Sneakerwave in Oregon, January 15, 2021

Area Forecast Discussion
National Weather Service Portland OR
251 PM PST Fri Jan 15 2021

.SYNOPSIS...A weak front has moved to the east of the area but low
clouds remain in the interior valleys tonight and Saturday morning,
but with clearing skies for the mountains.  The next front will also
be weak, clipping the region with some light rain and Cascades snow.
Mostly dry weather is expected early next week, but there will be
plenty of night and morning fog in the valleys.

&&

.SHORT TERM...Tonight through Monday...The weak front that moved in
overnight is now east of the area. Satellite show mid and high clouds
clearing from west to east, revealing abundant stratus filling the
interior valleys. There is some mixing evident on the higher terrain
and on the edges of the valley stratus. But given the time of year
and little mixing forecasted by the models the stratus will continue
into Saturday. Potential dense fog may be less of an issue than
earlier thought, but still expect to have fog tonight. With the
subsidence inversion lowering tonight will probably see the stratus
layer close enough to the surface for some reduction in visibility.
The low stratus will likely continue in the valley into Saturday
afternoon, but by then clouds from the next system will be moving in.
The next front arrives Sunday, with modest QPF and
snow levels above Cascade pass levels until the front moves through
and pcpn end. So again not much impact expected for either the
valleys or high terrain.  High pressure returns later Sunday into
Monday for a dry period. This time the upper ridge sets up offshore
resulting in more northerly flow closer to the surface with the
surface high pressure to the north and lower pressure along the south
Oregon coast. Temperatures through early next week will be
seasonable. /mh

.LONG TERM...Monday night through Friday...At the start of the long
term the upper ridge continues near 130W maintains the dry weather.
But trends in the models is for shortwave energy riding over the top
of the ridge and begin to carve out a trough over the west coast
toward the end of the week. Some pcpn may accompany a shortwave on
Tue night and Wed, but at this point models are not in good agreement
with this feature. Deterministic runs of the GFS and ECMWF show
stronger shortwave digging along the BC coast toward the PacNW
sometime Thu.  These systems often tease lowland snow, but usually
snow levels end up in the 1000-1500' range due to southerly or
onshore flow ahead of them. Once the air mass becomes cold enough for
snow levels to reach the valley floor, drier northerly flow usually
shuts off the precipitation. For now, we will keep snow levels around
1000 feet Thu night/Friday, except lower in and around the Hood River
Valley.   Up to then, expect dry weather with seasonal temperatures
along with some valley fog.

&&

.AVIATION...Satellite observations as of 23Z Friday showed low
stratus hanging strong across the interior valleys and over
portions of the central Oregon coast. Cigs with this stratus deck
continue to be in the LIFR to IFR range. The vast majority of
model guidance is not handling this stratus deck well, and had
suggested this stratus deck would break up by 21Z Friday. It
appears the only model that has been accurately depicting the
ongoing low stratus thus far is the NAM, so this guidance was
used more heavily for the 00Z TAFs. This model suggests low
stratus will stick around through Friday night and into Saturday
morning, which does make sense given the lack of low-level mixing
and calm to light and variable surface winds. Since the low
stratus is expected to stick around this evening through tonight,
the fog forecast becomes a bit trickier. There is the potential
that the low stratus will limit radiational cooling enough to
prevent widespread fog from developing tonight. That said, there
is also the potential that this stratus deck will simply lower to
the ground and result in widespread dense fog. Although
confidence is fairly low, gut feeling is that dense fog will form
at some point tonight over portions of the valley, between
06-12Z Saturday. It is unclear how widespread the potential dense
fog may become. Current thinking is that the central and
southern valley have the best chance for dense fog, with lower
chances to the north and along the coast.

Fog should begin to lift Saturday afternoon, but low stratus
will most likely linger over much of the Willamette Valley
through Saturday afternoon and into Saturday night.

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

KPDX AND APPROACHES...Expecting IFR cigs to continue through this
evening, before lowering to 300-500 feet early tonight. Fog may
also form at the terminal at some point tonight, most likely
beginning between 09-12Z Saturday. It in unclear if fog will be
dense at the terminal. Fog should lift by late Saturday morning,
giving way to low stratus which will attempt to break up Saturday
afternoon. -TK

&&

.MARINE...Buoy observations Friday afternoon showed relatively
light winds over the waters, sustained between 5-10 kt. Seas
were running between 12 and 15 feet with a dominant period around
13 to 15 seconds due to an ongoing westerly swell. Expect the
westerly swell to continue through tonight and into Saturday
morning, before seas fall slightly late Saturday morning into the
afternoon. By Saturday evening, guidance suggests seas will fall
to around 10 feet and then to around 8 feet Saturday night. A
weak front is also set to push across the waters Saturday evening
through Saturday night, so although seas will be on the decrease
expect winds to be on the increase. Winds may increase enough to
reach Small Craft Advisory criteria with gusts between 20-25 kt,
mainly behind the front Sunday morning.

High pressure than returns to the waters Saturday afternoon and
looks to continue through early next week and possibly into the
middle of next week. This setup will favor a prolonged period of
north to northeast winds over the waters from Sunday afternoon
through Tuesday morning. Winds do not look very strong during
that time, only reaching Small Craft Advisory criteria at best.

