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000
FXUS66 KPQR 260443
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
943 PM PDT Thu Apr 25 2024

.SYNOPSIS...Showery and unsettled conditions continue through
the weekend into next week as the Pacific Northwest remains
under the influence of a rather progressive spring-time weather
pattern. Beyond the more persistent chances for rainfall going
forward snow levels are expected to drop near pass level(4500ft)
tonight into Friday although outside of slushy pavement accumulation
most appreciable impacts stay above 5,500ft. The weather trends
even a touch cooler early next week.


.SHORT TERM...Tonight through Saturday night...This afternoon
satellite and radar indicate the bulk of the steadier
precipitation has begun to decrease and break to showers as the
frontal boundary moves inland ad we quickly transition to post-
frontal shower activity. With cooler air now filtering in aloft,
snow levels will gradually decrease tonight bottoming out near
4,300-4,500ft come sunrise Friday morning. As a result wet snow
likely returns to the higher pass areas like Santiam and
Willamette, though that’s not to say snow or a rain/snow mix
can’t mix down to the highest reaches of US-26 due to the more
convective nature of the precipitation. Still, even at Santiam
and Willamette pass the warm antecedent conditions will help to
limit pavement accumulation with the bulk of the impacts
occurring above 5,300-5,500ft. Due to the late season nature of
the snowfall will maintain the current Winter Weather Advisory
for the Cascades through Friday evening. It’s worth mentioning
as far as general precipitation chances are concerned through
Friday, models maintain the most frequent showers over the coast
range, Willapa Hills, and Cascades/Cascade foothills although
the passage of the broader trough axis through western WA/OR
Friday midday and afternoon likely servers to increase shower
activity region-wide; even across the Willamette Valley and SW
Washington.

Late Friday into Saturday the upper-level trough deepens and
quickly progress southeastward into the four corners region of
the Great Basin. We’ll briefly see upper-level heights rise over
the region due to the passage of a weak transient shortwave
ridge and both deterministic/ensemble guidance seem confident in
a lull or at least noticeable decrease in lingering showers over
the lower elevations, especially the central and southern
Willamette Valley. However, the arrival of fast moving upper-
level shortwave and frontal boundary extending southward off a
parent low parked over the gulf of Alaska increases chances for
precipitation Saturday afternoon into the evening. At least
precipitation amounts don’t look particularly noteworthy due to
the quick progression of the aforementioned feature on Saturday
with an additional ~0.1” for the inland valleys and 0.3-0.5” for
the coast range/Cascades. Once the front passes showers chances
generally revert back to the elevated terrain features around
western WA/OR the second half of the night. Snow levels Friday
night through Saturday night continue to fluctuate between
4500-5500ft.  -Schuldt

.LONG TERM...Sunday through Wednesday night...For the early to
middle portion of next week confidence is high the pattern stays
rather progressive, with fronts moving off the northeast Pacific
into the Pacific NW. During the late Sunday into Monday time period
yet another front will push across the region with post-frontal
showers on tap by at least the second half of Monday - model
uncertainty is higher regarding the exact timing of this
disturbance. Still a bit cooler than that expected for late
April, with overall temperatures in the lowlands in the 50s to
lower 60s. Snow levels will run 3000 to 4000 ft, which will
maintain some snow at times for the higher terrain of the
foothills, as well as most of the Cascades.

Few showers linger around region on Tuesday, but think most of
the day will end up being mostly dry for the inland valleys, as
a weak transient ridge glides over the region. But, models show
another potent front offshore later Tue night/early Wed, with
that front pushing inland late Wed into Wed night. With this,
does look to be more rainy that showery by Thursday. After
that, models still in quite a bit of flux with low forecast
confidence due to large discrepancies in the longwave pattern
over the eastern Pacific and CONUS. -Schuldt/Rockey

&&

.AVIATION...Showers continue through Friday as an upper level
trough slides west to east across the region. This will result in
mountain obscuration, while inland valley locations will see a mix
of VFR and MVFR. Some rainshadowing occurring east of the coast
range helping to bring areas of VFR in the valley as of 05Z Fri.
However, guidance indicating about 50-90 percent chance for cigs
2000-3000 ft through 00Z Sat, and a 30-50 percent chance for cigs
1000-2000 ft 09Z Fri to 21Z Fri. South winds will continue in the
8 to 12 kt range through Fri with gusts 15 to 20 kt returning
after 20Z Fri.

Notes: The ASOS at KTTD is only available via the dial in option.
The AWOS at KMMV is still out of commission. There is no
estimated time of repair.

PDX AND APPROACHES...A mix of VFR and MVFR with passing showers
through the TAF period. If there are any trends to the forecast,
HREF guidance indicating maybe more persistent MVFR cigs after 15Z
Fri with a 60- 70 percent chance for cigs 2000-3000 ft, then
deceasing to 30-50 percent chance after 21Z Fri.
/mh

&&

.MARINE...The warm front has passed, though post-frontal
conditions allow the Small Craft Advisory to continue, with gusts
up to 30 kt possible, decreasing after midnight tonight. Seas
are choppy, currently sitting around 7-10 ft at 9 seconds.

Winds turn more westerly/northwesterly Thursday night into Friday
as the low pressure system pushes inland. Winds begin to ease
slightly with gusts to 20-25 kt. However, a westerly swell will
enter the waters and build seas to around 9-11 ft. These elevated
seas are brief, as the swell height falls Friday night to
Saturday. The next frontal system arrives on Saturday, will return
gusty southwesterly winds. The latest NBM has decreased
confidence in gales, only around 10% on Saturday.

-Alviz/JLiu

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Winter Weather Advisory until midnight PDT Friday night for
     ORZ127-128.

WA...None.
PZ...Small Craft Advisory until 2 AM PDT Saturday for PZZ210-251>253-
     271>273.

&&

$$

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