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000
FXUS66 KPQR 210407 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
906 PM PDT Sat Apr 20 2024

Updated Aviation Discussion

.SYNOPSIS...A cool front moving onshore this afternoon will bring
clouds, breezy south to westerly winds and spotty light rain before
clearing and cooling a bit overnight into Sunday. Dry and mild
weather expected through early next week, with Tuesday likely seeing
the warmest temps into the lower 70s. Cool and showery conditions
are likely to return late in the week as an upper level trough
settles over the area.

&&

.SHORT TERM...TONIGHT THROUGH MONDAY NIGHT...Satellite imagery shows
a weak frontal system pushing onshore this afternoon. Clouds have
spread across the area with light returns on the radar but with
little rainfall making it to the ground, which indicates a layer of
very dry air near the surface. Dry and breezy conditions have also
been noted at surface observations with minimum RH values inland
falling to around 20-25% and southerly winds gusting up to 20-30
mph. Latest forecast precipitation amounts are quite paltry, around
a trace to 0.05" for the lowlands with this system while the higher
terrain may see upwards of 0.10-0.20" of rainfall. Winds will shift
southwest to westerly with the frontal passage with a few gusts up
to 35 mph possible. Then winds calm down again overnight.

Temperatures in the upper 60s to lower 70s this afternoon will cool
behind the front with highs around 60 degrees on Sunday. Conditions
expected to remain dry Sunday through Monday as high pressure builds
offshore. Winds turn northerly, while afternoon temps bounce back
again on Monday, warming into the upper 60s to lower 70s under
mostly sunny skies. Being still April, clearing skies overnight will
allow for good radiational cooling with low temperatures falling
into the 30s. The more rural locations still only have a 10-20%
chance of temps dipping below 35F Sunday and Monday mornings. /DH

.LONG TERM...TUESDAY THROUGH SATURDAY...On Tuesday, the
GEFS/ENS/GEPS ensemble means all show southwest flow aloft across
western WA/OR on before 500 mb flow veers to the west on Wednesday.
The aforementioned wind shift is in response to a weak upper level
trough brushing the forecast area to the north. Models and their
ensembles suggest mainly dry weather for northwest OR and southwest
WA on Tuesday with low chances for light rain showers Tuesday night
through Wednesday night (10-20% chance in the lowlands, 20-40%
chance in the mountains). Temps look to be a bit above normal,
especially on Tuesday when there is a 60-90% chance for high temps
at or above 70F. In fact, the NBM is showing a 20% chance for high
temps near 80F over the Portland metro during a period of dry east
winds. This seems like a bit of a stretch as model soundings do show
fairly thick high clouds over the area that day, which will most
likely keep highs in the low to mid 70s.

Conditions will become noticeably cooler on Thursday as highs fall
back into the 50s across the area. This is in response to a cool
upper level trough that is set to move overhead late in the week,
bringing higher chances for rain. While NBM 6-hr PoPs only peak
around 50-60% in the lowlands, 24-hr PoPs peak close to 70%. This is
due to model timing differences. Only a very small number of
ensemble members are showing no rain at all, suggesting rain is
likely to occur at some point on Thursday and/or Friday. In
addition, the NBM is showing a 30-40% chance for 24-hr rain amounts
in excess of 0.25" across all of northwest OR and southwest WA,
except 40-60% in the mountains.
  -TK

&&

.AVIATION...Widespread VFR under generally clear skies across the
air space, with lingering clouds along the Coast and Cascades
which could obscure the ranges at times. Onshore flow has
developed across the air space and is expected to persist through
the TAF period.

One thing we are watching in the Willamette Valley with a 5-15%
probability of fog developing starting around 15Z Sunday.
Currently, areas around KSLE and KEUG have the highest
probability for fog development tonight. Development of fog will
greatly depend on the presence of clouds overnight through early
Sunday morning. If any fog does develop, will likely be short
lived and scour out by 20Z Sunday. Afterwards, VFR conditions are
expected to dominate through the remainder of the TAF period.

Notes: The ASOS at KTTD is only available via the dial in option.
The AWOS at KMMV is still out of commission. As it is not
maintained locally by the National Weather Service, there is no
estimated time of repair.

PDX AND APPROACHES...VFR with mostly clear skies through the TAF
period. 5-10% probability for fog development between 15Z and 18Z
Sunday. Any fog that does develop, will likely be short lived and
scour out by 20Z Sunday. /42

&&

.MARINE...The cool front is moving inland today though progress
has been slow. The outer waters are starting to see winds slowly
subside behind the front, while nearshore waters are still seeing
those gusty winds. Will see those too quickly subside from the
current 15-20 kt with gusts to 30 kt to 10 to 15 kt with gusts to
20 kt. Struggling a bit with the small craft advisory in effect as
the winds will quickly dissipate behind the front, though the
timing of the front moving east is questionable. Likely will
extend for a few more hours to cover the bases for any rogue winds
that linger. The next surge of winds will arrive late Sunday
where we will likely see marginal Small Craft Advisory winds
again. Low pressure shifts over northern California increasing the
gradient and transitioning winds to the north. Could see gusts as
high as 30 kt at times in the central and south-central waters.

Seas will remain generally unchanged over the next few days around
6 to 9 ft at 11 seconds.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 3 AM PDT Sunday for PZZ251-252-271-
     272.
&&


$$

www.weather.gov/portland

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