Small Craft Advisory 224, NWS Portland, OR

Area Forecast Discussion...UPDATED
National Weather Service Portland OR
1230 AM PST Sun Dec 19 2021

Updated discussion including the short term and aviation
discussions.

.SYNOPSIS...A strong cold front has stalled out over northwest
Oregon, but will sag southward very slowly late tonight. Expect
periods of moderate to heavy rain with this frontal boundary tonight
and tomorrow, with snow for elevations above 500 to 1000 feet. Snow
levels may lower to the Columbia River Gorge and Upper Hood River
Valley late Sunday into Monday. Unsettled weather continues through
rest of next week, with snow levels lowering again later next week.

&&

.UPDATE...Snowfall has become more widespread throughout the
northern portions of the forecast area, especially throughout
the Greater Portland-Vancouver metro areas and the Columbia
River Gorge including the Hood River Valley. Additional accumulations
are expected as the cold front has stalled over the area.
Temperatures are hovering just above freezing, but due to the
higher rain rates, it has been enough to adiabatically cool the
environment enough to snow. Accumulations range from a trace of
snow near the northern Willamette Valley in the Oregon City, OR
area, to around 2 inches in the higher elevations of the Camas,
WA area. Based on observations from the public, areas around
Corbett and Boring, OR have seen some of the highest
accumulations thus far. Accumulations have been spotty and
variable due to the subtle changes in intensity and temperature.
Much of the snow has been described as "wet snow" or "chunky
rain". Areas of most concern for accumulation at this point are
the Cascade Foothills and the Hood River Valley. As
temperatures continue to cool overnight, snow likely will begin
to accumulate on roadways and may create slick conditions.

Several Winter Weather Advisories have been issued for the
South Washington Cascades, North Oregon Cascades, the associated
foothills, the greater Portland-Vancouver Metro Area, and the
north Oregon Coast Range. Snow will continue to accumulate in
these areas through the next few hours. If traveling through
these areas use winter driving techniques, have a winter prep
kit in vehicles, and call 5-1-1 for local road conditions.

Will continue to monitor as this is a very dynamic pattern with
many nuanced features.    -Muessle

.SHORT TERM...Tonight through Tuesday...A strong cold front has
pushed inland over western Washington and northwest Oregon, which has
become nearly stationary as of 930 PM PST Saturday. That said, this
front should sag southward very slowly late tonight. The main
forecast challenge remains how low snow levels will get tonight, and
at what time.

Models have been bit mixy as to solutions, with a few ensemble runs
being way way too bullish on low elevation snow. But, will trend
forecasts more towards a mix, leaning with the NBM solutions. Now,
To the north of the front, snow levels will tumble, dropping as low
as 1000 to 1500 feet. As such, have various winter weather advisories
up for elevations above 1000 feet for northwest Oregon into southwest
Washington. At moment, looks like accumulations of 3 to 8 inches for
the Willapa Hills and far north Coast Range, as well as the Cascade
Foothills of south Washington. Heavier snowfall for the higher
Cascades, where 8 to 12 inches likely tonight into early Sunday. But,
with the front stalled, should be a band of somewhat heavier
precipitation over west central Oregon back to the northeast towards
the north Oregon Cascades. As such, precipitation may be heavy enough
to maintain a cooling effect to the air mass, allowing snow levels to
drop as low as 500 feet or bit more for areas just north of the
front. This low snow area seems to align from Chehalem Mountains
around Newberg northward to Vernonia, and eastward across the
Portland West Hills and higher terrain of eastern Clark County. With
that, seems good bet will see 2 to 5 inches of snow for areas above
700 feet for that area, with up to and inch possible across lowlands
of Washington County to far west/northwest Multnomah County (such as
Sauvie Island and Scappoose, as well as across parts of Clark County.
At this time, rain may mix with snow at times, but expecting little
if any snow accumulation for low elevation across rest of Portland
metro, including downtown Portland and the Airport. Timing is the
other question. As Will take some time to cool down, but think the
generally towards midnight, and mainly afterwards. Snow levels will
rise Sunday morning, but precipitation waning. So, will put up Winter
Weather Advisory for areas above 700 feet in the Portland/Vancouver
metro.

