Small Craft Advisory 37, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
922 AM PDT Tue Apr 10 2018

.DISCUSSION...A cold front is weakening as it presses east of the
Cascades this morning. A period of light rain will accompany the
front as it moves through most east side areas the rest of the
morning into early this afternoon, with just some light showers
lingering behind it. Gusty southwest winds will continue up until
frontal passage over the east side through early afternoon, then
should ease a bit as winds aloft decrease. We still have a wind
advisory up at NPWMFR until 8 pm, but this may be cancelled before
then. The air mass behind this front isn't all that cold, but
snow levels ~7000 feet near the Cascades this morning should
lower to about 5500 feet by this evening. It should dry out for
most areas tonight into early Wednesday morning.

The next cold front will approach the coast and move onshore
Wednesday morning. While this front will likely be a more
efficient precipitation producer due to a strong temperature
gradient along it, better forcing for lift, and a distinct wind
shift, model guidance has backed off in terms of wind strength.
Peak 700 mb winds over northern CA and the east side Wednesday
afternoon are only ~45 kt. And, 850 winds along the coast only
peak around 50-55kt. As a result, even though we expect winds to
be gusty at times Wednesday, most areas should remain sub-advisory
level. In terms of precipitation, expect rain to arrive at the
coast 6-9 am Wednesday, then push inland during the day. Snow
levels initially will be 4000-4500 feet, but will lower to
2000-2500 feet Wednesday night post-front. Since steadier
precipitation will be moving in during the day over the mountains,
snow impacts won't be as significant as if the precipitation were
moving in during the night. Even so, expect some snow, probably
3-6 inches over the mountains above 5000 feet. Since snow levels
will be lowering Wednesday night, there may also be an inch or so
of snow over the lower elevations of the east side (Klamath
Falls/Lakeview/Alturas). While this in and of itself, isn't that
big of a deal, temperatures will be falling below freezing and any
wet/slushy roads may become icy by Thursday morning. We'll be
evaluating these potential impacts today to see if any advisories
are necessary. -Spilde

&&

.AVIATION...10/12Z TAF CYCLE...Gusty winds along the coast mainly
north of Cape Blanco are expected to be strongest early this
morning, then will gradually decrease this afternoon. Winds will
increase again tonight ahead of another front. VFR conditions are
expected to lower to MVFR for a few hours this morning (mainly
between 15 and 18z) followed by VFR this afternoon into this
evening. Cigs will lower tonight. For now, kept VFR cigs at the
North Bend TAF for tonight, but it could get close to MVFR towards
the end of the TAF period.

Inland...VFR conditions are expected through the TAF period. The
exception will be at Roseburg where they could hover near MVFR for a
couple of hours between 17-19z. Also terrain obscurations are
possible west of the Cascades westward this morning in showers.
Gusty winds will be a concern east of the Cascades, including
Klamath Falls into this evening. -Petrucelli

&&

.MARINE...Updated 200 AM PDT Tuesday, 10 April 2018...The IR image
shows the cold front just west of the outer waters. There's good
agreement the front will move into the waters early this morning,
then move onshore by mid morning at the latest. Therefore have
adjusted the end time of the gale warning and small craft for winds
to 8 am PDT.

Seas will remain hazardous after the winds subside this morning.
Another front will approach the waters early Wednesday morning and
move onshore Wednesday afternoon. Models are in good agreement the
gales could cover a larger portion of the waters, especially over
the northern outer waters, so expanded the gale watch to cover all
of marine zone 370.

Heavy west swell will develop behind the front, likely peaking
Thursday night around 17 feet at 15 seconds. The Wave Watch
Bulletin, ENP and ECMWF are in pretty good agreement with the timing
of then waves will peak out and the total wave height which lends to
higher confidence of a longer period heavy west swell. -Petrucelli

&&

.PREV DISCUSSION... /Issued 514 AM PDT Tue Apr 10 2018/

Updated Aviation Discussion.

SHORT TERM...A frontal system is approaching the coast this
morning. We are seeing a lot of radar returns spread inland ahead
of the front, but, judging by obs and webcams, little if any of
this represents rain actually reaching the ground. The main band
of precipitation with the front is developing off the coast from
Cape Blanco southward, and thus rain should arrive at the south
coast shortly. The coast and coastal mountains is where the bulk
of today's rain will fall as guidance shows this front weakening
as it moves inland today. The rest of the west side will likely
see sprinkles or light rain at times with some areas seeing enough
rain to wet the ground. Rain will be much spottier on the east
side today. Snow levels are high (above 9000 feet), and the
airmass behind this front isn't all that cold, so snow isn't
expected to be an issue anywhere except the highest peaks today or
tonight.

