High Wind in Oregon, October 27, 2018

Area Forecast Discussion
National Weather Service Medford OR
830 PM PDT Sat Oct 27 2018

.DISCUSSION...No updates are planned for this evening. The
wettest cold front we've seen so far this fall is approaching the
coast this evening. Over the last few hours, light rain has been
falling off and on, but most locations haven't received much more
than a few hundredths of an inch. That will change rapidly over
the next few hours as a rainband is now making its way into the
coast. The latest guidance shows a period of rather intense
rainfall as the front moves through this evening and tonight. For
example, 1 to 2 inches of rain is expected along the south coast
and adjacent mountains, and the bulk of this rain will come in a
period of about 3-6 hours. Further inland less rain is expected
(with a quarter to perhaps a half inch around Medford, for
example), but it will also come in a period of just a few hours.
We don't expect this to cause any notable problems, but we are
certain to see ponding of water on roadways during the heaviest
rainfall, which will be a hazard to motorists.

After the frontal band moves through later tonight and early
tomorrow, there will be a relative break in precipitation for a
while. But the upper trough axis moves in tomorrow afternoon, and
showers fill in again. These showers could be moderate to heavy
at times. While this is hardly unusual for late October, all of
this is going to be a dramatic change from anything we've
experienced so far this fall. -Wright

&&

.AVIATION...For the 28/00Z TAFs...Ceilings are VFR over all areas in
southern Oregon and northern California except for the immediate
coast where ceilings are MVFR with some local IFR. This is due to a
cold front that is moving onshore.  It's a slow moving front and not
very wide as radar and satellite show rapid clearing behind the
front.  While the front is taking its sweet time moving inland, it
will eventually cross the area overnight. As it does so, cigs will
drop to MVFR for all areas west of the Cascades along with mountain
tops becoming obscured. Figure on terrain above 7000 ft msl
definitely becoming obscured after midnight and lasting through
sunrise. Clouds will break up during the mid morning hours on Sunday
but there will be areas of MVFR associated with scattered shower
activity.  The Cascade range will do a job on the front to help
break it up enough such that areas east of the Cascades should
remain VFR with only isolated MVFR conditions but not until after
sunrise on Sunday.

&&

.MARINE...Updated 815 PM PDT Saturday 27 October 2018...A cold front
is moving onshore. This front is rather narrow and satellite imagery
shows back edge of cloud shield approximately 50 nm west of the
coastal zones with rapid clearing behind. The front will move inland
overnight and partly cloudy skies should be the rule over the
coastal waters by sunrise.  There will be scattered showers on
Sunday as the air mass will be a bit unstable. Winds have not been
impressive with the system so only expect small craft advisory winds
overnight which will drop below small craft advisory levels after
sunrise.

A large west swell arrives late Sunday morning. Steep seas are
expected to persist Sunday afternoon through Tuesday due to this
west swell. -Sargeant

&&

.PREV DISCUSSION... /Issued 241 PM PDT Sat Oct 27 2018/

SHORT TERM...A cold front is visible on satellite imagery off
the Oregon coast. This front will move onshore this evening then
inland tonight into Sunday morning bringing widespread rain and
some gusty winds. Behind the front expect numerous to scattered
showers late Sunday morning through Monday morning as an upper
level trough moves over the region and another disturbances moves
inland. The trough will bring a cooler airmass with lowering snow
levels and showers. So expect some light snow accumulations on
the higher mountains Sunday evening through Monday morning, mainly
above 5000 feet in the Southern Oregon Cascades. Other mountains
above 5000 feet may see a dusting of snow Sunday evening into
Monday morning.

Models remain on track with the front moving onshore this evening
then inland late this evening and tonight. Moderate rain is
expected for most areas from the Cascades west with mainly light
rain east of the Cascades. Rainfall amounts of around 1 to 2
inches are forecast along the coast, into the coastal mountains
and around 1 inch over the south central Oregon Cascades, mainly
north of highway 140. Valleys west of the Cascades will see
moderate rain of around 0.25 to 0.50 inches, except for lighter
amounts in the Rogue Valley near Medford/Ashland areas and in the
Scott and Shasta Valleys in northern California. East of the
Cascades expect mainly light rain in the valleys with some
moderate rainfall over the higher terrain.

