Area Forecast Discussion
Issued by NWS Portland, OR
FXUS66 KPQR 241037
Area Forecast Discussion
National Weather Service Portland Oregon
337 AM PDT Mon Oct 24 2016
.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...Previous discussion from 913 PM Sunday...will be updated
shortly...Rather benign tonight with light southerly flow aloft
and light east to southeasterly flow in lower levels. However some
gusty winds near the western end of the Columbia River Gorge.
Will see generally VFR tonight with variable mid/high clouds. May
see some patchy fog in inland valleys but not much. Front
approaching region Mon am, with clouds lowering to low VFR. May see
areas of MVFR along the coast with light rain after 12z. This rain
will spread inland through Mon am, but conditions look to remain
VFR over much of the interior on Mon.
KPDX AND APPROACHES...Winds out of the east will pick up at some
point tonight and may see gusts to around 20 kt for a few hours.
Clouds and vis should remain VFR. Bowen/Rockey
.MARINE...Previous discussion from 913 PM Sunday...will be updated
shortly...Not much in way of change to the current forecasts and
warnings. Generally south to southeast winds 15 kt or less into
this evening, with seas 5 to 7 ft.
An occluded front will push across the region later tonight into
Mon am. Southerly winds will increase over the central waters with
20 to 25 kt winds and gusts 30 to 35 kt. These winds will
gradually 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
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.
Models continue to suggest increasing potential for storm force
wind gusts, especially over the outer waters for Mon night. Have
issued a storm watch for the outer waters for Mon night, with
gusts 50 to 55 kt possible at that time. Still think that closer
to shore waters will see less wind, with gusts 40 to 45 kt. So
will maintain gale warning in the inner coastal waters.
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, with peak seas briefly 25 to 30 ft late Mon night. Seas and
winds subside on Tue.
Active weather continues for later Tue through Fri, but winds and
seas look to be less intense. Bowen/Rockey
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.
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.