Small Craft Advisory 8, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
200 PM PST Thu Jan 16 2020

.DISCUSSION...16/12Z NAM/GFS/EC in.

Post-frontal shower activity is diminishing this afternoon and
snow levels have risen just a bit, enough such that it is now
raining in Medford. Snow levels will fall again tonight as the
showers diminish.

An upper trough will finally move inland tonight and a ridge will
build in from the south. This will provide a relative break in
the action, but there will still be some light shower activity
over the area. Snow levels will drop down to around 1000 feet MSL
Friday morning. The break will end Saturday, when an incoming
upper level trough will drive another front onshore.  Overall,
this front looks weaker than yesterday's front with regard to
both winds and precipitation. Snow levels will be higher with this
system at 3000 to 4000 feet. The ensuing ridge will build in
quickly, and post frontal showers will diminish Saturday night.

A stronger ridge will build in Saturday night into Sunday, pumped
up by a digging trough well offshore. This will force the storm
track to the north. Post-frontal showers will wane Saturday night
and Sunday looks to be mostly dry.

LONG TERM...Monday-Thursday, January 20th-23rd...

The active pattern that we've been in for some time will continue
next week, but with some changes. Over the last week or so, most
weather systems have been arriving in a cold, but progressive north
and northwest flow aloft. But, the flow aloft, while still
progressive, will re-orient and become more west-southwesterly next
week. Several disturbances of Pacific origin will develop along the
eastern extension of a strong west-central Pacific jet (~150kt) that
stretches from Japan to north of Hawaii (between about 30 and 40 N
latitude). As is often the case at this range, models have been
struggling with timing and strength of individual disturbances, so
confidence remains lower than usual. However, there are a few things
that are more certain. First, snow levels will likely be higher than
we've had much of the last couple of weeks. While there will be some
fluctuations up and down, snow levels will average 4000-5000 feet,
keeping most of the accumulating snow around and above the higher
passes.

Next, despite the low confidence in the details, we are expecting a
few frontal systems to move in during the period. We have the lowest
confidence in the first of these systems on Monday. Most models are
showing a weakening frontal system arriving at the coast midday
Monday or Monday afternoon. But, there are still some models
bringing sub-tropical moisture northward into California in advance
of this system. Most guidance keeps this moisture suppressed and
well to our south. A blend of the guidance was used for now,
however, until a more agreed upon solution is reached. This keeps
fairly low precipitation chances across northern California and
along the coast, with a modest increase in southerly winds in the
usual spots like the Shasta Valley and over the east side.

We have more confidence in a stronger frontal system arriving at the
coast late Monday night, then moving onshore Tuesday. This should
bring a period of precipitation for most areas along with stronger
winds.

Since the flow is so fast across the Pacific, breaks between systems
should be relatively short-lived. As such, another Pacific frontal
system will probably arrive sometime mid next week. -Spilde

&&

.AVIATION...For the 16/18Z TAF Cycle....Precipitation will gradually
diminish from west to east during the day and we should see ceilings
and visibilities improve. Until then expect MVFR conditions with
temporary IFR conditions where precipitation is heaviest and
widespread terrain obscuration for all TAF's except for North Bend.
Freezing levels will hover around 2000 to 2500 feet, dropping to
1500 feet as this event tapers off this evening. If conditions are
stable enough later this evening. Fog and low clouds are possible
for Medford, Roseburg and Klamath Falls. The lower conditions are in
the TAF's but confidence on the timing and the event occurring is
low to medium, so watch for updates. -Petrucelli

&&

.MARINE...Updated 200 PM PST Thursday 16 Jan 2020...A series of
fronts will likely continue to result in high to very high and steep
to very steep seas over the next week.

A cold front has moved onshore. Winds and seas have begun to
diminish, but a fresh south swell will accompany high and steep
westerly swell dominated seas today.

Seas reach a minimum early Friday, but another very strong front is
expected to impact the waters beginning Friday afternoon with strong
gales likely Friday evening through mid-day Saturday, and seas
peaking at 15 to 20 feet on Saturday. Winds will come up quickly, so
have gone straight to a Gale warning a bit early rather than having
a short, less than 5 hours, period of small craft advisory prior to
the Gale warning. Conditions are forecast to barely improve Saturday
evening with continued southerly winds at advisory strength.

Seas will diminish but likely remain high and steep Sunday ahead of
the next front on Monday. The active pattern will likely keep seas
high and steep into Wednesday.  -Sven

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 4 PM PST this afternoon for
        ORZ029>031.
     Winter Storm Warning until 4 PM PST this afternoon for ORZ024.
     Winter Weather Advisory until 4 PM PST this afternoon for
        ORZ023.
     Winter Weather Advisory until 4 PM PST this afternoon for
        ORZ024-026.
     Winter Weather Advisory until 4 PM PST this afternoon for
        ORZ025-027-028.

CA...Winter Weather Advisory until 4 PM PST this afternoon for
        CAZ083>085.
     Winter Storm Warning until 4 PM PST this afternoon for
        CAZ082-083.
     Winter Weather Advisory until 4 PM PST this afternoon above 1500
        feet in the for CAZ080-081.
     Winter Storm Warning until 4 PM PST this afternoon above 1500
        feet in the for CAZ080.

Pacific Coastal Waters...Small Craft Advisory until 10 PM PST this
        evening for PZZ350-356-370-376.
     Gale Warning from 11 AM Friday to 10 AM PST Saturday for
        PZZ350-356-370-376.

15/18/04