National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS66 KPQR 230952
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
252 AM PDT Tue Apr 23 2024

.SYNOPSIS...Transient ridging will keep conditions warm and
dry through Tuesday with mostly sunny skies. A weak cool front
brushes southwest WA and the north OR coast on Wednesday, however
precip chances are low with trace amounts of rain. Transitioning to a
cool and wet weather pattern 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...Tuesday through Wednesday Night...Warm and dry with a
mix of sun and high clouds on Tuesday as a brief period of low-level
offshore flow develops. High clouds will be more prevalent during the
morning hours. Expect today will also be the warmest day over the
next week with widespread high temps in the low to mid 70s, except
lower 60s at the coast. Confidence is high, as the probability for
temps at or above 70 degrees is 70-95% according to the NBM and HREF
(highest chance across the Portland/Vancouver metro).

Low-level flow is set to turn back onshore Tuesday evening. Models
and their ensembles suggest onshore flow will then persist over the
next week. With the transition to onshore flow, a series of Pacific
fronts are expected to move inland and bring widespread rain to
western WA/OR. However, Wednesday is shaping up to be mainly dry as
the first front looks to hold off until Thursday. That being said,
cannot completely rule out a few light showers across southwest WA
and the north OR coast on Wednesday as a very weak/transient upper
level shortwave moves through the area. This is when the
aforementioned areas have a 20-40% chance of showers. Meanwhile, the
rest of the forecast area has under a 5-10% chance. Excess cloud
cover should keep high temps mainly in the 60s, around 5-10 degrees
cooler than Tuesday. Wednesday night looks mild with a light south
wind ahead of an incoming front; this front is set to bring
widespread rain to the area on Thursday. This system is discussed
below in the long term discussion. -TK

.LONG TERM...Thursday through Monday...On Thursday, a secondary more
potent shortwave trough will be approaching the coastal waters.
Meanwhile, a surface low near Vancouver Island will be deepen
slightly with a central pressure falling to around 1008mb. A more
potent cold front will be associated with this system and will
approach northwest Oregon and southwest Washington through
Thursday, eventually coming onshore Thursday evening. Rain chances
peak near 100% Thursday afternoon/evening, which is also when every
single ensemble member from the GEFS/GEPS/EPS show QPF. PoPs remain
above 80% into Friday afternoon with PoPs dropping below 50% across
the interior valleys Friday night into Saturday. Chances for showers
remain in the forecast Saturday night through Monday as additional
weak fronts move inland.

There remains some model spread regarding rainfall totals with this
system, however ensemble guidance continues to trend slightly wetter
each day. The 24 hr probability ending at 5am Friday of 0.25" or
greater across the lowlands has increased to around 80-90% across all
of southwest WA and northwest OR, except around 95% at the coast and
in the mountains. The probability of 0.50" during the same time
period across the interior valleys has also increased slightly to
25-50% and 70-95% across the higher terrain. 48 hr probabilities for
0.50" of rain or more ending at 5am Saturday are 50-80% for the
Willamette Valley. In general, this system looks like it will bring a
good soaking rain to the entire area Thursday through Friday.

Temperatures Thursday through Monday will be on the cooler side due
to cloud cover and occasional precipitation. Expect highs in the
upper 50s to low 60s across the interior valley and low to mid 50s
along the coast. WPC`s cluster analysis from 12z Monday showed good
agreement amongst models and their ensembles regarding the synoptic
scale pattern. All four clusters show some degree of troughing or
zonal flow over the Pacific Northwest Thursday through Monday,
resulting in a prolonged cool and showery weather pattern. -TK

&&

.AVIATION...High pressure will maintain VFR thresholds with dry
conditions across most terminals through the entire TAF period.
Expect scattered/broken high clouds over the region today. Most
winds will be out of the north/northwest, around 5-10 kt in the
Willamette Valley and 8-12 kt along the coast with gusts to 20 kt.
An exception would be KTTD, which will see east winds with gusts
to 20-25 kt. After 00z Wed, a cooling and moistening boundary
layer along the coast may support the development of low marine
stratus. Guidance suggests a 20-40% chance of IFR cigs or lower
along the coast after 00z Wed. After 06-09z Wed, a weakening front
will approach the region and begin returning IFR/MVFR cigs to the
south WA/north OR coast.

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
with scattered/broken high clouds. Winds will generally be under
10 kt, easterly in the morning turning northwesterly in the
afternoon/evening. -Alviz

&&

.MARINE...Observations at buoy 46050 as of 2 AM PDT show northerly
winds gusting to 25-30 kt with seas 8-9 ft at 7 seconds. High
pressure over the waters today will maintain northerly winds with
low-end Small Craft Advisory gusts of 20-25 kt. The bulk of the
gusty winds will be south of Cape Falcon and in the outer waters
beyond 10 NM through most of the morning.

After 10-11 AM, expect pressure gradients to tighten slightly as
a weakening front in the far northeast Pacific moves westward
toward the Pacific Northwest. As a result, expect northerly winds
to strengthen over the inner waters (Cape Shoalwater to Florence,
OR out 10 NM) to around 15-20 kt with gusts to 25 kt this
afternoon. Thus, a Small Craft Advisory will be re-issued for the
northern inner waters and Columbia River Bar after 11 AM. After
5-8 PM, winds will gradually weaken across all of the waters as
pressure gradients loosen, likely ending all Small Craft
Advisories around that time.

Tuesday night into Wednesday, high pressure breaks down over the
waters and winds will begin to turn more westerly. Expect winds
around 5-10 kt across the waters on Wednesday. Seas today and
tomorrow will generally remain between 4-6 ft. The next frontal
system arrives Thursday, which will return gusty southwesterly
winds. Current NBM/LREF guidance shows high confidence (greater
than 80% chance) of Small Craft Advisory winds exceeding 21 kt
across all waters Thursday. -Alviz

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory from 11 AM this morning to 8 PM PDT this
     evening for PZZ210-251.

     Small Craft Advisory until 8 PM PDT this evening for PZZ252-253-
     271>273.
&&

$$

www.weather.gov/portland

Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland