995
FXUS66 KPQR 151646 AAA
AFDPQR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
946 AM PDT Sat Jun 15 2024

Aviation Discussion Updated...

.SYNOPSIS...Low pressure brings cool and showery weather with a
chance of thunderstorms today and Sunday. The best chances will
be in the afternoon across northern portions of the forecast
area. Cool and showery conditions last into Monday, then warmer
and drier weather returns Tuesday through the end of next week.

&&

.SHORT TERM...Now through Monday Night...The pattern change is
well underway this morning as an upper level low centered over
Vancouver Island brings about a shift to cooler and wetter
weather which will persist through the next few days. Water
vapor imagery depicts a well defined shortwave embedded within
the larger scale trough swinging across western Oregon and
spurring an increase in shower activity across our area as a
weak surface front approaches the coast. Upper level troughing
will maintain widespread showers across much of the area today
in the post frontal air mass, with coverage generally
decreasing with southward extent and becoming a little spottier
in nature around Eugene by this afternoon. Model QPF amounts
remain on track from previous runs, depicting 0.50-0.75" and
locally higher amounts across the north Oregon and south
Washington Cascades through late this evening, but generally a
quarter inch or less across most other locations. Rain amounts
will be somewhat variable across the area given the hit or miss
nature of the activity, with locally higher amounts possible in
heavier showers.

Abundant cloud cover will help to hold temperatures 7-10
degrees below seasonal norms across the area today, with highs
struggling to reach the mid 60s in most locations. Both NBM and
SREF probabilistic guidance remain rather bullish on
thunderstorm potential as colder air filtering into the region
aloft serves to steepen mid level lapse rates. Have tempered
these expectations somewhat in the forecast as this potential
will be at least in part dependent on getting some breaks of sun
and resulting surface heating to generate sufficient
instability. Additionally, the most favorable jet dynamics and
upper level support are somewhat mistimed as they will be
departing the area by later this morning, and no upstream
lightning strikes have been noted in association with these
features thus far overnight. Despite those caveats, a few
rumbles of thunder are certainly possible across the area
through this evening. While the best chances will generally be
focused along and north of the Columbia River into southwest
Washington, a few strikes will be possible as far south as
Eugene through this afternoon.

The cool and showery weather will persist over the region on
Sunday as upper level troughing remains in place, with highs
across the area similar to today. Shower activity will increase
again in the afternoon as the main upper low shifts southeast
across Washington and Oregon, bringing a renewed chance of
thunderstorms across the north through early evening. The area
will begin to dry out but remain cool on Monday as northwest
flow takes hold behind the trough departing into the Rockies,
with light shower activity mostly confined to the higher
terrain and winding down through Monday night. /CB

.LONG TERM...Tuesday through Friday...Warmer weather looks to
return Tuesday through the end of next week as WPC ensemble
clusters agree on the weakening of the trough over the western
CONUS and subsequent increasing 500 mb heights across the
Pacific Northwest. Guidance suggests temperatures will rebound
back above normal into the upper 70s to low 80s by Tuesday as
this occurs. Wednesday and Thursday then appear to be the
hottest days of the coming week as most deterministic solutions
depict a weak Rex Block developing with a low amplitude ridge
over western Canada and an open trough over northern California.
This results in rather high confidence in NBM temperature
spreads showing highs in the mid to upper 80s for areas away
from the coast both Wednesday and Thursday, with only around a
25 percent chance to reach 90 from Portland to Salem and closer
to a 10 percent chance around Eugene. /CB

&&

.AVIATION...Post-frontal showers will linger until late this
evening, with intermittent rain showers briefly lowering CIGs to
MVFR along the coast until around 19Z Saturday (20% probability).
Inland terminals should remain in low-end VFR conditions
throughout the TAF period, with the exception of current MVFR CIGs
at KSLE/KUAO, but should improve after 18-19Z Saturday.

Isolated thunderstorms possible until 03Z Sunday (10-20%
probability), primarily north of KSLE. Any thunderstorms will have
the potential to produce small hail along with gusty and erratic
winds. Breaks in cloud cover this morning give increased
confidence in the occurrence of isolated thunderstorms this
afternoon, however these post-frontal showers may not remain
robust through the afternoon as they began very early this
morning.

Otherwise, southwesterly winds will slightly strengthen and
gradually turn westerly into late this morning (around 19-20Z).
These westerly winds will remain elevated to 10-15 kt with gusts
up to 20 kt until 00-03Z Sunday. Winds will become light and
variable thereafter, persisting into tonight.

PDX AND APPROACHES...Post-frontal showers will linger until late
this evening, with predominantly VFR conditions through the TAF
period. Possible isolated thunderstorms (20% probability) until
03z Sunday. Breaks in cloud cover have become more frequent this
morning, which will aid in thunderstorm development, however
showers may not remain robust enough into this afternoon due to
the early transition from rain to post-frontal showers this
morning.
-JH

&&

.MARINE...Fairly innocuous conditions for the near future. Seas
remain around 5 to 7 ft at 9 to 11 seconds. Post-frontal weather
currently bringing slightly stronger west winds no stronger than
20 kt through daytime hours Saturday. These decrease again going
into Saturday night. Late Sunday/early Monday strong northwesterly
winds will return and will likely bring marginal Small Craft
Winds to all waters. There is still some uncertainty in the timing
and strength of the Monday system /42/JLiu

&&

.PQR WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

www.weather.gov/portland

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