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000
FXUS66 KPQR 220956
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
256 AM PDT Mon Apr 22 2024

.SYNOPSIS...Low-level offshore flow will bring mild and dry weather
to the area Monday through Tuesday with a mix of sun and high clouds.
Tuesday will be the warmest day with inland high temps in the low to
mid 70s. A cool and showery weather pattern will begin on Thursday as
an upper level trough settles over the area. This trough will then
maintain cool and showery conditions through the upcoming weekend.

&&

.SHORT TERM...Monday through Wednesday night...Low level flow turns
more north to northeasterly Monday morning allowing for continued dry
conditions. Clear skies and light winds in sheltered rural areas has
allowed for areas of frost to develop early Monday morning. Surface
temperature observations from 230 AM Monday showed temps mainly in
the mid 30s where a Frost Advisory is in place, which includes the
Upper Hood River Valley, north OR Coast Range, Willapa Hills,
portions of northern Clark County and south WA Cascade foothills, as
well as portions of the north OR Cascade foothills. Temps remained a
bit too warm for frost elsewhere, as expected. Locations with frost
should see frost melt off around 8am, which is when the
aforementioned Frost Advisory is set to expire.

High pressure offshore with low pressure over the Great Basin will
maintain breezy north to northeast winds and dry conditions through
Monday. Plenty of sunshine will allow temps to warm quickly during
the morning/afternoon with highs rising into the upper 60s to lower
70s according to the deterministic NBM. Increasing clouds Monday
night will likely bump minimum temperatures 5-10 degrees warmer when
compared to Sunday night`s low temps. With the increasing cloud cover
and lows generally in the 40s Monday night, frost will no longer be a
concern. A mix of sun and clouds on Tuesday with warming 850mb temps
will allow for another warm day with highs in the low to mid 70s,
except around 60F along the coast. The probability for high temps of
75 degrees or warmer is at 70-85% over the northern Willamette Valley
and Portland/Vancouver metro. The central Willamette Valley has a
50-60% chance, and the south valley has a 20-25% chance.

The GEFS/ENS/GEPS ensemble mean all show 500 mb flow veering to the
west on Wednesday in response to a weak upper level trough brushing
the forecast area to the north. Models and their ensembles continue
to suggest the bulk of precipitation with this system will fall
over British Columbia, with very little to no rain at all across
southwest WA and northwest OR. NBM PoPs have decreased to 10% or
less, except 15-30% over southwest WA. Temperatures are shaping up to
be right around normal for this time of year on Wednesday with highs
in the low to mid 60s.-TK/DH

.LONG TERM...Thursday through Sunday night...Conditions will become
noticeably cooler on Thursday as highs fall 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 rain with it. Models and
their ensembles are now showing better agreement on timing. This has
resulted in an increase with the latest NBM 6-hr PoPs, which peak
Thursday afternoon through Friday afternoon at 85-95%. 24-hr PoPs are
now near 100%, which makes sense as every single ensemble member from
the GEFS/GEPS/ENS show at least some QPF. While confidence is very
high at least some rain will fall late in the week, confidence is not
as high regarding exact rain amounts as ensemble guidance continues
to show a large degree of model spread. At this point, the driest
ensemble members suggest around 0.25" of rain Thursday through Friday
while the wettest members suggest around 1-1.25". There is noticeable
ensemble clustering around 0.5-0.7", which is also in line with
WPC/NBM QPF guidance. Overall, ensemble guidance has been trending
wetter with the latest model runs. NBM probabilities for 24-hr rain
amounts in excess of 0.25" have increased dramatically from 20-40% to
70-80% in the lowlands and from 40-60% to around 90% in the
mountains. Regardless of exact rain amounts, it appears a true
wetting rain is in store. For those who may be wondering, snow levels
will be above pass level, thus no travel impacts are expected.

Over the upcoming weekend, the GEFS/GEPS/ENS ensemble mean all show
nearly zonal flow aloft across the region with a closed low pressure
system centered over the Gulf of Alaska. It appears this low will
send a series of cool fronts over the northeast Pacific and across
western WA/OR as it moves closer to the coast, maintaining cool and
showery conditions across the forecast area. -TK

&&

.AVIATION...Transient high pressure will maintain VFR thresholds
with dry conditions at all terminals through the entire TAF
period. Guidance suggests a 10-20% chance of LIFR fog between
12-16z Mon in the Willamette Valley, but dew points look a bit
too low for fog development. Expect mostly clear skies today, with
increasing high clouds in the evening as a weak frontal system
progresses through the NE Pacific. Winds will generally be
northerly/northwesterly today, with the strongest gusts in the
afternoon/evening (18z Mon-03z Tue) when pressure gradients are
the tightest. Gusts to 20-25 kt are possible during this
timeframe along the coast and parts of the Willamette Valley
(mainly the south Valley). Winds begin to weaken after 04-06z Tue
as pressure gradients loosen.

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 thresholds through the entire TAF period
under mostly clear skies. Guidance suggests a 10% chance of LIFR
fog between 12-16z Mon, but didn`t include in TAF due to low
confidence. Expect northwesterly winds around 6-9 kt today,
weakening after 06z Tue. -Alviz

&&

.MARINE...Observations at buoy 46050 as of 230 AM PDT show north-
northeasterly winds gusting to 25-30 kt with seas around 8-9 ft
at 11 seconds. The forecast looks on track, including the current
Small Craft Advisory. High pressure over the waters will maintain
these gusty northerly winds today with gusts to 25-30 kt. Locations
south of Cape Falcon have a 30-50% chance of occasional gusts up
to 35 kt between 5-10 PM Monday when the pressure gradient is
strongest. Due to low confidence in Gales and its potentially
sporadic nature, a Gale Warning was not issued.

Monday night to early Tuesday morning, pressure gradients loosen
and winds will gradually weaken from north to south. Northerly
gusts around 20-25 kt continue south of Cape Falcon Monday night,
so the Small Craft Advisory remains for the central and southern
waters (PZZ272-73 and PZZ252-53) through mid-morning Tuesday.
Minimal changes to wave heights are expected as the predominate
wind wave is from the north and the background swell is from the
northwest. Quiet conditions prevail Wednesday before the next
system arrives over the waters Thursday. -Alviz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Frost Advisory until 8 AM PDT this morning for ORZ104-106-109-
     121-123.

WA...Frost Advisory until 8 AM PDT this morning for WAZ202-203-205-
     208.

PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ210.

     Small Craft Advisory until 11 PM PDT this evening for
    PZZ251-271.

     Small Craft Advisory until 11 AM PDT Tuesday for PZZ252-253-272-
     273.
&&

$$

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