Area Forecast Discussion
Issued by NWS Medford, OR

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561
FXUS66 KMFR 022306
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
306 PM PST Fri Dec 2 2016

.DISCUSSION...The region heads into a cooler and active pattern
this upcoming week. A weak cold front will continue to bring
generally light showers that will decrease overnight as the front
dissipates. With the upper level ridge in place Saturday
precipitation will will be confined to the northern fringes of the
west side forecast area. The ridge weakens and transitions to a
northwest zonal flow pattern ahead of the next system that moves
in on the nose of a 155 kt jet. The bulk of the precipitation will
be on the warm side of the front and the passes on I-5 should see
just rain with this system. Elevations above 600 ft however will
see another substantial contribution to snow pack. A cold air
mass moves in behind this system ahead of the next system that
moves into the region Monday. The timing of this system will be
critical as the current models indicate that the the Rogue valley
will see enough clearing to allow temperatures to be near freezing
on the valley floor and with a saturated layer with no moisture in
the seeder zone freezing drizzle in possible. However, with
surface temperatures still warm if this does occur there should
not be any accumulations on road surfaces, including bridges and
overpasses, and should be collecting only on surfaces like cars.

The next system rolls in in this cooler air mass, and all passes
in the region will see snow by Tuesday morning. On the tail end of
the system snow level are expected to reach many of the west side
valley floors, but the valleys floors are only expected to see
light amounts, and with the still warm ground temperatures should
melt rapidly. -Sven

Extended...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, but have mostly come into agreement during the
12z run.

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 12 hours faster than the EC
in bringing in precipitation. So, went with a blend and kept mostly
slight chance pops for Wednesday afternoon, and ramping up chances
Thursday. With a cold air mass in place, this will likely mean snow
levels below 3000 feet on the east side. Again, model uncertainty is
high regarding the timing of the precipitation.

One note of concern is precipitation type with the Thursday
system. With the cold air in place ahead of the front, and the
models depicting significant overrunning with the warm front,
there is the potential for a period of freezing rain sometime
between Thursday morning and Thursday evening. Much will depend on
the timing of the warm front, with the earlier GFS solution
producing a morning event, while the later ECWMF produces an
evening event. Have introduced a slight chance of freezing rain to
the areas that seem the most susceptible, but until the models
begin to find some consensus in the timing and progression of the
system, confidence remains very low.

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...02/18Z 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 MVFR and VFR,
and any mountain obscurations should improve, but not clear
completely this afternoon.

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. Expect localized lower VIS in showers.
These lower ceilings, along with mountain obscuration, will move
inland late this afternoon and through the overnight hours. IFR CIGs
are possible at all TAF sites early tomorrow morning. -MSC


&&

.MARINE...Updated 130 PM PST Friday 2 December 2016...A weak front
will move onshore this evening. Steep northwest swell will build
Saturday morning. This swell will build seas up to around 16 feet at
19 seconds Saturday. Seas will subside to around 10 feet Monday...
building back up to 12 to 13 feet Monday night into Tuesday.  In the
meantime, two more weak fronts will move onshore Sunday and Monday.
A stronger front will move in Wednesday night.


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Beach Hazards Statement from late tonight through Saturday
     afternoon for ORZ021-022.

CA...None.

Pacific Coastal Waters...Small Craft Advisory for hazardous seas from 10 PM this evening
     to 4 PM PST Tuesday for PZZ350-356-376.
     Small Craft Advisory for hazardous seas until 4 PM PST Tuesday
     for PZZ370.

$$

SBN/SBN/SBN



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