Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 262152 RRA
AFDPQR

Area Forecast Discussion
National Weather Service Portland OR
252 PM PDT Wed Apr 26 2017

.SYNOPSIS...Strong NW flow aloft will bring continued showers tonight
through Thu. Snow levels will remain near or just below the higher
Cascades passes during this time. There will be a break in the
weather Fri and Sat, with dry and mild conditions. A weakening cold
front will bring the next round of rain Sat night into Sun. The trend
is then toward drier weather for the first half of next week,
especially toward the middle of next week.

&&

.SHORT TERM...(Tonight through Sat)...A cold front brought a period
of steady precip to SW WA and NW OR last night into this morning. The
front has pushed east of the Cascades and the region is now in a cool
and showery post-frontal airmass. Showers are widespread this
afternoon as temps have warmed enough for some surface-based
convection to develop. However, showers should become increasingly
driven by orographics this evening and overnight as surface
instability drops off with diurnal cooling. Decided to drop the
Winter Weather Advisory for the Cascades this afternoon, as
observations and webcams are just not showing any notable
accumulations.

There will be little change through Thu.  We will remain on the
poleward side of a strong Pacific jet stream that will bring
persistent NW flow aloft and keep decent orographic flow into the
Cascades. Thus, expect the best shower activity to remain over the
Cascades and the higher terrain of the Coast Range. Snow levels will
hover around 3000-4000 ft and several inches of snow are expected
near the higher Cascade passes. However, road temps should be warm
enough to prevent any significant travel impacts. Expect shower
activity to increase over the lowlands again Thu afternoon as the
fcst model soundings indicate temps again warm up enough to support
surface-based convection. It does not appear that convection will be
deep enough to support thunderstorm development, but would not be
totally surprised if there are a couple of isolated lightning strikes
detected in the afternoon, particularly if any sunbreaks are able to
develop during the morning hours.

An upper level ridge over the NE Pac will begin to strengthen over
the Pac NW Thu night into Fri. This will lead to gradually decreasing
shower activity Thu night. There may be a few weak showers lingering
over the higher terrain into Fri morning. However, think most
locations will be completely dry through the day. There will likely
be quite a bit of cloud cover to start, but expect a mix of sun and
clouds during the afternoon. Temps should recover back to near 60 for
the interior lowlands. The upper ridge axis will move over the region
on Sat, bringing another dry and even milder day. Think afternoon
highs will reach into the mid 60s for the lowlands, which believe it
or not, is right around average for this time of year. There should
be a sunny start to the day, but the fcst models are suggesting that
there will be increasing high clouds later in the day ahead of the
next approaching frontal system. Pyle

.LONG TERM...Sat night through Wed...A low pres system is modeled to
move into British Columbia late Sat, bringing a weakening cold front
onshore into Washington and Oregon Sat night. The fcst models
currently suggesting light rain develops on the coast Sat evening,
then moves through the interior overnight into Sun morning. Scattered
post-frontal showers likely lingering through much of Sun. Then the
upper ridge over the NE Pac is modeled to gradually strengthen again
over the Pac NW for the first half of next week. The ridge may not be
quite strong enough to prevent a few showers around the area Mon or
Tue, so will keep low chance PoPs in the fcst for now. By Wed, it
appears that the ridge strengthens considerably over the region. Most
of our fcst models now suggesting highs reaching into the 70s over
the lowlands Wed afternoon. Hopefully we have not jinxed it, but we
have gone with 70s in the fcst. Pyle

&&

.AVIATION...Scattered showers continue across the region this
afternoon and evening under lower VFR cloud deck. May see
occasional reductions to MVFR cigs and IFR vsbys at times,
particularly in vicinity of heavier showers. Showers should
decrease in areal coverage after sunset through overnight period,
with some patches of MVFR stratus settling in after 12z. Little
change to the pattern Thu so expect another round of more
widespread showers by Thu afternoon. Expect mountains to remain
obscured in clouds through the period.

KPDX AND APPROACHES...Generally VFR through overnight
period, but may see temporary MVFR cigs or lower vsbys in showers
through early evening. Small chance (about 15%) of MVFR cigs
developing overnight, but most likely VFR holds through the
overnight period. Showers will again develop Thu afternoon.
Cullen

&&

.MARINE...Winds continue to gradually becoming more benign this
afternoon, though some gustier winds are possible near showers
over the waters through the afternoon. Seas are also subsiding
and will remain at 5 to 8 feet through the evening. However,
conditions will be rather choppy as dominant periods remain
around 9 seconds. Broader high pressure builds over the NE
Pacific through Friday, maintaining a relative lull in winds.
Seas may reach 10-11 ft Thursday through early Friday as the
southern end of a swell train clips the northern waters. A
stronger front may brush the northern half of the waters
Saturday night, with advisory level gusts possible.  Cullen

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory for Rough Columbia River Bar until 8 PM
     PDT this evening.

     Small Craft Advisory for Rough Columbia River Bar from 3 AM to
     8 AM PDT Thursday.

&&

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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.



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