Winter Storm Warning 10, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
846 PM PST Mon Feb 18 2019

.UPDATE...Once again as last night clouds are piling up along the
Umpqua Divide and the Siskiyous. An increase i of clouds,
especially over the west side of Oregon, will result in similar
conditions as last night. With this current forecast looks on
track and will not update this evening. Sven

&&

.PREV DISCUSSION... /Issued 236 PM PST Mon Feb 18 2019/

SHORT TERM...An upper level trough is continuing to shift
southeastward. Behind this trough, mainly dry weather will
continue except for slight chance for light precipitation tonight
into Tuesday morning along the coastal waters, coast and in the
Cascades near Crater Lake and Diamond Lake.

A cold shortwave and frontal system are on track to move into the
area from the north Tuesday evening through Wednesday. This
system will bring another round of lower elevation snow into the
area. Models have trended quicker and moister with this shortwave
moving into the area. Models continue to show cold air with 850 mb
temperatures of -5 degrees C moving into the area late Tuesday
night into Wednesday morning and 1000-500 mb thickness values of
around 524. So expect snow levels to lower to around 2000 feet
Tuesday evening into Tuesday night as precipitation moves into
the region, then remain low Wednesday morning. Snow levels may
briefly lower down around 1500 feet at times, especially in
heavier precipitation bands with the front. This shortwave and
front are expected to bring 2 to 5 inches of snow (storm total) to
lower elevations of 2000 to 3000 feet late Tuesday through
Wednesday evening with higher accumulations of 6 to 12 inches
over the Southern Oregon Cascades and into higher portions of the
Siskiyous. Gusty west winds are also expected Tuesday night and
Wednesday in the Cascades, resulting in blowing snow and limited
visibilities. This may lead to near zero visibilities and
dangerous travel conditions at times, especially for higher
mountains in the Cascades that area exposed to west winds.

Of note, although snow levels lower to 2000 feet overnight and
early Wednesday, expect snow levels to fluctuate between 2000 to
2500 feet Wednesday afternoon due to daytime heating. While snow
may continue to fall down to 2000 feet Wednesday afternoon,
accumulations will be lesser during the day across lower
elevations due to warming daytime temperatures. Higher passes in
the Cascades will continue to see moderate to locally heavy snow
accumulations though. Also areas east of the Cascades and into
Northern California are expected to see light to locally moderate
precipitation.

Behind the front, Wednesday evening, expect light to moderate
showers over the area. Snow levels are expected lower to 1500
during the evening Wednesday, then down to 500 to 1000 feet
Wednesday night as showers decrease. Lower valley floors west of
the Cascades may see a dusting or light snow Wednesday evening and
nights. Given the northwest flow Wednesday evening into Wednesday
night, expect the best chance for increased snow showers to be
over northwest facing slopes of the Umpqua Divide, Siskiyous and
western slopes of the Southern Oregon Cascades. Areas near Ashland
may see an inch or more of snow fall Wednesday evening. Also lower
passes of I-5 from Canyon Mountain south to Sexton Summit may also
see another period of snow Wednesday evening in showers. Higher
passes in the Cascades and along I-5 at Siskiyou Summit and near
Mount Shasta may also expect light to moderate snow showers
Wednesday evening.

Winter weather advisories are in effect for areas above 2000 feet
west of the Cascades in Douglas, eastern Curry, Josephine, and
Jackson counties and in the Southern Oregon Cascades and higher
portions of the Siskiyous. Please see the WSWMFR for details.

Isolated to scattered very light showers may linger into Thursday
morning, then will diminish by late afternoon across the area as
the trough shifts southeast of the area.

LONG TERM...Friday 00z until Tuesday 12z...

High pressure will begin to build as a low departs towards the
southwest Friday.  Skies are expected to clear and temperatures will
plummet into the single digits east of the Cascades.

The next weather system will approach the region Saturday morning
through the weekend.  Models are still in disagreement with exactly
how this storm system will evolve.  However, one thing that is in
consensus is that it will precipitate with a snow level around 2500
feet on average.  This will result in more snow over the foothills,
mountains and areas East of the Cascades.  The lower passes on I-5
could see snow if the snow levels currently in the forecast end up
being a tad bit too high.

The last thing we wanted to mention is that we should warm up just a
tad after this weekend into next week.  Ensemble guidance is showing
850mb temperatures on a gradual warming trend through the end of
February.  Even with this warm up, we're still forecasting high
temperatures to remain about 10 degrees below average for this time
of year.  As of typing this discussion, February is currently
running 4.7 degrees below normal and 8th coldest on record with 11
days still to go(18th has not been recorded yet).

-Smith

AVIATION...For the 18/18Z TAFs...Mostly MVFR stratus ceilings are
affecting interior valleys west of the Cascades this morning, such
as KRBG and KMFR. These ceilings (and associated mountain
obscuration) are expected to scatter out to VFR early this
afternoon. MVFR ceilings are likely to return tonight to similar
areas, and at the coast too, including KOTH. By early Tuesday
morning, valley ceilings may dip to IFR. Elsewhere, VFR conditions
should continue through tonight. Keene

MARINE...Updated 230 PM PST Monday 18 February 2019...Offshore high
pressure and moderate north winds will keep choppy seas and small
craft advisory conditions going from Gold Beach southward through
Tuesday. The worst conditions in this area are expected in the
afternoon and evenings. Another front moving in from the north
Wednesday and Thursday brings steep to very steep seas and moderate
northwest winds to most locations. A long fetch of northwesterly
winds will bring the potentially very steep northwest swell into the
area, and this will be combined with gusty northwest winds. We've
issued a Hazardous Seas Watch for this potential. High pressure
builds late in the week, and winds and seas lower Thursday night
into Friday. -Keene

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 7 PM Tuesday to 10 PM PST Wednesday
     above 2000 feet in the for ORZ023>026.
     Winter Weather Advisory from 7 PM Tuesday to 10 PM PST Wednesday
     for ORZ027-028.

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 10 PM PST Tuesday for PZZ356-376.
     Hazardous Seas Watch from late Tuesday night through Thursday
     morning for PZZ350-356-370-376.

SBN/SBN/SBN