211
FXUS66 KPQR 212147
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
247 PM PDT Tue May 21 2024

.SYNOPSIS...Slow moving front continues to move southeast, gradually
blanketing the region with widespread rain. Rain will become
scattered showers tonight into Wednesday. Dry and warmer
Thursday before becoming unsettled for Friday into the weekend.

&&

.SHORT TERM...Tuesday afternoon through Thursday...Satellite
imagery around 2 PM Tuesday, front slowly moves southeast
bringing widespread rain through most of the region (North of
Eugene and Newport). With this front bringing northwesterly
winds at the surface, lowlands and south areas of the region are
expected to receive less rain due to the rain shadow effect.
Rain will turn showery this evening, then isolated overnight for
areas west of the Cascades.

Behind this front, a closed low moving south southeast through
western British Columbia will reach western Washington around 5 AM
Wednesday. This low will then drift southeast into northeast
Oregon through the rest of Wednesday. The core of this low will
just miss our region, resulting in showers, similar to today.
With northwesterly winds and the closed low coming from the
north, precipitation along the Coast Range will be limited, with
majority of the precipitation along the Cascades. Through
Wednesday evening, chances to exceed 0.5 in of precipitation
over 24 hours is 10-30% chance for the valley lowlands and
50-70% for coastal areas north of Tillamook. With the
aforementioned low just missing our region, instability will be
rather limited, therefore thunderstorm chances will be low
across the Cascade foothills. The high Cascades will receive
snow but snow levels will remain well above mountain passes.

Thursday, a weak shortwave ridge builds over the region as the
closed low moves east over the northern Rockies. This will bring
sunny skies and warm temperatures up into the upper 60s (20-30%
to exceed 70) for the interior lowlands and mid 50s/upper 50s
along the coast.
-JH

.LONG TERM...Friday through Monday...An unsettled weather
pattern is expected to continue through at least Saturday.
WPC`s 500 mb cluster analysis indicates a week shortwave could
bring light showers Friday followed by an upper level low
bringing slightly more showers to the region Saturday. Timing
and amount of precipitation continues to remain uncertain,
though temperatures are expected to be near seasonal normals.

The pattern becomes a bit more uncertain Sunday on whether
troughing will still be present to continue showers. By Monday,
dry conditions are expected, with 20% of clusters suggesting a
weak trough approaching and 80% of clusters suggesting a ridge
overhead or nearby (location and timing still uncertain). This
brings significant uncertainty in temperatures with NBM 25th to
75th percentiles for inland valleys ranging anywhere from upper
60s to low 80s.
-JH

&&

.AVIATION...The front is in the process of moving ashore, and rain
has begun at almost all areas. Cigs at the northern/central coast
(KAST) are bouncing between IFR and MVFR, while inland cigs are
high end MVFR/low end VFR. By 00z Wed, the coast sees 90%+ of
firmly IFR cigs. Southern terminals (KONP/KEUG) remain VFR as
precipitation is heavier up north, but will begin to lower within
the next few hours, by 00z Wed.

Between 06-10z Wed, conditions transition to post-frontal, and
most terminals will trend back to VFR, with the valley
transitioning faster. By 09z Wed, even the coast only sees 30-40%
chance of MVFR or lower ceilings. West/southwesterly winds will
also begin to pick up around that time, with gusts for most areas
up to 20 kts (25-30 kt at KAST).

PDX AND APPROACHES...VFR conditions are currently in place, but
all surrounding terminals have already dropped to high end MVFR;
expecting a drop in cigs down to MVFR within an hour or two, by
00z Wed. Conditions trend back to VFR around 08z, with less than
10% chance of MVFR conditions continuing past that time. Winds
will pick up slightly, with top gusts up to closer to 15-16 kt
from the west at that time. /JLiu

&&

.MARINE...The front is passing through, bringing higher seas and
gustier winds in the north and central waters. Winds are gusting
to 25 kt or so north of Cape Foulweather, spreading southward to
PZZ273 by 03Z, persisting at times through Tuesday night and
Wednesday. With the persistent northwest fetch in the post-
frontal environment, also expecting seas to become fairly steep
Tuesday night into Wednesday with greatest impacts to PZZ251 as
seas rise to 10 to 13 ft with a period 9 to 10 seconds.

As we move into Thursday, calmer winds/seas return for a day followed
by yet another weather disturbance moving into the region from the
NNW late Friday/Saturday continuing the rather progressive and
active weather pattern. Seas likely rise to 7-10 feet at 8-9
seconds on Saturday before decreasing Sunday into early next
week - wave steepness may again be a concern Saturday.
-mh/JLiu

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 5 PM PDT Wednesday for PZZ210.

     Small Craft Advisory until 5 PM PDT Wednesday for PZZ251-252-271-
     272.

     Small Craft Advisory from 8 PM this evening to 5 PM PDT
     Wednesday for PZZ273.
&&

$$

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