Winds will increase ahead of the frontal passage tonight into
Sunday, with breezy south to southwest winds developing over the
area. Models continue to show a 45 to 50 kt 700 mb jet moving
across the area late tonight and early Sunday and expect strong
gusty winds to develop across portions of the east side. These
strong winds will develop mainly in the mountains and higher
terrain across far eastern Klamath, Lake and eastern Modoc
counties tonight and Sunday morning. A wind advisory is in effect
for these areas. Please see the NPWMFR for details. Winds will
lower below advisory levels for the eastern mountains late Sunday
morning but expect breezy to gusty west winds across areas east of
the Cascades Sunday afternoon.

Behind the front, moist onshore flow is expected as the upper
trough moves in place. Model forecast support scattered to
numerous showers Sunday afternoon. Then as a disturbance moves
into the area Sunday evening through Monday morning, expect
increased shower activity and coverage from the Cascades west and
across northern Klamath and Lake counties.

Snow levels will lower behind the front Sunday  afternoon and
evening to 5500 to 6000 feet from the Cascades west and around
6000 to 7000 feet east of the Cascades. This combined with
ongoing showers will result in some light snow in the higher
mountains in the Southern Oregon Cascades at or above 6000 ft
elevation. Snow levels are expected to continue to lower late
Sunday evening through Monday morning down to around 5000 to 5500
feet across the area. With these lower snow levels and the
increase in showers, light snow accumulations are forecast above
5000 feet late Sunday evening into Monday morning. These snow
accumulations are expected mainly in the Southern Oregon Cascades
with only a light dusting on other higher mountains east of the
Cascades or in the Siskiyous. Total snowfall accumulations from
Sunday afternoon through Monday morning are expected to be around
1 to 3 inches in the Cascades between 5000 to 6000 feet elevation
with highest amounts near Diamond Lake and Crater Lake. Above 6000
feet elevation higher amounts of 4 to 6 inches are possible
during this period, especially near Crater Lake. Given the warmer
ground temperatures, snow may initially melt. However, heavier
showers may result in light accumulations on grassy areas or
briefly on roads. This will affect areas above 5000 feet
elevation, especially in the Southern Oregon Cascades.

A broad upper level trough and onshore moist flow will remain in
place through the day Monday with areas of continued light
showers, especially from the Southern Oregon Cascades west, over
Klamath and northern Lake and across western/central Siskiyou
County.

Monday night and Tuesday, a ridge builds offshore. However a
disturbance may move into the area from the northwest. Models
show more variability in this disturbance, with the surface low
expected to approached the southern Oregon coast then possibly
moving inland early Tuesday. Depending on the track and strength
of this low, the area may see additional showers.

LONG TERM...Wednesday 12z onward...

We'll start out with an area of high pressure over the region
Tuesday.  Eventually a warm front will push towards Oregon on
Wednesday morning.  Most areas will see rain, but we decided to
add some patchy freezing drizzle in the forecast east of the
Cascades.  Felt that temperatures in some of the valleys will be
cold enough in addition to the warmer air riding up over the
Cascades.  There is some dry air from the downsloping winds, so this
is not a widespread slam dunk event.

Warm air will push snow levels up again later on Wednesday.  The
weather forecast may play more tricks than treats for trick or
treaters on Halloween.  The GFS and ECMWF are both forecasting
precipitation north of the Umpqua divide on the 31st.  We'll see dry
weather for the start of November.  Rain is possible on Saturday
night on the 4 th.

-Smith

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 1 AM to 11 AM PDT Sunday for ORZ030-031.

CA...Wind Advisory from 1 AM to 11 AM PDT Sunday for CAZ085.

Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Sunday
     for PZZ356-376.
     Small Craft Advisory for hazardous seas from 11 AM Sunday to 5
     PM PDT Tuesday for PZZ350-356.
     Hazardous Seas Warning until 5 AM PDT Sunday for
     PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas from 5 AM Sunday to 5 PM
     PDT Tuesday for PZZ370-376.