770
FXUS66 KPQR 210459 AAA
AFDPQR

Area Forecast Discussion...Updated
National Weather Service Portland OR
957 PM PDT Mon May 20 2024

.UPDATE...Made a quick update to the forecast through Tuesday, as the
latest models have slowed the timing of precipitation considerably.
Tuesday morning now looks mostly dry for the forecast area, aside
from perhaps for our northern coastal zones. Latest HRRR now has rain
beginning in the PDX metro shortly after noon, and it may be evening
by the time rain reaches the Eugene area. The slower timing of
clouds/precip is expected to allow a warmer day for the Eugene area,
with temperatures now expected to climb well into the 60s and
possibly near 70 deg F, depending on the timing of increasing clouds.
No changes were made beyond Tuesday evening. Aviation section has
also been updated below.  Weagle

&&

.SYNOPSIS...Next front approaching, with increasing clouds later
tonight. That front will push across region on Tue, with areas of
rain. Showers Tue night into Wed as air mass turns more unstable.
Will maintain unsettled with daytime temperatures staying near to
slightly below that normally expected for mid-May.

&&

.SHORT TERM...(Monday afternoon through Wednesday)...
Onshore flow will keep region under pleasant temperatures through
rest of this afternoon into the evening.

Next front is well offshore, and approaching. As it does, will see
increasing clouds overnight. While most areas remain dry overnight,
do think will get spotty light rain spreading onto Washington coast,
and as far south as Tillamook toward daybreak Tuesday. Rain will will
spread across region through the morning, with rather cloudy and damp
day on tap for most. Rainfall will vary on location, with much
lighter rainfall as move southward across western Oregon. Current
expectations are a 0.50 up to 1 inch along the coast, and into the
North Oregon Coast Range and Willapa Hills, and in the South
Washington Cascades down to Mount Hood area. Farther south, 0.25 to
0.50 on the central Oregon coast as well as over the central
Cascades. Rainfall across the interior 0.25 to 0.50 in the Cowlitz
Valley to the Portland metro, with rainfall decreasing as move
southward, with 0.05 to 0.20 inch from Corvallis to Eugene.

Models still depicting the front moving onshore mid-late Tuesday
afternoon, and shifting eastward to the Cascades by mid-evening. May
have a brief lull between the rain with clouds breaks. But, cooler
air aloft will spread into the region. As such, this will create an
unstable air mass, with showers resulting for Tue night. On Wed, an
upper low over the Gulf of Alaska will drop southeast and inland over
the Pac NW. This will provide extra enhancement to the modest
instability over the region, with heftier showers, some with small
hail. At moment, the low should track from northwest Washington early
Wed am to northeast Oregon by Wed afternoon. Following that trend,
the late afternoon may end up being a bit drier for areas west of the
I-5 corridor, as showers become more Cascades focused as flow turns
more north to northwest behind the low. Interestingly, air mass
instability could be enough to support a thunderstorm or two, but for
now will not mention. But, bears watching, considering the track of
the upper low and associated cool pool aloft.

Weak ridging on Thursday will bring mostly dry day. But, still have
little energy rotating around the upper low that will be over the
northern Rockies. As such, could still have a shower to two over the
Cascades. But, with warming aloft, and meager moisture aloft, would
not be much of a chance.       /Rockey


.LONG TERM...(Friday through Sunday)...WPC 500 mb clusters continue
to indicate a general trough pattern Friday into the weekend,
though specific details on timing and location of weather
systems and any potential precipitation amounts are still very
uncertain at this time. One aspect that does seem a little more
certain is temperatures are expected to remain fairly mild
through the weekend. NBM indicates a 75-95% chance that interior
lowland temperatures will warm back into the 60s and remain in
the 60s through the weekend.       /HEC

&&


.AVIATION...Satellite imagery as of 0430z Tue shows party cloudy
skies across northwest Oregon and southwest Washington, with low
clouds just off the coast. We`re already starting to see high-end
MVFR cigs at KAST, and expect those MVFR cigs to spread along the
coast tonight. The north Oregon coast has the highest chance
(50-70%) of IFR cigs through 18z Tue. More mid to high level
cloud cover will also begin to filter in tonight ahead of the
front. Expect mostly VFR conditions in the Willamette Valley
tonight except the Portland Metro Area, where there is a 60-80%
chance of high-end MVFR cigs developing after 10-12z Tue. Winds
through early Tuesday morning will generally be light and
variable.

The next frontal system will arrive between 18-21z Tue, bringing
light rain and lowering cigs. Guidance suggests high confidence in
widespread LIFR/IFR cigs along the coast and MVFR cigs in the
Willamette Valley by 21z Tue-00z Wed. Winds will also pick up,
with southwest winds 5-10 kt with occasional gusts to 18-20 kt.

PDX AND APPROACHES...60-80% chance of high-end MVFR cig
development after 10-12z Tue. Could see cigs lift to high-end VFR
between 18-21z Tue. After 21z Tue-00z Wed, high confidence for
MVFR cigs as the next frontal system pushes inland. Winds will be
southwest and around 5-10 kt.  -Alviz

&&

.MARINE...Small Craft Advisory with steep seas of 7-8ft at 7-8
seconds, along with a small longer period (18 seconds) southwest
swell. Wind generally Northwest 10 to 15 kt with brief gusts to
20 kt through this evening. Calmer conditions return tonight into
early Tuesday morning, albeit briefly, before the next frontal
passage arrives on Tuesday bringing rain and Small Craft Advisory
Winds ahead and behind the front. Confidence is high (70-80%) wind
gusts reach into the 20-25 knot range for the outer waters north
of Cape Foulweather Tuesday morning ahead of the front and
evening/night in the post-frontal environment. With the persistent
northwest fetch in the post-frontal environment, will also see
seas become very steep Tuesday night into Wednesday with greatest
impacts to PZZ271 as seas rise to 10 to 13 ft with period 9 to 10
seconds.

Looking ahead, calmer winds/seas return Thursday followed by the
potential for yet another weather disturbance moving into the
region late Friday/Saturday continuing the rather progressive and
active weather pattern. /mh -Schuldt

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 1 PM to 9 PM PDT Tuesday for PZZ210.

     Small Craft Advisory from 10 AM Tuesday to 11 AM PDT Wednesday
     for PZZ251-252-271-272.

     Small Craft Advisory until 11 PM PDT this evening for
     PZZ271>273.

&&


$$

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