NWS Medford, OR wrote its last area forecast discussion before the first event at Dec 19, 8:59 AM PST, 48 minutes earlier.
Area forecast discussion, Dec 19, 8:59 AM PST, 48 minutes before
Area Forecast Discussion
National Weather Service Medford OR
859 AM PST Thu Dec 19 2019
.DISCUSSION...
A warm front will continue to bring periods of precipitation to
the area today as it stalls over the region. Precipitation will be
greatest in areas favored by a southwesterly flow, especially
Curry County. Snow levels will remain high generally between 5,500
and 6,500 feet. South and southeast winds will be on the increase
today into Saturday. Please be advised that there are many
headlines associated with wind potential across the forecast area
for later today into Saturday.
All forecast elements appear to be on track at this time, so no
updates will be sent this morning. ~Lutz
&&
.AVIATION...For the 19/12Z TAFs...A warm front is moving through
the area today resulting in areas of rain and snow with freezing
levels of 5000-6000 feet this morning, rising to 6000-7000 feet this
afternoon. VFR ceilings of 3500-5000 feet are common, but there are
areas of MVFR ceilings/visibility with widespread terrain
obscuration. Turbulence aloft is also expected today due to
increasing winds at ridge levels. -Spilde
&&
.MARINE...Updated 230 AM PST Thursday, 19 December 2019...A
warm front will lift northward through the coastal waters this
morning resulting in periods of rain, increasing south winds and
seas elevated and hazardous to small craft. Later this morning,
south winds will increase to gales marking the beginning of an
extended period of gale force winds with steep to very steep seas
that will last through at least Friday night. Periods of heavy rain
will affect northern areas beginning late tonight, then slowly shift
southward across all of the waters Friday into Saturday morning. Due
to the long duration of gale force winds, seas will become fully
arisen. The very high and very steep southerly wind waves combined
with high and steep northwest swell will likely result in very
hazardous seas reaching peak heights in the 20-25 foot range late
tonight through Friday night. Mariners should consider altering
their plans or remain in port until this long-lived storm passes.
Conditions will begin to improve Saturday. After a few days of
relatively calm conditions early next week, another system may
arrive around midweek. -Spilde
&&
.PREV DISCUSSION... /Issued 300 AM PST Thu Dec 19 2019/
DISCUSSION...19/00Z NAM/GFS/EC in.
The hemispheric projection continues to show a wave number of five
around the globe over the next seven days. This is usually a
progressive pattern, and that will be the case here. The coldest
spots are over Nunavut and Siberia, and that won't change much
through next Wednesday.
The transition to a period of wetter and windier weather is now
occurring. This will be a four day atmospheric river event
supported by a long fetch jet stream directed into the west coast.
The focus of the jet stream/atmospheric event will shift quite a
bit north and south during the event, so there will be variability
in the sensible weather over the Medford CWA.
The first event will be a warm front, which will move north
through the area Thursday. This will bring quite a bit of
precipitation to the area with rising snow levels. The coast and
Coast Range will see the greatest rainfall along with western
Siskiyou county.
As far as snow impacts go, snow levels will start out around 4000
feet, and this will bring a round of snow to Siskiyou Summit on
Interstate 5 and Klamath Falls with several inches expected. Snow
levels will rise later this morning, ending the event in those
locations. Higher elevation areas, including Snowmans Summit on
Highway 89, the Southern Oregon Cascades, and Highway 97 north of
Klamath Falls will see snow for a longer period of time, and a
Winter Weather Advisory is in effect for those areas. Precipitation
will diminish and and snow levels will rise further this afternoon,
ending the event in those locations.
The warm front, and thus the heaviest rainfall, will shift to the
north of the area Thursday night, but there will still be
significant precipitation over the area, particularly over the
higher terrain from western Siskiyou county arcing northeast into
the Kalmiopsis due to moist southwest flow aloft. South winds will
bring upslope flow to the Mount Shasta area, which will keep the
precipitation going there.
The cold front portion of the system will hang offshore, which
will support a prolonged wind event Thursday night into Saturday
afternoon, especially over the coastal waters, along the coast,
in the Shasta Valley, and the Summer Lake area east of the
Cascades.
