High Wind in California, December 15, 2018

Area Forecast Discussion
National Weather Service Medford OR
806 PM PST Sat Dec 15 2018

.DISCUSSION...Quite a few updates were made to the forecast from
this evening through tomorrow, and the updates were just sent. It
is already raining in the southerly upslope areas of our forecast
area, namely, the Curry coast and coastal mountains, the western
Siskiyou County mountains, and the Mt. Shasta area. And with
moist, southerly flow only increasing, it's likely to continue to
rain in these areas all night, so pops were ramped way up. The
wind forecast was also massaged to what is occurring right now as
well as toward the latest guidance through tomorrow. Forecast
winds weren't too bad, but timing was adjusted area-wide, and many
of the valley areas on the east side, including Klamath Falls,
were filled in with stronger winds (and also pulled into the wind
advisory). Finally, a slight chance for thunderstorms was added to
the coastal waters tomorrow afternoon and then onto the coastline
in the evening. 00Z guidance shows pretty good instability behind
the front and coincident with the upper trough. Also of note:
winds are already gusting to 52 mph in Weed, CA and at Humbug
Mountain along the coast, so hopefully folks have already battened
down the hatches for the night in these areas. -Wright

&&

.AVIATION...For the 16/00Z TAFs... Another cold front will move
towards the area Sunday increasing low level wind shear and bringing
rain to all of the TAF sites.  Low level wind shear is a concern for
most of the TAF sites as winds aloft are strong with the incoming
front.  The other topic is fog forming in the valleys.  We saw LIFR
conditions due to fog last night and we could possibly see it again
tonight. The upper level clouds appear a bit thicker, so we probably
won't see as much clearing.  Regardless, confidence is low that
we'll see LIFR and IFR in the valleys tonight due to fog.

&&

.MARINE...Updated 730 PM PST Saturday 15 December 2018...
Strong gales will occur tonight into Sunday and will combine with
another swell train that will bring the highest seas of the season
so far Sunday into Sunday night. The surf zone will become very
dangerous. Winds diminish Sunday night but long period west swell
will remain...with combined seas very steep in excess of 20 feet.
Another long-lived gale event is expected Monday night into
Tuesday. Another gale event is expected Thursday night.

Stavish/Smith

&&

.PREV DISCUSSION... /Issued 257 PM PST Sat Dec 15 2018/

DISCUSSION...

Short Term...Tonight through Tuesday Night...The wet and windy
pattern shows no real sign of slowing down. Currently, a large low
is swirling in the Gulf of Alaska, and appears quite impressive in
today's satellite imagery. A front emanating from this low looms
offshore of southern Oregon, and this will be our next big
weather-producer as it make its way into and across the forecast
area tonight and tomorrow.

Winds will be the primary concern, as mid-level wind profiles and
gradients look similar, but not quite as strong, as the event we
experienced yesterday. Tonight's front lacks the features and
timing of various features that combined just as the front moved
onshore, creating our notable wind event. Nevertheless, we do have
High Wind Warnings and Wind Advisories in effect across the
region, as the synoptic pattern and surface pressure gradients are
all conducive to gusty winds. Details on these can be found at
PDXNPWMFR. While we do expect a good deal of rain with his front,
snow levels will raise to above 6000 feet, so there is no threat
of significant winter weather impacts. Snow levels will drop to
around 4500 feet on the back side of the system Sunday night, but
by then, showers will be tapering off, and snowfall amounts will
be light.

As there is little rest for the weary, after only a brief break
Monday morning, the next front is set to arrive Monday afternoon
and evening. This front is traveling much slower, and is expected
to stall out as it crosses the area. This will result in an
extended period of rain and wind from Monday evening through
Tuesday night, with snow levels rising from around 4500 feet late
Monday to over 7000 feet Tuesday morning. Given the duration of
the event, rainfall totals will be substantial along and west of
the Coastal ranges, as well as in the Umpqua and along the
Cascades, where the prevailing west flow is likely to produce the
best lift along the terrain. Area rivers and streams should have
plenty of room for this rain, but we can not rule out the chances
for localized high water, especially in urban areas or small
streams. But once again, snow will not be a major concern for the
area passes. While winds once again look to be gusty, they should
be much weaker than the previous events. We will re-evaluate the
need for wind headlines over the next few forecast cycles. -BPN

LONG TERM...Wednesday through Saturday, December 19-22, 2018...
Overall, we'll maintain a progressive pattern across the area mid-
late next week with times of rain/wind, but nothing that suggests
anything too anomalous for this time of year. Initially, the cold
front that moves through Tuesday night will stall just to our
south due to strong ridging centered off the southern California
coast. Light precipitation associated with this front (mainly rain
due to snow levels >6000 feet) could linger in some areas on
Wednesday morning, especially along and west of the Cascades, but
largely, expect it to dry out. The mid and upper level flow will
back from west to southwesterly as the ridge to the south shifts
eastward and another trough/low pressure develops out near 140W.
This will allow the front to lift back to the north as a warm
front Wednesday. There could be some light precipitation along the
coast, but most areas remain dry Wednesday night into Thursday
morning. Mid-level warming will allow snow levels to rise further
to 7000-8000 feet during this time frame. The next cold front is
expected to arrive at the coast late Thursday, then move onshore
Thursday night. There is still some degree of spread in the
guidance associated with the timing of this front, so we have
maintained a broader approach to our POP/QPF grids, but have a
focus of the highest POPs/QPFs on Thursday evening/night as the
front moves onshore. Expect the bulk of the precipitation with
this event to be rain, but snow levels should settle back to
4500-5500 feet by Friday morning in lingering post- frontal
showers. We could catch another break Friday night into Saturday
with the next Pacific front arriving sometime the latter half of
next weekend. -Spilde

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 10 PM PST Sunday for ORZ030-031.
     Wind Advisory until 10 PM PST Sunday for ORZ029>031.
     Gale Watch from Monday afternoon through late Monday night for
     ORZ021.
     Hazardous Seas Warning from 4 PM Sunday to 4 PM PST Monday for
     ORZ021.
     High Wind Warning until 4 PM PST Sunday for ORZ021-022.
     High Surf Warning from 4 AM Sunday to 4 PM PST Monday for
     ORZ021-022.
     High Surf Advisory until 4 AM PST Sunday for ORZ021-022.
     Wind Advisory until 4 PM PST Sunday for ORZ023>025.
     Wind Advisory until 4 PM PST Sunday for ORZ026.

CA...High Wind Warning until 10 PM PST Sunday for CAZ085.
     Wind Advisory until 10 PM PST Sunday for CAZ083>085.
     High Wind Warning until 10 PM PST Sunday for CAZ081.
     Wind Advisory until 10 PM PST Sunday for CAZ081.

Pacific Coastal Waters...Gale Watch from Monday afternoon through late Monday night for
     PZZ350-356-370-376.
     Gale Warning until 4 PM PST Sunday for PZZ350-356-370-376.
     Hazardous Seas Warning from 4 PM Sunday to 4 PM PST Monday for
     PZZ350-356-370-376.