685
FXUS66 KPQR 280956
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
256 AM PDT Tue May 28 2024

.SYNOPSIS...A weak cold front moves over the region today, with the
postfrontal environment lingering through Wednesday and will bring
cooler temperatures. Precipitation will be light with the highest
accumulations along the terrain. Conditions will become showery late
Thursday through Wednesday. High pressure tries to form on
Thursday-Friday which will bring another round of springtime weather.

&&

.SHORT TERM...Today through Friday night...A long wave trough
extending from a parent low near the panhandle of Alaska will drag a
weak surface front across the region today through Wednesday. This
will maintain onshore flow across the region and result in cooler
temperatures as well as an increasing probability of light
precipitation through today. Therefore, expect daytime high and
overnight low temperatures below normal. This pattern is looking to
be a textbook example of a high PoP/low QPF event with the highest
precipitation totals expected in along the Coast (0.10-0.30 inches),
Coast Range (0.10-0.35 inches) and Cascades (0.10-0.50 inches) with
light accumulations (0.02-0.10 inches). The time frame in question
for this precipitation will be from approximately daybreak through
Wednesday afternoon. Wednesday will see minimal changes in
temperatures as the region transitions into a post frontal environment
with light showers lingering across the CWA. Snow levels will also be
around 4000-5000 ft from Tuesday through Wednesday so some light
snowfall is possible over the volcanoes with very little accumulation
expected.

Thursday, the region will undergo a relatively rapid pattern change
as a ridging pattern develops. Flow will become more northerly during
this time so could see slightly breezier conditions along the beaches
and through the Willamette Valley. Friday the ridge will continue to
strengthen over the Pacific NW as the axis moves eastward.
Temperatures will warm through the latter part of the week and into
the weekend. The most recent run of the NBM is still showing about a
10 to 15 degree spread between the 25-75th percentile. However,
models are starting to trend towards the cooler solutions at this
time. Will continue to monitor as there remains a significant spread
within the models and their families. /42


.LONG TERM...Saturday through Monday...Zonal flow takes
over on Saturday bringing a relatively benign weather pattern to the
forecast area. While the WPC 500 mb clusters show general ridging
over the Pac NW through at least Monday, deterministic models are
showing broad, surface lows moving into the region. If this scenario
manifests, this could result in rainfall to the region, but would not
be high amounts. As Sunday approaches, the pattern is a mess of
ridging, troughs, cold air intrusion, warming from the south and  can
best be described as a "mixed bag" of possibilities. This can further
be seen in some of the probabilities for temperatures, rainfall
totals,etc. In some cases, there is a 15-20 degree spread in the high
temperature forecast. So, with that in mind have leaned into the NBM
for the latter part of the forecast. /42

&&

.AVIATION...A weak cold front moves over the waters, bringing
MVFR conditions along the coast (70-90% probability) and expected to
persist through the TAF period. Chances for IFR conditions along the
coast until 20Z Tuesday remains around 10-30% (KONP currently IFR
CIGs as of 09Z Tuesday). This front may bring MVFR conditions to the
Willamette Valley (30-50% probability) between 14-20Z Tuesday.
Otherwise, expect light rain at the coast before noon and within
interior valleys during the afternoon.

PDX AND APPROACHES...The front will briefly shift NW winds to SW
between 5-10 knots with the passage of a cold front, around
18-20Z Tuesday. This front may also lower conditions to MVFR
(30-50%) around 14-15Z Tuesday and remain lowered until around
20-22Z Tuesday.
-JH

&&

.MARINE...A mostly quiet pattern is expected through at least the
middle of the week. Winds will briefly shift from NW to SW this
morning as the weak cold front passes. Thursday may bring
borderline Small Craft Advisory northerly winds with gusts up to 25
kt to zones PZZ273, PZZ253, PZZ252 and possibly PZZ272. Otherwise,
seas will remain 4-6 feet through this week.
-JH

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

OR...None.
WA...None.
PZ...None.

&&

$$

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