At this time, it looks like the coast will see winds meeting
warning criteria tonight into Saturday morning. The Shasta Valley
will see advisory level winds tonight into Friday evening, then
warning level winds Friday night into Saturday afternoon. The
Summer Lake area will see warning level gusts tonight into
Saturday morning. Other portions of the east side and possibly the
Rogue Valley will see advisory level winds. The warnings and
advisories will be updated soon.
The cold front will finally move onshore Saturday, and it will
bring widespread heavy precipitation from the Cascades west with
it. Once again, the heaviest amounts will fall along the coast, in
the Coast Range, and western Siskiyou county. At this time it
looks like there will not be any floods on main stem rivers, but
smaller streams may overflow with localized short duration small
stream and urban flooding.
Winds will diminish behind the front with plunging snow levels.
Confidence in timing for the return of significant snow is low at
this time based on some timing differences between model solutions.
But, there will likely be at least another 6 inches of snow in
the mountains above 4500 feet as the front pushes through on
Saturday. The Mount Shasta City may get significant snowfall
Saturday, but it's a borderline situation and confidence is too
low to issue any warnings this far out.
Long term discussion from the Wednesday afternoon AFD...Sun 22 Dec
through Wed 25 Dec 2019. A low pressure system will approach the
region from the southwest on Sunday while inland, a front remains
over central or eastern portions of the CWA. Precipitation may
increase along the front as the disturbance moves inland from the
southwest. Although there is variability on where the front will
linger on Sunday, overall expect light to moderate precipitation
across much of the area Sunday. Snow levels are expected near
4000 feet Sunday so some snow accumulations are possible across
higher passes. Sunday night, as the disturbance gradually moves
east and an upper trough remains in place, showers may linger
across inland areas. Meanwhile at the coast, another disturbance
may move just off the coast from north to south with continued
chances for showers across coastal areas as well.
An upper trough is forecast to remain over the area Monday. As the
upper trough is in place on Monday some continued light showers are
possible. Given the colder air mass, snow levels down to lower
passes are possible. However, models are in good agreement
indicating any showers would have only very light precipitation
amounts.
Monday night into Tuesday, a broad upper trough will remain with
main energy associated with earlier shortwave trough south to
southeast of the CWA. As a result, expect a cold pattern with only
weak chances for any precipitation. Temperatures may drop to
freezing or below in western valleys on Tuesday morning if there is
a break between weather systems and decreased cloud cover. Model
and ensemble solutions then indicate another low will approach the
region Tuesday night. Model variability increases Tuesday night into
Wednesday with low confidence in the track and strength of this low.
There is a range of possible solutions includes that the low may
track south along the coast before shifting inland south of the area
or the low may move inland over the area on Christmas Day with a
mix of light to moderate of rain and snow. Confidence is low on the
forecast details for the Christmas day period and we will continue
to monitor and update as confidence increases. -CC
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 10 PM this evening to 4 PM PST Saturday
for ORZ030-031.
Winter Weather Advisory until 1 PM PST this afternoon for
ORZ029>031.
Wind Advisory from 10 PM this evening to 4 PM PST Saturday for
ORZ030-031.
High Wind Warning from 7 PM this evening to 7 AM PST Saturday
for ORZ022.
High Surf Warning from 4 PM this afternoon to 4 AM PST Saturday
for ORZ021-022.
Winter Weather Advisory until 1 PM PST this afternoon for
ORZ027-028.
High Wind Warning from 7 PM this evening to 7 AM PST Saturday
for ORZ021.
Wind Advisory from 1 AM Friday to 10 AM PST Saturday for ORZ026.
CA...High Wind Warning from 10 PM this evening to 4 PM PST Saturday
for CAZ085.
Wind Advisory from 10 PM this evening to 4 PM PST Saturday for
CAZ085.
Winter Weather Advisory until 1 PM PST this afternoon for
CAZ082-083.
High Wind Warning from 10 PM Friday to 10 AM PST Saturday for
CAZ081.
Wind Advisory from 10 PM this evening to 10 AM PST Saturday for
CAZ081.
Pacific Coastal Waters...Small Craft Advisory until 10 AM PST this morning for
PZZ350-356-370-376.
Gale Warning until 4 AM PST Saturday for PZZ350-356-370-376.
BTL/NSK/CC