Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 021719

Area Forecast Discussion
National Weather Service Medford OR
914 AM PST Fri Dec 2 2016

.DISCUSSION...Morning update. Temperatures did not reach freezing at
the Medford airport this morning, but this is probably the only
place in the Rogue valley that has not dropped below freezing yet.
However, it is December and no further frost or freeze products will
be issued, unless there are extremely cold temperatures expected,
until the spring. Sven

.DISCUSSION...Low clouds have once again formed in the west side
valleys and brought radiational cooling to a screeching halt. In
fact, we`ve reached 36 so far this morning in Medford, but when
clouds formed we ticked back up to 37. Illinois Valley got as low
as 29 and is now back up to 36. While I think we`ve probably
bottomed out, many locations did reach freezing already, so I`ll
let the freeze warning continue through its natural expiration
later this morning.

Low clouds will likely break up around the same time they did
yesterday which was late morning to early afternoon. A weak warm
front will slide south along the Oregon coast today and gradually
spread light precipitation in over northern areas later today and
tonight. The warm front dissipates by tomorrow morning, but a
nebulous looking cold front will sag in from the north and bisect
Oregon from west to east through the remainder of the day. It
looks like Saturday will be largely precipitation free except for
the early light precipitation over northern areas. I think clouds
associated with the front will prevent a lot of low cloud/fog
formation, but some can`t be ruled out.

A much stronger cold front (in term of temperature gradients,
anyway) will move in from the north on Sunday. This front will
bring a good shot of rain to west side locations with a healthy
dose of snow in places like Crater Lake. Precipitation diminishes
Sunday night, but strong cold advection will bring the coldest
airmass we`ve seen this season with snow levels plummeting to
around 1500 feet on west side locations and to the surface on the
east side.

The next batch of precipitation arrives later Monday as the upper
trough moves in. The models differ in timing of this
precipitation, but it looks like it arrives during the day which
should preclude any impacts from snow in the west side valleys.
However, the mountains above about 2000 feet will see snow,
including all the Cascade passes and Siskiyou Summit. This may
also affect the passes along I5 north of Grants Pass Monday
afternoon and evening.

Things get more interesting as we head into Monday night and
Tuesday morning. All models show precipitation continuing through
the period, and snow levels will fall further - perhaps as low as
1000 feet. At this point, all the passes in the area will be
susceptible to impacts from snow (including the lower ones on I5
north of Grants Pass), and even some valley locations may get in
on the action. It`s too early to tell whether snow may accumulate
in Medford proper, but it is possible. What is more likely is that
snow impacts travel in the area, especially over the passes.
Residents may wish to start preparing in case snow does reach the
valleys, but travelers should certainly prepare for possible
wintry conditions if traveling through southwest Oregon or
Northern California from late Sunday through Tuesday. -Wright

Long term (from previous discussion)...Tuesday through Friday. On
Tuesday, precipitation will begin clearing as slight ridging
builds. Expect clearing to bring valley fog in west side valleys
Wednesday morning. A very cold dry surface air mass will move into
the forecast area, coming from the northern Rockies. This will
bring temperatures in the single digits to teens on the east side,
and in the twenties on the west side Wednesday morning. During the
second half of the week, we will transition to a wet pattern.
Models start to diverge somewhat during the day Wednesday.

Both the GFS and EC depict a strong low pressure system in the Gulf
of Alaska driving a warm front over the CWA, bringing precipitation
to the area. However, the GFS is roughly 24 hours faster than the EC
in bringing in precipitation. Leaned towards the GFS for this
forecast, thus chances of precipitation increase Wednesday. With a
cold air mass in place, this could mean snow levels below 2000 feet.
Again, model uncertainty is high regarding the timing of the
precipitation. After the warm front passes over, the cold front
associated with this low will bring high winds to the east side,
possibly hitting hazard criteria. MSC/FJB


.AVIATION...02/12Z TAF cycle...A rather stable late fall pattern is
yielding a mix of IFR and MVFR ceilings this morning, mainly focused
west of the Cascades. Isolated areas of fog are likely occurring in
some valleys this morning but are not being observed on any webcams
or observations this morning. Ceilings should lift to VFR, and any
mountain obscurations should improve, later this morning.

Coastal areas from Cape Blanco northward will likely have light rain
develop in the afternoon into the evening with areas of MVFR as a
warm front moves onshore. These lower ceilings, along with mountain
obscuration, will move inland late this afternoon and through the
overnight hours. Models suggest the potential for IFR conditions in
West Side valleys late Friday night, which makes sense in a warm
frontal pattern. SK


.MARINE...Updated 830 AM PST, Friday 2 December 2016...
An approaching weak front will bring increasing south winds to
mainly the waters north of Cape Blanco this afternoon. Winds shift
northwesterly behind the front tonight and a round of steep west
swell will build Saturday morning. This swell should ramp seas up to
the 14 to 17 foot at 18 second range on Saturday. A stronger front
will move in Sunday with blustery northwest winds spreading from
north to south across the waters behind the front, potentially
reaching small craft advisory level. Swell-dominated high and steep
seas should continue into next week.




Pacific Coastal Waters...Small Craft Advisory for hazardous seas from
     10 PM this evening to 2 PM PST Monday for PZZ350-356-376.
     Small Craft Advisory for hazardous seas from 10 AM this morning
     to 2 PM PST Monday for PZZ370.

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