Small Craft Advisory 97, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
1109 AM PST Thu Nov 29 2018

.AVIATION...For the 29/18Z TAFs...Light rain with MVFR or better
ceilings will continue to affect the area, including all
terminals, off and on today. There may be a break in between
rain bands late morning and early afternoon, but rain should
rotate back in from the west later this afternoon and this
evening. -Wright

&&

.PREV DISCUSSION... /Issued 912 AM PST Thu Nov 29 2018/

UPDATE...Snow levels are dropping with heavier precipitation
rates near Snowman Summit according to the road cameras. Satellite
is showing impressive looking band over the area, but
precipitation amount associated with this feature are not high
with the bulk of the precipitation well south of our area.
Updates for the lower snow levels in Northern California will be
issued shortly. Sven

PREV DISCUSSION... /Issued 631 AM PST Thu Nov 29 2018/

DISCUSSION...
Winter weather will be increasing across the forecast area the
rest of this week into this weekend as temperatures become colder,
snow levels lower, and accumulating snow falls down to about 2500
foot elevations. Please see the Winter Weather Message issued
this morning for the latest winter weather headlines. Also, expect
that a number of additional winter weather headlines are likely
to be issued in the next 24 hours.

This morning a broad, occluded frontal system is spinning into
Northern California sending moisture northward across the area.
While radar returns do not look particularly impressive, there
have been some moderate to briefly heavy precipitation rates
recorded. Automated weather stations in western and south-
central Siskiyou County are reporting precipitation amounts of a
half inch to an inch in just the last 6 hours. The Mount Shasta
Avalanche Center's Ski Bowl site at 7600 feet reported nearly 3
inches of new snow in 2 hours and rain changed to heavy, wet snow
down to Snowmans Summit on California Highway 89. Precipitation
rates have likely peaked and snow levels have likely bottomed out
in the Mount Shasta area for this morning. Since periods of snow
are likely to continue above 5kft there this morning we continue
to have a winter weather advisory in effect there through 10 AM
PST.

Showers are expected to continue across the forecast area today
into tonight as the current low shears out northeastward as it
gets pulled ahead of the next incoming trough of low pressure.
Snow levels are expected to hover around 5kft for most of the area
through tonight.

Light showers Friday morning will be followed by a band of
moderate to heavy precipitation late Friday afternoon through
early Saturday morning, and then followed by showers Saturday.
Winter Storm Watches have been issued for areas above 2500-3500
feet from the Mount Shasta area, western Siskiyou County, and
areas west of the Oregon Cascades for Friday evening through
Saturday. While some of the watch area may only get advisory level
snow amounts, guidance indicates areas above 3500 feet are likely
to see 8 to 15+ inches of new snow in 24 hours or less.
Additionally, the NAM12 has been very consistent for it's last
several runs in indicating precipitation rates of 0.30" to 0.60"
in just 3 hours as a strong cold front moves across the forecast
area late Friday afternoon through early Saturday morning. This
equates roughly to the potential for snowfall rates of 1 to 2
inches per hour as the front moves through. While the other models
are not quite as robust with precipitation amounts, they have a
similar theme, so confidence is high in the front moving through
with falling snow levels. Over the next 12-24 hours we'll be
getting QPF guidance in from the shorter term high resolution
models which should help us hone in on precipitation amounts. The
bottom line is, stay tuned for updates and be prepared to adjust
your travel plans for Friday evening through Saturday if your
plans take you over the mountains and hills above 2500 feet. If
you must travel above 2500 feet, make sure you and your vehicle
are prepared for snow covered roads and be prepared for possible
travel delays.

Saturday night through Sunday confidence in the overall forecast
deteriorates due to uncertainty in the models. The previous theme
had been showers winding down and then dry conditions with east
wind early next week. However, for the last 24-30 hours the GFS
and ECMWF have indicated the possibility of another frontal system
pushing in from the southwest. BTL

MARINE...Updated 300 AM PST Wednesday 28 November 2018...Steep
long period westerly swell will persist into the weekend. Winds will
increase out of the north today as low slides past us to our
south.  These winds will be hazardous to smaller crafts that venture
beyond 30 nm away from shore.  The next period of concern will be
Saturday night into Sunday when seas are expected to become very
steep.  Wave heights will be around 14 to 16 feet and wave periods
around 12 to 13 seconds at this time. Overall, the active weather
pattern will keep seas hazardous to smaller crafts through
Saturday. Seas are expected to lower Sunday and Monday.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Storm Watch from Friday afternoon through Saturday
     afternoon for ORZ024>026.

CA...Winter Storm Watch from Friday afternoon through Saturday
     afternoon for CAZ080-082.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas until 10 PM PST Sunday
     for PZZ350-356-370-376.
     Small Craft Advisory until 7 PM PST this evening for PZZ370-376.