Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 231619
Area Forecast Discussion
National Weather Service Portland Oregon
919 AM PDT Sun Oct 23 2016
.SYNOPSIS...Showers are easing over the region this morning, and the
rest of the day will be mostly dry. A complex low develops offshore
this afternoon and will remain a few hundred miles offshore through
Tuesday. This low will move a cold front across the region Monday and
possibly high winds along the coast Monday night. Large surf is also
likely along the beaches Monday night into Tuesday morning. Another
low is expected to bring more rain and gusty coastal
winds Wednesday. Forecast models suggest another large and complex
low will set up offshore again on Friday and linger through the
.UPDATE...A front is weakening over nw Oregon this morning, and have
reduced pops for the remainder of the morning. Isolated to scattered
showers will continue this morning with the greatest chances for
measurable rain over the higher terrain of the coast range and
Satellite imagery currently shows two surface lows between 130 and
140 W, one north of the other. The front stalls over nw Oregontoday
as the southern low swings towards the Oregon/California border. The
two lows offshore merge into one giant low this afternoon which moves
the front back offshore. A vort max swinging north along will
invigorates showers along the front this afternoon and evening, but
the front should have already moved offshore by this time, and rain
over land will be limited. There is a slight chance for rain along
the coast and coast range this afternoon and evening, but the rain
will remain offshore the rest of the night.
The low will remain offshore tonight and Monday before moving north
Monday night and Tuesday. The low will move a quick-moving front
across the region Monday for light rain. This low will likely
generate large seas offshore that will likely lead to dangerous surf
along the Washington and Oregon beaches overnight Monday into Tuesday
Previous SHORT TERM from 428 AM this morning...Today through
Tuesday...Complex forecast over the next 72 hours with a lot of
potential sources of error in regard to timing and strength of wind
Models show a good level of agreement in the overall pattern, with
deep and complex low pressure rapidly developing 300-400 miles off
the Oregon coast today. This low is expected to go from the current
nascent system to around 975 mb or possibly deeper by Monday morning.
This would be of obvious concern if it were expected to continue
toward the Pac NW coast, but there is a high level of confidence that
the low will stay near or west of 130W...limiting the wind impacts
for much of our forecast area.
A loosely defined baroclinic or frontal zone remains draped across
western WA/OR. A few showers are still occurring across the district,
but should dissipate today as warmer air aloft moves in ahead of the
developing low offshore and increasingly caps any instability. With
higher pressure east of the Cascades, some weak offshore flow will
develop, which will in turn dry out the lower levels of the
atmosphere a bit...further deterring shower activity this afternoon.
As a result today should be mild and mostly dry with temperatures
reaching into the 60s for most of the lowlands. Some high clouds will
keep it mostly cloudy at times through the day.
As the low blossoms offshore, the baroclinic zone will likely become
energized and infused with an increasing amount of moisture from the
S-SW. This will have to battle a bit with the offshore flow to really
spread rain across our forecast area, so we kept PoPs fairly low
until midday Monday. The better chances will be near the coast until
then. Pressure gradients remain offshore through Monday morning,
likely keeping most of the wind associated with this system off the
With the baroclinic zone draped N-S near the Oregon coast, a strong
low offshore, and a 70-110 kt S-SW jet stream lurking in the area at
times, there will be the potential for secondary cyclogenesis closer
to the Oregon coast at any time late tonight through Tue morning.
However models do not seem to be latching on to this idea at this
time. Therefore any strong winds will probably remain confined to the
coastal and offshore waters...and possibly the OR/WA beaches and
headlands. This is due to the orientation of the pressure gradients,
with isobars mainly parallel to the coast. If an unexpected secondary
low develops - which is very possible and probably would not be
well-initialized nor well-modeled - pressure gradients could turn
more southerly, opening the door for more widespread winds and/or
Otherwise, conditions will be fairly benign with some light to
moderate rain at times and a bit of wind on the beaches and headlands
through Tuesday...and this is what is currently reflected in the
.LONG TERM...No Changes. Previous discussion follows...Tuesday night
through Saturday...A surface low offshore will weaken Tuesday evening
and another low will approach from the south. The models vary on the
strength of this low, but it has the potential to support strong
gusty winds along the immediate coast as it moves south to north
offshore of the Oregon and Washington coast on Wed. Modeled
precipitable water values show that there could be quite a bit of
moisture available with this front and the Portland forecast area may
get a decent shot of rain with the warm front Tuesday night into Wed
morning, and again with the cold front Wednesday night. There may be
a break in wet weather Thursday before another complex low sets up
offshore Friday and Saturday. TJ
.AVIATION...light southerly flow aloft today and into tonight, as
region lies between weather fronts. Mostly VFR today, but will see
few pockets of MVFR ceilings this am, mainly against the Cascades.
While most of the day remains dry, will see a few showers today
over Coast Mtns and westward. Otherwise...mid/high level clouds
increasing today and tonight as an occluded front approaches from
the west. Clouds not all that solid tonight, so will see patchy
fog inland. MVFR with rain increases along coast later tonight...
but rain remains somewhat spotty as it spread inland Mon am.
KPDX AND APPROACHES...Rather benign, with VFR clouds today and
tonight. Easterly winds 8 to 15 kt through tonight. /Rockey.
.MARINE...Not much in way of change to the current forecasts and
warnings. Generally south to southeast winds 15 kt or less through
early afternoon, with seas 7 to 8 ft. Then return to breezy winds.
An occluded front will pushes across the region tonight. Will see
southerly winds increase over the central waters, with 20 to 25 kt
winds this afternoon, and gusts 30 to 35 kt. These winds will
spread northward tonight as the front pushes closer to the coast.
Current gale warning looks on track so no changes. Seas will climb
back to 12 to 15 ft range, with higher seas over the outer waters.
Now, will see rather active storm pattern over the NE Pac this
week, with several very strong storms arriving. But the low
centers will remain well offshore, mostly tracking north along
130W. This will maintain decent gradients over the coastal waters,
with Gales continuing on Mon, and likely through Wed at times.
Some potential for storm force winds, especially over the outer
waters. No Storm warnings yet, but will have to watch closely.
Seas will be on the increase with all the increased winds. Decent
fetch area to generate significant waves by later Mon and Tue. At
this time, with strong potential of seas above 20 ft later Mon
night, possibly reaching 25 ft by Tue am.
PZ...Small Craft Advisory for winds from 3 PM this afternoon to 9 PM
PDT this evening for Waters from Cape Shoalwater WA to
Cascade Head OR from 10 to 60 nm.
Gale Warning from 9 PM this evening to noon PDT Tuesday for
Waters from Cape Shoalwater WA to Cascade Head OR from 10
to 60 nm.
Small Craft Advisory for winds from 9 PM this evening to noon
PDT Monday for Coastal Waters from Cape Shoalwater WA to
Florence OR out 10 nm.
Gale Warning from noon Monday to noon PDT Tuesday for Coastal
Waters from Cape Shoalwater WA to Florence OR out 10 nm.
Gale Warning from 3 PM this afternoon to noon PDT Tuesday for
Waters from Cascade Head to Florence OR from 10 to 60 nm.
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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.