Hazardous Seas Warning 65, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
848 PM PDT SUN SEP 11 2016

.DISCUSSION...A minor update was just sent to adjust sky cover.
Stratus has not formed at the coast and may not tonight as the
flow gradually turns offshore. Guidance all shows at least some
stratus around dawn, but at any rate, with a current temp/dewpoint
spread of 5F at North Bend, it's not imminent. There are also some
cumulus over portions of the east side associated with a weak
surface trough moving across the area and some upper dynamics
moving in. I don't expect this to turn into anything, but clouds
will continue drifting across the east side tonight.

The rest of the forecast looks on track. Latest 12/00Z guidance
continues to show a breezy and very dry day tomorrow as an upper
trough axis swings across and vertically aligned offshore flow
dominates. This may also continue into the Monday night and
perhaps even Tuesday morning before finally relenting. This is
something we'll be looking at for possible extensions to the red
flag warnings tonight. -Wright

&&

.PREV DISCUSSION... /Issued 646 PM PDT SUN SEP 11 2016/

DISCUSSION... /Issued 251 PM PDT SUN SEP 11 2016/

DISCUSSION...Cooler temperatures today arrived as a result of a
dry cold front, which passed through overnight and early this
morning, then stalled out right along the Oregon and California
state line. Meanwhile, the upper level trough has continued to
dig south, and by tonight, the trough axis should pass overhead.
By this time tomorrow, the trough will close off over central
California, and our forecast area will lie between the newly
formed closed low and upper level ridging just to our north.

Much time has spent spent during the shift today attempting to
find some consensus on the strength of winds we can expect while
trapped between cool temperatures and high pressure to the north
and east, and warm temperatures and low presure to the south and
west. A few of the more excitable model guidance suites have
suggested sustained winds could reach up to 45 mph in some
locations, but that seems a bit excessive. That is not to say it
won't be breezy, as it most definitely will. However, we do not
expect strong sustained winds, as there is little in the way of
support above the surface. Therefore no wind advisories are
deemed necessary. Instead, the flow will be gradient and terrain
driven, thus peaks and ridges, mountain gaps, and northeast to
southwest trending valleys will see the stronger sustained winds,
while most other areas should remain in the 10 to 15 mph range.
These winds, in conjunction with low humidity, will primarily be a
fire weather concern, and has prompted the issuance of Red Flag
Warnings for much of the area west of the Cascades. See the fire
weather discussion below for more details.

There will also be some wrap-around moisture on the eastern side of
the low, but by the time the moisture is able to make it far enough
north, the low will have started to track further east towards
Nevada. Have therefore started scaling back the chances for showers
and thunderstorms on the East Side Monday and Tuesday, but left in
some areas of slight chance should the low be slower to slide east.

Once the low does slide east and out of our area, we will return to
warm and dry conditions with ridging aloft, and that familiar
pattern should continue through the remainder of the forecast term.
-BPN

AVIATION...12/00Z TAF CYCLE...Gusty and strong north winds will
continue into late this evening across most of the area, especially
across southern Oregon. A strong offshore component to the wind
tonight through Monday morning and the fact that the models are
already over forecasting low cloud cover along and near the coast
now yields moderate confidence that conditions will remain VFR at
KOTH tonight through Monday morning. Localized IFR is possible in
the lower Coquille River Basin, primarily in Coos County. Elsewhere
VFR will continue through the TAF period. Strong gusty northeast
winds will develop east of the Cascades and across the upper slopes
and ridges Monday morning and then will expand across the west side
Monday afternoon through Monday night. BTL

MARINE...Updated 600 PM PDT, Sunday 11 September 2016...
High pressure offshore and a thermal trough inland will continue to
result in moderate to strong winds and steep to very steep seas
across much of the southern portion of the Coastal Waters through
late this evening. Warning level conditions are expected to be
mainly south of Gold Beach and beyond 5 nautical miles from the
coast.

Tonight through Monday evening winds and seas will diminish some and
then increase again, but not quite to the levels attained this
evening as the pressure gradient between the offshore high and
inland thermal trough weakens. Warning level seas are still expected
west of Point Saint George, and these are expected to cover a wider
portion of the PZZ376 Monday afternoon and evening due to the
duration and fetch of the north wind field. Conditions are expected
to gradually improve Tuesday into Wednesday. BTL

FIRE WEATHER...Updated 615 PM PDT Sunday 11 September 2016...
A dry cold front moving southward this evening is pushing winds and
relative humidities very near critical levels. It appears that there
is enough of an RH rise to prevent critical conditions. However,
Monday through Tuesday we expect this is very likely to change as
moderate to strong north through east winds develop over the area.
Red Flag Warnings have been issued for FWZs 615, 618, 619, 620, 622
in Oregon and FWZs 280, 281, and 282 in Northern California for
Monday afternoon and evening from 2pm-11pm. The warning for FWZs 280
and 619 are in effect through 11am PDT Tuesday.

In summary, a dry cold front moving through this evening from the
north will be followed by strong subsidence Monday afternoon through
Tuesday morning. While the air mass will cool, north through east
winds will be substantial. Numerical models indicate winds at the
5000 foot level to will be 25 to 35 knots on the west side Monday
afternoon through early Tuesday morning. Output from a good number
of the numerical models indicate that ridge and gap locations from
the Cascades westward are likely to experience such sustained winds.
Expect that some of the windier locations such as Red Mound, Slater
Butte, and Parker Mountain are likely to gust in excess of 40 mph
Monday night into Tuesday morning.

The focus overnight will be trying to pin down the location and
magnitude of these winds and the RH recoveries Tuesday morning.
Models hint at enough east side cooling during this time period to
raise RHs enough to prevent overnight critical east wind conditions
except in FWZ 280 and 618 Monday night through Tuesday morning.
However, with winds peaking across the area Monday evening through
Tuesday morning, we might need to extend some of the warnings and/or
add a zone or zones.

Regarding the thunderstorm threat Monday and Tuesday across
southeastern sections of the area, it appears that development on
Monday will be in the Lassen National Park to Susanville area,
pretty well south of the Modoc. Tuesday bears some watching, though
model guidance that usually performs best keeps thunderstorms south
and east of us once again. BTL

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 2 PM Monday to 11 AM PDT Tuesday for
     ORZ619.
     Red Flag Warning from 2 PM to 11 PM PDT Monday for ORZ620-622.
     Red Flag Warning from 2 PM to 11 PM PDT Monday for ORZ615.
     Red Flag Warning from 2 PM Monday to 11 AM PDT Tuesday for
     ORZ618.

CA...Red Flag Warning from 2 PM to 11 PM PDT Monday for CAZ281-282.
     Red Flag Warning from 2 PM Monday to 11 AM PDT Tuesday for
     CAZ280.

Pacific Coastal Waters...Small Craft Advisory for winds until 11 PM
     PDT Monday for PZZ356-376.
     Small Craft Advisory until 5 AM PDT Tuesday for
     PZZ350-356-370-376.
     Gale Warning until 11 PM PDT this evening for PZZ356-376.
     Hazardous Seas Warning until 11 PM PDT Monday for PZZ356-376.