Small Craft Advisory 110, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
913 PM PDT MON OCT 31 2016

.DISCUSSION...The 00Z GFS data has begun to arrive and supports
the current short term forecast. Isolated to scattered showers
this evening are diminishing and mainly over Siskiyou County. The
associated area of low pressure will move east across far northern
California overnight. By morning, a few remaining showers will
likely be occurring over the Warner Mountains of eastern Modoc
County. A weak shortwave in northwest flow will also bring a push
of marine air into west side valleys with a slight chance of light
showers. A ridge will build into our area from the southwest on
Tuesday and result in decreasing clouds with the beginning of a
warming trend.

A warm front will brush past Tuesday night into Wednesday on its
way northeastward into Washington. This will bring an increase in
high clouds and...with a stable layer in place...there will also
be areas of valley low clouds and fog into Wednesday morning.

A focus for the night shift will be fine tuning the details of the
next frontal passage. It is likely to be of weak to moderate
strength as it brings rain to the immediate coast by Wednesday
evening. It is then expected to weaken as it moves inland over
the west side during Wednesday night. Its remnants will reach the
east side early Thursday morning.

Another break between systems is expected Thursday into early
Saturday. A more important focus for the night shift will be
looking for better model agreement regarding the details of what
is very likely to be a stronger front and then a trailing surface
trough that will both impact our area with wind, rain, and high
elevation snow this weekend. The early outlook is for another
break between systems next Monday.

&&

.AVIATION...01/00Z TAF cycle...Showers will taper off over most
of the area this evening, but linger overnight from around Mount
Shasta eastward. Areas of MVFR cigs will develop over the valleys
tonight with higher terrain obscured. Those areas will clear to
VFR by late morning Tuesday...then VFR conditions will persist
through Tuesday evening. -JRS

Note: The ceilometer at FAA site KOTH is out of service, so there
will be no ceiling observations available generally between the
hours of 04Z and 14Z.

&&

.MARINE...Updated 830 PM PDT Monday 31 October 2016...A front has
moved onshore. Winds and seas will diminish tonight and remain
relatively low (below small craft advisory levels) through Tuesday.
South winds will increase again Tuesday night as the next front
approaches. Small craft conditions will likely develop late Tuesday
night into Wednesday morning. Gale force winds are likely Wednesday
afternoon and night, so a Gale Watch will remain in effect for a bit
longer until the timing can be better defined.

There will be a break between fronts Thursday and Friday, but a
large, long period west swell will likely keep the entire area
inhospitable to small craft at least. It may also make for heavy
surf conditions along the coast. The next front will move in
Saturday with possible gales and heavy seas. -JRS

&&

.PREV DISCUSSION... /Issued 303 PM PDT MON OCT 31 2016/

DISCUSSION...A weak closed low swinging up from offshore of
northern California will bring showers to the southern Oregon
coast by 2 PM. Isolated thunderstorms are occuring in the coastal
waters of northern california at this time with a cold pool with
500 MB temperatures near -25 C bringing instablity on the back
edge of the showers, with a thunderstorm possible on the extreme
southern coast of Oregon by 4 PM. Showers are expected to move
into all of Curry county, southern Coos county, southern
Josephine and western Siskiyou county by around 3 PM. The showers
will continue to spread inland from the southwest and reach into
northern Coos county, Douglas and jackson county west of I-5, and
into the mt. Shasta area by around 4 PM. Showers are expected to
spread across to east of the Cascades around and after 5 PM.
Showers are expected to mix with snow in the Cascades passes
tonight, but is not expected to accumulate on the road surfaces
more than very briefly.

The closed low will open and the front will dissipate with
showers tapering off through Tuesday morning and clearing in the
afternoon as a ridge builds over the PAC NW. This slowly migrates
east over the great basing with the next system moving into the
coast Wednesday afternoon.

With the ridge still strong over the great basin this front washes
out with precipitation largely remaining west of the Cascades
through Thursday morning. Winds become offshore by Thursday
afternoon, clearing skies and warming temperatures. Sven

Long Term...Friday, Nov 4th through Monday, Nov 7th...
Model guidance is well agreed on high pressure ridging holding in
for Friday. Thus, mild temperatures with no precipitation will allow
for some drying. Temperatures will be around 10 degrees above
normal, which should put highs in valleys in the upper 50s to upper
60s.

Models are also well agreed on a strong front impacting the forecast
area this weekend. While there are slight timing differences of
about 6 hours among most of the models, it appears that this front
should result in maximum rainfall at the coast on Saturday morning
and across the interior West Side Saturday afternoon through
Saturday evening. Integrated moisture transport (IVT) graphics from
the GFS Ensemble models indicate a high (>80%) probability of a
significant precipitation event across the area during this time
period, so have increased precipitation probabilities accordingly.
This same guidance indicates a good inland penetration of the
moisture from this storm system.

There have been a couple of changes in today's guidance as compared
to yesterday's regarding the weekend storm system. The first is that
the cold air with this system is slower to get to us, so snow levels
take longer to drop to below 7kft. The second related change is that
the front and resultant atmospheric river (AR) looks as if it will
linger over the area for a longer period of time, possibly through
Sunday and into Sunday night. This means that precipitation amounts
are likely to be heavier. For example, previous solutions indicated
that the Bear Creek portion of the Rogue Valley would get a quarter
to a half inch of water from the weekend storm system. Current
guidance indicates a half inch to a full inch. Obviously, this
forecast is for days 6 and 7, so details could easily change. The
heavier amounts indicated on the current guidance are more
consistent with anomalies shown by the CFSv2 ensemble over the last
several days, so are more likely to verify. BTL

&&

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

CA...None.

Pacific Coastal Waters...Gale Watch from Wednesday morning through
     late Wednesday night for PZZ350-356-370-376.
     Small Craft Advisory from 11 PM Tuesday to 11 AM PDT Wednesday
     for PZZ370-376.

DW/SBN/JRS