Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 191608
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
908 AM PDT Thu Oct 19 2017

.SHORT TERM...An incoming front is bringing increased winds along
the coast and light to moderate rain early this morning. This
strong front will bring moderate to heavy rain along with areas of
strong gusty winds. Behind this front a showery and colder
pattern moves into place tonight and Friday. This will bring
lowered snow levels down to 4000 to 5000 feet and light to
moderate snow on passes in the Cascades tonight and Friday.

The 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.

Ahead of the front gusty south winds have developed along the
coast and over the ridges with gusts of 30 to 45 mph early this
morning. These winds will increase today and expect most areas to
see gusty winds. Strongest winds will develop over the mountains,
into the Shasta Valley and for locations east of the Cascades with
gusts of 40 to 60 mph this afternoon into this evening. A high
winds warning is in effect for higher terrain in Lake and Modoc
counties and wind advisories are in effect for the valleys in
Klamath, Lake, central and eastern Siskiyou and Modoc counties.
Please see the NPWMFR for details.

Today, rain has begun along the coast this morning. Rain will
increase and become moderate heavy along the coast through the
afternoon. Inland western locations will see rain gradually
spread across west side areas late this morning through this
afternoon then continue into the evening. Moderate rain is
expected from the Cascades west, mainly in the late afternoon and
early evening. Rain is expect to across areas east of the
Cascades this evening.

In addition to rainfall creating slippery conditions and water on
roadways, heavy rain may create significant impacts in and around
recent burn scars near the coast and in extreme western Siskiyou
County. This includes the Chetco Bar and Eclipse burn scars. Heavy
rainfall will bring the potential for rock or mud slides or
debris flows near these burn scars. Peak rainfall rates of 0.3 to
0.5 inches per hour are possible this afternoon in Curry County
and extreme western Joesphine county. Peak rainfall rates of
around 0.3 inches are possible late this afternoon and early this
evening for the burn scars in extreme western Siskiyou county.
Those who live, work or travel in or near these burn scars should
take extra caution during and after the heavy rain. Stay alert and
never drive through flooded roadways. A flash flood watch is in
effect for these areas of concern. Please see the FFAMFR for
details.

Coastal areas and those who will be on area beaches or along the
coast today should also be aware of hazardous high surf conditions
today. A large northwest swell will impact the coast late this
afternoon into this evening and continue into Friday. This will
bring dangerous wave run ups on the beach and high surf
conditions. Beach goers and those along the coast should stay
alert. Also never turn your back on the ocean. A high surf
advisory is in effect for late today and tonight. Please see the
CFWMFR for details.

After this storm, the concern will shift to the cold showery
pattern on Friday. Lowered snow levels are expected to result in
light to moderate snow over the passes in the Southern Oregon
Cascades.

Then Friday night, expect a warm front to approach the area and
move inland Saturday. Ahead of this front, expect a period of
lowered snow levels before warm air moves into the area and snow
levels rise. This will bring the potential for moderate snow to
fall in the Cascades and western mountains Friday night and early
Saturday morning. This will mainly affect areas in the Southern
Oregon Cascades above 4000 feet elevation. Timing on snow levels
rising will be the main factor in determining how much snow may
fall during this period. Otherwise, expect moderate rain with this
front across western portions of the area on Saturday. Another
round of gusty winds is also possible along the coast and over the
mountains on Saturday.


&&

.AVIATION...19/12Z 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 becoming
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. Low-level wind shear is possible in some
areas as well. -Spilde/Schaaf

&&

.MARINE...Updated 300 AM PDT Thursday 19 October 2017...A strong
cold from will spread southerly gales across the waters this morning
and will affect most areas north of Brookings. We have expanded the
area of gales to areas south of Cape Blanco and closer to shore,
based on the consensus of the latest model data. Heavy, long period
northwest swell will build into the waters late today into Friday
behind the front, 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. SK


&&

.PREV DISCUSSION (edited)... /Issued 333 AM PDT Thu Oct 19 2017/

Behind this front widespread to numerous showers are expected
tomorrow night into Friday along with snow levels lowering to 4000
to 5000 feet. This will bring light to moderate snow to the
passes in the Cascades Thursday night through Friday afternoon.
Around 4 to 7 inches of snow is expected in the Diamond Lake and
Crater Lake areas with around 3 inches near Lake of the Woods.
However, relatively warm road temperatures may limit the amount of
snow that accumulates on roadways during this period. The peak
snowfall is expected tomorrow night through Friday morning. Snow
showers are possible during the afternoon on Friday but
accumulations are expected to be light except for over higher
locations such as near Crater Lake.

Expect only a brief break in the active pattern Friday evening
then a strong and moist warm front will spread precipitation into
the area Friday night and Saturday. This next front  will bring
moderate rain from the Cascades west with light to moderate
precipitation east of the Cascades and in Northern California.
Although snow levels are expected to rise to above pass levels on
Saturday, moderate snow (more than what is forecast for the Friday
system) is expected to fall across the Cascades above 5000 feet,
but would also include Chemult. This could cause travel concerns
as the rain/snow fall could lower road temperatures enough for
accumulations before things warm up as the front passes. Another
period of strong or gusty winds is possible with this warm front
on Saturday. The strong winds will be mainly over the mountains,
although gusty winds are likely over much of the area on Saturday.
-Schaaf/CC

LONG TERM...Monday through Thursday Night... The extended period
dries out on Monday with overall calmer conditions. Models are
showing temperatures to rebound nicely as conditions dry out. That
being said, with the amount of precipitation we will see in the
short-term period, nights across the long-term forecast could be
socked in with valley fog--particularly west of the Cascades.

That being said, the models begin to become less certain with the
forecast. The GFS weakens the thermal trough near the coast and
brings a weak front into the offshore waters Thursday morning.
Meanwhile, the EC hangs on to a strong trough with offshore flow
continuing into Thursday. Have leaned toward the ECMWF as it seems
to be doing better in the long-term. Offshore POPs do return Wednesday
night, but the precipitation is expected to remain well offshore
through Wednesday night. -Schaaf


&&

.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 through 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 through 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 from 2 PM this afternoon to 11 PM PDT
     Friday for PZZ350.

$$

CC


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