Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 161633 AAA

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
933 AM PDT Sun Jun 16 2024

Aviation Discussion Updated...

.SYNOPSIS...Low pressure maintains cool and showery conditions
today, with a chance of thunderstorms across much of the area
this afternoon and evening. A few showers linger into Monday then
much warmer and drier weather returns Tuesday through the end
of next week.


.SHORT TERM...Now through Monday Night...An elongated upper
level trough has shifted southward from British Columbia to
Washington and remains the dominant feature over the Pacific
Northwest this morning. Latest satellite imagery shows broken
cloud cover lingering across northwest Oregon and southwest
Washington, with a lull in shower activity as radar echos are
mainly confined to northern coastal areas and parts of the
Cascades as of 2 AM Sunday. Expect a similar day to Saturday as
unseasonably cold air aloft yields another day of highs topping
out in the mid 60s. Shower activity will increase in coverage
with daytime heating as the trough axis shifts southeast across
the area, with steep mid level lapse rates and modest
instability again contributing to a chance of thunderstorms. The
best thunderstorm potential will reside from roughly Salem
north through early evening, but can`t rule out a few lightning
strikes with southward extent towards Eugene as well. Shower
activity will trend downward through Monday with temperatures
remaining in the 60s as northwest flow takes hold in the wake of
the departing trough. Showers will remain light and mostly be
confined to the higher terrain through Monday afternoon, then
wind down through Monday night and set the stage for the next
stretch of warmer and drier weather beginning Tuesday. /CB

.LONG TERM...Tuesday through Saturday...More summerlike weather
returns to the region on Tuesday as WPC ensemble clusters
continue to show broad agreement on the weakening of the trough
over the western CONUS and subsequent increasing 500 mb heights
across the Pacific Northwest. This will send temps back above
seasonal norms as highs climb into the mid to upper 70s across
the interior lowlands on Tuesday afternoon. Wednesday through
Friday looks to be the hottest stretch for the coming week as
most ensemble and deterministic solutions continue to depict a
weak Rex Block characterized by a low amplitude ridge over
western Canada and an open trough over northern California.
Ensemble temperature spreads have nudged slightly upward for the
latter half of the week, with probabilistic guidance now
peaking with around a 50 percent chance to reach 90 degrees in
the Portland area on Thursday and a 25-35 percent chance both
Wednesday and Friday. Notably, the probability to reach 95
degrees on any of these days is less than 10 percent from
Portland to Salem and closer to one percent in other locations,
serving to underscore the relatively high confidence in the
range of temperature outcomes for the coming week. The bulk of
the guidance then suggests that temperatures will begin to
trend back down next weekend with the approach of another
trough. /CB


.AVIATION...Rain showers will return between 18Z Sunday and 06Z
Monday as the low moves southeast into our region. Most of the
airspace will be VFR between these times, with the only concern of
possible MVFR CIGs in KAST (10-20% probability). Additionally,
scattered thunderstorms throughout the region remain a
possibility (20-30%) today, until 03Z Monday. With ongoing
clearing this morning expected to improve warming in the
afternoon, instability should increase enough to maintain
thunderstorm development through the afternoon. Could see some
hail and brief gusty winds with these thunderstorms.

After the showers dissipate around 05-06Z Monday, northwesterly
to westerly winds will weaken to below 10 kt and potential for
MVFR CIGs will increase. Most terminals will have a 10-20% chance
of MVFR CIGs from 06-18Z Monday, with probabilities as high as
40-50% for coastal terminals, primarily north of KTMK.

PDX AND APPROACHES...Showers between 18Z Sunday and 03-06Z
Monday, with predominantly VFR conditions through the TAF period.
A 20-30% chance of scattered thunderstorms is possible until 03Z
Monday, with potential to see hail and brief gusty winds. After
06Z Monday, northwesterly winds will weaken and chances of MVFR
CIGs will increase to 10-20% until 18Z Monday.


.MARINE...Seas around 5 to 7 ft at 9 to 11 seconds for the near
future. Winds are currently negligible, but will increase
following the weak frontal passage up to just under Small Craft
Advisory level Sunday evening. A stray gust of two above SCA
criteria may be possible Sunday night, but by and large the
majority of waters will remain under, with only a 10% chance of
SCA level winds. Next chance at more impactful conditions will be
Tuesday night, though uncertainty is still relatively high.
Marginal SCA winds look possible from Tuesday evening onwards,
with breezier marginal winds possible until at least the weekend.






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