Small Craft Advisory 6, NWS Portland, OR

Area Forecast Discussion...UPDATE
National Weather Service Portland OR
910 PM PST Tue Jan 12 2021

Updated Hydrology discussion...

.SYNOPSIS...A warm front has pushed inland while a weak cold front
will trail behind. Moderate to heavy rain will persist through
Wednesday with the potential for river, rural, and urban flooding.
Strong winds are expected along the Oregon coast through tonight,
with breezy conditions for the Willamette Valley this evening. Large
surf and high tides will result in hazardous conditions for the
beaches and low-lying coastal areas through Wednesday. Dry weather on
Thursday will allow rivers to recede before the next weaker front
that is expected Thursday night.

&&

.SHORT TERM...Tonight through Thursday night...Quite an active day
composed of rain, wind and flooding which will persist through
Wednesday. Synoptically, the pattern is comprised of a broad area of
low pressure with several embedded fronts within the general flow.
The jet stream at 30,000 ft is southwest to northeast oriented with
the main jet streak sitting just north of the forecast area over
north and central Washington. Within the streak wind speeds are
reaching around 120 kt. This jet stream is supporting the surface
fronts which is allowing them to be quite strong and active.

The first front of the series was a quasi-stationary warm front which
produced a significant amount of rain overnight into today. This
front has continued to be a big rain maker although satellite and
radar do show some slight erosion and weakening of rainfall. With the
prolonged period of moderate and sometimes heavy rain, there have
been several urban and rural rivers throughout the area that have
reached bank full or have flooded. Tidal overflow was also a major
concern this afternoon with high tides to nearly 13 ft along the
south Washington coast. As high tide has passed, it should no longer
be a concern but it may take a while for water to recede, especially
due to local rivers being quite full. High winds along the coast are
likely to persist for several more hours but should slowly dissipate
overnight.

The second front, a slightly cooler front, is beginning to drop down
towards the area this evening. This front is rejuvenating the rain
along the coast and will continue to do so overnight. Likely going to
see another bout of heavier rain overnight tonight into early
Wednesday morning. This will especially be true along the coast and
the central Cascades. Hi-res model guidance and the track of the
front shows the bulk of the rain avoiding the northern portions of
the forecast area and the south Washington Cascades...although can't
rule out more rain than what is currently forecast. Either way,
expect additional rainfall accumulations which will likely keep
rivers full.

On Wednesday though a change is in store. The fronts will have both
passed and a weak area of high pressure will build in behind them.
This ridge will allow for a few sun breaks and the rain will taper
off through the early afternoon. this will be the trend through
Thursday as well. Southwesterly flow will dominate the area Wednesday
night through Thursday which will usher in dry and warmer air from
the CONUS southwest. Temperatures around 5000 ft will range from 5-9C
so expecting daytime temperatures to be slightly warmer. The break
will be much needed as another front will advance over the area very
early Friday.	-Muessle

.LONG TERM...Friday through Monday night...Another front is expected
to move onshore Thursday evening but it will be a bit weaker than the
ones experienced earlier in the week. Recent model runs are
suggesting a weak atmospheric river event with IVT values near 250
kg/ms. As there is still quite a bit of time between now and this
event, not hanging a hat on an atmospheric river forecast. There is
also significantly less upper level support as the jet stream is much
weaker and is falling apart just before reaching the area. While
there is ample moisture available to this system, the lack of
dynamics means that there will need to be some sort of change in
order to tap into it, and create the heavier rain. The front
should move through the area rather quickly and over by Friday
afternoon with rainfall totals likely remaining below an inch even
across the terrain favored areas. Snow levels will be at or above
5000 feet and do not anticipate much if any snow from this front.
High pressure rebuilds Friday night and Saturday for a brief period
of dry weather in the wake of this front. Models are in good
agreement on another non impressive front Saturday night through
Sunday followed by dry weather next Monday. -Muessle/TJ

&&

.HYDROLOGY...The next round of moderate to heavy rainfall is
currently ongoing Tuesday evening with the main frontal band surging
along the Oregon/Washington coast. As it pushes inland expect max
hourly rainfall rates to increase during a 2-3 hour period. Mainstem
rivers currently above flood stage include the Grays River near
Rosburg, Wilson River near Tillamook, and Siuslaw River near
Mapleton. The Grays and Wilson Rivers have already crested but are
not expected to fall below flood stage until Wednesday morning.
Other coastal and inland rivers at bankfull that are expected to rise
above minor flood stage include the Cowlitz River at Kelso, Nehalem
River at Foss, Siletz River at Siletz, Tualatin River near Dilley,
Marys River near Philomath, Luckiamute River near Suver, as well as
the Clackamas River near Estacada.

