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afdpqr

Area forecast discussion
National Weather Service Portland or
326 am PST Tue Feb 21 2017

Synopsis...another moderately strong low is forecast to move onshore
and inland across southern and central Oregon today, spreading
abundant moisture into northwest Oregon and less into southwest
Washington. Any gusty winds should be confined closer to the Lane
County Cascades today. Also expect another decent dose of mountain
snow today. Colder air associated with the parent upper trough will
sag into the forecast area starting tonight and significantly lower
snow levels Wednesday that will remain low through the weekend.
Precipitation amounts will remain relatively light but could mix in
snowflakes to sea level under the heaviest showers.
&&

Short term...today through Thursday...another strong low was moving
onshore into southwest Oregon early this morning and will move inland
across Oregon mainly south of our forecast area. Some wind could
brush eastern Lane County but will probably stay below high wind
criteria.

Another deformation zone to the north of the low will be across
northwest Oregon today for another period of significant rain with
snow in the mountains. The axis of the heaviest precipitation will be
a little south of that which fell on Monday, likely centered more
across the central Willamette Valley. Look for significant snow in
the adjacent Cascades, and have a Snow Advisory out for that with
accumulations expected to be on the high end of criteria.

The low will move east of the Cascades by this afternoon, but it will
take into this evening before the snow in the Cascades eases.
Precipitation west of the Cascades will also ease up by this evening
as well.

The associated larger scale colder upper trough will slowly spread
onshore into the Pacific northwest tonight and Wednesday. The models
indicate a weak surface low will develop off the coast Wednesday and
lead to the development of some cyclonic onshore low level flow that
will spread showers onshore, especially in the afternoon. In
addition, the snow level will lower to around 1000 feet, with
possibly some mixed rain and snow showers reaching the valley floors
in any heavier showers. It is not out of the question to see an inch
of snow accumulation down to around 1000 feet on Wednesday, in places
such as The West Hills of Portland and in the hills around Hockinson
and near Sandy. However, accumulations are not expected at the valley
floors.

The models say a piece of energy with this trough will drop south
Wednesday night and Thursday with a decreasing chance of rain or snow
showers. However, we might see a few showers develop over the Coast
Range Thursday afternoon and drift out over the valleys in the
afternoon. Amounts will be on the spotty side and light, but snow
levels could be closer to 500 feet on Thursday. Tolleson

Long term...no changes. Previous discussion follows...Wednesday
night through Monday...the cold upper low will continue funneling
colder modified Arctic air from the Pacific and then over the Pacific
northwest. Most days will see some threat of shower activity with
perhaps Saturday afternoon and night as the most likely to stay dry.
Outside of that period, there will be plenty of shower activity and
low snow levels through the extended. Fortunately, moisture will
remain rather limited for each day and that should limit any threat
of major storms. However, elevations above 1,500 feet and The
Gorge/Hood River Valley could pick up an inch or two each day.
Elsewhere, fully expect there will be times where snow may fall down
to sea level, but do not expect accumulations to persist below 1,000
feet for more than a couple hours at a stretch. Even then, it will
take a rather robust shower to bring any accumulating snow down to
sea level. /Jbonk
&&

Aviation...low stratus and fog began to develop ahead of the front,
but as light rain has spread over the area, enough mixing has
commenced to improve ceilings to VFR at most locations. The only
exceptions are kkls, kuao, and ksle where the lower cigs are holding
on. Expect this to be short lived with most locations improving to
VFR cigs for a period this morning. Some locations may hold onto MVFR
visibilities as precipitation overspreads the area today. The area
with the greatest visibility restrictions due to rain will likely be
ksle and keug. In addition, ceilings will also drop to MVFR this
morning as the precipitation intensity increases. These MVFR
conditions will prevail for a majority of the day, but will begin to
improve to VFR by later in the afternoon once the surface low moves
east of the area.

Kpdx and approaches...borderline MVFR/VFR cigs will continue through
the early morning hours before ceilings drop around mid morning and
keep MVFR conditions around for most of the day. Conditions will once
again improve to VFR later this afternoon once the surface low moves
away. /Bentley
&&

Marine...other than a brief period of small craft winds today and
low end rough Columbia River bar conditions, marine weather will be
quite benign through the period. Seas will generally remain between 7
and 9 feet through the week. This will cause borderline rough
Columbia River bar conditions during the ebbs. Given how high the
seas got today (~14 feet) during the Ebb, confidence was high enough
to issue a Small Craft Advisory for rough Columbia River bar for the
afternoon Ebb. Otherwise, northwesterly winds will strengthen today
as a surface low makes landfall in southern Oregon. It appears gusts
may reach gales in the south Oregon waters, but north of the surface
low, winds will not gust any higher than 30 knots. /Bentley
&&

Pqr watches/warnings/advisories...
or...Winter Weather Advisory until 6 PM PST this evening for
northern Oregon Cascades.

Winter Weather Advisory until 10 PM PST this evening for
Cascades in Lane County.

Washington...none.
Pz...Small Craft Advisory for winds until 4 PM PST this afternoon
for coastal waters from Cape Shoalwater Washington to Florence or
out 60 nm.

Small Craft Advisory for rough Columbia River bar from 11 am
this morning to 5 PM PST this afternoon.

&&

$$

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