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afdmfr

Area forecast discussion
National Weather Service Medford or
333 am PDT Thu Oct 19 2017

Short term...tonight through Sunday night...

There are two storm systems approaching our area for
this weekend. Impacts expected from the incoming storm include:

*rain impacts: ponding on roadways, debris flows or mud slides
possible near recent burn scars near the Curry coast and in
western Siskiyou County on Thursday into Thursday night.
*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.
*Moderate to heavy snow expected on Friday night into Saturday
morning across the Cascades above 5000 feet, including Chemult.



Satellite observations are showing that the cloud shield
associated with pre-frontal precipitation is arriving across the
Pacific northwest, and will continue to drift southeastward today.
A few showers have already been reported at Brookings, but North
Bend has yet to receive any precipitation. This will change in the
coming hours. The system arriving will bring precipitation across
the area, with the heaviest rain occurring across the coast and
the coastal range late this morning through the evening. Rain
rates across this area are expected to be around a quarter of an
inch an hour across Red Mound and Brookings per the hrrr, and even
peaks at a half an inch (higher for some of the nearby peaks) at
Brookings by the early afternoon. Moderate rain is also expected
across the southern Oregon Cascades and into western Siskiyou
County. Elsewhere will see light to moderate precipitation.
Despite dry soils, have continued the flash flood watches for
debris flows along the Chetco Bar wildfire burn area in southern
Oregon and the western eclipse wildfire complex area in western
Siskiyou County (details at ffamfr). Additionally, debris from the
Chetco Bar fire will more than likely enter the Chetco and pistol
rivers and travel downstream. Although the river levels themselves
are not expected to be a problem, the debris combined with high
surf will create dangerous bar conditions at the mouths of these
rivers.

Regarding winds, we expect south winds to increase over the
ridges, along the coast and over the coastal waters. Winds will
peak at the coast tomorrow morning and expect wind gusts in the 30
to 45 mph range along the coast with higher gusts up to 60 mph at
Cape Blanco. Winds will increase over inland areas tomorrow
afternoon and evening, when a strong mid level jet is forecast to
move into the area. Although most all areas will see gusty winds,
the strongest winds are expected in areas east of the Cascades, in
the southern Shasta Valley as well as over the higher mountains.
South winds are expected to gust to around 40 to 50 mph in many
valleys east of the Cascades and in the southern Shasta Valley on
Thursday with higher gusts of 60 mph possible in portions of Lake
County and over the Warner Mountains in eastern Modoc County. Of
note, these strong winds over eastern areas will develop in
advance of the precipitation Thursday afternoon with rain moving
into the Shasta Valley and areas east of the Cascades late
Thursday afternoon into Thursday evening.These winds will lower
Thursday night behind the frontal passage. A High Wind Warning and
Wind Advisory is in effect for these areas. Please see the npwmfr
for details.

Also of concern behind the front, expect a large northwest swell
to reach the coast. This will bring large wave run ups on the
beach and dangerous high surf conditions. A high surf advisory is
in effect for the southern Oregon coast Thursday evening into
Friday. Please see the cfwmfr for details.

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/cirrocumulus



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 European model (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



&&

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...

*dangerous seas developing through Friday. Strong gale force winds
will accompany these seas through Thursday morning.

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

&&

Mfr watches/warnings/advisories...
or...High Wind Warning from 11 am this morning to 11 PM PDT this
evening for orz030-031.
Wind Advisory from 11 am this morning to 11 PM PDT this evening
for orz029>031.
Flash Flood Watch from 8 am PDT this morning through this
evening for orz022-024.
High surf advisory from 5 PM this afternoon to 11 PM PDT Friday
for orz021-022.

California...High Wind Warning from 11 am this morning to 11 PM PDT this
evening for caz085.
Wind Advisory from 11 am this morning to 11 PM PDT this evening
for caz084-085.
Flash Flood Watch from 8 am PDT this morning through this
evening for caz080.
Wind Advisory from 8 am this morning to 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.

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