Strong Wind in Oregon, May 22, 2021

Area Forecast Discussion
National Weather Service Portland OR
210 PM PDT Sat May 22 2021

.SYNOPSIS...Scattered showers will continue today into tonight
mainly over the Cascades as an upper level low pressure pulls away
to the east. A weak warm front approaches the coast this evening,
the moves inland Sunday bringing chances for light rain. A weak cold
front moves in late Sunday night and Monday bringing more chances
for rain, followed by showers lasting into Tuesday.

&&

.SHORT TERM...Tonight through Tuesday...Satellite imagery continues
to show a complex upper low over the Great Basin. Models
generally split the low into two primary centers, with the southern
low slowly moving east through tonight, while the northern
lobe rotates counter clockwise brushing the Cascades before kicking
out to the east on Sunday. This will keep a chance for showers over
the Cascades through this evening. At the same time a shortwave upper
ridge is pushing in from the west tonight and Sunday. Models all
generally suggest a weak warm front pushes onto the coast tonight and
early Sunday, which will bring a chance of light rain along the
coast. A chance for precipitation lingers into Sunday afternoon and
evening as the front slowly moves across the CWA.

The overall pattern becomes more progressive by early next week, as
the shortwave upper ridge moves east and another trough arrives late
Monday.  A cold front accompanying the upper trough late Sunday night
and Monday adds stronger lift, so will keep pops relatively high as
the front moves through Monday, with showers following late in the
day. Model guidance shows increasing instability enough to support a
slight chance for thunder over the Lane and Linn County Cascades as
the post frontal showers as the upper low swings across. /42

.LONG TERM...Tuesday night through Saturday...Models show the Monday
upper trough continuing to move slowly east into Tuesday, with
chances for showers decreasing. Models in good agreement indicating
a transient ridge moving across Tuesday night and Wednesday for a
break from rain chances, but a deepening trough offshore potentially
returns some chance for rain Wednesday and Thursday as models
suggest a cold front sagging southeast into the region. Operational
model runs still in good agreement into Friday, bringing another
shortwave trough through for more chances of showers into the start
of the Memorial Day weekend. /42

&&

.AVIATION...Preliminary Analysis for 00Z TAFS: Early this
afternoon visible satellite imagery showed diminishing low cloud
cover along the coast and in the interior lowlands. As of 21Z
local MVFR was noted from KPDX north into Clark County and in
the Cascade foothills. Isolated MVFR could be seen along the
coast between KONP and K6S2. The 12Z high resolution ensemble mean
low cloud guidance suggests VFR conditions along the coast to
prevail into early evening. MVFR looks to return to the coastal
areas between 00Z and 03Z Sun, with areas of IFR likely by 06Z.
Widespread IFR develops between 06Z and 12Z Sun with areas of
drizzle or light rain. Conditions improve to MVFR in the mid to
late morning hours. Expect MVFR cigs to fill the southwest
Washington interior lowlands by 09Z Sun and then push down the
Columbia River to KPDX and the west end of the Gorge between 09Z
and 12Z Sun, with widespread MVFR developing between 12Z and 15Z
Sun. There is the potential for local IFR in the southwest
Washington lowlands generally west of Interstate 5 late tonight
through Sun morning. MVFR cigs may persist well into the
afternoon for interior lowlands north of KSLE.

For detailed regional Pac NW aviation weather information, go
online to: https://weather.gov/zse

KPDX AND APPROACHES...VFR at the terminal and to the west as of
21Z. Scattered cigs 025-030 persist between KPDX and KTTD, but
will dissipate through the afternoon. Increasing mid- level clouds
this evening. MVFR cigs return to the terminal between 09Z and
12Z Sun and is expected to persist into early afternoon. Cannot
rule out periods of drizzle Sun morning. Weishaar

&&

.MARINE...Fairly benign marine conditions for the next few days.
Wind speeds generally 10 kt or less through Sun. Models in good
agreement showing the wind backing to S to SW Sun evening ahead
of the next frontal system. The 12Z NAM and GFS show a narrow
band of 20-25 kt boundary layer wind speeds 12Z-15Z Mon. Believe
these speeds may be a little high and have limited gusts to 22
kt. Not expecting small craft advisory wind with this system, but
would not be surprised if there were a few gusts to 25 kt.

Wind speeds decrease Mon afternoon. Models agree that a surface
trough will reside over the waters Mon night into Tue morning.
High pressure returns to the waters by 18Z Tue and holds through
Wed. Another frontal system is forecast to move through the
waters Thu. The ECMWF appears to be weaker with this system
compared to the GFS.

Wave heights generally 4-6 ft for the next few days. Guidance
maintains wave heights well below 10 ft through late next week.
Weishaar

&&

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

&&

Interact with us via social media:
www.facebook.com/NWSPortland
www.twitter.com/NWSPortland