High Wind in Oregon, December 18, 2018

Area Forecast Discussion
National Weather Service Medford OR
938 PM PST Mon Dec 17 2018

.AVIATION...For the 18/06Z TAFs...Ceilings are mostly VFR across
the area this evening as winds keep things mixed ahead of an
approaching front. Expect conditions to deteriorate overnight at
the coast as rain becomes heavier, and these conditions will
spread inland tomorrow morning along with the rain. The west side
exception will be at KMFR where downsloping winds will keep VFR
conditions in place through late tomorrow morning. Conditions will
also remain VFR on the east side until rain arrives later
tomorrow morning.

At North Bend, Roseburg and Medford, winds at the surface will be
much lower than just above the ground. Wind speeds at 1500-2000
AGL will be in the 35-50 kt range inland from the coast, but up
to 65 kt along the coast. This will result in turbulence and low
level wind shear, so expect some bumpy rides with arrivals and
departures through Tuesday morning. A period of very strong
surface winds with gusts to 45 kt could impact the coast,
including KOTH, as the front moves onshore Tuesday morning.
-Spilde/Wright

&&

.PREV DISCUSSION... /Issued 826 PM PST Mon Dec 17 2018/

DISCUSSION...An update was already made this evening to increase
snow amounts and issue a winter weather advisory for the high
Cascades around Crater and Diamond Lake. It has been snowing hard
there for a couple of hours, and webcams show it's still coming
down and piling up around Diamond Lake with temperatures hovering
right around freezing. It has also started to snow on highway 140
at Lake of the Woods, but temperatures are around 35F, so it
shouldn't pose too much of a problem there. The incoming airmass
is warm, and snow levels will rise through the night, and thus it
should change over to rain at Diamond Lake, but we've seen cold
air hang on there longer than expected many times, so the advisory
goes through the night. See WSWMFR for details.

The rest of the forecast looks on track, so no further updates are
expected this evening. An atmospheric river (a.k.a. pineapple
express) is pointed right at the PacNW this evening. The focus of
the deepest moisture with precipitable water values of around
1.25 inches, is just north of us. However, this will gradually sag
southward across our area through tomorrow bringing moderate to
heavy rain to most west side locations. The other aspect of this
storm is the wind. We've been seeing gales with occasional storm
force gusts over the waters all day, and strong winds are starting
to work onto the coast with a recent gusts of over 60 MPH at Cape
Blanco. Winds have also picked up in the Shasta Valley with gusts
to 34 MPH at Weed. These winds will spread inland tomorrow and
affect the east side as well. With models showing Redding to
Medford pressure gradients of around 10 millibars tomorrow
morning, it's hard not to think about strong winds getting into
the Rogue Valley. However, by the time the gradients peak, winds
aloft are from the southwest - i.e. not aligned from the southeast
(which is the way we usually get strong winds). Furthermore, none
of the guidance (including MOS) shows winds in Medford, so we'll
just keep an eye on it. -Wright

PREV DISCUSSION... /Issued 402 PM PST Mon Dec 17 2018/

SHORT TERM...A strong and moist front is approaching the region
today. This front will bring heavy rain to the coast with areas of
moderate precipitation inland. Strong winds are also expected for
coastal areas with areas of moderate to strong winds inland.

Models continue indicate that this is a very moist system with
precipitable water values of over an inch along the coast. This
will allow heavy rain to fall over coastal areas. Moderate rain
is expected to develop along the coast by this evening, becoming
heavy late tonight into Tuesday. Then showers are expected behind
the front into Tuesday evening and night.

For areas inland of the coastal mountains, expect light to
moderate precipitation to spread inland this evening through
Tuesday morning then widespread light to moderate precipitation
Tuesday afternoon into early Tuesday evening. Snow levels will
rise from around 4500 to 5000 feet this evening to 6000 to 7000
feet Tuesday morning as precipitation increases inland, except for
lower snow levels of 5000 to 5500 feet east of the Cascades and
in the Mount Shasta area. As precipitation becomes widespread
inland Tuesday afternoon and evening, snow levels will peak at
around 7000 to 7500 feet from the Cascades west and at around 6000
to 7000 feet east of the Cascades and in the Mount Shasta area.
With rising snow levels expect most the precipitation to fall as
rain. However, some snow is expected before the changeover to rain
as the system moves into the area this evening into early
Tuesday, mainly for higher mountain locations above 5000 feet in
the Southern Oregon Cascades and Mount Shasta area. Light to
moderate snow is expected for these locations with locally heavy
snow possible over higher mountains such as in the Crater Lake
area. During the day Tuesday, expect precipitation for all but the
highest mountains to change over to rain.

Storm total rainfall of 2 to 5 inches and locally up to 6 inches
is expected along the coast this evening through Tuesday evening.
Most the rain will fall in a 12 hour period from late tonight
through early Tuesday afternoon for coastal areas. With the
potential for heavy rain in a short period of time over recent
wildfire burn scars, a flash flood watch has been issues for the
areas within the Klondike/Taylor and Chetco burn scars. Please see
the FFWMFR for details. Inland amounts will be more variable but
expect moderate to locally heavy precipitation with storm totals
around 1 to 2 inches and locally higher amounts over Douglas,
Josephine, western Siskiyou County, as well as over the Southern
Oregon Cascades and northern Klamath county. Area rivers and
streams are expected to see rises but no mainstem river flooding
is forecast. Please see the ESFMFR for details.

