Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 270405
Area Forecast Discussion
National Weather Service Portland OR
904 PM PDT Sun Mar 26 2017
.SYNOPSIS...Showers tonight and Monday, with snow in the Cascades.
Showers decrease Mon evening, with a brief break in rain
on later Mon night into Tue. But, that short lived as another round
of rain will spread into the region Tue night. Rainy Wed morning,
then showers by afternoon as the front moves across region. But,
there is hope, as looking good for few dry and mild days later this
week as we close March.
.SHORT TERM...(Tonight through Wednesday)...Cold front is now east of
the Cascades. Moist onshore flow tonight, with scattered showers this
evening. But, showers will be increasing after midnight as an upper
level disturbance, currently about 500 miles to west of Astoria,
moves into the region later tonight. Now, this disturbance also just
happens to be sitting the coolest air aloft, which will contribute to
boosting shower potential. Again, this cool pool aloft and
disturbance will shift across the region late tonight and Monday
morning. With this timing, thunderstorm potential rather minimal,
mainly along the coast and westward. But, decent instability will
ensure some rather hefty but brief downpours. As Monday progresses,
will see some slight warming aloft, with showers slowly decreasing.
May not be until late in the afternoon before see significant
decrease of showers over the higher terrain of the Cascades.
Meanwhile, snow levels still holding near 4000 to 5000 feet, highest
over Lane County. But these will drop back down behind the front
tonight, generally sitting at 3000 to 3500 feet. While precipitation
will become more showery this evening, still think good potential for
3 to 8 inches of snow at the passes for tonight through Monday, with
8 to 15 inches at higher elevations. So, will maintain current winter
weather advisory for the Cascades through Mon afternoon.
Weak high pres builds into the region later Mon night and early Tue,
but will be rather transient as another frontal boundary to our
northwest will slowly approach. Plenty of clouds over region on Tue
with some spotty rain for areas north of a Newport to Portland line.
Still think areas inland to south of Salem will be mostly dry on Tue.
Will maintain this trend. However, it not out of the question that
the rain threat may shift bit northward on Tue, with more areas
inland being dry.
But makes no matter, as that front will sag southeastward into the
region Tue night. Will see increasing rain at that time. Models have
hinted as some upper level moisture enhancement with this system, so
could see locally heavy rain over the Coast Range and Willapa Hills
late Tue night into Wed am. Fairly potent low pres area will pass to
our northwest Wed am, with cold front pushing inland later Wed am
into early afternoon. Pressure gradients do tighten, probably enough
to produce breezy conditions with gusts 35 to 45 mph at times along
the coast in the morning. Then back to showers with moderate onshore
flow by Wed afternoon. Rockey.
.LONG TERM...(Wednesday night through Sunday) Upper-level ridge
builds over the Pacific Northwest late this week. This means
decreasing showers on Thursday with clearing skies Thursday night. A
dry sunny spring day is in order for next Friday, as the models are
in good agreement with the ridge moving over the Pacific Northwest.
Models diverge on how quickly the rain returns. ECMWF flattens the
ridge bringing rain back on Saturday, while the GFS doesn`t flatten
the ridge until Sunday. ECMWF has been more consistent with the
ridge breaking down on Saturday, so this is more likely the scenario
we will see. However, there is still a chance for a dry day for at
least the southern half of our area. By Sunday night, the chance of
rain goes up even more with a wet pattern returning for next week.
Snow levels come back down to 3000 to 4000 feet behind the front on
Thursday as showers are winding down. With the ridge building in on
Friday however, snow levels come back up to around 6000 to 8000 feet
for the next system Saturday or Sunday. Temperatures start a bit
cooler than normal on Thursday, rising to around normal Friday
and hovering near normal through the weekend. -McCoy
.AVIATION...An unstable showery weather pattern will produce
primarily VFR conditions at most ta sites through 06z Tuesday.
KONP will be the most susceptible to periodic MVFR conditions
tonight, but even KAST may experience a bout or two as heavier
showers pass overhead or nearby. Models do hint that shower
activity may become a bit more organized between 9-13z Monday along
the coast and 12-16z Monday inland so put an MVFR group in the
tafs accordingly. However, confidence is not terribly high these
will materialize and suspect any restrictions will be short
KPDX AND APPROACHES...An unstable showery weather pattern will
produce primarily VFR conditions through 06z Tuesday. Models hint
that shower activity may become a bit more organized between
12-16z Monday so put a tempo MVFR group in the taf, but confidence
is not terribly high these conditions will materialize. /Neuman
.MARINE...A showery and relatively benign southwesterly wind
pattern has set up across the waters this evening after a cold
front pushed ashore late this afternoon. Seas are currently
hovering around 8-10 ft with a dominant period of 9-10 seconds so
extended the Small Craft Advisory for Hazardous Seas to account
for the steep seas. Seas should subside another foot or two later
tonight and fall more solidly below square seas criteria.
However, this break will be short lived as two larger swell
trains push seas back above 10 ft late Monday morning.
A front will then drop southeastward towards the waters Monday
night and Tuesday and likely result in southerly winds increasing
into solid small craft advisory criteria of 25-30 kt. This front
will stall across the northeast Pacific as a surface low
pressure system develops along it in the eastern Pacific. This
will likely strengthen the front and winds across our waters
Tuesday night and early Wednesday. Gale Force winds of 35 to 40
kt are appearing more and more likely. A weak trough dropping
southeastward will turn the flow more northerly and produce a
more summer-like northerly wind pattern as we move into Friday
and possibly next weekend. /Neuman
OR...Winter Weather Advisory until 4 PM PDT Monday for Cascades in
Lane County-Northern Oregon Cascades.
WA...Winter Weather Advisory until 4 PM PDT Monday for South
PZ...Small Craft Advisory for hazardous seas until 5 PM PDT Tuesday
for Coastal Waters from Cape Shoalwater WA to Florence OR
out 60 nm.
Small Craft Advisory for Rough Columbia River Bar from 3 AM to
7 AM PDT Monday.
Small Craft Advisory for Rough Columbia River Bar from 3 PM to
8 PM PDT Monday.
Interact with us via social media:
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.