675
FXUS66 KPQR 280313 AAA
AFDPQR

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

...EVENING UPDATE, for aviation weather...

.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...Front offshore will slowly approach, with increasing mid
and high clouds rest of tonight. Will likely see CIGS lower to mix
of VFR and MVFR along the coast by 10Z, with occasional light rain
or drizzle. Conditions along the coast will persist through Tue am,
Front will push onshore towards early afternoon, with slow
improvement to lower VFR in the afternoon.

Farther inland, increasing mid/high clouds tonight with increasing
onshore flow as well. Will see 3000 to 3500 ft CIGS developing after
10Z to 12Z, mainly as clouds form against the Cascades foothills and
backbuild. Mix of upper MVFR and lower VFR will continue through at
least mid afternoon, with areas of light rain increasing between 16Z
and 19Z, mainly to north of Salem.

.PDX AND APPROACHES...VFR through 10Z or 11Z, but will see MVFR deck
around 3000 ft spreading across OPs area afterwards. Then, will have
persistent MVFR through early afternoon, with light rain after 17Z.
Not much change for afternoon, with light rain and MVFR.
&&

.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.
&&

$$

www.weather.gov/portland

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