NWS Medford, OR wrote its last area forecast discussion before the first event at Nov 12, 8:42 PM PST, 5 hours 19 minutes earlier.
Area forecast discussion, Nov 12, 8:42 PM PST, 5 hours 19 minutes before
Area Forecast Discussion
National Weather Service Medford OR
842 PM PST Thu Nov 12 2020
.UPDATE...A few light RADAR returns are beginning to move onshore,
while winds at the coast and at our offshore buoys have started to
increase. These are the leading edges of the system that will
push through the region tomorrow, bringing us plenty of wind, rain
,and mountain snow. Winter storm headlines and wind headlines
remain in effect for much of tomorrow. The latest model runs do
show the system moving through slightly faster than previously
thought, but that is the only change overall. The models are also
beginning to ramp up the strength of the next system, due to pass
through the area Saturday. These will be the main forecast
concerns tonight.
Overall, the forecast appears to be right on track, so no updates
were needed. More details can be found in the previous discussion
below. -BPN
&&
.AVIATION...For the 13/00Z TAFS...VFR conditions will prevail over
most of the area through this evening, and across the east side and
northern California through tonight. On Friday , widespread low
flight conditions, precipitation, and terrain obscurations are
expected through Friday evening.
Areas of MVFR cigs in low clouds and rain will develop over the
coastal waters this evening, moving onto the coast by 08Z. The first
front will stall briefly before a stronger front early Friday
morning drives MVFR conditions inland to the southern Oregon
Cascades. After 15Z, terrain obscurations will become more
widespread for Oregon and northern California west of the
Cascades. At KLMT expect precipitation to start as snow, then
transition to rain late Friday morning, before turning back to
snow later Friday afternoon into Friday evening.
Also, wind shear is a concern at KOTH and also is possible for KRBG,
KMFR, and KLMT during Friday morning; Concerns will be for very
strong speed shear. -Miles/DW
&&
.MARINE...Updated 800 PM PST Thursday 12 Nov 2020...
A front will arrive this evening followed by a very strong front
early Friday morning. Winds will reach gale force late Tonight and
peak Friday at storm force near shore from Port Orford northward.
Heavy northwest swell will follow and build into Saturday with peak
seas of 15 to 20 feet seas Friday night into Saturday night.
Seas will remain northwest swell dominated and high to very high
Sunday. Conditions briefly improve Monday, but the next strong front
is likely to bring very high seas Tuesday through Tuesday night.
Model data is beginning to show less run-to-run variability. Also,
there is confidence that the active pattern will continue through
next week with several significant fronts moving across the
waters.
&&
.PREV DISCUSSION... /Issued 331 PM PST Thu Nov 12 2020/
SHORT TERM...A front to the northwest will gradually move into
the area late tonight and Friday. Models continue to indicate this
front will strengthen as a low moves into the southern portion of
the front tonight. This will bring a potent frontal system into
the region on Friday with heavy mountain snow, heavy rain near the
coast, moderate rain across inland valleys west of the Cascades
and strong gusty winds.
Model solutions have trended about 3 hours faster with the timing
of the front. So precipitation and winds are expected to increase
along the coast early Friday morning and inland Friday morning
and afternoon with continuing moderate precipitation through
Friday evening some mountain areas.
Winds: Strong gusty winds are expected across much of the area,
including at the coast, in the mountains and areas east of the
Cascades. Winds at the coast are expected to peak in the morning
and early afternoon with gusts of 50 to 65 mph. Models continue
to point to a strong surface pressure gradient (around 10 mb
gradient from Medford to Redding) as well as a strong mid level
jet of 50 to 75 mph moving over the area. So there is high
confidence that inland areas will also see strong and gusty winds,
especially across the higher mountains, including over the
Cascades and east of the Cascades as well as in the Summer Lake
area. Other areas east of the Cascades, will see gusty advisory
level winds with gusts of 40 to 55 mph. Note, these winds will
combine with snow, especially across higher terrain from the
Cascades east, and result in blowing snow and limited
visibilities. High resolutions models are also indicating that
advisory level winds are likely in several valleys and lower
mountains west of the Cascades including the Shasta Valley, the
Illinois Valley and the Interstate 5 corridor between Sunny Valley
and Tri- City as well higher terrain in Josephine, eastern Curry
and southwestern Douglas counties. Winds in the Rogue Valley
(Medford to Ashland) are forecast to be gusty, especially in the
early afternoon with the frontal passage, but are expected to
remain just below advisory criteria with winds around 15 to 20
mph and gust to 35 to 40 mph. For additional details on the winds
please see the current high wind warnings and wind
advisories(NPWMFR).
