Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 241126
Area Forecast Discussion
National Weather Service Portland Oregon
425 AM PDT Mon Oct 24 2016
Updated Aviation and Marine sections.
.SYNOPSIS...Strong low pressure continues to develop well off the
Oregon coast this morning, pushing a strong but slow-moving frontal
system toward the coast. This is causing spotty light rain to
gradually increase in coverage this morning. The main cold front will
drift onshore throughout the day, with rain filling in across the
district before tapering back to showers later this afternoon. This
system will bring gusty S-SE winds and large surf to the coast today
through Tuesday. The broad low will weaken and lift north Tuesday,
but another is likely to take its place Wednesday. This next low will
push a wet warm front across the region from the south Tue night/Wed.
Similar systems will keep a chance of rain and occasionally gusty
coastal winds through next weekend.
.SHORT TERM...Today through Wednesday...Satellite imagery this
morning reveals a very impressive low pressure system centered near
44N/131W, with a textbook Norwegian Cyclone Model frontal structure.
Tough to tell the exact central pressure at this time, but it appears
to be nearing 975 mb based on surrounding buoy data. As is often the
case, the ECMWF initialized this system best of the 00z
models...showing the closest pressure to that reported by nearby Buoy
46002 at 06z. The buoy reported 981 mb at that time, the ECMWF was
showing 983 mb and the GFS/NAM in the mid to high 980s. The 00z ECMWF
also seems to have the best handle on the low`s structure and
placement. So, much of the forecast based on this low was developed
based on the 00z ECMWF.
All that said, the impacts on land appear to be minimal compared to
most lows of this size, mainly due to the offshore component to our
pressure gradients. KAST-KPDT gradients are down to around -7 mb,
with -5.3 mb KTTD-KDLS. East winds are starting to become gusty
through the Columbia Gorge; Crown Point has been gusting 45-60 mph
much of the night. But aside from some locally gusty winds near the
Columbia Gorge, we will have difficulty accessing the strengthening S
winds aloft except perhaps near immediate coastal areas like beaches
and headlands. 00z ECMWF shows 900 mb winds up to 65 kt as low as 900
mb with the incoming cold front, so beaches and headlands could
briefly gust 40-50 mph or locally higher as the front nears the coast
this morning. However the stronger winds appear to remain Cape Blanco
southward, closer to where a triple point appears to be developing.
Given the strength and broadness of the parent low, model wind fields
are impressive with 50-60 kt winds as low as 900-950 mb all the way
through Tuesday morning over the coast and coastal waters. Cooler air
moving in aloft may allow a bit more mixing down of some of this wind
tonight and Tuesday morning, especially along the coast. Current wind
forecast of 45-55 mph gusts along the coast appears good, so we will
refrain from issuing a beaches and headlands High Wind Warning...but
it will probably be close.
After a few scattered showers this morning, rain is expected to
briefly fill in across our area as the front drifts slowly across the
CWA later this morning into this afternoon. The front is expected to
weaken and split as it moves across the Cascades, so rain will taper
back to just a few showers by this evening, favoring the coast.
The current large low is forecast by the 00z ECMWF to start moving
N-NW Tuesday, slowly filling in the process. This will make way for
the next developing low to move north from the N CA offshore waters
late Tue through Wed. Models show excellent isentropic lift
developing across the district Tue night, so the developing low`s
warm front will probably push widespread rain south to north across
our CWA Tue night/Wed. GFS/ECMWF/NAM are all showing this system
tapping into deeper moisture than the previous one, with total
precipitable water values over 1 inch. This will probably couple with
increasing southerly low-level winds to bring some respectable
rainfall totals to the Coast Range...likely on the order of 1-2
inches with some upside potential from there. Areas east of the Coast
Range will probably see most of their rain from the warm front Tue
night/early Wed, with about 0.25-0.50 inch expected and possibly
another tenth or two of an inch later Wed as the cold front drifts
onshore. Given that this is a developing low fairly close to our
coast, we will need to watch the track closely for any wind issues.
However, given current model forecasts it appears winds will not be
all that strong Tue night/Wed on land, aside from a modest east wind
event through the Columbia Gorge and perhaps 35-45 mph southerly
gusts beaches and headlands. Weagle
.LONG TERM...Wednesday night through Sunday...A complex weather
pattern continues offshore late in the week into next weekend. The
low that will bring rain to the area Wednesday moves north Wednesday
night and brings a cold front across the region on Thursday. The low
then moves inland as an open trough Thursday night as two other
Pacific lows move into the offshore waters. One low approaches from
the south, and another larger low approaches from the northwest. This
will result in dry weather for the Portland forecast area Thursday
night. The northern low deepens over the ne Pacific Friday allowing
an upper ridge to amplify over the Pacific NW, and keeping the
southern low south of northwest Oregon. The southern low moves inland
across north California and east Oregon Friday or Saturday for
showers over the Portland forecast area. The second low then moves
onshore on Sunday for a continued threat of rain. Snow levels will
remain well above the Cascade passes. TJ
.AVIATION...An upper level trough will persist over the NE Pac
this week. Will see southerly flow aloft increase today as a
strong frontal system moves across the forecast area. Expect
primarily VFR conditions today and tonight with cigs lowering to
around 5000 ft. Brief periods of reduced flight conditions
possible this morning south of KCVO due to patchy fog and low
stratus. The front will bring light rain to the coast after 12Z,
with rain spreading inland through the morning. Gusty east winds
continue near the Columbia River Gorge through this afternoon.
Gusty southerly winds expected along the coast after 18Z, with
gusts to 30 kt likely.
KPDX AND APPROACHES...Primarily VFR with cigs lowering to 5000 ft
this afternoon. Light rain expected after 18Z.
.MARINE...A strong frontal system will continue to move across the
waters today with southerly winds generally around 20 to 30 kt and
gusts 30 to 40 kt. These winds will spread into the inner waters
this afternoon as the front pushes closer to the coast. As such,
the current gale warning remains on track this morning. Seas will
climb back to 12 to 15 ft range, with higher seas over the outer
Will see a rather active storm pattern over the NE Pac this week,
with several very strong storms impacting the waters. However, the
lows look to remain well offshore, generally around 130W. This
will maintain decent gradients over the coastal waters, with
periods of gales continuing through Wednesday. Models continue to
suggest the potential for a few gusts to 50 kt tonight. However,
do not think these will be frequent nor widespread enough to
warrant upgrading to a storm warning, so will extend the current
gale warning until Tuesday morning over all waters.
Seas will be on the increase with all the increased winds. A
decent fetch will allow significant waves to impact the waters
later today and tonight. Expect seas to climb above 20 ft by
tonight, and peak near 30 ft late tonight/early Tuesday. Winds and
seas briefly subside on Tuesday.
Active weather continues for later Tue through Fri, but winds and
seas look to be less intense.
PZ...Gale Warning until noon PDT Tuesday for Waters from Cape
Shoalwater WA to Florence OR from 10 to 60 nm.
Small Craft Advisory for winds until noon PDT today for Coastal
Waters from Cape Shoalwater WA to Florence OR out 10 nm.
Gale Warning from noon today to noon PDT Tuesday for Coastal
Waters from Cape Shoalwater WA to Florence OR out 10 nm.
Small Craft Advisory for Rough Columbia River Bar from noon
today to noon PDT Tuesday.
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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.