High Wind Watch 1, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
855 PM PST Tue Jan 9 2018

.DISCUSSION...A warm front will move into the coastal waters
tonight. Rain is expected at the coast around midnight, spreading
into the Umpqua Basin around 3 AM, and down into the Rogue Valley
and south of the Siskiyous around daybreak. HiRes short term
models bring rain east of the Cascades through the Klamath Basin
into Lakeview and Alturas by mid to late Wednesday morning.
Precipitation is expected to taper off in the afternoon but the
next front is expected to bring another round of stead rain to the
west side Thursday. Snow levels will be in the 4500-5000 foot
range in the Cascades and Siskiyous Wednesday rising to 6500-7000
foot range on Thursday.

The latest 00Z GFS still show a drying period from Friday through
the weekend, then the pattern changes to a more active storm track
next week which would bring beneficial rain and mountain snow to
our area. /FB

&&

.AVIATION...10/00Z TAF CYCLE...A mix of MVFR and VFR with
scattered showers and terrain partially obscured this evening. A
warm front will lift northward into the area overnight into
Wednesday morning with widespread light rain and total terrain
obscuration. Ceilings/visibilities will likely lower at the TAF
sites to a mix of MVFR and IFR during this time frame with some
light snow possible at Klamath Falls. Conditions will slowly
improve to mostly VFR Wednesday afternoon, but with partial terrain
obscuration persisting. -Spilde

&&

.MARINE...Updated 830 PM PST Tuesday 9 Jan 2018...High pressure
offshore will weaken tonight. A weak front will move onshore late
tonight. A stronger front will move onshore Thursday. The models are
in pretty good agreement showing a onshore component at 925mb with
winds between 50-55 kts peaking around 10 am pst Thursday. Meanwhile
boundary layer winds show gale force winds during the same time
period. At the very least we'll have high end small craft conditions
with gale force winds possible for portions of the northern waters.
If winds were to reach gales, it may only be for a 3-6 hour period
Thursday afternoon. Because of this, no changes will be made to the
headlines. Keep in mind this could change, so watch for updates.

There will be two moderate to heavy swell events. The first will
begin Thursday and peak Thursday night. The latest model runs have
significantly increased the swell, and now it is forecast to peak at
18 feet at 16 seconds Thursday night. A Hazardous Seas Watch has
been issued, and these conditions will likely support High Surf
Advisory conditions. That will be issued later if the current
forecast persists.

The second round of heavy swell will occur Sunday night and it is
forecast to peak at 15 feet at 18 seconds.

&&

.PREV DISCUSSION... /Issued 345 PM PST Tue Jan 9 2018/

SHORT TERM...

An active weather pattern will continue for the work week with
some lingering showers expected Wednesday morning and more
precipitation Thursday.

Flow will stay north westerly as a short wave trough moves through
the region on Tuesday and some more energy in the wave will give
us the chance for more showers Wednesday morning. Snow levels
will have fallen to 3500 feet by this time as we are on the
backside of the trough. So snow is expected on Siskiyou Summit and
the other higher passes in the Cascades in addition to Snowman's
Summit. The snowfall is expected to be around 1-2 inches with the
higher totals in that range on the mountains such as Mt. Ashland
and Crater Lake.

Thursday is a bit more interesting weather wise. The trough will
stay to our north, which will keep us on the warm side of things.
Snow levels are expected to jump up to 7000 feet Thursday morning
ahead of the trough along the warm front. The other important
feature with this system is the strong westerly flow up into the
Cascades. The NAM is showing 700mb 45-55 knot westerly winds
Thursday, but the lower 850 mb flow is a bit more southerly, which
is expected with a warm front.

This should suggest some very good orographic lift along the
Cascades and the Coastal Range. Overall, we should see at least
0.5 inches up to 1 inch of precipitation along the coast and
Cascades throughout this event. Eventually, a cold front will come
through and drop snow levels down to 5000 feet Friday morning.
Storm total snow accumulations will be around 2-4 inches above
6000 feet, so Mt. Ashland and Crater Lake should see some snow
from this system.