Rain: Moderate to heavy rain is expected to spread into the coast
and coastal mountains Friday morning with moderate rain continuing
into the afternoon. Coastal areas are expected to receive 1 to 4
inches of rain with the highest amounts over the coastal
mountains. Moderate precipitation will quickly spread inland on
Friday. Storm total rainfall of 0.5 to 1.0 inch is expect across
many valleys west of the Cascades, except for higher amounts in
the Klamath River Valley in Western Siskiyou County. Also the
Rogue Valley and Shasta valley may see lower amounts due to the
effect of downslope winds.
Snow: Heavy snow will be a significant concern with this system
as very moist onshore flow and upper level dynamics bring
significant snow accumulations to the mountains and higher terrain
on the east side. Heavy snow if 1 to 2 feet is expected in the
Southern Oregon Cascades for elevations of 5000 feet and higher.
Also around 7 to 10 inches is expected over Mount Ashland. Light
to locally moderate snow accumulations are expected between 4000
to 5000 ft in the Southern Oregon Cascades and Siskiyous. Snow
levels may fluctuate during the day, starting out around 4000 ft
in the morning, briefly rising above 5000 ft in the afternoon,
then lowering to 4000 ft Friday evening and night. Snow showers
will decrease in coverage and intensity late Friday evening into
Friday night.
In the Cascades, with the heavy snow there will be strong gusty
winds. Exposed areas in higher portions of the Southern Oregon
Cascades, such as Crater Lake, are expected to see winds gusting
to 50 to 60 mph. More protected areas will still see winds gusting
into the 30 to 45 mph range. Strongest winds and heaviest snow
are expected late Friday morning through Friday evening. The
combination of strong gusty winds winds and heavy snow will bring
extremely dangerous winter storm conditions to the higher
mountains in the Cascades with the potential for extensive tree
damage. White out conditions may occur. Roads may be impassible at
times. A winter storm warning is in effect Friday morning through
early Saturday morning.
East of the Cascades heavy snow is expected in the Chemult area
and the higher mountains in eastern Klamath and western Lake
Counties with around 6 to 10 inches in these areas. Areas of
moderate snow accumulations are expected south of Chemult into the
Klamath basin. Snow levels are expected down to valley floors,
rising to around 5000 to 5500 in the late afternoon then lowering
back down in the evening. Winter storm and winter weather
advisories remain in effect for these area.
In Northern California, the main area of concern for heavy snow
is the in the Mount Shasta area where snow levels are expected to
be lower ahead of the frontal passage. Heavy snow is expected
above 4000 feet in the Mount Shasta area with heavy snow impacting
areas of Highway 89 near Snowmans summit and over the higher
terrain. Strong gusty winds are expected in these areas as well
with strongest wind above 5000 feet. So expect periods of blowing
snow and near white out conditions for these areas. Also wet snow
combined with strong gusty winds may result in trees down. For
areas below 4000 feet, moderate snow is expected Friday morning
into Friday afternoon. Snow levels are expected to start out low
around 3000 feet then rise to 3500 feet Friday afternoon then to
4000 feet in the late afternoon and early evening. Given the trend
towards models showing lower snow levels and bringing
precipitation into the area earlier, expect moderate wet snow
accumulations of 3 to 6 inches down to 3000 feet in the Mount
Shasta City area and along the I-5 corridor between Weed and
Dunsmuir. Please see the WSWMFR for the most current winter storm
details.
LONG TERM...(Sunday morning through Wednesday night)...Saturday,
another front moves through bringing moderate rain to the Coast
Range and Cascades. Amounts will range from 0.5" to 0.75". Some rain
shadowing is expected for the Rogue valley and rain amounts will
barely reach a tenth. Another round of gusty winds is expected along
ridges and peaks, as well as all areas east of the Cascades. Snow
will be less of an impact, with snow levels rising form around 3500
feet to 4500-5000 feet.
