848
FXUS66 KPQR 022148
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
248 PM PDT Wed Apr 2 2025

.SYNOPSIS...Showers persist today dissipating overnight as high
pressure builds. Clear days and mostly clear evenings will set
the stage for fog/frost development tonight and Thur night/Fri
morning. Increasing temperatures on Saturday will be above
normal. Frontal system arrives Sunday through early next week.

&&

.SHORT TERM...Now through Friday Night...Satellite shows patchy
skies associated with post frontal showers. These showers have
brought periods of heavy rain and small hail to the region. A
dry slot will be moving inland later this evening which will
cause skies to clear or become partically clear. The clear skies
combined with colder air will promote fog development
throughout the Willamette Valley, and coastal valleys
especially. There are some limiting factors though, the first of
which being cloud cover. If the clouds are too dense,
radiational cooling will not be enough to reach the dewpoint.
However, the amount of available moisture from the previous
day`s showers will provide the moisture needed fo saturation.

High pressure persists through Saturday with clearer skies each
day. The next weather factor to consider occurs Thursday night
into Friday morning. Overnight temperatures will dip into the
30s. This, combined with light winds and drier conditions, can
produce frost through the area. This would be the first frost of
the growing season so it is something we are watching closely.
In order to get frost we need a few ingredients: calm winds,
temperatures between 33-38 deg F, a drier atmosphere initially,
then temperatures reaching the dewpoint temperature (the
temperature an airmass has to cool to inorder to become
saturated). Light easterly winds during the day will create the
decreased moisture and cooler air filtering in; winds are
expected to then go calm. Probabilitistcally there are a few
concerns. First: temperatures are sitting on the upper threshold
for frost formation closer to 37-40 deg F overnight. While the
10th percentile would be cold enough, any fluctuation to warmer
would not. In addition, the spread between the dew point
depression is around 3 degrees which may be just large enough to
prevent frost. Ultimately, it`s not a bad idea if you`re below
1500 ft in the valleys (coastal, inland, Cowlitz, and Gorge) to
prepare for patchy to widespread frost. Areas most at risk will
be rural areas and the southern Willamette Valley.

Once the sun rises, any frost that did form will melt off and
conditions will warm to a spring-like day. -Muessle


.LONG TERM...Saturday through Wednesday...Saturday will be
anyother springy day giving us a break before the next rain
arrives on Sunday. High pressure will usher in warmer air from
the south aloft, which will mix down causing highs to increase
into the upper 60s to lower 70s. Along the coast, will remain
seasonable, but sunnier than we have seen the last week. Inland
areas will be warmer than normal. Models still have some
discontinuity with the overall high temperature forecast. For
example, the NBM ranges from 70 deg F to nearly 76 deg F (the
90th percentile). The deterministic forecast though sat right
along the 25th percentile and in some areas even below this
value. Decided to incorporate and nudge to the 50th percentile
in the forecast in the Willamette Valley, Clark County, and the
lowlands of Cowlitz county. If easterly winds are elevated,
these tempeatures may be less if close to the Cascades or the
Gorge.

Enjoy the sun as a frontal system will move in Sunday night with
a series of shortwaves through Wednesday. Overall troughing is
not necessarily well realized by models at this point, and
precipitation amounts will be low in comparison to what we
typically see this time of year. The coast though will be the
exception as the ECMWF is depicting anywhere from a quarter of
an inch in 24 hours, to some of the ensembles of greater than
1.25 inches. The GFS is less wet with much lower amounts (closer
to 0.25 inch). -Muessle


&&

.AVIATION...Radar, satellite and surface observations continue to
show mostly generally VFR conditions with scattered showers
moving into the airspace from the northwest. These showers will
persist throughout the day and will result in predominately VFR
conditions with FL030 to FL050. Showers could result in brief
periods of MVFR conditions (15%-30% probability) through 00Z-03Z
Thursday. For inland locations there is also a 20% probability for
thunderstorms through 03Z Thursday as well. Any thunderstorm that
does develop could produce small hail as well as gusty and
erratic winds.

Afterwards, conditions will gradually dry up and result
in widespread VFR. However, as we clear out, there will be a 20%
probability of fog development within the Willamette Valley
starting around 13Z Thursday. Expect westerly to northwesterly
winds across all terminals around up to 10 kt.

KAST anemometer is still inoperative. Therefore, TAFs limited to
CIG and VIS.

PDX AND APPROACHES...Predominately VFR conditions with scattered
showers through 03Z Thursday. Any showers could result in brief
periods of MVFR conditions (15%-30% probability) through 03Z
Thursday. Afterwards, widespread VFR. Westerly winds become more
northwesterly, generally less than 10 kt. -42

&&

.MARINE...High pressure over the northeast Pacific and lower
pressure inland will maintain northerly to northwesterly winds
under 15 kt through the end of the week. The next front arrives
Saturday evening into Sunday and that will bring a return to
breezy southerly winds across all waters. As the front approaches,
there is a 15-30% probability for Gale-force southerly wind gusts
up to 40 kt on Sunday. Seas generally 3 to 6 ft through Sunday.
As the front approaches the waters, seas will build towards 10 to
12 ft as a fresh westerly swell pushes into the waters.

Another strong ebb is expected Thursday morning; however, seas
with this ebb are forecast around 4 to 5 ft. -42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...None.
&&

$$

www.weather.gov/portland

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