478
FXUS66 KPQR 272226
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
326 PM PDT Mon May 27 2024

.SYNOPSIS...Weak cold front moves over the region on Tuesday and
lingers through Wednesday. 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...Now through Friday...A long wave trough extends
southward over the region with persistent onshore flow. A low
level jet is forming with 500 mb winds around 55 kt, and 850
winds closer to 45-50 kt on Tuesday. This jet streak is
collocated with the most enhanced time frame of the front.
Overall, looking at a cooler and wetter pattern. High confidence
in the temperature forecast with below normal highs, and cooler
low temperatures. Cloudy skies though will act like a blanket
and stop the radiational cooling thus overnight temperatures
will be warmer than the previous day. Wednesday will see minimal
changes other than being post frontal with lingering showers.
Snow levels will be right around 4500-5000 ft so some light
snowfall is possible over the volcanoes.

By Thursday, we will begin the quick transition into a ridging
pattern. The trough that brought the cooler temperatures will
move over the northern Rockies and high pressure builds over
the Pacific. Flow will become more northerly during this time so
could see slightly breezier conditions along the beaches and
through the Willamette Valley. Friday will see this high
pressure intensify and the northerly winds increase even more.
The main ridge axis sits well offshore though so will not see
any strong easterly or southerly winds. Temperatures will warm
though. The NBM is showing about a 10 degree spread between the
25-75th percentile - though is trending towards the 25th
percentile in the deterministic forecast. If Thursday ends up
being clearer, then Friday has a strong chance of warming more
than currently forecast. Because of that, have increased
temperatures a bit, especially within the Willamette Valley.
-Muessle

.LONG TERM...Friday Night through Sunday...Zonal flow takes
over on Saturday with neutral onshore winds. Will be a benign
weather day with no notable features. Some of the ensembles are
attempting to bring in a shortwave trough (around 31% of the
members and specifically within the Canadian). This would bring
rainfall to the region, but would not be high amounts. Because
there is background westerly flow that`s zonal, I am trending
towards a slightly wetter pattern that could be a bit more
drizzly. As we near Sunday, the pattern is a mess of ridging,
troughs, cold air intrusion, warming from the south and it feels
like a mixed bag. This overall unrealized scenario persists
through early next week as well. This can further be seen in
some of the probabilities for temperatures, rainfall totals,
etc. In some cases, there is nearly a 20 degree spread in the
high temperature forecast. -Muessle


&&

.AVIATION...High pressure will maintain light NW flow across the
area this evening and overnight. VFR conditions will give way to
MVFR conditions around 6Z along the coast (70-80%) and around
8-9Z across the Willamette Valley (60-90%). There is also a chance
(50-60%) for IFR CIGs along the coast to develop but confidence is
slightly lower. A weak cold front will pass through the area
tomorrow, bringing light rain to the coast before noon and during
the afternoon for the interior valleys.

PDX AND APPROACHES...Light NW winds around 5 knots will become
light and variable overnight. SW winds will pick up to between
5-10 knots tomorrow with the passage of a cold front. VFR cigs
will be maintained into the overnight with an MVFR cloud deck
developing later tonight. -Batz

&&

.MARINE...A mostly quiet pattern is expected through at least the
middle of the week. Surface high pressure will maintain light,
onshore winds less than 10 knots. A quick moving trough will
support a weak cold front that will pass through the area tonight
but won`t bring substantial impacts, just a wind shift from the NW
to the SW tomorrow. Seas will remain 4-6 feet through a least
Friday. A late week system may bring borderline Small Craft
Advisory conditions to portions of the forecast area but
confidence is not high at this time. -Batz

&&

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

$$

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