Winds, on the other hand, will be strong in a few places, namely:
eastern Klamath and Lake counties. Wind advisories are in effect
there, and it wouldn't be surprising to see a few gusts approach
60 mph as the front crosses that area later this morning. We don't
expect to reach advisory criteria in the Shasta Valley, but it
will be breezy. We'll have to keep an eye on the winds there.

Some showers may linger in the mountains tonight, but tonight will
be dry for most of us. It will be short-lived, however, as the
next front (currently plowing through 150W) will move in
Wednesday. This system is much stronger, more dynamic, brings
much colder air, and is making more of a direct hit on our area
than today's front. As a result, we expect more wind and rain to
be more widespread and heavier. Cool, moist, onshore flow behind
the front will likely keep precipitation going along the coast and
in the mountains Wednesday night and Thursday, which may lead to
snow impacts in some of the mountains as well. The main question
with the snow is timing. Snow at night in the mountains will
probably cause issues. Due to strong April sun, however, daytime
snow will likely melt on contact with roads. -Wright

LONG TERM...Friday through Tuesday... Ridging over the
northeastern Pacific will build Thursday night into Friday,
generally bringing calm, warm conditions Friday and Saturday. A
weak warm front will brush through the region Friday, bringing
possible light precipitation. Highest chances will be along the
coast and north of the Umpqua Divide. Regardless of precipitation,
cloud cover from this front will keep temperatures around 5
degrees below normal. Saturday will likely be the warmest day of
the week (after today). Models are coming into agreement that the
ridge won't stick around long... a low will develop in the Gulf of
Alaska and drift towards the PacNW Sunday. This will bring strong
winds to the east side Sunday morning, and potential
precipitation over much of the forecast area Sunday, with highest
amounts likely over the southern Coastal mountains. Temperatures
aloft will drop substantially as the low moves overhead Sunday
into Monday, bringing potential light snow down to 3000 feet. -M&M

AVIATION...10/12Z TAF CYCLE...Gusty winds along the coast mainly
north of Cape Blanco are expected to be strongest early this
morning, then will gradually decrease this afternoon. Winds will
increase again tonight ahead of another front. VFR conditions are
expected to lower to MVFR for a few hours this morning (mainly
between 15 and 18z) followed by VFR this afternoon into this
evening. Cigs will lower tonight. For now, kept VFR cigs at the
North Bend TAF for tonight, but it could get close to MVFR towards
the end of the TAF period.

Inland...VFR conditions are expected through the TAF period. The
exception will be at Roseburg where they could hover near MVFR for a
couple of hours between 17-19z. Also terrain obscurations are
possible west of the Cascades westward this morning in showers.
Gusty winds will be a concern east of the Cascades, including
Klamath Falls into this evening. -Petrucelli

MARINE...Updated 200 AM PDT Tuesday, 10 April 2018...The IR image
shows the cold front just west of the outer waters. There's good
agreement the front will move into the waters early this morning,
then move onshore by mid morning at the latest. Therefore have
adjusted the end time of the gale warning and small craft for
winds to 8 am PDT.

Seas will remain hazardous after the winds subside this morning.
Another front will approach the waters early Wednesday morning and
move onshore Wednesday afternoon. Models are in good agreement the
gales could cover a larger portion of the waters, especially over
the northern outer waters, so expanded the gale watch to cover
all of marine zone 370.

Heavy west swell will develop behind the front, likely peaking
Thursday night around 17 feet at 15 seconds. The Wave Watch
Bulletin, ENP and ECMWF are in pretty good agreement with the
timing of then waves will peak out and the total wave height
which lends to higher confidence of a longer period heavy west
swell. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 8 PM PDT this evening for ORZ030-031.

CA...Wind Advisory until 8 PM PDT this evening for CAZ085.

Pacific Coastal Waters...Gale Watch from late tonight through
     Wednesday morning for PZZ350-356-370-376.
     Small Craft Advisory for hazardous seas until 11 AM PDT
     Wednesday for PZZ350-356-370-376.
     Hazardous Seas Warning until 2 AM PDT Wednesday for
     PZZ350-370-376.

MAS/TRW/MAP