Small Craft Advisory 102, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
843 AM PST Tue Nov 14 2017

.DISCUSSION...No major updates this morning. A small area of fog
is lingering in portions of the Rogue Valley, and should lift later
this morning. A mostly dry day is on tap for the forecast area
today, but this will change tomorrow as a strong front moves into
the area and brings moderate to heavy precipitation, along with
winds. Snow levels will lower behind the front Wednesday night.

Please see the previous discussion below for details on the
upcoming weather system and expected impacts.

&&

.AVIATION...14/12Z TAF CYCLE...Marginal stability this morning
will lead to mainly VFR conditions, though isolated areas of MVFR
are possible in the morning hours. Partial terrain obscurations
will also occur across most mountain areas. Southeast winds are
expected at most locations this morning, and then are likely to
turn south to southwest this afternoon into the evening. Showers
will be possible along the coast today, especially later in the
day, and rain is expected along and near the coast beginning
around 06z. MVFR conditions are expected after 06Z along portions
of the coast. Terrain obscurations are expected in the mountains
this afternoon and evening. Increasing winds aloft today and
especially tonight into Wed morning are likely to result in
turbulence. Wind shear is possible along and near the coast after
00Z, especially in areas where surface winds fail to increase due
to terrain blocking. BTL

&&

.MARINE...Updated 400 AM PST Tuesday 14 November 2017...Winds
decreased briefly last night, but they will increase again today as
a frontal system approaches. South winds are expected to reach gales
by this afternoon and continue through Wednesday. We may even see
some storm force gusts just prior to the frontal passage Wednesday
morning. Corresponding seas will be very steep due to a combination
of swell and building wind wave through this afternoon the primarily
from wind waves tonight until the front passes tomorrow. Winds
become west and diminish behind the front later Wednesday, but seas
will likely remain high through Thursday. The active pattern will
continue for the foreseeable future, with more fronts possible over
the next 7 to 10 days. Expect conditions to remain unsettled and
seas to remain elevated through at least the weekend. -BPN/Wright

&&

.PREV DISCUSSION... /Issued 454 AM PST Tue Nov 14 2017/

SHORT TERM...A lot of updates were made in the short term,
primarily related to wind and snow headlines. A strong frontal
system will approach today and then move through tomorrow,
bringing heavy rain to the coast, snow to the mountains, and wind
to some of the valleys. Complicating the forecast considerably is
the possibility of deepening low pressure moving along the front
as it moves onshore tomorrow. The problems with this are two-fold:
1. the passage of low pressure will strengthen pressure gradients
south of its path and weaken them to its north (which affects the
wind forecast), and 2. very heavy precipitation (both valley rain
and mountain snow) is likely near the low which may sap some of
the moisture from locations away from the low. All that said, the
possibility of low pressure both increases the chance of
significant wind and precipitation in some places and lessens it
in others. At the moment, guidance has the low moving onshore
somewhere between Cape Mendocino and Brookings Wednesday afternoon
and then scoots it off to the northeast across southwest Oregon
Wednesday night. I'll break this short term discussion into the
two most important parts, wind and snow.

Wind: High resolution guidance shows strong winds in the Shasta
Valley Wednesday, and forecast MFR-RDD gradients of -6 mb and
strong winds aloft support the idea. Models also show 700 mb winds
peaking at 70-75 knots briefly across the east side Wednesday
evening, and this is certainly sufficient for high wind there.
Low pressure could certainly disrupt the gradients and short-
circuit winds in the Shasta Valley. Nevertheless, the potential is
high enough to warrant high wind watches in both locations, and
those have been issued. Gradients are also tight enough to bring
winds into the Rogue Valley, and model soundings do show a low
level inversion which tends to force winds to funnel through the
terrain. Also of note, SREF plume diagrams show similar winds to
Sunday evening in the Rogue Valley, which you may remember were
quite breezy. We don't think winds will be high enough to warrant
a high wind watch, but they also aren't nothing, so a wind
advisory was issued for the Rogue Valley.

Snow: The low pressure may also affect snowfall in the mountains
with higher amounts near and north of the low and lesser amounts
away from it. Guidance still shows a significant burst of snow
Wednesday afternoon and evening from the Siskiyous north through
the Cascades, and it is these potentially high snowfall rates that
are the main driver of the winter storm watch that was issued.
While overall amounts are not expected to be anything unusual for
November, most of it could come in a short time. The good thing is
that snow levels will be fairly high, 5500 feet or so, and this
keeps snow impacts above I-5 and highway 140 (the two most heavily
traveled mountain routes through our area).

The front moves inland Wednesday night and then east of us
Thursday. At this point, most of us are left with showers of no
particular significance. However, as the upper trough arrives,
colder air moves in, and snow levels lower, precipitation becomes
concentrated over the Cascades. As a result, we could see another
period of heavy snow in the Cascades Thursday afternoon and
evening, and this one may very well affect I-5 and highway 140.
That said, Siskiyou Summit is often blocked from the heaviest snow
in this kind of pattern, but we will probably see at least some
snow down to I-5 Thursday afternoon through night. -Wright

LONG TERM...Fri (11/17) through Mon (11/20)...Models are out of
phase for Friday with the GFS building a short term but large
ridge over the Pacific NW; whereas, the ECMWF has a weak short
wave ridging in NW flow. We've kept rain chance to the coast,
Umpqua Basin and part of Josephine county in a nod to the ECMWF
solution. A similar discrepancy extends into Saturday. As a
result, we have lowered rain chance for Saturday and keep them
mainly from the Cascades west.

The models come into good agreement that a wave of subtropical
moisture will move over us from the southwest during the latter
part of next weekend. If this is correct, it could bring a batch
of hefty precipitation and high snow levels to our area. Ensemble
IVT moisture transport shows a decent amount on Sunday and Monday,
but it also shows a lesser amount of moisture beyond Monday for
most of next week. /FB

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Watch from Wednesday morning through Wednesday evening
     for ORZ030-031.
     Wind Advisory from 7 AM to 4 PM PST Wednesday for ORZ026.
     Winter Storm Watch from Wednesday morning through Wednesday
     evening above 5500 feet in the for ORZ028.
     Winter Storm Watch from Wednesday morning through Wednesday
     evening above 5500 feet in the for ORZ027.

CA...High Wind Watch from Wednesday morning through Wednesday evening
     for CAZ085.
     Winter Storm Watch from late tonight through Wednesday evening
     above 5500 feet in the for CAZ080.
     High Wind Watch from late tonight through Wednesday evening for
     CAZ081.

Pacific Coastal Waters...Gale Warning from 7 PM this evening to 4 PM PST Wednesday for
     PZZ356-376.
     Hazardous Seas Warning until 7 PM PST this evening for
     PZZ350-356-370.
     Gale Warning from 1 PM this afternoon to 4 PM PST Wednesday for
     PZZ350-370.
     Hazardous Seas Warning until 4 PM PST Wednesday for PZZ376.

NSK/TRW/BTL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MEDFORD OR
1037 AM PST TUE NOV 14 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1034 AM     HEAVY RAIN       6 SE SELMA              42.23N 123.52W
11/14/2017  M1.02 INCH       JOSEPHINE          OR   TRAINED SPOTTER

            9AM-9AM. THE DURATION OF THE HEAVY RAIN
            EVENT WAS 24 HOURS.

&&

SBN