Now, along and to the south of the front, expect much higher snow
levels, with rain continuing. No low elevation snow for areas south
of Woodburn. Even across the Cascades, will see big differences in
the snow level. For example, snow levels running at 2000 feet for Mt
Hood area, but 4500 to 5500 feet towards Santiam Pass, and 6000 to
6500 feet at Willamette Pass. With accumulations of 8 to 12 inches
tonight into Sunday, with more expected Sunday into Monday morning,
will extend the current winter weather advisories for the South WA
Cascades and the North OR Cascades out to Monday morning. The stalled
front will lift north a bit Monday night into Tuesday, with not much
change in snow levels for the Cascades. As such, snow level will
generally above Santiam and Willamette Passes through Monday.

As earlier shift said:	not to be lost in all this is the concern
about heavy rain and resultant hydrologic issues. The front looks to
move fast enough to keep rainfall below what would prompt flood
concerns, though rainfall rates with the front itself may be heavy
enough to cause brief localized issues in areas of poor drainage. As
the front stalls and deep moisture continues to be forced over the
front, there may be an area of the Oregon Coast Range which receives
particularly heavy rainfall totals. It is difficult to say exactly
where this would be given all the moving parts to this forecast, but
right now the area between the Siletz and Siuslaw Rivers appear to
have the greatest chance of seeing 2+ inches of rain.

Later Sunday night into Monday, will see the low pressure that sits
offshore slow draw bit closer. As it does, flow with the low will
gradually pivot the stalled front over northwest Oregon back to the
north. As it does, will see increasing low level offshore flow, with
drier cooler air at lower levels getting pushed back to the west
through the Columbia Gorge. As such, air mass supports low elevation
snow for those areas again. Snow levels will be down, running from
river level to 500 feet in the Gorge. NBM still supporting moderate
potential of accumulations in those areas, and think will have enough
to support winter weather advisories for the Gorge as well as Hood
River Valley later Sunday night into Monday. But, want to see a few
more model runs before issuing any winter weather for those areas.

Pattern not changing all that much for later Monday into Tuesday. Low
pressure offshore moves little, and in fact, looks to be replaced by
another low on Tuesday. But that low(s) appear to be getting kept bit
more offshore, and drifting to the south a tad. Front that was
lifting north across the region on Monday will be gone by Monday
night, lifting well to the north. Will see some moisture in the
southerly flow being pushed up against the south Oregon coast Monday
night, and lifting up across rest of western Oregon on Tuesday. Could
be dry period with not much precipitation for a while Tuesday morning
into the early afternoon. But, too early at moment to bite on that,
as will keep PoPs in 50 to 70 pct. But, any precipitation does seem
to stay on the light side.				     /Rockey

&&

.LONG TERM...Wednesday through Friday...With diverging model
solutions there isn't too much confidence moving into the long term
forecast. Over the last 24 hours the 12Z EC has become more inline
with the 12Z GEM solution; these solutions show a deep upper level
trough moving south along the B.C. coastline and shifts inland near
Vancouver Island early Thursday morning. While the 12Z GFS shows the
trough staying offshore and dropping south towards northern
California Thursday morning. The latest 12Z run of the GEM is
stronger, slower and drops the trough axis right across the Pacific
NW into Thursday morning. The associated surface front will move on
to the north Oregon coast Wednesday afternoon [according to the GEM]
and bring a cool and showery pattern across the area Thursday.
Temperatures aloft will drop to around -3 to -5 C at 850 mb Thursday
which will aid in dropping snow levels to around 2500 to 3000 ft by
Thursday. With post frontal showers, snow will have a good chance
for accumulating up in the Cascades.

