Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 240553

Area Forecast Discussion
National Weather Service Medford OR
1053 PM PDT Sun Apr 23 2017

Updated AVIATION Section

.DISCUSSION...A strong Pacific jet stream is directed right at
the PacNW tonight. The first wave associated with the strong jet
is arriving now and will push onshore Monday. This will bring
periods of precipitation, some heavy, along the coast, the
adjacent coast ranges, western Siskiyou County and into the
Cascades. Precipitation amounts of 2-3 inches will be common along
the Curry coast and coast ranges with 1-2 inches in the Cascades.
Lesser but still significant amounts can be expected elsewhere
inland. Snow levels will be mostly above 5000 feet for this event,
and with the low to mid-level flow directed right into the
mountains, we expect a pretty good snowstorm around Crater Lake.
Check out WSWMFR for the details regarding the winter storm
warning for the Cascades and the advisory in the Siskiyous near Mt
Ashland. There will also be a few inches of snow over the pass on
Highway 140 near Lake of the Woods. Right now, it appears the
snow level will remain high enough to preclude snow accumulation
on Interstate 5 at Siskiyou Summit, but it`s also not out of the
question rain mixes with or changes to snow briefly there Monday
morning. Even if it does, the roadway should just remain wet. By
Monday afternoon, precipitation will become more showery as the
associated frontal system pushes east of the Cascades, but showers
will remain widespread along and west of the Cascades as westerly
upslope flow continues. A brief break is expected Monday night,
but the next fast-moving Pacific system will arrive at the coast
Tuesday. -Spilde


.AVIATION...24/06Z TAF CYCLE...Over the coastal waters...along the
coast...and in the Umpqua Basin...Areas of MVFR cigs/vsbys and local
IFR cigs in rain and rain showers with higher terrain obscured will
persist through Monday evening. Low level wind shear will affect
KOTH and KRBG late tonight into early Monday morning with turbulence
possible on approaches and takeoffs elsewhere. Over the remainder of
the area...VFR with local MVFR cigs and areas of higher terrain
obscured in rain/snow will persist through Monday evening.
Freezing levels will be 4500-5000 feet. Gusty winds to 35 kt are
possible at KLMT for a few hours Monday afternoon. -Spilde


.MARINE...Updated 200 PM PDT Sunday 23 April 2017...A strong front
will move onshore late tonight into Monday morning with strong south
winds and steep to very steep seas. A brief period of gales is
possible north of Cape Blanco early Monday morning. Winds and seas
will peak early Monday morning. Another front will move through
Tuesday into Wednesday. High pressure will build Thursday into the
weekend...bringing north winds to the area.


.PREV DISCUSSION... /Issued 214 PM PDT Sun Apr 23 2017/

DISCUSSION...The weather into this evening should remain fairly
quiet with little in the way of showers. Could not rule out a few
showers mainly north of the Umpqua Divide, the coast and northern

A strong jet along with a deep moisture plume over the eastern
Pacific will push into our area tonight. Meanwhile, low pressure
will form along the jet tonight and move into northwest Oregon on
Monday. Very heavy precipitation is a given and would affect much of
the area. Especially along the coast and Cascades, specifically the
west facing slopes due to favorable orographic flow. Rainfall from
the first system (tonight through Monday) could amount to 2-3 inches
or more along the Curry coast and adjacent mountains with lesser but
still significant amounts inland.

All of this precipitation will fall as snow in the higher mountains
around 5500 feet, but could briefly fall to near 4500 feet at times
in heavier precipitation. Snow will also be especially heavy along
the west slopes of the Cascades which typically favors Crater Lake
for heavy snow. Confidence is high enough at least the Crater Lake
area will get heavy snow from this and a winter storm watch has been
upgraded to a warning. In addition, moderate to heavy snow could
also impact the Mount Ashland Ski area and possibly near Diamond
Lake area, therefore decided to issue a winter weather advisory for
these areas. Please see WSWMFR for more details.

This system will be very dynamic, but the orientation of surface
gradients and the fact that winds aloft are almost all westerly
really only favors the east side for strong winds. Even then the
window of opportunity may only be for a few hours at most Monday
afternoon. Confidence at this time is not high enough to issue a
wind advisory, but later shifts may want to take another look at

There will be a brief break in the action Monday night, but the next
low pressure system arrives Tuesday morning at the coast, then
moving onshore during the day. This system is not expected to bring
significant precipitation as the jet lifts slightly to our north,
but we can still expect significant rainfall along the coast, snow
in the mountains, and breezy winds in the wind- prone areas on

We`ll catch another brief break Tuesday night, then another system
will bring yet another round of moderate to heavy precipitation
mainly along and west of the Cascades with the highest QPF amounts
along the coast, coastal mountains and Cascades on Wednesday.
Showers will continue Wednesday night with a continued moist onshore
flow. -Petrucelli

Extended discussion, Thursday through Sunday. The extended
portion forecast begins with a system over the region on the nose
of a very strong +150 kt jet. However, this system is showing only
light to moderate precipitation as the flow from the surface
pretty much all the way up is from the northwest. On Friday a
system slides down the back side of an upper level ridge that is
slowly building into the region. Again with the flow becoming even
more northerly this will bring generally light precipitation over
most of the region. By Saturday morning the upper level ridge has
built over the Pacific Northwest with a thermal trough already
deep along the coast and offshore flow across into the east side.
The offshore flow and the thermal trough the night Saturday, and
on Sunday the thermal trough moves inland with Sunday seeing the
warmest temperatures of the stretch. Sven


OR...Winter Weather Advisory until 11 PM PDT Monday for ORZ027-028.
     Winter Storm Warning until 11 PM PDT Monday for ORZ027.


Pacific Coastal Waters...Small Craft Advisory until 5 AM PDT Tuesday for
     Small Craft Advisory for hazardous seas until 11 PM PDT this
     evening for PZZ350-356-370-376.
     Hazardous Seas Warning until 11 AM PDT Monday for PZZ350-370.


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