Strong winds will also develop along the coast as this front
pushes into the area this evening through Tuesday. Models
indicate winds along the coast will peak late tonight through
early Tuesday afternoon. Gusty winds are also expected tonight
into Tuesday for some areas west of the Cascades, especially in
the southern Shasta Valley, southern Illinois Valley and over the
mountains in Coos, Curry, western Douglas and western Josephine
counties. East side locations will also see strong winds develop
Tuesday afternoon and evening, especially over the mountains and
in the Summer Lake area. High wind warnings and wind advisories
are in place for these areas. Please see the NPWMFR for details.

Showers are expected behind the front late Tuesday evening into
Tuesday night with showers tapering off Wednesday morning as the
front lifts north and a weak upper ridge builds into place. With
ample low level moisture and decreasing showers, patchy or areas
of fog are possible across inland valleys Wednesday morning.

A cold front will approach the area Wednesday night and may spread
light rain into the coast.

LONG TERM...Thursday to Monday, December 20-24, 2018...An
amplified upper level ridge axis will shift to the east of the area
Thursday while the Pacific jet stream continues to send disturbances
into the Pacific Northwest. The amplified flow initially will result
in a fairly deep Pacific cyclone to intensify as it heads toward
Vancouver Island/SW British Columbia. Despite some relatively
minor timing differences, models have been pretty consistent showing
the frontal system associated with this storm to move onshore in SW
Oregon Thursday, then push eastward through the area Thursday night.
Expect another round of wind/rain for the coast, though not as much
as with Tuesday's system. It is notable, however, that most of the
guidance shows a good soaking as the front moves through the west
side valleys with a solid 0.33-0.50 of an inch of rain. Even most
East Side areas are expected to get 0.10-0.25 of an inch. Snow
levels will be quite high though - up around or above 6000 feet -
so, snow accumulations will be reserved for the highest elevations.
Some of the high passes (Hwy 140) may get a dusting of snow as snow
levels drop Thursday night.

Following that front, mainly zonal flow will set up Friday into
Saturday with snow levels settling in the 3500-4500 foot range
beneath a slightly colder air mass. A disturbance may skim northern
areas during this time frame, but overall, chances for precipitation
across most of the CWA will be low.

The next significant energetic system will arrive from the Pacific
Saturday night into Sunday, followed quickly by another one on
Christmas Eve. These will be the systems to keep an eye on for the
next several days since there will be some colder air in place and
the potential for snow impacts. This is a concern, especially for
the high passes on I-5 (Black Butte/Siskiyou Summits) during a peak
in holiday travel. Timing and strength details as well as exactly
where the snow levels set up will be ironed out over the coming
days, so stay tuned. -Spilde

MARINE...Updated 200 PM PST Monday 17 December 2018...South winds
are already ramping up ahead of the next front with gusts
approaching gales at buoy 15 and 27. Winds will only increase over
time with solid gales into Tuesday morning. There's good
agreement among the models showing winds shifting southwest and
decreasing below gales over the northwest part of the waters by
mid morning Tuesday, then late morning over the southern inner
waters. For now we'll keep the gale warning until Tuesday
afternoon because hazardous seas warning conditions are likely
with very high seas and dangerous surf conditions. Winds briefly
diminish Tuesday night through Wednesday but seas will remain high
to very high through mid- week. Yet another cold front with south
gales is expected late Wednesday night into Thursday.

There will be relative break in the swell tonight into Tuesday, then
another heavy swell will arrive Wednesday. Even with the brief
improvement, conditions will still be dangerous at bar crossings and
the surf zone due to strong currents and breaking waves.

There's some agreement that conditions could settle down briefly late
in the week, but it may only be temporary. We'll continue to monitor
this. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 10 AM to 10 PM PST Tuesday for
     ORZ030-031.
     Wind Advisory from 10 AM to 10 PM PST Tuesday for ORZ029>031.
     Winter Weather Advisory until 10 AM PST Tuesday for ORZ027.
     High Wind Warning until 4 PM PST Tuesday for ORZ021-022.
     Flash Flood Watch from 4 AM PST Tuesday through Tuesday evening
     for ORZ022-024.
     Wind Advisory until 4 PM PST Tuesday for ORZ023-024.
     High Surf Warning until 10 PM PST Wednesday for ORZ021-022.

CA...High Wind Warning from 10 AM to 10 PM PST Tuesday for CAZ085.
     Wind Advisory from 10 AM to 10 PM PST Tuesday for CAZ084-085.
     Wind Advisory until 4 PM PST Tuesday for CAZ081.

Pacific Coastal Waters...Gale Warning until 4 PM PST Tuesday for PZZ350-356-370-376.
     Hazardous Seas Warning from 4 PM Tuesday to 10 PM PST Wednesday
     for PZZ350-356-370-376.