A secondary, weak front will move through the northwesterly flow and
provide enough lift to bring another round of heavier showers Friday.
Snow levels will also progressively drop Friday as the arctic air
mass over Canada pushes south. Overnight lows across Willamette
Valley sites will likely dipping into the mid 30s. Snow levels will
drop to around 2000 ft and potentially 1500 ft by end of day Friday.
NBM shows a 10-15% chance that lowlands in the northern Willamette
Valley will see very light (around 0.1 inches) snow through the day
Friday. 			  /BMuhlestein

&&

.AVIATION...Widespread MVFR cigs will continue along with
increasing precipitation overnight. Snow is falling north of
KSLE with some mixed precipitation around KUAO. Snow
accumulations are quite heavy around the Portland-Metro area with
accumulations around a half inch at KPDX. Snow and winds will
reduce visibility through the Columbia River Gorge, along the
Cascades and the Coast Range. Expecting additional accumulations
through the night. The cold front is passing over the area
causing temperatures to decrease...and thus aiding snowfall.
Given the wet state of the snowfall, a concern is the near
freezing temperatures behind the front which may create slick
conditions along more exposed surfaces. The coastal terminals and
areas south of KSLE should remain as rain through the next 24
hours.

Expect a slow warm up across the area after 18Z Sunday as well
as winds becoming easterly, which is being caused by a surface
low and associated warm front pushing northward along the coast.
Also, could see some gusty east winds near the mouth of the
Columbia River Gorge.

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

KPDX AND APPROACHES...MVFR CIGs with snow expected through the
next few hours. The snow would be considered a "wet" snow which a
high water content which may create some slick or even icy
conditions if it melts then refreezes in the early morning.
Accumulation wise looking at around 1 inch. Easterly winds will
persist through the period. Near freezing temperatures expected
again after 06Z Monday.   -Muessle

&&

.MARINE...A low pressure will push inland into western Canada
through the overnight hours. As the low moves inland, it will
drag a cold front across the waters and will form a coastal jet
through Sunday morning. As of this afternoon, a westerly wind
shift has been observed at Bouy 46029 and a similar shift is
expected at Buoy 46050 this evening. Currently, westerly small
craft wind gusts are present in zones PZZ270 and PZZ250 along
with southerly gale force winds in zones PZZ275 and PZZ255. These
gale force conditions should subside slightly and become
westerly this evening as the front moves eastward.

Sunday, winds will become offshore and then southerly as a
surface low moves northward towards the Olympic Peninsula
through Monday. At this time winds are expected to be below small
craft advisory criteria Sunday and increase by Monday.

Seas, in general, are expected to remain in the 8 to 12 ft
range. However, expect choppy and chaotic conditions as multiple
swell trains and varying wind directions will impact all waters
through the start of the week. This means that there could be
periods of time when seas are in the mid teens in overall wave
height. /42

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until noon PST today for Coast Range of
     Northwest Oregon-Upper Hood River Valley.

     Winter Storm Watch from noon PST today through Monday morning
     for Central Columbia River Gorge-Upper Hood River Valley.

     Winter Weather Advisory until 10 AM PST this morning for
     Central Willamette Valley-Greater Portland Metro Area-
     Northern Oregon Cascade Foothills-Western Columbia River
     Gorge.

     Flood Watch through Monday morning for Central Coast Range of
     Western Oregon-Central Oregon Coast-Central Willamette
     Valley-Northern Oregon Cascade Foothills-South Willamette
     Valley.

     Winter Weather Advisory until noon PST Monday for Northern
     Oregon Cascades.

WA...Winter Weather Advisory until noon PST today for I-5 Corridor
     in Cowlitz County-South Washington Cascade Foothills-
     Willapa Hills.

     Winter Storm Watch from noon PST today through Monday morning
     for Central Columbia River Gorge.