As for Friday, this trough is expected to move out of the area
leading to just some lingering showers Friday morning and
afternoon. Drier air can be seen entering the forecast during
Friday evening.

-Smith

LONG TERM...

Saturday, January 13th, through Tuesday, January 16th...The extended
forecast will begin with an upper level ridge along the West Coast
with dry weather this weekend, but all signs point to a break down
of the ridge by early next week with a period of wet, unsettled
weather to affect much of the region during next week.

Models are well-aligned both Saturday and Sunday showing the upper
ridge overhead with surface high pressure centered near Idaho. This
will result in a thermal trough along the northern California coast
with a period of mostly weak offshore (east) winds. However, they'll
be stronger at the upper slopes and ridges of SW Oregon and NW
California. Sun angles are now increasing each day, but it is still
only mid-January and this pattern will likely result in steep
inversions that will be difficult to break in some of the west side
valleys. Overnight and morning fog will be stubborn and probably
last into the afternoons in some areas. Have therefore lowered
maximum temps a bit in the valleys, while also raising them over the
higher terrain and along the SW Oregon coast, where the offshore
winds will be strongest.

The upper ridge axis will shift to the east of the area Sunday night
and this will allow a frontal system offshore to approach the coast.
This initial system looks pretty weak and will likely fall apart as
it runs into the upper ridge.

However, a stronger trough will then become established over the NE
Pacific and this will allow a strong Pacific jet stream to be
directed into the Pacific Northwest next week with a series of wet
and, at times, windy disturbances moving into the area. The first of
these systems is expected to arrive Monday, then push through Monday
night into Tuesday. Then, another system likely follows right behind
it at midweek (Wednesday). Subtle timing and strength differences in
the models persist with each disturbance, so have favored a blend at
this point with a slight lean toward the ECMWF. But, there is still
plenty of time to fine tune the details, such as precipitation
amounts and snow levels. The Climate Prediction Center places
very highs odds of above normal precipitation during the 6-10 day
time frame, which should finally help to put a dent in our
precipitation deficits and build the mountain snowpack.

-Spilde

AVIATION...10/00Z TAF CYCLE...A mix of MVFR and VFR with
scattered showers and terrain partially obscured this evening. A
warm front will lift northward into the area overnight into
Wednesday morning with widespread light rain and total terrain
obscuration. Ceilings/visibilities will likely lower at the TAF
sites to a mix of MVFR and IFR during this time frame with some
light snow possible at Klamath Falls. Conditions will slowly
improve to mostly VFR Wednesday afternoon, but with partial terrain
obscuration persisting.

-Spilde

MARINE...Updated 200 PM PST Tuesday 9 Jan 2018...High pressure
offshore will weaken tonight. A weak front will move onshore late
tonight. A stronger front will move onshore Thursday. Models
indicate small craft winds and seas will occur with this front,
along with a few patches of gale force winds near and north of Cape
Blanco. Will not go with a Gale Watch since those areas are small
and not representative of conditions over the whole zone.

There will be two moderate to heavy swell events in the next week.
The first will begin Thursday and peak Thursday night. The latest
model runs have significantly increased the swell, and now it is
forecast to peak at 18 feet at 16 seconds Thursday night. A
Hazardous Seas Watch has been issued, and these conditions will
likely support High Surf Advisory conditions. That will be issued
later if the current forecast persists.

The second round of heavy swell will occur Sunday night and it is
forecast to peak at 15 feet at 18 seconds.

Looking further out, both the EC and GFS support a strong front
moving onshore next Wednesday with areas of storm force winds. Stay
tuned.

-Stockton

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

Pacific Coastal Waters...Small Craft Advisory from 4 PM Wednesday to 4 PM PST Thursday
     for PZZ350-356-370-376.
     Hazardous Seas Watch from Thursday afternoon through late
     Thursday night for PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas until 1 AM PST Wednesday
     for PZZ350-356-370-376.

FJB/FJB/MAP