566
FXUS66 KPQR 192128
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
223 PM PDT Sat Apr 19 2025

.SYNOPSIS...An upper level trough will bring near normal to slightly
below normal temperatures through Monday along with chances for rain
showers on Sunday. Then, an upper level ridge will bring dry weather
and warmer temperatures Tuesday through Thursday with plentiful
sunshine. Chances for rain showers return to the area Thursday night
into Friday.

&&

.SHORT TERM...Now through Monday night...The short term forecast is
highlighted by near normal to slightly below normal temperatures and
mainly dry conditions aside from Sunday which features a chance of
rain showers for most locations. Satellite observations from 1-2 PM
Saturday depicted mostly clear skies across much of northwest OR and
southwest WA, aside from an area of broken cloud cover in the Oregon
Cascades and adjacent foothills to the south of a line extending from
Mill City to Detroit to Mt. Jefferson. Broken clouds were also being
observed on the WA coast and north OR coast to the north of Lincoln
City. This trend will continue through tonight, aside from the OR
Cascades where cloud cover should temporarily scatter out this
evening before redeveloping late tonight.

Cloud cover will begin increasing across all of southwest WA and most
of northwest OR late tonight into tomorrow as a weak upper level
shortwave trough moves over the area with increasing mid-level
moisture between 950-800 mb. Forecast soundings for various points
over the Willamette Valley suggest there will be enough moisture to
support rain showers producing measurable rain at the surface. With a
dry stable layer above 700 mb, convection will be shallow. The NAM
suggests equilibrium levels will extend up to only -5 to -10 degrees
Celsius, which means mixed-phased clouds capable of charge
separation will be tough to come by aside from only the strongest
cell updrafts. In other words, do not expect any lightning and/or
hail with the showery activity on Sunday, aside from one or two
isolated cells that may overperform and produce brief small hail
under the size of peas and a flash or two of lightning. NBM thunder
probabilities are under 15% and HREF probabilities are under 10%,
which seems reasonable given the setup described above. Note these
probabilities are not high enough to warrant a mention of
thunderstorms in the forecast, despite the isolated threat. It`s also
worth mentioning very little to no showery activity is expected in
Lane County, aside from the Cascades. Showers will be most frequent
over southwest WA and locations to the north of a line extending from
Newport to Salem.

Conditions dry out Sunday night into Monday under northwest flow.
Areas of cloud cover Sunday night and Monday morning should give way
to decreasing clouds Monday afternoon through Monday night. This will
set the stage for radiational cooling Monday night given the calm
winds and high pressure in place. As such, this night looks to be the
coldest night of the week. The deterministic NBM suggests widespread
lows in the upper 30s, except mid 30s in the southern Willamette
Valley, Cascade foothills and Upper Hood River Valley. These colder
zones will see potential frost, and the Parkdale area could see
sub-freezing temperatures around 30 degrees. Targeted frost
advisories may be warranted with future forecast updates once
confidence increases in the exact low temperature forecast. For now,
probabilities for low temps of 35 degrees or colder (which would be
ideal for frost) range between 5-15% in the Portland/Vancouver metro,
aside from 50% in Battle Ground and 25% in Hillsboro. Probabilities
range between 20-40% over the central Willamette Valley and 40-60%
for the southern Willamette Valley. The Upper Hood River Valley has a
80-90% chance from Odell to Parkdale. -TK

.LONG TERM...Tuesday through Friday night...The long term forecast is
highlighted by warmer and drier weather with plenty of sunshine,
aside from Friday when conditions turn cooler and cloudier with
increasing chances for rain showers. Prior to the potential frontal
system on Friday, models and their ensembles are in good agreement
each day will be warmer than the previous day from Tuesday through
Thursday. This is in response to an upper level ridge that will be
moving over the Pacific Northwest at that time. Model spread for high
temperatures is low, generally 10 degrees or less, suggesting
confidence is high in the temperature forecast. Expect widespread
highs well into the 60s to lower 70s on both Wednesday and Thursday,
except upper 50s to lower 60s at the coast. Cannot rule out highs
upwards of 75 to 80 degrees for the Willamette Valley and
Portland/Vancouver metro (5-15% chance Wednesday and a 10-30% chance
Thursday).

After a few warm and dry days, cloud cover will begin to increase
Thursday night into Friday in response to an incoming Pacific frontal
system. Although there are a few ensemble members from the GEPS/ENS
that are dry on Friday, the vast majority are not. No members are dry
in the GEFS ensemble. The main differences lie with the exact timing
of precip and when it will move into the area. This is why NBM 6-hr
PoPs on Friday only peak between 40-60% while 24-hr PoPs are near
70-80%. In other words, at least some rain in likely on Friday,
however the exact timing is uncertain. The probability for 0.25
inches of rain or more falling between 5am Friday and 5am Saturday
ranges between 25-50%, with the highest probabilities in the
Cascades. -TK

&&

.AVIATION...Northwest flow aloft will continue today as a front
continues to move east of the Cascades. A few areas of MVFR cigs
lingering this morning will lift this afternoon, with
predominately VFR conditions expected through this evening.
Northwest winds along the coast increase this afternoon with
gusts up to 20-25 kt. Another weak front pushes inland later
tonight into Sunday morning, with increasing clouds and chances
for rain showers, mainly north of KSLE. CIGs likely to drop back
into MVFR along the north Oregon coast after 06z Sunday, while
inland locations are more likely to see a mix of VFR and MVFR
conditions after 12Z Sunday, with about a 30-60% chance of MVFR
CIGs, highest near KPDX and KTTD.

PDX AND APPROACHES...Predominately VFR conditions expected
through tonight. Lingering shallow MVFR clouds near KTTD through
20z today. CIGs lower again after 12z Sunday with a chance of rain
showers through Sunday morning. Northwest winds expected around
6-10 kt today. /DH

&&

.MARINE...Strong high pressure offshore will maintain northerly
winds across the coastal waters through the weekend. A weak
surface front is moving across the waters this morning. Northerly
winds with gusts 20-25 kts will peak this morning with gusts up
to 25-30 kt. Additionally, will build to 8 to 10 ft at 10 seconds
this morning, continuing through the evening. Will maintain the
Small Craft Advisory through Saturday evening. Winds decrease
tonight with gusts below 20 kts as do waves to 5 to 8 ft at 10 to
11 seconds.

Another weak front moves across the waters on Sunday night.
Northerly winds increase slightly with occasional gusts 20-25
kts, though not widespread enough to consider a Small Craft
Advisory at this time. Waves will also increase slightly to 8 to
10 feet at 10 seconds Sunday night and early Monday morning. By
late Monday, the thermal trough strengthens over the southern
Oregon coast, increasing the northerly pressure gradients again
for early next week. Northerly winds off the central Oregon coast
could increase to gusts of 20-25 kts. Seas are expected to persist
around 6 to 7 ft at 10-13 seconds. -DH/HEC

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for
     PZZ251>253-271>273.
&&

$$

www.weather.gov/portland

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