     Winter Weather Advisory until 10 AM PST this morning for
     Western Columbia River Gorge.

     Winter Weather Advisory until noon PST Monday for South
     Washington Cascades.

     Winter Weather Advisory until 6 AM PST early this morning for
     Greater Vancouver Area.

PZ...Small Craft Advisory until 3 PM PST this afternoon for coastal
     waters from Cape Shoalwater WA to Florence OR out 60 nm.

     Gale Watch from this afternoon through Monday morning for
     coastal waters from Cascade Head OR to Florence OR out 60
     nm.

     Small Craft Advisory until 6 AM PST early this morning for
     Columbia River Bar.

&&

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE PORTLAND OR
1251 AM PST SUN DEC 19 2021

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

1125 PM     SNOW             2 W PROEBSTEL           45.67N 122.48W
12/18/2021  E2.0 INCH        CLARK              WA   PUBLIC

1245 AM     SNOW             2 ENE CAMAS             45.60N 122.38W
12/19/2021  M1.0 INCH        CLARK              WA   TRAINED SPOTTER

            OVERNIGHT SNOWFALL THUS FAR.

&&

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE PORTLAND OR
230 AM PST SUN DEC 19 2021

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

0157 AM     SNOW             3 SE CAMP BONNEVILLE    45.67N 122.38W
12/19/2021  M4.0 INCH        CLARK              WA   TRAINED SPOTTER

            STORM TOTAL.

1200 AM     SNOW             2 W CAMAS               45.59N 122.46W
12/19/2021  M2.8 INCH        CLARK              WA   PUBLIC

1125 PM     SNOW             2 W PROEBSTEL           45.67N 122.48W
12/18/2021  E2.0 INCH        CLARK              WA   PUBLIC

1200 AM     SNOW             GREEN MOUNTAIN IN CAMAS 45.59N 122.41W
12/19/2021  M2.0 INCH        CLARK              WA   PUBLIC

1220 AM     SNOW             PRUNE HILL IN CAMAS, WA 45.59N 122.40W
12/19/2021  E2.0 INCH        CLARK              WA   PUBLIC

0100 AM     SNOW             1 SE EVERGREEN          45.62N 122.50W
12/19/2021  E2.0 INCH        CLARK              WA   PUBLIC

0130 AM     SNOW             1 WNW ALPINE            45.80N 122.46W
12/19/2021  E2.0 INCH        CLARK              WA   PUBLIC

0200 AM     SNOW             FERN PRAIRIE            45.64N 122.40W
12/19/2021  E2.0 INCH        CLARK              WA   PUBLIC

1240 AM     SNOW             NEAR 129TH IN HAPPY VAL 45.45N 122.53W
12/19/2021  M1.5 INCH        CLACKAMAS          OR   PUBLIC

1130 PM     SNOW             1 ENE CAMAS             45.59N 122.41W
12/18/2021  M1.3 INCH        CLARK              WA   PUBLIC

            AROUND 500 FT IN ALTITUDE.

1200 AM     SNOW             1 SSW EVERGREEN         45.62N 122.53W
12/19/2021  E1.0 INCH        CLARK              WA   TRAINED SPOTTER

1215 AM     SNOW             TROUTDALE               45.54N 122.39W
12/19/2021  E1.0 INCH        MULTNOMAH          OR   PUBLIC

1245 AM     SNOW             2 ENE CAMAS             45.60N 122.38W
12/19/2021  M1.0 INCH        CLARK              WA   TRAINED SPOTTER

            OVERNIGHT SNOWFALL THUS FAR.

0100 AM     SNOW             1 ESE BATTLE GROUND     45.78N 122.52W
12/19/2021  E1.0 INCH        CLARK              WA   PUBLIC

0125 AM     SNOW             NEAR ANDRESEN & 119TH A 45.71N 122.60W
12/19/2021  E1.0 INCH        CLARK              WA   PUBLIC

&&