Despite the rather unimpressive winds, westerly swell will build
again Sunday afternoon and evening, peaking around 15 feet Sunday
night before falling Monday into Tuesday. Once seas fall below 10
feet on Tuesday, guidance suggests conditions will stay that way
through at least Thursday morning. -TK

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 4 PM PST Saturday for coastal waters
     from Cape Shoalwater WA to Florence OR out 10 NM-Columbia
     River Bar-Coastal waters from Cape Shoalwater WA to
     Florence OR from 10 to 60 NM.

&&

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PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE PORTLAND OR
1040 AM PST FRI JAN 15 2021

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

1145 AM     FLOOD            GRAYS RIVER             46.35N 123.58W
01/12/2021                   WAHKIAKUM          WA   OTHER FEDERAL

            BELOW FLOOD STAGE AT 215 AM PST ON
            1/14/2021. CRESTED AT 15.54 FT. FLOOD STAGE
            IS 12.0 FT.

0115 PM     FLOOD            COWLITZ NEAR KELSO      46.14N 122.92W
01/13/2021                   COWLITZ            WA   OTHER FEDERAL

            BELOW FLOOD STAGE AT 100 AM PST ON
            1/14/2021. CRESTED AT 22.20 FT. FLOOD STAGE
            IS 21.5 FT.

0730 AM     FLOOD            TUALATIN AT DILLEY      45.47N 123.13W
01/13/2021                   WASHINGTON         OR   OTHER FEDERAL

            BELOW FLOOD STAGE AT 1130 AM PST 1/14/2021.
            CRESTED AT 18.09 FT. FLOOD STAGE IS 17.5 FT.

0915 AM     FLOOD            TRASK                   45.45N 123.71W
01/13/2021                   TILLAMOOK          OR   OTHER FEDERAL

            BELOW FLOOD STAGE AT 1145 AM ON 1/13/2021.
            CRESTED AT 17.10 FT. FLOOD STAGE IS 16.5 FT.

0600 AM     FLOOD            NEHALEM NEAR FOSS       45.70N 123.75W
01/13/2021                   TILLAMOOK          OR   OTHER FEDERAL

            BELOW FLOOD STAGE AT 800 AM PST ON
            1/14/2021. CRESTED AT 17.73 FT. FLOOD STAGE
            IS 15.0 FT.

0315 PM     FLOOD            WILSON NEAR TILLAMOOK   45.48N 123.72W
01/12/2021                   TILLAMOOK          OR   OTHER FEDERAL

            BELOW FLOOD STAGE AT 1100 PM PST ON
            1/13/2021. CRESTED AT 16.73 FT. FLOOD STAGE
            IS 12.0 FT. MODERATE FLOOD STAGE IS 15.5 FT.

0805 AM     FLOOD            LUCKIAMUTE NEAR SUVER   44.78N 123.23W
01/13/2021                   POLK               OR   OTHER FEDERAL

            BELOW FLOOD STAGE AT 600 AM PST ON
            1/15/2021. CRESTED AT 31.29 FT. FLOOD STAGE
            IS 27.0 FT.

1015 AM     FLOOD            JOHNSON CREEK AT SEYCAM 44.48N 122.51W
01/13/2021                   LINN               OR   OTHER FEDERAL

            BELOW FLOOD STAGE AT 215 PM PST ON
            1/13/2021. CRESTED AT 11.33 FT. FLOOD STAGE
            IS 11.0 FT.

0900 AM     FLOOD            ALSEA NEAR TIDEWATER    44.39N 123.83W
01/13/2021                   LINCOLN            OR   OTHER FEDERAL

            BELOW FLOOD STAGE AT 1000 PM PST ON
            1/13/2020. CRESTED AT 20.83 FT. FLOOD STAGE
            IS 18.0 FT.

0145 AM     FLOOD            SIUSLAW NEAR MAPLETON   44.06N 123.88W
01/13/2021                   LANE               OR   OTHER FEDERAL

            BELOW FLOOD STAGE AT 115 AM PST ON
            1/14/2021. CRESTED AT 21.26 FT. FLOOD STAGE
            IS 18.0 FT.

1015 AM     FLOOD            NEHALEM NEAR VERNONIA   45.81N 123.28W
01/13/2021                   COLUMBIA           OR   OTHER FEDERAL

            BELOW FLOOD STAGE AT 1145 PM ON 1/13/2021.
            CRESTED AT 12.17 FT. FLOOD STAGE IS 12.0 FT.

1245 PM     FLOOD            CLACKAMAS AT ESTACADA   45.30N 122.35W
01/13/2021                   CLACKAMAS          OR   OTHER FEDERAL

            BELOW FLOOD STAGE AT 945 PM PST ON
            1/13/2021. CRESTED AT 21.3 FT. FLOOD STAGE
            IS 20.0 FT.

0530 AM     FLOOD            MARYS NEAR PHILOMATH    44.52N 123.33W
01/13/2021                   BENTON             OR   OTHER FEDERAL

            BELOW FLOOD STAGE AT 100 PM PST ON
            1/14/2021. CRESTED AT 21.23 FT. FLOOD STAGE
            IS 20.0 FT.

0415 AM     FLOOD            SILETZ NEAR SILETZ      44.72N 123.33W
01/13/2021                   BENTON             OR   OTHER FEDERAL

            BELOW FLOOD STAGE AT 900 PM PST ON
            1/13/2021. CRESTED AT 21.62 FT. FLOOD STAGE
            IS 16.0 FT. MODERATE FLOOD STAGE IS 20.0 FT.

&&