Funnel Cloud in Oregon, May 21, 2019

Area Forecast Discussion
National Weather Service Portland OR
944 AM PDT Tue May 21 2019

.SYNOPSIS...Isolated showers will decrease in the north today.
Afternoon and evening showers and a few thunderstorms will develop
over the Lane County Cascades, central coast range of Oregon and even
over the southern Willamette Valley.  Onshore flow will bring low
clouds in to the Willamette Valley tonight and Wednesday.
Gradual warming is expected Wednesday and Thursday with the main
threat for showers over the Cascades in the afternoons.

&&

.SHORT TERM...Today through Thursday...Upper low off
Newport OR will drift slowly southeast today and tonight. As a result
there are two areas of light precipitation this morning. One is
associated with wrap around deformation to the north of the low over
southwest Washington and extreme northern Oregon. This is producing
very light stratiform precipitation and should weekend some during
the
day. The second area of precipitation this morning is over southwest
Oregon associated with the instability near the upper low. In between
these areas is some cleaning that will allow some sunshine to filter
through this morning. Temperatures will be slightly below normal in
most areas due to the clouds. By this afternoon the models indicate
enough low level warming will occur to produce instability over the
southern half of our forecast area. The Short Range Ensemble
Thunderstorm probabilities get up into the 45% range over much of
Lane county by mid afternoon. Showers should produce amounts of
0.10 to 0.35 inch with small hail possible.  The steering winds are
out of the northeast for a rather unusual storm motion for our area.
Any storms that form should dissipate after sunset.

Upper low will move slowly Southeast Wednesday and the shower threat
should end in most areas. But a few showers will persist over the
Cascades. Schneider

Remainder of previous discussion follows...
There will be little change in the pressure pattern Wednesday night
and Thursday and expect a cloudy start to the day on Thursday
followed by Cascade showers in the afternoon. Daytime temperatures
will gradually warm Wednesday and Thursday. /mh ~TJ

.LONG TERM...Thursday night through Monday...Dry weather is expected
for Friday as the upper ridge asserts itself over the Pacific NW. The
ridge is not very strong though as upper troughs moving over the
ridge will return a threat for showers for the weekend. The models
are showing these troughs to deepen and form an upper low over NW
Oregon by Saturday for cooler conditions and periods of rain for
Saturday and Sunday. Drier weather is possible on Monday, but expect
showers over the Cascades in the afternoon as the upper low moves
inland and increases the chance for diffluent flow aloft.~TJ

&&

.AVIATION...Generally VFR across the forecast area as of 16Z.
Surface low circulation just west of K6S2 at 16Z. Shower activity
this morning focused on the south end of the forecast area,
mainly south of a KONP to KSLE line. Expect VFR to be the primary
category through at least 08Z Wed. Models suggest the potential
for MVFR stratus to settle along the coast between 03Z and 06Z
due to northwest to north low-level flow. MVFR likely to spread
to the inland sites between 10Z and 12Z.

KPDX AND APPROACHES...VFR at the terminal and vicinity as of 16Z,
but there are some patches of SCT010 clouds at the terminal. Not
likely to see this become an IFR cig. VFR to prevail through at
least 10Z Wed. Models hint at MVFR marine stratus developing at
the terminal and east to KTTD around 10Z. Weishaar

&&

.MARINE...Minimal changes to current forecast. Surface low was
located about 75 nm west of Heceta Head at 16Z. East wind 15 kt
or less this morning. The low is expected to move inland near
Cape Blanco around 21Z. The 12Z model runs in good agreement
showing the wind backing to the north as the low tracks
southeast. Small craft advisory level speeds develop mid to late
afternoon. Strongest wind will be beyond 20 nm, with gusts to 30
kt likely this evening through Wed. Small craft advisory
conditions likely to persist over the outer zones through Wed.
Speeds expected to fall just below criteria for the inner zones
Wed. This northerly wind pattern continues through at least Fri,
with small craft advisory conditions to persist over the outer
zones.

Seas have risen to 10 to 12 ft this morning and will be in the 11
to 13 foot range today. Wave heights slowly ease to 10 to 11 ft
by this evening, but will hold at or near 10 ft tonight through
Wed. Weishaar

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for winds from 2 PM this afternoon to 9 AM
     PDT Wednesday for Coastal Waters from Cape Shoalwater WA
     to Florence OR out 60 NM.

     Small Craft Advisory for hazardous seas until 9 AM PDT
     Wednesday for Coastal Waters from Cape Shoalwater WA to
     Florence OR out 60 NM.

     Small Craft Advisory for Rough Columbia River Bar until 9 AM
     PDT this morning.

&&

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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.