Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 201339
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
639 AM PDT Sat Apr 20 2019

Updated Marine Section

.SYNOPSIS...Rain gradually tapering off for most of the district this
morning, but some showers will probably continue for the mountain
into this evening. High pressure will bring clearing skies and
seasonable temperatures this weekend. Another weak system may clip
our northern zones with some rain Monday and Tuesday, while the
southern half of the forecast area remains mostly dry and mild.

&&

.SHORT TERM...Today through Monday...Light precipitation continues
this morning mainly east of a Portland to Newport line. There are a
few showers over the coast range to the west.  Models have been and
continue to be too fast moving this system east of the forecast area.
The area of pcpn will gradually shift east by this afternoon.
However some of the hires models show showers popping up over the
mountains, primarily over the Cascades in the afternoon. Lowlands
locations should see a decent amount of sunshine this afternoon and
early evening.Marine clouds should push in from the coast late
tonight and Sunday morning as a weak marine push develops.  The
clouds will mostly clear for the interior with some sunshine at
coastal locations Sunday afternoon. High temps for the lowlands
Sunday should mostly be in the 60s inland and 50s along the
coast...pretty close to normal for the time of year.

Zonal Pacific jet aimed toward British Columbia Sunday will try to
sag a bit southward Monday, spreading rain into WA and possibly far
enough south to clip our northern zones with some rain or drizzle by
Monday evening. Less persistent cloud cover is expected south of the
PDX metro, with temps possibly reaching the lower 70s Salem southward
Monday afternoon.  /mh Weagle

.LONG TERM...Monday night through Friday...Weak shortwave ridging
begins to flatten out into a more zonal upper-level flow pattern
Monday night as a weak impulse moves into Western Washington.
This may result in some light rain along out northern zones
(mostly north of a Tillamook to Kelso Line), but otherwise the
predominant impact will be a little bit of cooling and increased
cloud cover. However, stronger onshore flow will perhaps lead to
showers later on Tuesday across a larger portion of the area.
With a reasonable spread in ensemble solutions, elected to
maintain at least a slight chance mention of showers for most of
the area, though the coast and mountains will stand the best
chance of measurable precipitation. Models begin to diverge a bit
more for the late stages of next week, but nevertheless remain
consistent in the suggestion for a mostly dry weak despite at
least some onshore flow. Temperatures were trended a few degrees
cooler Wednesday through Friday, holding close to seasonal
normals.   Cullen


&&

.AVIATION...Onshore low-level flow over the area early this
morning behind a departing cold front. Conditions as of 09Z a mix
of MVFR and VFR, but some isolated IFR along the coast. High-
resolution model guidance suggests considerable MVFR for the
coast and interior valleys through the morning, with cigs
012-022. Improvement to VFR at interior TAF sites 18Z to 20Z.
KAST and KONP may be in and out of MVFR this afternoon with
continued low-level NW flow. Expect predominant MVFR for the
coast by 03Z Sun and then spreading inland through the major
river drainages and eventually reaching the Willamette Valley
overnight. Model soundings for KPDX, KSLE and other north valley
TAF sites indicate cigs 020-025 with tops to around 035 Sun
morning. Cigs likely a little lower at KEUG.

KPDX AND APPROACHES...Conditions at 09Z at high-end MVFR and
would expect MVFR to be the predominant category through 18Z.
Cigs may lower into the 012-020 range late tonight. Improvement
to VFR after 18Z. Models suggest MVFR likely to return between
09Z and 12Z Sun. Weishaar

&&

.MARINE...Updated: Spectral analysis and 13Z buoy observations
clearly show 7 to 9 second period as the dominant wave set. There
is also a 10 to 11 second wave group, but its energy is less.
Thus, issued a small craft advisory for hazardous seas through
01Z Sun. Guidance shows wave heights slowly subsiding this
evening, which should be enough to avoid square sea conditions.

Remainder of the discussion follows: The 08Z observations showed
wind gusts at or slightly below small craft advisory thresholds.
The 06Z NAM and GFS look to be a little strong with the 3-hr
boundary layer wind forecast as both models indicate widespread
25 kt. The overall trend through Sat is for gradually decreasing
wind, easing to 15 kt or less by 06Z Sun. Opted to remove PZZ255
from the small craft advisory and shortened the advisory for the
outer waters to 04Z Sun.

Fairly quiet wind conditions for the waters Sat night through
Sun night. Next frontal system reaches the NW waters late Sun
night or Mon morning with 20-25 kt possible for the north half of
PZZ270 Mon. Models in good agreement showing a more typical
summer-time pattern of NW-N wind beginning Wed and continuing
through the extended period. Gusts 25-30 kt likely during this
time.

Longer period swell will continue subsiding over the next 24
hours with combined seas becoming more wind wave driven. However
still do not expect there will be enough to justify a SCA for
seas based on combined seas alone. Seas to remain below 10 ft
through early next week. By mid to late next week, a uniwave
pattern could develop with a dominant fresh swell and a small
(2-4 ft) background west swell. This could result in square sea
conditions. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds until 9 PM PDT this evening for
     Waters from Cape Shoalwater WA to Florence OR from 10 to
     60 NM.

     Small Craft Advisory for hazardous seas until 6 PM PDT this
     evening for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 60 NM.

&&


$$

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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. This area is
commonly referred to as the forecast area.


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