Area Forecast Discussion
Issued by NWS Portland, OR

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS66 KPQR 172058

Area Forecast Discussion
National Weather Service Portland OR
158 PM PDT Sat Mar 17 2018

.SYNOPSIS..The flow is turning more onshore this afternoon as showers
continue at times the remainder of today and Sunday. A secondary low
has developed near Vancouver Island and will slowly move south to off
the Washington and north Oregon coasts tonight and Sunday. The low
weakens and shears out Monday for decreasing showers as a piece moves
westward offshore and another moves east of the forecast area. Snow
levels will be below the Cascade passes through the weekend, with
some occasional light accumulations expected. Low wet bulb zero
heights will lead to possible small hail at times as well. After a
bit of a break in the weather early next week, more precipitation is
expected by the middle of next week. Snow levels are expected to
lower late next week and likely to include at least Cascade foothills
and the coastal mountains late next week.

.SHORT TERM...Tonight through Tuesday...The low level flow is turning
more northwesterly and onshore this afternoon due to a low near
Vancouver Island and the the slow departure of the low from Friday
that is now in southeast Oregon. Showers are spreading in from the
northwest this afternoon, most pronounced over the higher terrain.
These showers will continue to be fed by daytime heating this
afternoon, and will likely move across the valleys at times. The
showers this afternoon are showing a bit more intensity than they
have at this time the past few days. Model soundings were a little
more unstable for this afternoon than for past afternoons as well. We
have seen lightning near Independence and Brooks, so we will include
some thunder for this afternoon and evening.

The low near Vancouver Island will move south tonight and Sunday and
set up along the Washington and north Oregon coasts, maintaining the
threat of showers in west or southwesterly onshore flow. The showers
will have a diurnal component to them, peaking in the afternoons and
evenings. Snow levels will continue in the 2000 to 3000 foot range in
the Cascades, with modest accumulations here and there due to the
showery nature of the precipitation. Wet bulb zero heights will
continue to be low, which will be conducive to producing small hail.

The low that will be near the coast Sunday will stretch or shear
apart on Monday, with a piece drifting westward farther offshore and
a piece headed eastward into the Rocky Mountain region. The net
result will be that the showers will decrease on Monday, though a few
will be around especially in the afternoon and evening, especially
near the higher terrain, though we cannot rule out a few showers
drifting off the coast range and across the valleys.

The models continue to suggest that Tuesday will be dry, though a few
showers could get close to the Cascades in southeast Lane County.

Temperatures will tend to be a little below normal through Monday,
but may reach or slightly exceed normal on Tuesday. Tolleson

.LONG TERM...Tuesday night through Saturday...A broad upper level low
deepens over the far northeastern Pacific off the coast of B.C.
during the middle part of next week. A series of embedded shortwaves
in the flow will bring rounds of enhanced precipitation at times, but
confidence remains on the low end in the timing of these impulses.
Nonetheless, expect temperatures returning below normal as well as
fairly widespread precipitation across the forecast area for the
midweek period. The trough then finally slides inland late next week,
ushering in a colder air mass and bringing snow levels down to at
least the Cascade foothill/high Coast Range elevations Friday night.
Forecast models diverge more significantly next weekend, so
maintained a blend of models for next weekend`s forecast as a
compromise.   Cullen

.AVIATION...A mix of MVFR and VFR across the area early this
afternoon. MVFR a little more persistent than expected. Coast and
interior lowlands forecast to be more VFR than MVFR through 09Z Sun,
then look for increasing MVFR. Areas of IFR possible 12Z through 17Z
Sun. Would expect enough cloud cover to prevent LIFR fog development.

KPDX AND APPROACHES...Low-end VFR at the terminal early this
afternoon, but has been oscillating between MVFR and VFR since 18Z.
Flight restrictions may return to MVFR after 10Z Sun, with IFR
possible in the Tualatin Valley toward sunrise. Weishaar

.MARINE...Wind speeds generally 15 kt or less through at least Tue
morning. Possible gusts to 20 kt Tue afternoon in a north wind
pattern. GFS and ECMWF in reasonable agreement showing a much more
active weather pattern the latter half of next week. The GFS would
imply possible gale force wind late Wed night or Thu. At a minimum,
small craft advisory level wind speeds seem likely Thu night through
Fri night.

Seas well under 10 ft for the next several days. ENP guidance then
brings 10 ft seas to the waters Thu morning, peaking at 12 to 14 ft
Thu evening. Weishaar




Interact with us via social media:

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 CWA or forecast area. is the U.S. government's official web portal to all federal, state and local government web resources and services.