River Flood Warning 25, NWS Portland, OR

Area Forecast Discussion
National Weather Service Portland OR
251 AM PST Thu Jan 14 2021

.SYNOPSIS...High pressure will lead to fair weather today, allowing
rivers to continue to recede after Tuesday night's heavy rain event.
Patchy morning fog should give way to partly sunny skies under some
high clouds today. The next front arrives tonight and Friday morning,
then another Saturday night and Sunday morning for some light rain
and mountain snow. In between systems there will be plenty of night
and morning fog in the valleys.

&&

.SHORT TERM...Today through Saturday...High pressure is building into
the Pac NW this morning, both at the surface and aloft. This should
lead to fair weather today with temperatures somewhat above
mid-January normals. Easterly MSLP gradients are ramping up through
the Columbia Gorge, with KTTD-KDLS gradients standing at -4.3 mb as
of 09z. East winds are beginning to ramp up through the Columbia
Gorge in turn, with gusts generally 25-35 mph at the west end. 00z
NAM suggests KTTD-KDLS gradients will tighten to -6 to -7 mb by 18z,
which suggests gusts will reach 25-35 mph at KTTD and up to 50 mph
around Corbett.

The increasing offshore flow will likely inhibit fog development
across the eastern PDX metro and probably along the coast as well.
Elsewhere, fog has also been slow to develop, likely due to high
clouds passing overhead associated with a warm front aloft. Area
radars are picking up some light echoes from this front, which are
very likely just virga aloft. High clouds should thin or clear out
shortly after sunrise, but may hang on long enough to keep valley fog
from being too widespread this morning.

A 967-969 mb low in the Gulf of Alaska will rotate a weak front
across the Pacific Northwest Thursday night and Friday morning. Snow
levels will be rather high, 6000-7000 ft with this system and QPF is
rather low - so snow accumulation will be light and mainly over the
highest parts of the Cascades. Will need to keep an eye
on temperatures in the Hood River Valley as precip spreads that way
Friday morning, but NBM suggests temperatures generally above
freezing with low to moderate chances for freezing rain at Parkdale
Friday morning. Any ice accumulation would be very light and brief,
and mainly confined to the uppermost portions of the Hood River
Valley. Pcpn ends by Friday afternoon and should be dry through
Saturday.  Weagle

.LONG TERM...Saturday night through Wednesday...The rather benign
weather continues into the extended with the mean upper level ridge
position near 130W with weak systems occasionally depressing the
ridge to bring some pcpn. Overall the air mass will be on the mild
side but during periods of high pressure over the region with
clearing skies, valley temperatures likely cool to more seasonal
temperatures. Longer range ECMWF/GEFS ensemble means suggest more
significant cooling is possible toward the middle or latter portion
of next week, but both ensembles maintain a handful of warmer
members. Therefore any transition to a colder pattern is far from
certain at this point.	Weagle

&&

.HYDROLOGY...With the Nehalem River near Foss falling below flood
stage, all coastal rivers are now below flood stage. A handful of
Willamette tributaries remain above flood stage, but most have
crested. The main exceptions are the Tualatin and Pudding Rivers,
which tend to drain slower than most. Expect the lower Willamette
River to be on the rise this week and likely exceed bankfull in
places, but at this point it appears it should remain well below
minor flood stage at our various forecast points along the river.
Fortunately, relatively drier weather will allow several days for
rivers to process the water from our recent heavy rain event.  Weagle

&&

.AVIATION...High pressure inland and an approaching frontal system
will result in primarily VFR conditions and light east to
southeast winds over the next 24 hours across most of northwest
Oregon and southwest Washington. The main exception to this will
be along the coast beginning between 00-06z Friday when light
rain and MVFR conditions will push onto the coast as a front
pushes towards the region. This will likely spread inland
between 09-12z Friday.

For detailed regional Pac NW weather information, go online to:
http://weather.gov/zse

KPDX AND APPROACHES...High pressure inland and an approaching
frontal system will result in primarily VFR conditions over the
next 24 hours. This should enable winds to shift from light
westerly early this morning to easterly between 17-20z Thursday.
Light rain and MVFR conditions will likely push towards the
terminal between 09-12z Friday as the front draws closer to the
region. /Neuman

&&

.MARINE...High pressure inland and an approaching frontal system
will result in primarily east to southeast winds across the
waters today. Expect winds to gradually turn more southerly late
this afternoon and evening and increase into Small Craft Advisory
level thresholds of 25 to 30 kt. These winds should subside
rather quickly behind the front late tonight. However, a
building westerly swell will push into the waters late tonight
and likely peak in the 15 to 17 ft range Friday.

Another weak frontal storm system should bring a burst of Small
Craft Advisory level wind gusts of 25 kt to the waters Saturday
night. In addition, another westerly swell should push seas back
into the mid teens late Sunday into early Monday. High pressure
then appears likely to return to the Pacific Northwest and
results in light winds across the waters. This should allow seas
to subside below 10 ft sometime early to mid next week. /Neuman

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 3 PM PST Friday for coastal waters
     from Cape Shoalwater WA to Florence OR out 60 NM.

     Small Craft Advisory from 3 PM this afternoon to 3 PM PST
     Friday for Columbia River Bar.

&&

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