090
FXUS66 KPQR 220434
AFDPQR

Area Forecast Discussion...Updated Aviation
National Weather Service Portland OR
934 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 has passed, and we slowly transition into a
post-frontal environment for the rest of Tuesday night. Continued
showers at the coast will keep conditions there MVFR or lower
at least until 10z Wed. The northern coast (KAST) continues to
see MVFR conditions, while the southern coast (KONP) sees LIFR
conditions. Ceilings slowly begin to rise around 10z Wed, but this
will be a gradual process, with periods of lowered cigs still
possible (40-60%) for the rest of the period.

Further inland, northern terminals in the Willamette Valley have
already mostly transitioned to VFR conditions, and will likely
remain that way for the rest of the TAF period. The southern
Willamette Valley continues to see some showers intermittently
lowering cigs to MVFR, but these end by 10-12z Wed, after which
VFR conditions dominate (90% confidence).

Winds are also expected to begin to increase after sunrise on
Wed, with stronger gusts up to 25 kt possible at all terminals
from the west. KAST will be the exception, and could see slightly
stronger gusts up to 30 kt.


PDX AND APPROACHES...The front has passed through the area, and
VFR conditions are expected to dominate through the rest of the
TAF period with 90% confidence. Winds will pick up after around
18z Wed from the west, with gusts up to 20 kt possible. /JLiu

&&

.MARINE...Post frontal conditions are creating breezier winds and
elevated seas for all waters except inner southern waters.
Currently the northern waters are gusting to around 25-30 kt, with
the southern waters closer to 20-25 kt. Seas in the northern
waters will see a sharp but temporary increase in wave heights,
peaking around 12-13 ft at 9 seconds Wednesday morning. The
southern waters should not be affected. The Small Craft Advisory
thus continues until Thursday afternoon as winds and seas remain
elevated.

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
PZZ210-251-252-
     271>273.

&&

$$

www.weather.gov/portland

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