164
FXUS66 KPQR 281813
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
1112 AM PDT Tue May 28 2024


.SYNOPSIS...After some light rain today and a few showers on
Wednesday, drier weather returns Thursday and Friday. A wetter
weather pattern returns over the weekend into early next week.


&&


.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 will push into southwest Washington
and northwest Oregon over the next couple of hours. As it does so,
light rain and low clouds will keep probabilities of MVFR
conditions remaining near or above 50% at any given hour through
~22z Tuesday for most TAF sites across northwest Oregon.
Thereafter, daytime heating coupled with low level moisture will
create a more showery weather pattern, which should result in most
locations turning predominantly VFR. Statistical guidance does
suggest a 15% chance for a short lived thunderstorm for KPDX and
KTTD between 22z Tuesday and 02z Wednesday, but high resolution
statistical model output has probabilities less than 10% during
that same time. Given the pattern and high probability of false
alarming will continue to keep a mention of thunder out of the
official TAF for these sites for now. Nonetheless, any intense
shower or thunderstorm would almost certainly bring a brief dip
into MVFR thresholds as well. High resolution model guidance does
suggest probabilities for MVFR conditions climbs briefly around
17z Wednesday as daytime heating and low level moisture produce an
increased likelihood of some MVFR ceilings.

PDX AND APPROACHES...Expect a mixture of MVFR and VFR conditions
through ~22z Tuesday as a weak front and light rain traverse the
region. Conditions should trend to predominantly VFR thereafter.
There is a ~10-15% chance for a brief thunderstorm to impact the
terminal between 22z Tuesday and 02z Wednesday. Nonetheless, any
intense shower or thunderstorm would almost certainly bring a
brief dip into MVFR thresholds as well. /Neuman


&&


.MARINE...A weak front is currently crossing the waters today, but
few impacts are anticipated. Weak high pressure will build across
the northeast Pacific Wednesday into Thursday and lead to
increasing northerly winds across the waters. The strongest winds
will be off the central coast of Oregon. For example, there is a
>90% chance for wind gusts in excess of 20 kt across those waters
by Thursday afternoon and evening. Most model guidance suggests
winds will back off a bit for Friday, but there is still a high
probability (>75% chance) wind gusts will climb above 20 kt
across the waters off the central coast of Oregon.

There is increasing agreement a more organized and stronger storm
system will move into the northeast Pacific over the weekend.
This will bring a high probability (>80% chance) for winds to turn
southerly and wind gusts to at least climb into Small Craft
Advisory thresholds of 25-30 kt. In addition, there is a 30-40%
chance for at least a brief period of unusually late season Gale
Force southerly wind gusts of 35 kt developing sometime Sunday
into Monday across the waters. Probabilities of this happening are
highest off the far north Oregon and south Washington coasts than
areas farther south towards Lane County. /Neuman


&&


.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&


$$

www.weather.gov/portland

Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland