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776
FXUS66 KPQR 202133
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
231 PM PDT Mon May 20 2024

.SYNOPSIS...
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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.
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&&

.SHORT TERM...
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(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
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&&


.AVIATION...
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Stratocumulus continues this afternoon with most
coverage north of KSLE as onshore flow strongest there. VFR
prevailing with cigs 4000-5000 feet. Expect cloud coverage to
decrease some through the afternoon and evening hours. But onshore
flow continues ahead of next front for later Tuesday. So, overnight
expect MVFR to IFR to develop at the coast, while inland remains VFR
with mid-level cigs around 4000-6000 ft developing overnight. Lower
cigs form inland early Tuesday with HREF indicating 40-70% chance
for MVFR cigs 2000-3000 ft roughly 12-16Z Tue. There should be
several hours of VFR conditions, then as the rain spreads inland
through Tue afternoon, so does the MVFR cigs.

Winds will be mostly light then pick up to 5-10 kt. Occasional gusts
to 18-22 kt possible during the afternoon into the early evening
along the coast before decreasing again overnight.

PDX AND APPROACHES...VFR continues with cigs around 4000 ft which is
expected to become more scattered this evening. With continued
onshore flow expect low VFR to MVFR cigs to redevelop Tuesday
morning. HREF indicating around 70% chance for MVFR 12-16Z Tue,
followed by a break, then MVFR likely returning (60-80% chance)
after 21Z Tue as rain spreads inland. Winds will be northwesterly
and around 5-10 kt although gusts around 15-20 knots will be
possible around 00-04z.
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&&

.MARINE...
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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
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&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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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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&&

$$

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