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561
FXUS66 KMFR 192157
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
257 PM PDT Thu Oct 19 2017

.SHORT TERM...A strong front is moving into the Oregon coast this
afternoon and will move across inland areas this evening into
tonight. Winds have increased over the area and will peak late
this afternoon into this evening. Strongest winds will impact the
mountains, Shasta Valley and areas east of the Cascades. Models
continue to show rainfall peaking late this afternoon along the
coast and this evening for inland areas. A high winds warning and
wind advisory are in effect for these areas. Please see the NPWMFR
for details. Moderate to heavy rain and areas of strong winds
will bring significant impacts to the area. Highest rain rates are
expected along the coast and into western Siskiyou county with up
to 0.3 to 0.5 inches per hour for 1-3 hours. In addition to
slippery roads and water ponding on roads, the main concern is
with how heavy rain will impact area burn scars. Heavy rain may
lead to mud/rock slides or debris flow on recent burn scars in
Curry, extreme western Josephine, and extreme western Siskiyou
counties. This includes the Chetco Bar and Eclipse burn scars. A
flash flood watch is in effect for these area. Please see the
FFAMFR for details. In addition to rain and wind, another concern
with and behind the front will be incoming large northwest swell.
This will result in dangerous high surf conditions along the
souther Oregon coast late this afternoon into Friday. Behind the
front, expect a cold showery pattern to move into place. This
will result in lowered snow levels with light to moderate snow on
the mountain passes.

The primary impacts expected today and Friday from these weather
systems include:

*Rain Impacts: Slippery wet roadways today. Areas of ponding on
 roadways possible where there is heavy rain. Debris flows or mud
 slides possible near recent burn scars in southern Curry county
 and extreme western Josephine county as well as in extreme
 western Siskiyou County today and tonight.
*Rock falls will be possible across highway 138 in Douglas County
 between mile posts 45 to 53 (near the Umpqua North Complex
 wildfire burn area).
*Wind Impacts: Travel may become difficult for high profile
 vehicles due to strong southerly winds along the coastal
 headlands, Shasta Valley, and east of the Cascades.
*Isolated trees may fall near burn scars due to high winds.
*Dangerous conditions for beach goers with high surf conditions
 along the coast late Thursday afternoon through Friday.
*Debris in the Chetco and Pistol Rivers combined with high surf
 will make for dangerous bar conditions.
*Snow Impacts: Slippery, snow-covered roads over the higher passes
 in the Cascades near Crater Lake and Diamond Lake on Friday.
 Light snow on highway 140 near Lake of the Woods on Friday.

On Friday, the main concern will be with snow showers affecting
the mountains. Models continue to show snow levels lowering to
4000 to 4500 feet tonight and remaining around 4500 to 5000 feet
on Friday. Behind the front, an area of showers is visible on
stilt and model forecasts support showers moving into western
areas tonight and Friday. The period of highest shower activity is
expected to occur late tonight and Friday morning. Light to
moderate snow accumulations are possible on the passes in the
southern Oregon Cascades during this period with greatest amounts
of 4 to 7 inches near Diamond Lake and 6 to 9 inches possible near
crater Lake. Snow accumulations on the roadways may be limited
some by relatively warm ground temperatures though.

There is little if any break in the active pattern with models
continuing to show a moist warm front moving into the area Friday
night into Saturday. Ahead of the warm front, snow levels are
expected to be low, generally around 4000 feet elevation. Snow
levels are expected to rise around by mid morning on Saturday to
above pass levels. However, the GFS, SREF, and NAM show a very
moist air mass with the potential for significant precipitation
while snow levels are still low. The ECMWF has shown lesser
precipitation amounts but has trended higher. So, there is medium
confidence for significant snow accumulations above 4000 ft in
the Southern Oregon Cascades. This may impact all higher passes,
including areas near Diamond Lake, Crater Lake, Willamette pass
and Lake of the Woods. Peak snowfall is forecast Friday night
through early Saturday morning with snowfall amounts of 6 to 9
inches possible. The GFS and NAM soundings support a cold layer
persisting in the lower levels for a period late Saturday morning
as the warm air aloft moves into place. This may result in a
brief period of sleet or freezing rain before snow transitions to
freezing rain. The NAM shows this potential slightly higher than
the GFS and indicates it for the mountains in the Cascades and
east. Will need to monitor additional forecasts for these concerns
with the Friday night and Saturday front.

On Sunday a frontal system moves into northwest portions of the
area. This will mainly bring precipitation to the coast, into
Douglas county and into the Southern Oregon Cascades Sunday.


.LONG TERM...Monday through Thursday, a high pressure ridge builds
into the area and brings dry weather early next week. Warmer
temperatures are expected Monday and Tuesday with highs in the 70s
for western valleys and in the 60s for eastern valleys. This
ridge is forecast to weaken Tuesday night and Wednesday as a front
moves inland to the north. A slight chance for light
precipitation is expected on Wednesday for portions of the coast
and into the Umpqua Valley.



&&

.AVIATION...19/18Z TAF Cycle...Conditions will deteriorate Today as
a cold front brings wind and rain to the region. Expect widespread
MVFR/IFR along the coast and coastal waters into Thursday evening
with gusty south winds. Lower ceilings, mostly MVFR, will gradually
spread inland today with terrain obscured west of the Cascades by
evening. The lower conditions will push east of the Cascades
Thursday evening. Strong winds will occur from the Cascades eastward
Thursday and this will result in plenty of turbulence. Confidence is
high that LMT will see wind gust around 35 knots between 21Z this
afternoon and 03Z this evening. Moreover, areas west of the Cascades
will experience low level wind shear due to light winds at the
ground and very strong winds about 2000 feet above ground. /FB


&&

.MARINE...Updated 200 PM PDT Thursday 19 October 2017...Winds are
expected to decrease below gale around 2 PM this afternoon as the
cold front move inland. However a very high long period NW swell
will move quickly into the coastal waters late this after and will
maintain hazardous seas overnight. Combined seas are expected to
build to the 20-25 foot range, especially beyond 10 nm from shore,
creating very high and steep seas and dangerous surf and bar
conditions.

Another round of potentially strong south winds arrives Friday night
along a warm front. Some guidance suggests the potential for storm
force winds beyond 10 NM from shore north of Cape Blanco. Generally
calmer conditions are expected by Monday, though northerly winds
will be gusty south of Cape Blanco in a thermal trough pattern.
/FB


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 11 PM PDT this evening for ORZ030-031.
     Wind Advisory until 11 PM PDT this evening for ORZ029>031.
     Flash Flood Watch until 11 PM PDT this evening for ORZ022-024.
     High Surf Advisory from 5 PM this afternoon to 11 PM PDT Friday
     for ORZ021-022.

CA...High Wind Warning until 11 PM PDT this evening for CAZ085.
     Wind Advisory until 11 PM PDT this evening for CAZ084-085.
     Flash Flood Watch until 11 PM PDT this evening for CAZ080.
     Wind Advisory until 8 PM PDT this evening for CAZ081.

Pacific Coastal Waters...Small Craft Advisory until 2 PM PDT this afternoon for
     PZZ356-376.
     Gale Warning until 2 PM PDT this afternoon for
     PZZ350-356-370-376.
     Hazardous Seas Warning until 11 PM PDT Friday for
     PZZ356-370-376.
     Hazardous Seas Warning until 11 PM PDT Friday for PZZ350.

$$

CC