Small Craft Advisory 23, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
927 AM PST Sat Feb 24 2018

.DISCUSSION...
No updates are needed this morning. The current forecast looks
well on track so far this morning and through tomorrow, so we'll
leave the refinements to the longer range portions of the
forecast for the afternoon package.

A pre-frontal band of rain and snow has brought and continues to
bring about one hour period of rain and snow across the area, with
snow levels in the 1,000 to 2,000 foot range. Valley accumulations
have been around a half of an inch or less below 2kft.
Interestingly, we had snow here at the Medford Airport while it
rained in much of the Applegate Valley. East of the Cascades a
spotter reported 7 inches of new snow in Crescent this morning.
SNOTELS and ODOT reports in that area are mostly in the 2-5 inch
range, so the advisory looks to be generally most representative
for that areas of now. There also appears to be some blowing snow
along Highway 97 from Klamath Falls to Chemult, so use extra
caution in that area. Behind the initial band of precipitation
temperatures have risen a few degrees in the west side valleys and
precipitation is focusing more along and near the Cascades.

Through this afternoon and evening, we do expect more
precipitation, mainly in the form of showers, though more
consistent precipitation is likely in the Oregon Cascades. Due to
colder air moving in aloft behind the cold front, we expect snow
levels will work their way back down, especially in more
appreciable showers. However, accumulations will be minimal
outside of warning and advisory areas due to above freezing
surface temperatures and warmer road and ground temperatures in
the west side valleys due to the February sun.

Today we'll be focusing on the Sunday through Monday storm system
and also fill in more about what is very likely to be another
wintry week. BTL

&&

.AVIATION...24/12Z TAF CYCLE...A frontal system will continue
to bring rain to the coast and a mix of rain and snow to much of the
west side valleys this morning. Snow is more likely at KMFR this
morning than other west side terminals as it is already cold and
precipitation arrives during the coldest time of the morning but it
will still likely be mixed or change to a mix.

Conditions are expected to be mostly MVFR in rain, but where it
changes to snow, IFR conditions are likely. This precipitation
spreads to the east side this morning with MVFR to IFR conditions in
snow. The precipitation will become more showery in the afternoon
and turn to all rain showers in the westside valleys.
Sandler

&&

.MARINE...Updated 415 AM PST Saturday 24 Feb 2018...West winds will
peak this afternoon, then diminish tonight. At the same time, a west
swell will build and reach 10 to 12 feet today, pushing combined
seas to small craft advisory levels. A stronger front is expected to
bring both stronger west winds and larger seas to the area on
Sunday. While winds diminish Monday, another even larger swell will
keep very steep seas going through Monday. Seas remain steep Monday
afternoon, but lengthening periods will allow overall sea conditions
to improve. Sandler

&&

.PREV DISCUSSION... /Issued 354 AM PST Sat Feb 24 2018/

DISCUSSION...A frontal system is ushering low valley rain and higher
elevation snow (generally above 1000 feet per latest web cams).
Steadier precipitation will move through early this morning,
reaching Medford later this morning. Snow is expected to continue
to affect areas about 1000 feet and lower this morning, with
generally light accumulations south of Sexton Pass and west of the
Cascades, and higher accumulations (1-3 inches) from Sexton Pass
northward...and of course over the Cascades. Precipitation will
turn showery this afternoon, and impacts should generally
decrease, partially because of less precipitation but also because
of increasing road temperatures and more melting of snow on
roadways. A Winter Weather Advisory continues for portions of the
forecast area along and West of the Cascades, above valley
floors, with a small Warning area in Eastern Douglas County.

10000 foot winds, a good proxy for wind impacts to our forecast
area, are westerly at 50kt and this is statistically on the tails
for wind speeds this time of year. The west winds that are forecast
are in the top 1 to 3% for speeds this time of year. We therefore
continue a Wind Advisory for some areas east of the Cascades.

Attention turns to yet another cold system Sunday into Monday
morning. We maintain a Winter Storm Watch for the Cascades and
areas just east and west (from Highway 97 to the east and portions
of Highway 138 to the west). Snowfall rates and accumulations
will generally be at least 25 percent higher for Sunday's system
compared to this morning's. Snow levels look like they will be
right around the critical 2000 feet (important for impacts to
lower mountain passes between Grants Pass and Roseburg on I-5)
late Sunday afternoon and early Sunday evening as the front passes
through. We have lowered snow levels by several hundred feet for
Sunday evening on this forecast shift, and the dayshift can
evaluate further to see when that changeover from rain to snow is
expected on those passes. Higher passes are guaranteed to see some
heavy snow, especially in the Cascades due to strong upsloping
westerly flow. Siskiyou Summit on I-5 could see a period of
moderate to heavy snow as well, given the antecedent cold air and
the arrival of snow near to after sunset. A handful of SREF
members are showing 1 inch per hour snowfall rates between 4pm and
10pm Sunday at Siskiyou Summit.

Conditions quiet down Monday afternoon through Tuesday, then the
flow shifts from the deep northerly winds we've seen for a week+
now, to westerly then southwesterly Wednesday into Thursday,
signaling deeper moisture and more precipitation. The next frontal
system arrives late Wednesday and looks like a big snow-producer for
elevations generally above 3000 feet...with moderate to heavy rain
below those elevations. After a season of pretty large model
discrepancies on day 5+, it's noteworthy that both the EC and GFS
have good agreement on the overall pattern from Thursday through
Friday.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 4 PM PST this afternoon for
     ORZ029-030.
     Wind Advisory until 10 PM PST this evening for ORZ029>031.
     Winter Storm Watch from Sunday morning through late Sunday night
     for ORZ029-030.
     Winter Weather Advisory until 4 PM PST this afternoon for
     ORZ021-023>026.
     Winter Storm Warning until 4 PM PST this afternoon for ORZ025.
     Winter Storm Watch from Sunday morning through late Sunday night
     for ORZ025-027-028.
     Winter Weather Advisory until 4 PM PST this afternoon for
     ORZ027-028.

CA...Wind Advisory until 10 PM PST this evening for CAZ084-085.

Pacific Coastal Waters...
- Small Craft Advisory until 4 PM PST this afternoon for
  PZZ350-356-370-376.
- Hazardous Seas Warning from 4 PM this afternoon to 10 AM PST
  Monday for PZZ350-356-370-376.

BTL/NSK/RES