747
FXUS66 KPQR 151029
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
329 AM PDT Sat Jun 15 2024

.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...A front is currently in the process of pushing through
the area, allowing for intermittent rain showers and the
possibility of brief lowering of ceilings to MVFR, mostly at the
coast. Inland terminals should mostly see low-end VFR conditions
once the front fully pushes in by 14-15z Sat; chance of MVFR or
lower ceilings is around 15-25% for all inland terminals.

While the front is pushing in, all terminals could see a low
chance of an isolated thunderstorm or two, though chances are even
lower south of KCVO. Chances will generally be 10-20% of a
thunderstorm at most terminals north of there, with threat ending
around 3z Sun. Any thunderstorms will have the potential to produce
small hail along with gusty and erratic winds.

Weak southwesterly winds will gradually turn westerly and
slightly strengthen throughout daytime hours Saturday, but gusts
should top out around 15-20 kts. Winds will become light and
variable over Saturday night again.

PDX AND APPROACHES...Scattered cloud decks will turn to low-end
broken clouds once the front fully pushes in around 13-14z Sat.
The chance of ceilings dropping to MVFR or lower is around 15-30%,
and the majority of the TAF period should remain VFR. The front
fully moves through the area by 20z Sat, and VFR conditions will
remain locked in place afterwards. There will be a low chance of
thunderstorms from 12z Sat to 3z Sun, with highest chances
Saturday afternoon; chance of a weak isolated thunderstorm is
around 25%. /Jliu

&&

.MARINE...Fairly innocuous conditions for the near future. Seas
remain around 5 to 7 ft at 9 to 11 seconds. A front is currently
passing through, allowing for 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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