Area Forecast Discussion
Issued by NWS Medford, OR

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
FXUS66 KMFR 222152

Area Forecast Discussion
National Weather Service Medford OR
252 PM PDT Thu Mar 22 2018

.DISCUSSION...The cold front is now east of the Cascades and cold
air aloft is beginning to move over the forecast area. This is
evidenced by the popcorn configuration of clouds over the eastern
Pacific. We should catch a relative break in the action the rest of
the afternoon into early this evening.

The main concern will be later tonight into at least Friday morning.
Another cold front will move into our area tonight. This front will
be energized by a strong upper jet and deep moisture and orographic
enhancement will likely result in moderate to heavy precipitation
initially along the coast, then spreading into the inland westside
locations and Siskiyou County during the day Friday. Cold air aloft
will already be in place and snow levels are expected to lower to
around 1500 feet tonight, but could briefly lower in areas that get
moderate to heavy precipitation. Road snow is certain for the coastal
Mountains in Southwest Oregon. Road snow could also impact portions
of Highway 199 including Hays Hill Summit, Sexton Summit and highway
42 at Camas Mountain. Snow levels are expected to come up briefly
Friday. This in combination with a stronger March sun should allow
road temperatures to warm up enough to limit or result in wet roads
between 1500 and 2000 feet.

The front and core of heavier precipitation will gradually shift
inland during the day Friday and road snow concerns will shift to
include the the higher passes along the Cascades and Siskiyous. The
coastal mountains in southwest Oregon will continue to get hammered.
The Siskiyous further east and the Cascades are likely to see
significant snow as well, but there is more uncertainty regarding
amounts. Some guidance hits them with a lot of precipitation as
well, but often on the events from the southwest, moisture gets
wrung out by the coastal ranges which limits amounts. One area of
particular concern is Mt. Ashland. This is a good setup not only for
heavy snow at Mt. Ashland, but also for strong winds. With a 130 KT
jet aloft, and model soundings showing winds of 40 knots descending
to very near the top of the mountain by Friday afternoon, we could
see blizzard conditions at times at the ski area.

Confidence is increasing for significant snow around the Mount
Shasta Area. A strong westerly jet remains, but it still looks like
we`ll get decent upslope flow in the lower levels and the models
continue to show a lot of precipitation and good thermodynamics.
This is also a favorable set up for northern Klamath with strong
south, upslope flow and an airmass that will certainly be cold
enough. The only question there is how much moisture is able to get
over the Cascades. The models show the heaviest precipitation in
these areas Late Friday afternoon and night, so the opportunity is
there for snow covered roads and hazardous driving conditions for
portions of Highway 97 north from Chemult to Crescent, Interstate 5
just south of Weed to Dunsmuir and Highway 89.

Given the above mentioned. Winter storm warning and advisories will
be in effect. For details please see WSWMFR for more details.

The main message is driving will be difficult if not hazardous later
tonight through Friday night. Conditions may improve some during the
day, but it`s not a guarantee. Therefore the best advice is to stay
tuned for the latest forecast updates. For the latest road
conditions call 511 in Oregon. In California call 511 or 1-800-427-
7623. You can also check with tripcheck for the latest road
conditions. -Petrucelli

.LONG TERM...Sunday through Thursday...The upper trough
will gradually shift east Sunday into Sunday night but models
continue to show a chance for showers with a weak disturbance moving
into the region and moist northwest flow. Also expect continued cool
temperatures across the area on Sunday. Model solutions support a
transition to a drier pattern early next week with an upper level
ridge building offshore and nudging into the region. For Monday and
Tuesday the ECMWF does indicate disturbances moving over the ridge
and into northern and central Oregon though. So depending on how
strong the ridge is on Monday and Tuesday, may continue to see a
chance for precipitation, mainly from the Cascades west in southern
Oregon.  Temperatures will be cool Sunday into Monday and expect
a potential for low temperatures in the lower 30s in valleys west of
the Southern Oregon Cascades. Then Tuesday into Wednesday, expect
a warming trend with models showing temperatures rising to seasonal
norms by Tuesday then above normal on Wednesday. The dry and warm
conditions then are expected to continue into Thursday with models
showing the upper level ridge building further inland and the storm
track shifting north. -CC


.AVIATION...22/18Z TAF CYCLE...VFR conditions are expected through
this evening. However, higher terrain could remain partly obscured
until at least 2z. Gusty winds are expected east of the Cascades,
including Klamath Falls.  Also moderate turbulence is expected in
the area into this evening. Isolated thunderstorms are possible
along the coast and over the coastal water this afternoon and
evening and this has been added to the TAF at North Bend.

MVFR Cigs will likely develop around 8z along the coast, then late
tonight in the Umpqua Basin into Friday morning as the next wave of
precipitation moves in. VFR Cigs are expected through the TAF period
at Medford and Klamath Falls. -Petrucelli


.MARINE...Updated 200 PM PDT Thursday 22 Mar 2018....South winds
will increase ahead of a another cold front late this afternoon and
continue into tonight. The combination of wind generated waves and
mixed swell will result in chaotic seas.

Active weather will continue into Friday, with widespread showers
and isolated thunderstorms. Thunderstorms will be capable of
producing locally gusty winds and small hail. Waterspouts are also a

A surface low moving southeast near the outer waters Saturday. The
placement and strength of the low varies between the models, so it
remains to be seen how strong the winds will be. There`s growing
confidence they will reach small craft conditions Saturday morning,
so we`ll extend the end time of the small craft for seas until late
Saturday morning.

Confidence is moderate to higher of another heavy west swell in the
11 to 12 foot range moving into the waters Saturday evening and
night. Right now the models vary with the swell height, but it looks
like the highest swell may be confined to the southern waters.

There`s good agreement conditions will improve Sunday and lasting
into at least next Tuesday. An upper ridge will build over the
waters and a thermal trough will set up along the Oregon/California
border and north winds will be increasing Tuesday afternoon,
possibly reaching small craft by Tuesday night. -Petrucelli


OR...Wind Advisory until 5 PM PDT this afternoon for ORZ030-031.
     Winter Storm Watch from Friday morning through Friday evening
     for ORZ030.
     Winter Storm Warning from 11 PM this evening to 11 PM PDT Friday
     for ORZ024.
     Winter Storm Watch from late tonight through Friday evening
     above 2500 feet in the for ORZ025.
     Winter Storm Watch from late tonight through Friday evening for
     Winter Storm Watch from late tonight through Friday evening for

CA...Wind Advisory until 5 PM PDT this afternoon for CAZ085.
     Winter Storm Warning from 11 PM this evening to 11 PM PDT Friday
     for CAZ080.
     Winter Storm Watch from late tonight through Friday evening for
     Wind Advisory from 8 AM to 11 PM PDT Friday for CAZ081.

Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT Friday for
     Hazardous Seas Warning until 11 AM PDT Friday for
     Small Craft Advisory for hazardous seas until 5 PM PDT this
     afternoon for PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas from 11 AM Friday to 5
     AM PDT Saturday for PZZ350-356-370-376.

$$ is the U.S. government's official web portal to all federal, state and local government web resources and services.