Blizzard and Heavy Snow in California, February 9, 2019

Area Forecast Discussion
National Weather Service Medford OR
754 PM PST Fri Feb 8 2019

.UPDATE...Colder air mass is moving at this time with
observations on Sexton Summit and other west side raws locations
indicating snow levels around 2800 feet. Most significant update
that was made this evening was bringing in snow in the illinois
valley earlier. Otherwise current forecast for tonight looks on
track. Sven

&&

.PREV DISCUSSION... /Issued 339 PM PST Fri Feb 8 2019/

SHORT TERM...A strong, cold, wet low pressure system is now
emerging out of B.C. and will move down the coast and bring
widespread snow to our area tonight and tomorrow. In the meantime,
we have a few sprinkles or light snow flurries, but nothing
significant yet. Snow levels are currently running 2000 to 2500
feet and this will hold through the evening and into the overnight
period. However, as the low pressure moves down the coast, a front
will move onshore late this evening and then into the Cascades by
tomorrow morning. This will send snow levels down overnight and
then they will crash to the valley floors tomorrow morning. Heavy
snow is a sure bet in the west side mountains above 1500 feet as
well as the Cascades/Siskiyous above 2000 feet, and a variety of
winter storm warnings remain in effect for these areas. The I-5
passes between Grants Pass and Roseburg, I-5 at Siskiyou Summit,
and even some lower roadways such as Hayes Hill and Jacksonville
Hill are expected to get heavy snow and potentially significant
travel impacts. Timing for the peak of the snowfall in these
locations is as follows:

* Lower I-5 passes (Sexton, Smith Hill, Stage Road, Canyonville):
  3-7 AM.

* Hayes Hill: 7-10 AM.

* Siskiyou Summit: 7-10 AM.

* Cascades from Highway 140 North: All day.

In the valleys, the scenario plays out a little differently. As
mentioned, snow levels are above the valley floors and will
gradually come down tonight and then crash to the valley floors
during the frontal passage. In the valley bottoms, Grants Pass and
Medford for example, precipitation may come in as a mix of rain
and snow overnight, but is expected to change to snow as the front
arrives. The factors working in favor of snow in the valleys this
time are that the front will be coming into an airmass that is
already fairly cold, and the precipitation will be arriving around
dawn, which is normally the coldest time of day. That said,
unless it snows really hard along the front (possible), most of
our accumulations with the front and during the day Saturday in
the valley bottoms may be confined to grassy surfaces. Of course,
we could get accumulations on the roads in any heavier showers
during the day as well as when the sun sets Saturday.

During the evening Saturday, models show the upper low right over
the coast, and this is the time when the coast is most likely to
see accumulating snows. While I wouldn't expect widespread snow
along the coast, this kind of setup could bring some pretty hefty
accumulations to a few isolated locations.

On the east side and much of northern California, this looks like
a significant winter storm as well, and winter weather advisories
and warnings are also in effect in many of these areas. Please see
MFRWSW or weather.gov/medford for details.

Snow tapers off quickly Saturday night, and this sets the stage
for a very cold night, especially where it has snowed.

This will be a major winter storm for the mountains for sure, and
all valley locations are expected to see at least a little snow.
As a result, all residents of and expected travelers through
southwest Oregon and Northern California should be prepared for
winter weather this weekend. -Wright

LONG TERM...Sunday night through Friday...A cold, very active
weather pattern will continue during this period. Truckloads of
snow are expected in the mountains, where it will be measured in
feet, not inches. And, there is more opportunity for low-
elevation snow too. For a little historical perspective, we are
predicting around 10 inches of snowfall in Ashland for the 5-day
period starting Saturday and ending Wednesday night. That could
land in the Top 10 snowiest 5-day periods in the last 75 years. Of
course, a lot will depend on the snow level, which is expected to
waver above Ashland at times. But, suffice it to say, it will be
very wintry in SW Oregon and northern California early to mid next
week.

This period will encompass 3 events with one fast-moving
disturbance Sunday night into Monday, then another stronger,
wetter and probably a little milder system Monday night through
Tuesday. The third disturbance will lower snow levels again
Tuesday night into Wednesday.

The Sunday night/Monday system will follow the cold weekend storm
that will have laid down snow just about everywhere across the
CWA. As a result, snow levels will be quite low when it arrives
(about 500-1000 feet west of the Cascades). Right now, we are
forecasting about 1-3 inches across the Rogue Valley (Grants Pass
to Ashland). Coastal snow is less likely with this event since
some Pacific air should get into the mix keeping snow levels up a
bit. Of course, surrounding mountains will have quite a bit more
snow.

A warm front will push north of the area Monday afternoon and a
much wetter frontal system will move into the area Monday night
into Tuesday. Right now, models are showing snow levels rising to
around 3000 feet ahead of it, but we are concerned about the
amount of cold air that could get trapped in the more sheltered
areas west of the Cascades. This happens frequently when new snow
is on the ground and models sometimes have difficulty projecting
just how much of this cold air gets scoured out. Also, with
heavier precipitation rates expected, dynamic cooling could cause
snow levels to be lower than models currently project. Right now,
we have kept snow levels at a conservative 2000 to 2500 feet to
allow some wiggle room in either direction. Of course, just a
little wiggle will have large implications on snow amounts. Stay
tuned!

