Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 232159
Area Forecast Discussion
National Weather Service Portland OR
258 PM PDT Sun Apr 23 2017
.SYNOPSIS...An upper level trough swinging through the Pacific
Northwest this afternoon and early this evening was producing some
rain or showers across the forecast area, with snow in the Cascades.
This will be followed quickly by the first in a series of systems
riding a strong Pacific jet stream that will spread more rain and
Cascade snow across the forecast area tonight and Monday, with breezy
conditions as well. This will be followed by another decent system
for more rain and Cascade snow and breezy conditions Tuesday into
Tuesday night. Moist onshore flow will continue the threat of showers
Wednesday and Thursday and into Friday before some drying is expected
early next weekend.
.SHORT TERM...Tonight through Wednesday...National Weather Service
Doppler radar shows the showers filling in and becoming more
widespread across the forecast area this afternoon. Snow levels are
just above the Cascade passes this afternoon.
This will be followed rather quickly this evening and tonight by the
first in a series of decent weather systems that will ride a rather
strong late April Pacific jet stream into southwest Washington and
northwest Oregon. This system will spread rain and Cascade snow into
our forecast area beginning later this evening, continuing overnight
tonight and through Monday morning. The associated cold front will
move through in the afternoon on Monday, followed by decent showers
into early Monday evening. Precipitation amounts still look like 1-2
inches in the Cascades, coast range, and the coast, with 0.5-0.75
inch in the valleys. Snow levels will hover around the Cascade
passes, with snow totals in the Cascades tonight and Monday 6 to 12
inches except lesser amounts near the passes due to initially warm
roads that will take some time to cool. Have issued a snow advisory
for the Cascades for tonight through late Monday, with the main
impacts above the passes.
The models continue to show an associated surface low that will move
onshore somewhere along the north Oregon coast around midday Monday
and inland close to the Columbia River. Expect brisk south winds to
the south of the low center track, with gusts to 40 or 45 mph near
the coast and perhaps 30 to 35 mph inland. With trees leafing out and
the very wet ground we have, we will have to see if this might be
enough for some tree damage and possibly need a wind advisory inland.
Showers ease up overnight Monday night before the next system arrives
during the day Tuesday. Snow levels may rise a bit with the Tuesday
system, rising above pass levels during the day. But look for
increasing rain again. The track of the associated surface low is
farther north, but we should see some breezy south winds again along
the coast and inland Tuesday afternoon and evening.
Onshore flow will keep a considerable amount of showers across the
forecast area Tuesday night and Wednesday. Snow levels are expected
to lower back down to near the Cascade passes later Tuesday night and
Wednesday. It appears there will be a wave moving through Wednesday
that would bump up the shower coverage during the day Wednesday.
.LONG TERM...Wednesday night through Sunday...Showers will continue
across the forecast area Wednesday night into Friday as a couple of
more disturbances ride through on a jet stream that turns more
northwesterly through through Friday. The models are now in better
agreement that enough of an upper ridge will build early in the
weekend for some drying. The next system is expected about Sunday.
.AVIATION...Predominantly MVFR along the coast, and predominantly VFR
inland with cigs and vis occasionally lowering to MVFR under heavier
showers. Cigs inland are generally hovering around 3000 to 5000 feet.
A stronger front approaches the Coast later tonight, which will bring
winds up along Oregon`s central coast overnight, impacting KONP, and
in the central and south Willamette Valley Monday morning (KSLE and
KEUG). Cigs this evening will lower to predominantly MVFR inland with
the approach of this next front. Rainfall in the morning will make
cigs stay down around 2000-3000 feet through midday Monday.
KPDX AND APPROACHES...Predominantly VFR conditions this afternoon.
Cigs will lower to around 2000-3000 feet around 05Z and remain MVFR
overnight through Monday morning. -McCoy
.MARINE...Weak front moved across the waters this morning. Winds are
starting to pick up along the Central Oregon coast this afternoon.
The next system which is just an open wave right now around 40N, 135W
is approaching and looks like it will make landfall between Tillamook
and Cascade head. Models suggest marginal gales or high-end small
craft advisory winds, so am leaving the decision whether or not to
issue a gale warning to the next shifts who will have another run or
two to look at. Beyond Monday there is another system on Tuesday that
could bring high-end small craft advisory or low-end gales midday
Tuesday, and an active pattern continues through the end of the week.
Seas hovering around 8 to 10 ft today. Seas south of Cascade Head
will start to build this evening, building up to 10 to 12 ft later
tonight as winds ramp up with the approaching low. Seas start to come
back down Monday afternoon as this system moves inland. Tuesday seas
look to remain around 7 to 9 ft. Next time seas get up above 10 ft
looks to be Thursday with a fetch developing from a Low off the Coast
of British Columbia. With this system models have backed off, now
only bringing seas up to 10 to 12 ft. Seas start to fall late Friday
and look to stay below 10 ft through next weekend. -McCoy
OR...Winter Weather Advisory from 8 PM this evening to 8 PM PDT
Monday for Cascades in Lane County-Northern Oregon Cascades.
WA...Winter Weather Advisory from 8 PM this evening to 8 PM PDT
Monday for South Washington Cascades.
PZ...Small Craft Advisory for winds from 11 PM this evening to 2 PM
PDT Monday for Coastal Waters from Cape Shoalwater WA to Cascade
Head OR out 60 nm.
Small Craft Advisory for hazardous seas until 11 PM PDT this
evening for Coastal Waters from Cape Shoalwater WA to
Cascade Head OR out 60 nm.
Small Craft Advisory for winds from 2 PM this afternoon to 2 PM
PDT Monday for Coastal Waters from Cascade Head OR to
Florence OR out 60 nm.
Small Craft Advisory for hazardous seas until 5 PM PDT Monday
for Coastal Waters from Cascade Head OR to Florence OR out
Small Craft Advisory for Rough Columbia River Bar from 1 PM
this afternoon to 6 PM PDT this evening.
This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. The area is
commonly referred to as the forecast area.