Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 182203
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
203 PM PST Thu Jan 18 2018

.DISCUSSION...A short wave will rotate around the base of the
trough into our forecast area this evening. This trough is quite
unstable with plenty of cold air aloft and satellite imagery shows
plenty of cold air cumulus. A few lightning strikes at the coast
is possible. As the trough moves inland, it will also generate
widespread showers across our area. Snow levels will range from
around 3500 feet over the Umpqua Divide to around 4500 feet over
the Cascades and east side. Snow levels lowers to 2700-3500 foot
range tonight and could lower to 2500 feet by Friday morning. Time
height forecast of the Cascades show plenty of vertical lift and
confidence is high on accumulating snow at Crater Lake as well as
at Mount Ashland. Scattered showers will continue into Friday
after this main short wave has moved through. There will also be a
moderate onshore flow and Curry County and the coastal range could
see another 1 to 1.5 inches of rain from Friday through Friday
night.

Saturday is expected to be a relatively quiet day as the next
storm moves into the coastal waters. Models show occasional light
shower from the Umpqua Basin north and south to southeast winds
will enhance downslope flow into southern Jackson County.

Extended Discussion Sunday through Thursday...Confidence remains
high we`ll remain fairly active during the forecast period. Any
relative break in the action may be far and few in between. Right
now it looks we`ll get a relative break on Monday. Even then it
won`t be a 100% dry.

There remains good agreement with the timing of the front on Sunday.
There are still some differences with the timing of the front, but
overall the models are in much better agreement compared to
yesterday. The ECMWF is still a bit slower with the arrival of the
front compared to the other operational models.

Winds are still going to be the main impact on Sunday, especially in
the Shasta Valley and eastside. These areas will at least reach
advisory levels with high wind warning criteria possible in the
south end of the Shasta Valley near Weed and higher elevations like
Summer Lake east of the Cascades. There is good agreement winds will
be aligned just right for gusty winds to develop in the Rogue
Valley. In fact the south end of the Rogue Valley from around
Phoenix to Ashland could reach advisory criteria. Winds in the
Shasta and Rogue valleys are expected to be strongest from late
Sunday morning into Sunday evening, but this could change depending
on the timing of the front, so watch for updates. Meanwhile winds
will be strongest east of the Cascades from Sunday afternoon through
Sunday evening.

Gusty winds are also expected along the coast and headlands Sunday
morning. The models have trended a but stronger with the magnitude
and pressure gradient between Arcata and North Bend. So we could be
looking at high wind potential there.

The highest precip amounts on Sunday are going to be in the usual
areas. The coast and coastal mountains and the Cascades. The front
won`t move onshore Sunday evening, therefore snow levels during the
day will end up higher. They should start out around 3500 feet
Sunday morning then rise to around 4500 feet Sunday afternoon. This
is when the bulk of the precipitation will come in. For now road
snow concerns will be confined to the highway 140 near Lake of the
Woods, Diamond Lake, Crater Lake and Mount Ashland Ski area. Siksyou
Summit and Mount Shasta region could pick up couple of inches at
best Sunday morning with little or nothing Sunday afternoon as snow
levels come up. Keep in mind the details on this could change.

The front will move through the area Sunday night. Winds will
decrease over most locations. Snow levels will come down, but by
then precipitation will also be on the decrease which should limit
the amount of accumulating snow. However, we`ll still have to deal
with accumulating snow Sunday evening around Diamond Lake, Crater
Lake, Lake of the Woods and Highway 89 east of Mount Shasta. Siksyou
Summit could pick up and additional inch or two Sunday evening.

Were still lined up to catch a relative break in the action Monday.
Moist northwest flow on Monday will result in showers mainly
confined to the coast.

The jury is out for Monday night through Tuesday. The models show
moisture spreading into southeast Oregon and northwest California
late Monday night. However there is a new development, in particular
with the ECMWF. The ECMWF shows a surface low rapidly developing
overnight Monday, moving inside of 130W sometime Tuesday morning,
then moving onshore near Newport Oregon Tuesday evening. If this
pans out, we could be looking at strong winds along the coast,
headlands, Shasta Valley and maybe eastside. The GFS has a weaker
surface low and also has it positioned farther north which would not
have nearly the same impact. Of note: the Canadian solution is
almost similar to yesterday`s ECMWF and GFS solution which showed
weak ridging.

Wednesday through Thursday looks cooler and unsettled with snow
levels possibly getting down between 2000 and 2500 feet. No big
storms, but a cool trough will be near by with moist northwest flow.
-Petrucelli

&&

.AVIATION...18/18Z TAF CYCLE...Mostly VFR conditions will prevail
into this evening, though there will be some MVFR cigs with
higher terrain.  MVFR cigs/vsbys will become more widespread
tonight, especially over higher terrain where the rain showers will
turn to show showers. Freezing levels near 5500 feet MSL today will
lower to 2500-3000 feet MSL tonight.

&&

.MARINE...Updated 200 PM PST Thursday 18 Jan 2018...Very heavy
westerly swell will gradually subside through Friday night, but will
remain very high and very steep. Moderate southwest winds are
expected, but higher gusts will occur in and around showers and
isolated thunderstorms. Swell dominated seas will diminish Saturday
into Saturday night. However, another strong front will move through
late Saturday night into Sunday, bringing south gale force winds and
high seas. High pressure will build briefly Monday, but another
front will move onshore Tuesday.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Surf Advisory from 11 PM this evening to 4 AM PST Saturday
        for ORZ021-022.
     High Surf Warning until 11 PM PST this evening for ORZ021-022.
     Winter Weather Advisory until 10 AM PST Friday for ORZ027-028.

CA...Winter Weather Advisory until 10 AM PST Friday for CAZ080.

Pacific Coastal Waters...Gale Watch from Saturday evening through
        Sunday afternoon for PZZ350-356-370-376.
     Hazardous Seas Warning until 4 AM PST Saturday for
        PZZ350-356-370-376.

$$

08/10/15


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