Winter Storm Warning 8, NWS Medford, OR

Area Forecast Discussion
National Weather Service Medford OR
925 AM PST Tue Feb 12 2019

.DISCUSSION...A major winter storm will impact portions of the forecast
area today and tonight. Let's start off with what will most
likely be the most significant impact from this storm--very heavy
snow over Interstate 5 from Dunsmuir through Siskiyou Summit
(heaviest near Mount Shasta City and Siskiyou Summit and lighter
from Gazelle to Yreka). Almost every piece of model data points to
snowfall rates exceeding one inch per hour (2 inches per hour
likely at times) between about 10pm tonight and 4am Wednesday
morning, with enhanced snowfall perhaps continuing into the mid
morning hours. Heavy snow will also impact areas in the Cascades
and Kalmiopsis, with snow levels somewhere between 2500 and 3000
feet. Heavy snow in those locations should occur between 10pm and
10am. We maintain Winter Storm Warnings at WSWMFR for these
impacts.

Winds will be strong in places with this storm as well, impacting
the coast, Shasta Valley, high terrain, and areas east of the
Cascades. Exposed mountain areas will likely see tree fall because
of this robust south to southwest flow. Please see NPWMFR for more
details on the winds.

No major updates were made this morning, but precipitation was
lowered for daylight hours based on latest model output. Please see
the previous discussion below for more details on this storm and the
continued active weather pattern through the weekend.

&&

.AVIATION...For the 12/18Z TAFs...From the Cascades west...Areas of
MVFR/IFR cigs/vsbys in rain and snow along with gusty winds and
obscuration of higher terrain will all occur along the coast and
over the coastal waters through Tuesday night tonight as a front
approaches and stalls nearby. Much of the same will occur over the
inland west side as well, although winds will trend weaker east of
the Coast Range. The exception will be the Rogue Valley, including
KMFR, which will see gusty south winds, but rain will hold off until
later this afternoon or evening. LLWS will also be an issue,
affecting KOTH and KRBG today, and KMFR today into this evening.
Conditions will slowly improve Wednesday.

East of the Cascades...Cigs will be mainly VFR with local MVFR, but
winds will be gusty at times. Snow and blowing snow will make for
areas of MVFR/IFR vsbys. Conditions will slowly improve Wednesday,
especially near valleys floors where the snow will be changing to
rain.

&&

.MARINE...Updated 800 AM PST Tuesday 12 February 2019...A front will
move onshore this afternoon and evening, then a surface low will
move onshore near Brookings Wednesday night. South gales and very
steep seas will persist through this afternoon, but will be
diminishing from the northwest. Winds will shift to the east this
evening, but seas will remain very steep through Wednesday night due
to continuing west swell and fresh southerly swell.

Fronts will move onshore Thursday and Friday. The fronts won't be
strong, but very heavy west to northwest swell will develop Friday,
and this will bring very steep seas, heavy surf, and hazardous bar
conditions to the area Friday into Saturday afternoon. The Wavewatch
model is trending up with the swell, and is now advertising it
peaking at 27 feet at 16 seconds Friday evening. Conditions will
gradually improve beginning Sunday.

&&

.PREV DISCUSSION... /Issued 549 AM PST Tue Feb 12 2019/

SHORT TERM...Today through Wednesday night...The forecast is
largely consistent with the previous issuance. Yesterday,
adjustments were made to reflect a slower arrival of a strong
cold front. The two main features of interest today will be
moderate to heavy rain from the coastal range westward, and
continued gusty southerly winds...strongest at the Coos County and
northern Curry County coast, and in the southern Shasta Valley.
In the Rogue Valley and Shasta Valley, downslope winds will
strongly limit precipitation during the day-time.

Confidence remains high in more widespread, more impactful
weather beginning late this afternoon and continuing into
Wednesday. The southerly flow will strength and be upslope near
Mt. Shasta. Heavy wet snow will be focused on western and southern
Siskiyou County with the most intense wind and snow to occur late
tonight into early Wednesday morning. 1 to 2 feet of snow is still
expected for the Mount Shasta region with substantial snowfall at
all locations above 2500 to 3000 feet.

While this is occurring, a low will be closing off near 40N 132W.
The main short term forecast uncertainty remains with the both
precipitation amounts and the extent to which snow levels will
warm/rise ahead of this low on Wednesday afternoon into Wednesday
night. In accordance with the trend in the latest data, snow
levels were nudged higher by about 500 feet to around 4000 to 5000
feet during that period. Any future update still looks more
likely to be for a further rise.

LONG TERM...Thursday through Monday...Models continue to
trend warmer and remain very wet for Thursday, as energy off the Pacific
Northwest coast digs far southwest offshore before moving northeastward
into northern California. Snow levels are expected at 4000 to 5000 feet
then lower again on Thursday night into Friday, likely to around 2000 feet,
with a kicker trough diving southeastward from the Gulf of Alaska
and producing light to occasionally moderate precipitation on
Thursday night into Friday. It will reach a position just off
the coast of Vancouver Island Thursday night into Friday. The cold
front associated with this disturbance is forecast to arrive at
the coast late Thursday night, then push across the CWA on
Friday. A period of steady precipitation and a drop in snow levels accompanies
the frontal passage.

Additional disturbances likely keep post-frontal showers going
later Friday through Saturday into Sunday morning, focused from
the Cascades westward, as the upper trough moves onshore. Low-
elevation snow is once again a possibility during this period,
with the snow level most likely around 2000 feet.

The trough axis is forecast to shift south and east of the area
Sunday through Sunday night, so coverage of showers should
gradually diminish in the NNW flow aloft. Next week, the mean
trough position will be east of the area early on, but will likely
return back to the West Coast, which means we'll maintain mostly
NNW flow and temperatures than remain below average for this time
of year. -Spilde/DW

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
     Wednesday for ORZ029>031.
     Wind Advisory until 4 PM PST this afternoon for ORZ030-031.
     High Wind Warning until 1 PM PST this afternoon for ORZ021-022.
     Winter Storm Warning until 10 AM PST Wednesday above 2500 feet
     in the for ORZ024.
     Winter Storm Warning from 4 PM this afternoon to 10 AM PST
     Wednesday above 2500 feet in the for ORZ025.
     Winter Storm Warning from 4 PM this afternoon to 10 AM PST
     Wednesday for ORZ028.
     Winter Storm Warning until 10 AM PST Wednesday for ORZ027.
     Winter Storm Warning from 4 PM this afternoon to 10 AM PST
     Wednesday above 2500 feet in the for ORZ026.

CA...Winter Weather Advisory from 4 PM this afternoon to 10 AM PST
     Wednesday for CAZ084-085.
     Winter Weather Advisory until 4 PM PST this afternoon above 2500
     feet in the for CAZ082-083.
     Winter Storm Warning from 4 PM this afternoon to 4 PM PST
     Wednesday for CAZ082-083.
     Winter Storm Warning from 4 PM this afternoon to 4 PM PST
     Wednesday above 3000 feet in the for CAZ080.
     High Wind Warning until 10 PM PST this evening for CAZ081.
     Winter Weather Advisory from 10 PM this evening to 10 AM PST
     Wednesday for CAZ081.
     Wind Advisory until 4 PM PST this afternoon for CAZ084-085.

Pacific Coastal Waters...Gale Warning until 4 PM PST this afternoon for PZZ356-376.
     Hazardous Seas Warning until 4 PM PST Wednesday for
     PZZ350-356-370-376.
     Gale Warning until 10 AM PST this morning for PZZ350-370.