Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 231301
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
501 AM PST Fri Feb 23 2018

.DISCUSSION...Late winter impacts continue this week as the
forecast area remains on the eastern periphery on the upper ridge,
keeping snow levels generally between 2000 and 3000 feet, and
bringing in more moisture from the Northeast Pacific Ocean.

The consensus is that the air mass won`t get as cold again through
the next week as it is this morning, with the morning balloon
sounding showing 5000 ft temperatures at -9.5C, which is one of
the coldest ever for this date since 1948 (and the very coldest
between 1948 and 2014, but we don`t have the records for the past
3 years readily available). Even though the air mass warms some
in the upcoming days, it will still be cold enough to produce some
snow impacts to lower passes on Interstate 5 between Grants Pass
and Roseburg and significant impacts on higher mountain passes,
above 2000 feet. For the first in a series of storms, Winter
Weather Advisories continue for areas generally above 2000 feet
from the Cascades westward for this evening through Saturday
afternoon. Additionally, a Winter Storm Warning continues for
eastern Douglas County. Lastly, Highway 97 north of Klamath Falls may
get a quick 2-3 inches of snow Saturday morning, so we will
consider an Advisory for this area on the dayshift.

The upcoming front will bring increasing winds to the mountains and
East Side, and we`ve issued a Wind Advisory for some areas east of
the Cascades, to include Highway 31 from Valley Falls to Silver
Lake. Some snow will accompany these winds and will result in
blowing snow and reduced visibility. GEFS anomalies suggest 700mb
winds will be in the top 1-3% of wind speeds for this time of year,
so it`s worth highlighting, especially since blowing snow could also
have an impact.

A more potent front will move in Sunday, with snow levels starting
out between 2000 and 3000 feet, then falling Sunday night to
somewhere between 1000 and 2000 feet. This will eventually bring
winter travel conditions to all mountain passes and potentially
lower on the tail end of the front Monday morning. We`ll be looking
to highlight this in the form of a Winter hazard product in the
upcoming shift. Please see the previous long-term discussion that
still

Long-term from previous discussion...Monday through next
Thursday...Operational 12Z models start to diverge Monday, but the
18Z GFS has come more in line with the 12Z operational ECMWF. The
ensemble mean for the GFS and EC were very close however, and
leaned towards whatever operational run was closest to the
ensemble mean for that period. Winter continues to make up for
being absent in our lives for December by doting upon us with cold
and low level snow through most of next week.

On Monday the tail end of a system moves through Monday morning,
and unlike today there should be enough clearing and with nearly due
north flow at 700MB, there should be enough clearing to allow
temperature to rise into the mid 40s and melt the previous snow on
sun exposed road and sidewalk surfaces. The upper low digs south
into central CA by Tuesday morning, with the upper level ridge
nudging into the region with weak offshore flow indicating clearing
before early Tuesday morning allowing temperature to drop below
freezing in the west side valleys, and well below freezing on the
east side. The ridge retrogrades and the next, wetter system moves
in Late Tuesday afternoon to evening. Although the entire forecast
for the next week looks interesting, Wednesday could be very
interesting with 850 MB temps indicating below -5 C during the warm
conveyor time. However, confidence is not high this far out and will
not stress this period until we get closer. -Sven

&&

.AVIATION...23/12Z TAF CYCLE...Precipitation has diminished and
expect mostly clear skies over the west side through this
evening...with the exception of the Umpqua Basin, which may see some
fog around sunrise. Patchy fog/ IFR cigs is possible along the
coast, but winds with a slight offshore component may prevent
conditions from dropping at KOTH. A weak front tonight will bring
increasing cloud cover with possible MVFR cigs and showers, with
snow levels below 1000 feet MSL. -MSC

&&

.MARINE...Updated 500 AM PST Friday 23 Feb 2018...North winds
will diminish this morning as high pressure builds offshore, but
seas will remain steep to very steep through Saturday. Winds will
shift to southerly 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.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 10 AM to 10 PM PST Saturday for ORZ029>031.
     Winter Weather Advisory from 10 PM this evening to 4 PM PST
     Saturday for ORZ027-028.
     Freeze Warning until 10 AM PST this morning for ORZ021-022.
     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.

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

Pacific Coastal Waters...Hazardous Seas Warning from 4 AM to 10 PM PST Saturday for
     PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas until 10 PM PST Saturday
     for PZZ350-356-376.
     Small Craft Advisory for hazardous seas until 4 AM PST Saturday
     for PZZ370.

$$

NSK/MSC



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