Funnel Cloud in Oregon, April 21, 2025

Area Forecast Discussion
National Weather Service Portland OR
346 AM PDT Mon Apr 21 2025

.SYNOPSIS...An upper level trough will bring near normal to
slightly below normal temperatures today. Then, an upper level
ridge will bring dry weather, warmer temperatures, and clear
skies Tuesday through Thursday. Chances for rain showers return
to the area Thursday night and into the weekend, bringing a
return to cooler temperatures.

&&

.SHORT TERM...Now through Tuesday Night... A colder night is
expected tonight as clear skies, light winds, and high pressure
create ideal conditions for radiational cooling. Temperatures
are expected to dip into the 33-36 degree range across much of
the interior, particularly in sheltered valleys and outlying
rural areas. This will set the stage for patchy frost formation
late tonight into early Tuesday morning. Highest probabilities
for temperatures at or near freezing (50-90%) are focused on the
central and southern Willamette Valley, the Upper Hood River
Valley, the Cascade foothills, and portions of the Coast Range.

Areas with lower confidence for frost - including the Cowlitz
Valley and other marginal locations, still show a 20-40%
probability of reaching frost thresholds. The coast and much of
the Portland/Vancouver metro are expected to remain above 36
degrees, though some fringes (such as Battle Ground and
Hillsboro) may briefly approach colder temps.

Sensitive outdoor vegetation should be protected tonight with
covers or moved indoors where possible. With relatively high
confidence in frost formation tonight for inland valleys,
excluding Portland and Vancouver, the currently issued Frost
Advisory will remain. Another cold night is possible Tuesday
night, although slightly warmer air may keep low temperatures
2-3 degrees higher, especially in western zones. Any lingering
frost risk Tuesday night will likely be confined to the Upper
Hood River Valley and higher elevations of the southern
Willamette Valley and Cascade foothills.

High temperatures will trend upward through midweek. Expect
highs in the upper 50s to lower 60s today and Tuesday, warming
into the upper 60s and low 70s by Wednesday under dry and
mostly sunny conditions.
~Hall

.LONG TERM...Wednesday through Saturday night...
A warm and dry pattern will persist through midweek, with the
ridge aloft peaking on Wednesday. Most valley locations will
reach the upper 60s to mid 70s, with ensemble guidance showing
only minor spread in high temperatures. By Thursday, the ridge
begins to weaken as a Pacific trough approaches. Model solutions
diverge on timing and intensity, but NBM guidance shows highs
ranging from the low 70s (10th percentile) to the low 80s (90th
percentile) depending on the progression of the frontal system.
As of now, looks like Thursday may be the warmest day of the
week. Above-normal temperatures are expected across the board.

Precipitation chances increase late Thursday into Friday as the
system moves inland. Ensemble guidance from the GEFS, GEPS, and
EPS all suggest measurable rainfall, though the timing remains
variable. Rain could begin as early as Thursday evening in some
solutions, while others delay onset until Friday evening. NBM
probabilities for at least 0.25 inches of rain from 5AM Friday
to 5AM Saturday range between 25-50% for most areas, with the
highest values focused on the Cascades and Coast Range. Cooler
and more unsettled weather is expected to continue into the
weekend.
~Hall

&&

.AVIATION...Expect mainly VFR conditions through the TAF period as
northwest flow persists aloft. Lingering light showers continue
into Monday morning, generally along and north of a line from
Clatsop County to Clackamas County. CIGs generally remain at or
around 3.5-5kft through the period excluding KONP which will hold
onto MVFR CIGs until ~12z Monday. Probabilities for MVFR CIGs
inland are only around 10-30%. However, probabilities for MVFR
ceilings across the area increase if rain showers move overhead.
With some clearing currently developing over the central and
southern Willamette Valley, we'll also have to watch for patchy
sunrise fog development. However, confidence in placement and
timing is low at this time as model guidance only indicates around
a 10% chance of fog. Winds remain generally less than 10 kts,
although gusts around 20 knots appear likely at KONP Monday
afternoon.

PDX AND APPROACHES...Expecting generally low end VFR CIGs through
the overnight hours with occasional MVFR CIGs in showers. Expect
CIGs around 2.5-4kft gradually raising above 4-5kft by later
Monday afternoon. A few showers are possible through 20z Monday,
which could bring CIGs below 3kft. Winds stay fairly light from
the west to northwest, generally less than 10 knots. -Schuldt/HEC

&&

.MARINE...Strong high pressure offshore along with a surface
level thermal trough developing and strengthening over the
southern and central Oregon coast will maintain northerly winds
across all waters through the middle of the week. Central Oregon
coastal waters will see increasing winds this evening into Tuesday
morning with gusts of 20-25 kts at times. A Small Craft Advisory
remains in effect for zone PZZ273. As the thermal trough
strengthens over the coast, these winds are expected to spread
north along the northern Oregon and southern Washington coastal
waters late Tuesday into Wednesday night, with gusts up to 30 kts
possible at times. Strongest winds are expected to ebb and flow
diurnally, strongest in the late afternoon to overnight hours,
backing off in the morning hours. Seas are expected to persist
around 6 to 8 ft around 10 seconds through the middle of the
week. -HEC

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...Frost Advisory from midnight tonight to 9 AM PDT Tuesday for
     ORZ104>109-113>119-121-123>125.

WA...Frost Advisory from midnight tonight to 9 AM PDT Tuesday for
     WAZ203>205-208.

PZ...Small Craft Advisory from 5 PM this afternoon to 2 AM PDT
     Tuesday for PZZ273.
&&

www.weather.gov/portland

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