Hazardous Seas Warning 59, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
851 PM PDT Thu Oct 12 2017

.SHORT TERM...The forecast remains on track with models continuing
to support numerous showers continuing across the northwest
parts of the area as moisture onshore flow continues and an upper
level disturbance moves into the area tonight and Friday. The
main focus for showers tonight and Friday will be along the coast,
into the Umpqua basin and along the Southern Oregon Cascades as
well as east into northern Klamath and Lake counties. Snow levels
have lowered to around 5000 feet, and locally lower, in the
Southern Oregon Cascades. Snow levels near the Southern Oregon
Cascades are expected to lower to around 4500 to 5000 feet
tonight, and will be locally lower at times, then rise to 5500
feet Friday afternoon. Areas of moderate snow accumulation are
expected above 4500 feet in the Cascades tonight through Friday
morning. This will mainly affect areas near Crater Lake, Diamond
Lake and northward to near Willamette Pass. Other areas further
south of the Umpqua Divide are expected to see lighter
precipitation in showers. Strong gusty winds are also expected to
develop by Friday afternoon over the mountains and east of the
Cascades and a mid level jet of 30 to 40 kt moves over the area
and winds mix down to the surface.

Showers will diminish Friday evening into Friday night as the
upper trough over the region shifts east and an upper ridge builds
offshore. This will bring dry weather with a warming trend on the
weekend. However, expect gusty northeast to east winds to develop
on the ridges Friday night through Sunday morning.

&&

.AVIATION...12/00Z TAF CYCLE...Along the coast, across the
coastal waters, and in the Umpqua Valley...areas of MVFR
cigs/vsbys in showers will become widespread tonight into Friday
morning. Areas of MVFR cigs are also expected to develop at times
in showers across areas south of the Umpqua Divide in Jackson and
Josephine counties tonight into Friday morning. Widespread
mountain obscurations are expected from the Southern Oregon
Cascades westward and along the Siskiyous. East of the Cascades
and over Northern Calfiornia expect mainly VFR with occasional
MVFR cigs in showers. Also expect areas of mountain obscurations
on the east side and into Northern California. Conditions will
gradually improve to VFR across most the area Friday afternoon
but expect local MVFR cigs to continue in showers, especially in
the Umpqua Valley as well as continued mountain obscurations. -CC

&&

.MARINE...Updated 830 PM PDT Thursday 12 October 2017...Seas will
be dominated by steep northwest swell through Friday night while
a series of disturbances bring occasional showers. Showers will be
most numerous north of Cape Blanco. A thermal trough will develop
late Friday and deepen into the weekend. This will bring strong
north winds and choppy wind driven seas to the area Saturday and
Sunday, especially south of Cape Blanco beyond 10 NM from shore.
Winds and seas will peak Saturday afternoon and evening. The
thermal trough will weaken Monday, and winds and seas will
diminish at that time. The first in a series of fronts will move
onshore Wednesday. These fronts will be the strongest of the
season thus far and may bring south gale force winds and very
steep seas to the area.

&&

.PREV DISCUSSION... /Issued 254 PM PDT Thu Oct 12 2017/

SHORT TERM...Wintry weather continues above 4500 feet tonight
over the southern Oregon Cascades, mainly north of Highway 140.
Satellite imagery shows the strong short wave trough is expected
to move across the Cascades tonight. This will help to enhance
upslope precipitation. The latest guidance shows this trough will
not be as deep as on previous run but there will still be enough
moisture and instability to generate up to a foot of new snow. The
higher elevation between Diamond Lake and Crescent Lake could see
up to 15 inches but they will be above the willamette Pass. The
winter weather advisory continues through Friday afternoon but
snow is expected to turn to snow showers by late Friday morning.

Elsewhere scattered showers are expected across the west side of
the Cascade and part of the east side from the Klamath Basin
north. It does not look like Modoc County or the Tulelake Basin
will see any showers with this system. The cloudy sky will keep
temperatures higher tonight but Friday night could be a cold night
in the valleys from clear sky.

However confidence is very high that the thermal trough will set
up along the coast again Friday night. This will lead to offshore
flow for southern Curry County, the Kalmiopsis Wilderness and
western Siskiyou County with warm and dry nights in those areas.

The atmosphere will warm up this weekend as a ridge builds
northward. Highs in the Rogue Valley could climb to the lower to
middle 70s.

LONG TERM (Monday through Thursday)...Monday and possibly Tuesday
could be the last warm days of the month. Both ECMWF and GFS agree
on the pattern changing around Tuesday night. The models bring
rain chance to Coos and Douglas Counties as early as Tuesday
afternoon, and by Wednesday evening wetting rain is forecast for
most of the western valleys and western Siskiyou County. Both
models hold off on precipitation for the east side of the Cascades
until Thursday. With the jetstream forecast to become more zonal
during the second half of next week, confidence is moderate to
high about precipitation.

FIRE WEATHER...Updated 200 PM PDT Thursday, 12 October 2017...
Cool and unsettled weather will continue for the next couple of days
with higher relative humidity. Most of the precipitation into this
evening will be mainly west of the Cascades and north of the
California/Oregon border. Gusty winds are expected again into this
evening, mainly east of the Cascades, portions of the Shasta Valley
and mid slopes and ridges in fire zone 280. Similar conditions are
expected Friday, however models are in fairly good agreement showing
stronger 700 and 600 mb winds east of the Cascades. Given we'll be
in a convective environment, there's a chance some of these stronger
winds could mix down. Therefore were expecting stronger winds Friday
afternoon and evening. Precipitation once again will be most
frequent along and west of the Cascades and north of the
California/Oregon border. However there's a chance the eastside
north of the California/Oregon border could get more frequent rain
and higher elevation snow showers Friday afternoon and early Friday
evening.

A return to warmer and drier weather is in the cards Saturday
through at least Monday. Offshore flow will be strong early Saturday
morning as the thermal trough develops and strengthens, but
overnight recoveries are expected to be moderate at the mid slopes
and ridges in southwest Oregon and western Siskiyou county.

Offshore flow will remain a concern overnight Saturday into Sunday,
especially at the mid slopes and ridges in fire zones 618, 619, 620,
621 and western fire zone 280. The models have trended higher with
the strength of the offshore flow and thus east to northeast winds.
Right now the consensus is wind speeds could be similar to Saturday
morning. Overnight recoveries Saturday night into Sunday morning
could be moderate to occasionally poor. If this continues to be the
case, then the combination of the above mention scenario could
warrant at least a fire weather watch. especially where fires are
still active.

Dry and warm weather continues Monday with continued offshore flow,
but it will be weaker compared to Saturday and Sunday mornings.
Overnight recoveries are still expected to be moderate to poor.

Tuesday should remain dry, but with increasing onshore flow. At
least at the coast. The ECMWF shows a weak front moving through the
area which would bring cooler temperatures over most areas. The GFS
is weaker with the onshore flow at the coast and has the thermal
trough moving over the westside valleys in the afternoon. So it's
all going to come down to the timing and details.

There is increasing evidence we'll be heading into a cooler and
wetter pattern from about the middle of next week into next weekend,
but it's not locked in stone yet. Bottom line it remains to be seen
if this will end up being a season ending event. It's still a ways
out there and the details could change. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 5 PM PDT Friday above 4500 feet in
     the for ORZ027-028.

CA...None.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas until 5 AM PDT Saturday
     for PZZ350-356-370-376.
     Gale Watch from Saturday morning through Sunday morning for
     PZZ376.

CC/CC/CC