Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 240441

Area Forecast Discussion
National Weather Service Medford OR
841 PM PST Thu Feb 23 2017

.EVENING UPDATE...With the showers becoming more and more isolated
have adjusted down the min temps tonight. With dewpoints in the
upper 20s did not go with the MAV low of 20 at Medford, and the
ADJECE guidance seemed more reasonable. Not sure how much of the
moisture will be deposited as frost with the moist layer extending
up at least 5000 ft MSL and have kept the patchy fog in the
forecast. Also have updated to add a frost advisory to the coast
north of Cape Blanco with temps expected to drop below 36 tonight,
and current temperatures are already below 36 in that area. With
clouds expected to move in the middle of the night temperatures are
not expected to go below freezing except in isolated spots on the
coast. Sven

.SHORT TERM...Tonight through Saturday Night...Current Radar
observations are indicating that showers are picking up around
southern Oregon and northern California. Despite there being
silent 10 precipitation chances around the area right now, have
increased to blanket the forecast area in a slight chance of
precipitation. Snow levels remain low today and are still prone to
large fluctuations in heavy showers. This is evident because it
snowed at the office while temperatures were 41 degrees.

Things will calm down slightly tonight and clear skies at
Brookings and the Curry County coast could lead to freezing
temperatures. Cloud cover should increase tomorrow morning ahead
of the next system, and may increase temperatures quickly.
Regardless, have issued a freeze warning for the Curry County
coast including Brookings mainly as a precaution as there is a
good chance that temperatures will be low enough for long enough
to damage crops and sensitive vegetation.

On Friday, the next low pressure system will arrive from the north
and bring showers with it. Snow levels will remain low--around
1500 feet or so, but heavier showers will allow for snow to reach
the valley floors during the day. Snow levels will fall to about
200 feet above sea level and snow could fall into the umpqua
basin. Some of these snow showers may be heavier--particularly in
the coastal mountains and Highway 199 in the Illinois Valley.
Additionally, I-5 near Sexton Pass through Canyon Creek Pass could
also see impacts. Have issued Winter Storm Warnings for areas
above 2000 feet and Advisories for areas above 1500 feet. Highway
89 in south central Siskiyou County could also see impactful snow
with upslope flow in the showers, but am not confident enough in
the advisories over there. This is due to the models starting to
back off on snowfall amounts, and that if the low tracks further
away from the coast, will lead to less amounts. The ECMWF and NAM
are still show the most precipitation with this storm, and blended
these two models with heavier reliance on the ECMWF.

.LONG TERM...Sunday through Thursday...The models are in pretty good
agreement through early next week. Another upper trough is projected
to move south along the Washington/Oregon coast during the day
Sunday. Unlike the one coming in Friday night, this one is expected
to track closer to the coast and will be coming in during the day.
This should mitigate the threat for low elevation snow, but it still
exist due to a combination of existing cold air in place and
precipitation rates which if high enough could drag the snow level
down lower than what`s in the forecast. Snow levels are expected to
start out around 1200 feet Sunday morning, therefore precipitation
could start out as snow in the Illinois and Rogue valleys. Snow
levels should come up some (near 2000 feet) Sunday afternoon, but it
could end up lower in heavier precipitation. The models have not
changed much with the timing and track of the upper low. So this
leads to higher confidence that at least areas above 2000 feet will
get snow. At this point its still too early to speculate on timing
and track of the upper low and snow amounts, but it`s something that
we`ll have to watch closely.

We`ll see some improvement in the weather Monday, at least in terms
of precipitation with most of it focused in northern California and
east of the Cascades. It will remain cool to cold with scattered
showers and snow levels between 1500 and 2000 feet.

A cool northwest flow will continue Tuesday. The models still hint
at some QPF, but suspect this may be overdone given 500mb heights
will be on the rise and any shortwave activity should stay east of
our forecast area.

Wednesday and Thursday will be dry as an upper ridge builds over the
area with the storm track shifting north. Temperatures on the ridges
will be milder in the afternoons, but the valleys could stay cool
due to increasing subsidence inversions. -Petrucelli


.AVIATION...24/00z TAF CYCLE...Scattered MVFR and local IFR snow
showers exist east of the Cascades this evening, especially across
southern Lake County near Lakeview. These should gradually end with
conditions improving to VFR late this evening and overnight.
Isolated rain and snow showers will end this evening west of the

Local IFR cigs may develop in the Umpqua Basin tonight, including at
Roseburg, between 11 and 16z. Some rain will arrive at the coast
Friday morning with MVFR cigs and terrain becoming obscured. While
conditions become mostly VFR inland after 16z, expect some rain and
snow showers by Friday afternoon that could briefly lower conditions
to MVFR along and west of the Cascades with partial terrain
obscuration. -Spilde


.MARINE...Updated 200 PM PST Thursday 23 February 2017...Steep
seas from earlier today will continue to ease this afternoon and
evening settling in the 5-7 foot range. The remaining waves will be
mostly short period - around 9 seconds. This is not quite high
enough for an advisory, but it could still be a bit choppy for
smaller craft planning to venture out. Low pressure moving down the
Pacific Northwest coast on Friday will bring increasing winds and
seas, but southwest winds will likely remain below small craft
advisory levels. Another disturbance will shift southward into the
Pacific Northwest staying right near the coast on Sunday then moving
inland Sunday night into Monday. This will bring mainly northwest
winds with a mix of choppy wind waves and northwest swell, perhaps
reaching small craft advisory levels. Northwest winds will persist
into Tuesday, but subside. High pressure will build over the area at
midweek with light to moderate northerly flow expected, strongest
south of Cape Blanco. -Spilde


OR...Freeze Warning from midnight tonight to 8 AM PST Friday for
     Winter Weather Advisory from 1 PM Friday to 10 AM PST Saturday
     for ORZ023-024-026.
     Winter Storm Warning from 1 PM Friday to 10 AM PST Saturday for

CA...Winter Weather Advisory from 1 PM Friday to 10 AM PST Saturday
     for CAZ080.
     Winter Storm Warning from 1 PM Friday to 10 AM PST Saturday for

Pacific Coastal Waters...None.


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