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Area Forecast Discussion
Issued by NWS Portland, OR
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FXUS66 KPQR 202212
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
311 PM PDT Sat Apr 20 2024

.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...The front that has been expected today has finally
reached the coast but has dissipated greatly which has caused
conditions to be better than previously expected. Coastal
terminals around KONP are the only ones to have observed rain and
reduced VIS/CIGs to low-end MVFR levels thus far. May still see
them near KAST, but it will take quite a bit of saturation for
that to occur. Inland areas are VFR and will continue to be so as
the lower levels of the atmosphere are very dry. With these dry
conditions, any falling rain is evaporating, and clouds are unable
to form. If any MVFR CIGs do form, the highest probability is
around KSLE and KEUG. Confidence is low though as to whether we
will see MVFR conditions in regards to rain or CIGs. Winds have
been east/southeasterly today but are in the process of
transitioning to the west. This will bring breezier conditions
along the coast and south/southwest aligned terminals. Will see
winds ease behind the front.

One thing we are watching in the Willamette Valley is the
possibility for fog around KSLE and KEUG. It will greatly depend
on the presence of clouds in the evening and early morning. If
enough radiational cooling occurs, cannot rule out MIFG at those
terminals - though would be short lived.

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 a 20-30% chance of MVFR CIGS between
13-16Z Sunday. This is likely due to radiational cooling but will
depend on clouds dissipating overnight which is low. Gusty winds
continue this afternoon and evening from the east with periods of
gusts up to 30 kt along the leading edge of the front. Not
expecting them to be long lasting though models do tend to
dissipate them faster than observations would suggest. Winds ease
overnight behind the front. -Muessle

&&

.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 4 PM PDT this afternoon for PZZ210-
     253-273.

     Small Craft Advisory until 2 AM PDT Sunday for PZZ251-252-271-
     272.

&&

$$

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