Besides Mainstem rivers, small streams and creeks will also rise,
and possibly flood tonight. Minor urban flooding in poorly drained
areas is also possible. Will continue the Flood Watch for the same
areas to account for all of the flooding concerns. The saturated
soils will also likely lead to land slides. /DDH

&&

.AVIATION...Widespread MVFR conditions, occasionally dipping into
IFR category especially along the coast, will continue with periods
of rain through the evening ahead of a cold front. A few areas in
the Willamette Valley will continue to see areas of VFR conditions
as well. A cold front moving southeast across the region tonight
will allow the rain to taper off behind the front after 03Z-09Z.
Expect gusty southerly winds to temporarily pick up as the front
moves through between 02Z and 08Z along the coast, and from 05Z-09Z
inland. MVFR ceilings will still be widespread behind the front
after 07Z-09Z, but improvement to VFR category can be expected
Wednesday, as early as 09-12Z on the north coast, to as late as 18
to 22Z in the South Willamette Valley.

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

KPDX AND APPROACHES...MVFR conditions, occasionally IFR conditions
can be expected to continue through about 09Z tonight. Gusty south
winds may pick up temporarily ahead of a cold front between 05Z and
09Z. Behind the front rain will taper off, but it is likely MVFR
ceilings continue into the morning Wednesday, before VFR conditions
return after 17Z-20Z.
&&

.MARINE...A westerly swell continues tonight and through Wednesday,
with a slow decrease in heights and periods expected. Southerly
Gales will continue through the evening ahead of a southeast moving
cold front, with a few storm force gusts still likely south of Cape
Shoalwater. As the cold front moves through during the evening,
winds will switch around to the west and decrease to under 30 kt.
Steep wind driven seas out of the south will continue as a fresh
swell, decreasing late tonight and Wednesday. Combined seas from the
west and southerly swells were running 20 to 24 ft Tuesday
afternoon, and should begin to drop under 20 ft late tonight.

As high pressure moves in behind the front Wednesday, winds and seas
will continue to diminish, likely below 20 kt by Wednesday afternoon
and below 15 ft by Wednesday evening.

A much weaker cold front is expected to move into the waters
Thursday night bringing small craft advisory level winds, followed
by another long period westerly swell train arriving Friday and
building seas back into the range of 15 to 20 ft late Friday
and Friday night.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Flood Watch through Wednesday morning for Cascade Foothills in
     Lane County-Cascades in Lane County-Central Coast Range of
     Western Oregon-Central Columbia River Gorge-Central Oregon
     Coast-Central Willamette Valley-Coast Range of Northwest
     Oregon-Greater Portland Metro Area-Lower Columbia-North
     Oregon Coast-Northern Oregon Cascade Foothills-Northern
     Oregon Cascades-South Willamette Valley-Western Columbia
     River Gorge.

     High Surf Advisory until 9 PM PST this evening for Central
     Oregon Coast-North Oregon Coast.

     Coastal Flood Advisory until 4 PM PST Wednesday for Central
     Oregon Coast-North Oregon Coast.

     High Wind Warning until 2 AM PST Wednesday for Central Oregon
     Coast.

     High Wind Warning until midnight PST tonight for North Oregon
     Coast.

WA...Flood Watch through Wednesday morning for Central Columbia
     River Gorge-Greater Vancouver Area-I-5 Corridor in Cowlitz
     County-South Washington Cascade Foothills-South Washington
     Cascades-South Washington Coast-Western Columbia River
     Gorge-Willapa Hills.

     High Surf Advisory until 9 PM PST this evening for South
     Washington Coast.

     Coastal Flood Advisory until 4 PM PST Wednesday for South
     Washington Coast.

PZ...Gale Warning until 10 PM PST this evening for coastal waters
     from Cape Shoalwater WA to Cascade Head OR out 60
     NM.Waters from Cascade Head to Florence OR from 10 to 60
     NM.

     Small Craft Advisory until 6 PM PST Wednesday for Columbia
     River Bar.

     Storm Warning until 10 PM PST this evening for Coastal waters
     from Cascade Head to Florence OR out 10 NM.

&&

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PORTLAND OR
928 PM PST TUE JAN 12 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0920 PM     HEAVY RAIN       2 E MAPLETON            44.03N 123.83W
01/12/2021  M1.25 INCH       LANE               OR   TRAINED SPOTTER

            VERY WINDY AS WELL.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PORTLAND OR
1119 PM PST TUE JAN 12 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1113 PM     FLOOD            2 S RALEIGH HILLS       45.46N 122.75W
01/12/2021                   WASHINGTON         OR   NWS EMPLOYEE

            ASH CREEK JUMPED ITS BANKS, WITH WATER
            ENTERING FINISHED BASEMENT OF HOME.

&&

SMW