The trough begins to flatten out as heavy shower activity decreases,
but one final front, a warm front, will approach the area Sunday
morning. Snow levels will steadily rise through the morning above
above 6500 feet across the whole area. Moderate rainfall is probable
over the Coast Range and Cascades, but the trend has been for the
heaviest rain to shift north and be slightly weaker with each run.
Only a small amount of light rain should be anticipated in valleys
west of the Cascades and south of the Umpqua divide. Winds will also
begin to ease, except along the highest peaks where winds could stay
elevated through to Sunday night.
Model trends have begun to confirm that a ridge will build in strong
enough to eliminate any rain potential on Monday. This stronger
ridge solution has increased from 23% of total members to 76% of
members in the WPC clusters. Still, can't rule out terrain driven
rain along the coast range, so have left some precip with very low
PoPs, but expect some further reductions as we get closer in time if
this trend continues to hold.
Another low will track towards the Oregon coast after Monday. An
increase in model variability has occured, lead by differences in
timing. The ENS ensemble suite favors the timing of the low to bring
impacts to southern Oregon on Tuesday evening, while the GEFS is
maintaining the ridge longer and bringing the low in Wednesday
afternoon.
So far, the leading solution is for the low to remain weaker than
the one moving through the region tomorrow. This will keep winds
light in the valleys, though ridges along the Cascades and the east
side in Lake County are likely to experience breezy winds. The ridge
is also showing signs of further strengthening over the Rocky
mountains. This combined with a less deep low indicates that fronts
from this low will struggle to advance beyond the Cascades. Expect
rain that does form to be terrain locked, while the heaviest amounts
stay isolated to the Coast Range.
One final note is that the low will be warmer than the low this
Friday and will be preceded by a day of warming. This will result
in less snow and more liquid precipitation, as early snow level
predictions are above 7000 feet with the first front. After nearly a
week of snow and rain, rivers will be on the rise (even if only by a
few feet). And while not near flood stage, they will still be higher
than at any time since spring. So, caution should be taken when
around rivers as their waters will be cold and underestimation of
river current strength may lead to serious injuries. -Miles
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 7 AM to 10 PM PST Friday for ORZ030-031.
Winter Weather Advisory from 7 AM Friday to 1 AM PST Saturday
below 5000 feet in the for ORZ030-031.
Winter Storm Warning from 7 AM Friday to 1 AM PST Saturday above
5000 feet in the for ORZ030-031.
Wind Advisory from 10 AM to 10 PM PST Friday for ORZ031.
High Wind Warning from 4 AM to 4 PM PST Friday for ORZ021-022.
Wind Advisory from 4 AM to 2 PM PST Friday for ORZ023-024.
Winter Storm Warning from 4 AM Friday to 4 AM PST Saturday above
5000 feet in the for ORZ027-028.
Winter Weather Advisory from 7 AM Friday to 1 AM PST Saturday
for ORZ029.
CA...High Wind Warning from 7 AM to 10 PM PST Friday for CAZ085.
Wind Advisory from 10 AM to 10 PM PST Friday for CAZ084-085.
Winter Weather Advisory from 4 AM to 4 PM PST Friday above 3000
feet in the for CAZ082.
Winter Storm Warning from 4 AM to 10 PM PST Friday above 4000
feet in the for CAZ082.
Wind Advisory from 7 AM to 7 PM PST Friday for CAZ081.
Pacific Coastal Waters...Small Craft Advisory until 1 AM PST Friday for
PZZ350-356-370-376.
Storm Warning from 4 AM to 10 AM PST Friday for
PZZ350-356-370-376.
Gale Warning from 1 AM to 10 AM PST Friday for PZZ356-370-376.
Hazardous Seas Warning from 10 AM Friday to 4 AM PST Saturday
for PZZ350-356-370-376.
Gale Warning from 1 AM to 4 AM PST Friday for PZZ350.
Hazardous Seas Warning until 1 AM PST Friday for PZZ350-370.