in on a
better pattern. The other component to feature with this is a
weak north to easterly wind throughout most of the forecast
area. This will enhance warming, and drying with humidity
plummeting ranging from 20-30% with the driest conditions along
the Cascades and the Columbia River Gorge. The east wind could
increase downslope and warming which may be contributing to the
higher temperatures.

Saturday will be the transitional day as a long wave trough
begins to drop down from the Gulf of Alaska. 500 mb heights are
lowering to the north, and the bulk of the low aloft will
transcend along the WA/Canadian border. This system will usher
in cooler air dropping temperatures on Sunday. Precipitation is
possible with southwesterly flow, but accumulations will be
minimal and not impactful. -Muessle


&&

.AVIATION...Scattered showers continue this afternoon in northwest
flow on the backside of a trough. Most of the shower activity and
associated MVFR conditions are north of the Lincoln City to Salem
line. Showers are expected to diminish through the afternoon and
evening but with moist onshore flow continuing into Tuesday
mountains could be obscured at times. For the TAF sites there is
a 30-50% chance for MVFR cigs in the Willamette Valley north of
KSLE from about 11Z to 17Z Tue.

PDX AND APPROACHES...Brief MVFR with with passing showers through
about 00Z Tue, then should trend to VFR. Guidance shows about a
40% chance for MVFR cigs near 3000 ft 12-17Z Tue in the area.
Northwest winds increase to around 6-8 kt this afternoon into the
evening before easing. /mh

&&

.MARINE...High pressure offshore is expected to persist through
the week. Northwest winds 10-15 kt across coastal waters today
becoming northerly on Tuesday. North winds begin to increase later
Tuesday afternoon as a thermal trough strengthens from northern CA
into southern OR, so have issued a Small Craft Advisory for PZZ
253, 273, but may need to be extended further north. Expect will
see periods of winds gusting up to 25 kt through Friday during the
late afternoon and evenings. Seas around 4 to 6 feet will
generally be wind driven through the week. /mh /DH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 2 PM Tuesday to 4 AM PDT Wednesday for
     PZZ253-273.
&&

$$

www.weather.gov/portland

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