Once the cold front moves east of the Cascades Tuesday evening,
snow levels will drop again to around 1000 feet Tuesday night
into Wednesday morning with showers continuing. This could bring
some accumulating snow back to west side valley floors.

We should catch a relative break Wednesday night into Thursday
morning as the upper trough axis shifts to our east, but models
show yet another system arriving later Thursday/Friday. -Spilde

.AVIATION...For the 09/00Z TAFs...Scattered to numerous light
showers will continue this evening with VFR and areas of MVFR/IFR as
well as terrain obscuration. A cold front will move into the area
after 06Z tonight, with deteriorating conditions in most areas. Late
tonight through Saturday, expect rain and snow with freezing levels
falling from around 3500 FT MSL to 2000 FT MSL, widespread MVFR
cigs/vis with mountain obscuration and areas of IFR cigs/vis. A
period of moderate snowfall could occur as the front passes through
Klamath Falls late Saturday morning, producing a quick inch or two
of snow on the runway. While some snow may also occur at Roseburg
and Medford, daytime accumulation should mostly be reserved for non-
paved surfaces. Overall, expect widespread MVFR with local IFR and
terrain obscured all day Saturday. -Spilde

MARINE...Updated 200 PM PST Friday 8 February 2019...Weak high
pressure between low pressure systems will persist over the waters
this afternoon. A cold front will arrive from the northwest and
sweep through the waters later this evening into Saturday morning.
This is the first in a series of strong, cold lows that will move
in from the north with snow into early next week.

Conditions will remain below criteria levels through this evening.
Seas will build early Saturday morning and quickly become high and
very steep. Seas will peak Saturday night around 16 to 18 feet with
a dominant west-northwest swell. There will be a mix of long
period 19 to 22 second swell and a larger 11 to 13 second swell.
Very steep and hazardous seas will make for rough bar conditions
Saturday morning into Sunday afternoon. Also, along beaches,
dangerous sneaker waves are possible on Saturday through Saturday
night. In addition, advisory level northwest winds are expected
during Saturday. Winds may approach gales at times, especially
over the outer waters, but should remain at high end advisory
level for the most part. Seas will gradually subside Sunday into
Sunday night, but remain high and steep into early Sunday evening.

Winds and seas will increase again with the next front late Sunday
night into Monday. Model uncertainty increases beyond Monday, but
the pattern is likely to remain active with periods of high and
steep seas through the week. /DW

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory until 10 PM PST Saturday for ORZ029>031.
     Winter Storm Warning until 10 PM PST Saturday for ORZ029-030.
     Winter Storm Warning from 4 AM to 10 PM PST Saturday above 4500
     feet in the for ORZ031.
     Beach Hazards Statement from 4 AM PST Saturday through late
     Saturday night for ORZ021-022.
     Winter Storm Warning until 4 AM PST Sunday above 1500 feet in
     the for ORZ024.
     Winter Weather Advisory until 4 AM PST Saturday below 2000 feet
     in the for ORZ025.
     Winter Weather Advisory from 4 PM Saturday to 4 AM PST Sunday
     below 1500 feet in the for ORZ021-022.
     Winter Storm Warning until 4 AM PST Sunday above 1500 feet in
     the for ORZ021-022.
     Winter Weather Advisory from 4 AM to 10 PM PST Saturday below
     2000 feet in the for ORZ026.
     Winter Weather Advisory from 4 AM to 10 PM PST Saturday below
     1500 feet in the for ORZ023.
     Winter Storm Warning until 10 PM PST Saturday above 1500 feet in
     the for ORZ023.
     Winter Storm Warning until 10 PM PST Saturday above 2000 feet in
     the for ORZ025.
     Winter Weather Advisory from 4 AM Saturday to 4 AM PST Sunday
     below 1500 feet in the for ORZ024.
     Winter Storm Warning until 10 PM PST Saturday for ORZ027-028.
     Winter Storm Warning until 10 PM PST Saturday above 2000 feet in
     the for ORZ026.

CA...Winter Weather Advisory until 10 PM PST Saturday for CAZ085.
     Winter Storm Warning until 4 AM PST Sunday above 4500 feet in
     the for CAZ085.
     Winter Storm Warning until 4 AM PST Sunday above 4000 feet in
     the for CAZ080>083.
     Winter Weather Advisory until 4 AM PST Sunday below 4000 feet in
     the for CAZ080-081-083-084.

Pacific Coastal Waters...Small Craft Advisory from 4 AM to 10 AM PST Saturday for
     PZZ350-356-376.
     Hazardous Seas Warning from 4 AM Saturday to 4 PM PST Sunday for
     PZZ350-356-370-376.

SBN/SBN/SBN