High Wind in Oregon, November 26 to 27, 2018

Area Forecast Discussion
National Weather Service Medford OR
816 PM PST Mon Nov 26 2018

.DISCUSSION...Only update this evening was to bump up winds in the
Shasta Valley a bit. Weed airport is reporting south winds of 25
mph with gusts to 46 mph and have adjusted the forecast to reflect
this. Otherwise, the remainder of the forecast looks on track and
no other updates were needed.

A strong front is approaching the coast this evening and winds
are increasing in response to this. A High Wind Warning and Wind
Advisories are in effect for the typically windy areas (Coast,
Shasta Valley, portions of the East Side) and the details can be
found at NPWMFR. There are some light returns on the radar
already, but most of that isn't making it to the ground and what
is, isn't amounting to much. That will change as the night
progresses and the front makes it's way inland. Periods of heavy
rain will start at the coast in the next few hours, spreading
inland by the early morning hours. Snow levels will remain
relatively high, above 7,000 feet, so we aren't expecting any
travel impacts due to snow. See the previous discussion below for
more details on this and as well as the weather to follow. /BR-y

&&

.AVIATION...For the 27/00Z TAFs...VFR conditions will prevail
initially, but an incoming front will bring deteriorating
conditions.  Areas of MVFR cigs/vsbys and isolated IFR cigs/vsbys in
low clouds, fog, and rain over the coastal waters will move onshore
tonight, spreading east to the Cascades by daybreak Tuesday with
higher terrain becoming obscured. Areas more affected by downslope
drying like KMFR and KLMT will likely take until mid-morning
tomorrow to see any significant cig/vsbys reductions due to rain.
Even so, conditions east of the Cascades will remain mostly VFR
through Tuesday, although higher terrain will become obscured.

LLWS will be a concern at KOTH, KRBG, and KMFR until the front
passes through the area.

&&

.MARINE...Updated 800 PM PST Monday 26 November 2018...South gales
and very steep wind driven seas are now developing as a strong front
moves into the coastal waters. Winds and seas will peak as the front
moves through later tonight into Monday morning. The worst
conditions will occur within a coastal jet that will develop as the
front nears the coastline around dawn tomorrow. While gales are
already expected, some storm force gusts will be possible in this
area. In addition to the wind and seas hazards, the front
will bring heavy rain, and there will be a slight chance for
thunderstorms both along the front and in the cold air behind the
front.

Heavy long period west swell will build in behind the front later
tomorrow and persist into Wednesday. These waves will pose a
significant risk for damage to bars and harbors, offshore equipment,
and other exposed coastal infrastructure.

Once the front moves inland tomorrow, conditions will gradually
improve. However, steep seas are expected to continue through much
of the upcoming week. For clarity and simplicity, small craft
advisories were not issued for later periods, but they will be
issued once the front moves inland.

More fronts will follow Wednesday into Saturday, but they will not
be as strong.

&&

.PREV DISCUSSION... /Issued 235 PM PST Mon Nov 26 2018/

DISCUSSION...High and mid level clouds are moving into the area
ahead of the next incoming system. This one will pack a good punch
in terms of wind along the coast, Shasta Valley and higher terrain
in Lake and far eastern Klamath County. There is fairly good
agreement the pressure gradient between Arcata and North Bend will
be close to 7.4 mb which could bring strong winds reaching high wind
warning criteria to exposed areas along highway 101, capes and
headlands. Therefore the decision was made to upgrade the high wind
watch to a warning. Also the wind advisory for east of the Cascades
was expanded to include more of the higher terrain. Winds along the
coast are expected to be strongest later this evening into early
Tuesday morning, then will decreasing. Winds will get going east of
the Cascades late tonight into Tuesday morning. Winds will also get
going in the Shasta Valley later this evening into Tuesday morning.
Details for all of this can be found at NPWMFR. One other thing of
note, winds could be favorable for stronger winds to surface in the
south end of the Rogue Valley near Ashland. Right now, Confidence is
not high enough to go with any headlines, but later shifts will want
to take another look at this.

This system will also bring a good shot of precipitation to many
locations. We still expect a period of heavy rainfall at the coast,
Coast Range, and in Western Siskiyou County high terrain Tuesday
morning. Rainfall rates could approach 0.5 in/hr as some of the high
resolution model data is suggesting. Tuesday will be wet in most
areas. The Rogue Valley will see less rain amounts tonight due to
downsloping, but there's a chance for a 4-6 hour period of moderate
to occasionally heavy rain starting early Tuesday morning. Showers
are a good bet behind the front late Tuesday morning through Tuesday
afternoon with the focus for heavier amounts along the coast, coast
range, Cascades and higher terrain in Siskiyou County.

Snow levels with the first system will be high, generally from
Crater Lake and higher through Tuesday night, lowering to around
5000 feet as precipitation tapers off Wednesday morning.
Therefore, we don't expect major winter weather impacts with this
first system.

We should catch a relative break in the weather Wednesday. There is
a hint of weak ridging, but a moist west to southwest flow remains
along with weak disturbances moving through. Showers will still
linger into Wednesday, but they should more isolated and most
confined to the higher terrain west of the Cascades.

The next system arrives Thursday, and models have come into better
agreement with the low center moving into Northern California
Thursday morning. Latest GEFS data confirms this trend towards
better agreement and thus higher confidence for precipitation in
Northern California. In Oregon it's not as clear because, the models
show varying solutions with the northward extent of precipitation.
-Petrucelli

Friday through Monday...Models continue to project a wet pattern
with a Gulf of Alaska low approaching the Pacific Northwest Friday.
Expect the warm front to bring substantial precip, especially to
coastal areas. The big question for Friday into Saturday is not so
much if there's precipitation, but how much. A low currently located
roughly 1000 miles east of of Japan will progress eastward
throughout this week, drawing moisture from the subtropics and
tropics. Current model solutions have sped the progression of the
Gulf of AK low and slowed the subtropical low, largely preventing
the subtropical low from serving as a moisture source for the Friday
to Saturday system. However, given the run to run differences, it's
hard to have confidence in QPF Friday into Saturday as a slight
change in the synoptic pattern expected could make a big difference
in QPF.

Also of note, 500mb temperatures in the center of the Gulf
of AK low are projected to hover around -30 deg C, which could
facilitate thunderstorms offshore on Saturday, when the low is
overhead. The trailing cold front of the main low will drop snow
levels further early Saturday morning, resulting in potential for
widespread snow showers down to 3000 feet. Expect strong south winds
ahead of the cold front, especially in the Shasta Valley and higher
elevations east of the Cascades.

A ridge will build in behind the low, bringing a return to cold, dry
weather early next week. -McAuley

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 7 AM PST Tuesday for ORZ021-022.
     High Surf Advisory until 10 AM PST Wednesday for ORZ021-022.
     Wind Advisory from 1 AM to 4 PM PST Tuesday for ORZ030-031.

CA...Wind Advisory until 10 AM PST Tuesday for CAZ081.

Pacific Coastal Waters...High Wind Warning until 7 AM PST Tuesday for PZZ356.
     High Surf Advisory until 10 AM PST Wednesday for PZZ350-356.
     Gale Warning until 7 AM PST Tuesday for PZZ350-356-370-376.
     Hazardous Seas Warning from 7 AM to 10 AM PST Tuesday for
     PZZ350-356.
     Hazardous Seas Warning from 4 AM to 10 AM PST Tuesday for
     PZZ370-376.

MNF/MAP/MSM