Hazardous Seas Warning 61, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
1255 PM PDT FRI SEP 2 2016

Updated Aviation Section

.DISCUSSION...A well-defined upper trough will maintain
temperatures well below normal through Sunday and help to generate
morning cloud cover, especially west of the Cascades. Winds will be
breezy for much of the forecast area the next few days as onshore
flow increases.

A few hundredths of an inch has been observed in portions of
coastal Douglas, Coos, and Curry Counties this morning. This is
expected again tonight, perhaps reaching a bit further south and
east per the latest ARW/NMM model output.

One of the elements we'll be focusing on this morning is the
upper low tracking over the forecast area late Saturday, and this
will bring the chance for showers and thunderstorms to mainly
areas east of the Cascades. Areas west of the Cascades should
trend sunnier in the afternoons after morning clouds clear out.

Lastly, smoke from the Gap Fire continues to be pushed to the
south and east by lower level northwest wind flow, affecting
areas like Fort Jones with unhealthy air quality. Future smoke
impacts will of course depend highly on the fire's smoke
production.

Please see the previous discussion below for more details on the
cool and potentially showery conditions this weekend.

&&

.AVIATION...02/18Z TAF CYCLE...
With a cool air mass in place today and good vertical mixing, VFR is
expected, with some areas of MVFR and partial terrain obscurations
along and near the Coastal Mountains, Umpqua Divide, and Oregon
Cascades. Ceilings this morning will rise and mostly dissipate at
most locations later this afternoon into this evening. Later this
evening through mid-late Saturday morning MVFR to IFR low clouds and
patchy fog are expected from the Upper Klamath Basin westward. Smoke
from the Gap Fire is also expected to continue to result in IFR to
MVFR visibilities from Happy Camp eastward up the Klamath River
Canyon, to near Interstate 5 and southward through the Shasta
Valley. BTL

&&

.MARINE...Updated 800 AM PDT Friday 1 September 2016...Winds will
remain light through Friday. A thermal trough will develop near
the coast this weekend...and this will bring increasing north
winds and choppy seas to the area...especially south of Cape
Blanco. Small craft conditions are possible for areas south of
Cape Blanco Saturday afternoon through Sunday evening and possibly
Tuesday afternoon and evening.

&&

.PREV DISCUSSION... /Issued 355 AM PDT FRI SEP 2 2016/

DISCUSSION...The most notable changes to the 7-day forecast were
to increase the wind speeds expected on Saturday, reduce the area
covered by a slight chance of thunderstorms on Saturday afternoon
and evening, add a slight chance of showers and thunderstorms to
Modoc County late Saturday night into Sunday morning, and to
modestly expand the coverage of sky cover through the first half
of next week.

Model agreement is very good through the first half of next week.
The holiday weekend will be mainly dry but with temperatures at 5
to 10 degrees below normal as a series of disturbances brush past
our area.

A broad upper level trough is in place over the Pacific Northwest.
It will produce instability showers today mainly from the
Columbia Gorge across western Washington into BC, but a few light
showers may extend into northern Coos County or northwest Douglas
County. The main effect for our area will be substantial upper
level cloud cover this morning that is expected to thin during the
afternoon and evening.

The center of the main low will track northeast across Canada on
Saturday while a fast-moving shortwave in northerly flow on the
back side of the trough reaches the vicinity of the southern
Oregon coast. It is forecast to then track inland on Saturday
night. There is still some uncertainty regarding the strength and
timing of the shortwave. As with its previous run, the 00Z GFS
indicates that this disturbance will generate weak instability on
Saturday afternoon with a slight chance of showers and
thunderstorms in northern Klamath County and Lake County. The near
surface convective parameters are unimpressive with relatively
cool temperatures and low dew points. But, shortwave induced
elevated convection may develop with the GFS indicating weak
850-500MB MU CAPE of 50 to 100 J/KG and Lifted Indices of 0 to -1.
The possibility of east side showers or thunderstorms continues
late Saturday evening and overnight for Modoc County, and may
persist for Lake County as well.

As the trough sweeps across our area, it will increase the
pressure gradient. Northwest winds will be breezy and a bit
stronger than typical on Saturday afternoon and evening across our
area. This pattern with a vertical profile of winds varying
between west and north will keep most of the smoke from the Gap
wildfire south of the Siskiyou Mountains.

From Sunday through Tuesday...the large scale pattern will evolve
slowly with a few weak shortwaves passing through in a northwest
flow aloft. These weak waves will continue night and morning low
clouds at the coast into the Umpqua Valley. The strongest wave
looks to arrive on Tuesday with a slight chance to chance of Coos
and Douglas County showers.

Wednesday into Friday...it is not certain to what extent the
upper level pattern will be progressive. In a role reversal from
the usual, the ECMWF is more progressive and shows more noticeable
warming and drying as an offshore ridge moves toward the coast.

&&

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

CA...None.

Pacific Coastal Waters...None.

NSK/DW/JRS