Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 232244
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
244 PM PST Fri Feb 23 2018

.DISCUSSION...A couple of systems will move in from the northwest
this weekend bringing moderate to heavy snow along the Cascades and
a chance for lower elevation snow west of the Cascades.

The latest visible image shows high and mid level clouds already
moving into the area ahead of the first disturbance. The difference
with this one compared to Wednesday night/Thursday morning is there
is not as much over water trajectory. Therefore precipitation
amounts should be kept in check somewhat. Despite this, it will
still be a tricky forecast in that we could see snow levels get
close to the valley floor late tonight into Saturday morning, come
up briefly to 1500 to 2000 feet Saturday afternoon, then lower again
Saturday evening. Right now we think the heaviest precipitation will
be Saturday morning, possibly into early Saturday afternoon, then
decreasing Saturday evening. Meanwhile there is increasing concern
for snow to accumulate along highway 97 north of Chiloquin. Given
the above mentioned reasoning, made some adjustments to the current
snow advisory to include portions of highway 199 just south of Selma
and highway 97 north of Chiloquin. Please see WSWMFR for more
details.

Winds will be another concern Saturday with 700 mb winds between 45-
55 kts and a wind advisory remains in affect. Please see NPWMFR for
more details.

We`ll catch a brief break in the action Saturday evening, then our
next focus of concern will be around late Sunday morning through
Sunday night. Another upper trough will dive southward and this one
is expected to have more over water trajectory which could spell
trouble for the Cascades and Siskiyous. These areas could get
hammered with heavy snow from Sunday morning through Sunday evening
with 1-2 feet possible along the Cascades and up to a foot possible
over the Siskiyous, including mount Ashland. The heaviest
precipitation is expected to be from Sunday morning into Sunday
evening, then gradually decreasing Sunday night as the front pushes
south. There is also concern for lower elevation snow west of the
Cascades, especially Sunday morning, then again Sunday evening as
colder air moves overhead. Right now, we think snow levels will
start out between 2000 and 3000 feet, then falling Sunday night to
somewhere between 1000 and 2000 feet. Its likely another winter
weather advisory will be issued after the current one for tonight
into Saturday expires.

This much is certain, winter travel conditions are likely with
hazardous road conditions over the higher mountain passes and
possibly over the passes along I-5, especially Sunday evening.
Therefore have issued a winter storm watch to address this concern.
please see WSWMFR for more details.

.Long term discussion...Tuesday through Friday...Models show good
agreement with an active pattern over the Pacific Northwest next
week. The upper ridge is forecast to shift further west and an upper
trough will be located over the region with an active jet stream
aloft. This will open the door for several weather systems to move
down from the northwest and impact the area Tuesday through Friday.
One of these fronts, which is forecast to move into the area
Wednesday night into Thursday, may be strong and bring a potential
for moderate heavy rain or snow and strong gusty winds.

The disturbance which moves into the area on Tuesday, may be
relatively weak with only light to moderate precipitation. The
position of the ridge and track of this disturbance will be factors
in how strong and moist this front is as it moves inland. Overall,
models support generally light to locally moderate precipitation as
this system moves into the area Tuesday into Wednesday.

A surface low is then forecast to approach the region and bring a
strong front inland Wednesday night and Thursday. Models indicate
that this system will have abundant moisture with it and there is a
potential for moderate to heavy precipitation to develop over the
area, especially from the Cascades west. Some of this may fall as
heavy snow on area passes with snow levels forecast around 2500 to
3000 feet. Also with the surface low deepening as it nears the
Pacific Northwest coast on Thursday, strong gusty winds may develop
over portions of the area. Of note, there is variability in model
forecasts on the track and strength of the low; so confidence is low
on the impacts with this storm. Will need to monitor this system
with additional model runs.

The active pattern may then continue Friday as an upper trough
remains in place over the region and another disturbance moves down
into the area from the northwest. -CMC

&&

.AVIATION...23/18Z TAF CYCLE...Except for some scattered low cu
latched onto the ridges the area is clear this morning. A weak front
tonight will bring increasing cloud cover with possible MVFR cigs
and showers, with snow levels below 1000 feet MSL. -MSC/Sven


&&

.MARINE...Updated 245 PM PST Friday 23 Feb 2018...Seas will remain
steep to very steep through Saturday. Winds will shift to southerly
later this afternoon, then a weak front will move onshore this
evening, bringing increased west winds and a steep northwest swell.
A stronger front will move onshore early Sunday, and it will bring
steep, heavy northwest swell with it. Even heavier swell will move
in Monday. Yet another weak front will approach the area Tuesday
with another round of high and very long period swell possible
Wednesday. -Sven


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 10 PM this evening to 4 PM PST
     Saturday for ORZ029-030.
     Wind Advisory from 10 AM to 10 PM PST Saturday for ORZ029>031.
     Winter Storm Watch from Sunday morning through late Sunday night
     for ORZ029-030.
     Winter Weather Advisory from 10 PM this evening to 4 PM PST
     Saturday for ORZ021-023>026.
     Winter Storm Warning from 10 PM this evening to 4 PM PST
     Saturday for ORZ025.
     Winter Storm Watch from Sunday morning through late Sunday night
     for ORZ025-027-028.
     Winter Weather Advisory from 10 PM this evening to 4 PM PST
     Saturday for ORZ027-028.

CA...Wind Advisory from 10 AM to 10 PM PST Saturday for CAZ084-085.

Pacific Coastal Waters...Small Craft Advisory from 4 AM to 4 PM PST Saturday for
     PZZ350-356-370-376.
     Hazardous Seas Warning from 4 PM Saturday to 1 AM PST Sunday for
     PZZ350-356-370-376.

$$



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