NWS Medford, OR wrote its last area forecast discussion before the first event at Nov 14, 2:34 PM PST, 3 hours 5 minutes earlier.
Area forecast discussion, Nov 14, 2:34 PM PST, 3 hours 5 minutes before
Area Forecast Discussion
National Weather Service Medford OR
234 PM PST Sat Nov 14 2020
.DISCUSSION...A warm front is moving towards the coast, and winds are
increasing across most of the forecast area. These winds will
ramp up to 60mph+ this evening at much of the Oregon coastline and
some areas east of the Cascades to include Highway 31 near Summer
Lake. Expect dangerous driving conditions and the potential for
power outages in these areas. High Wind Warnings continue for
these areas. To a lesser degree, gusty winds will also impact the
Shasta Valley and some areas west of the Cascades to include
portions of Josephine and Douglas/Eastern Coos Counties. High
terrain areas will see strong winds as well, but not quite
reaching our 75mph criteria for a High Wind Warning. Breezy
conditions will affect other areas like the Rogue Valley, but
winds aloft are too westerly to bring strong winds to these areas.
Snow levels are around 4000 ft this afternoon and will rise through
the night. Before snow levels rise above pass levels, we expect a
period of significant snowfall north of Highway 140, affecting
Highway 62 near Crater Lake and Highways 138 and 230 near Diamond
Lake. By midnight snow levels over the Cascades should be above
6000ft, so passes shouldn't be impacted. East of the Cascades, there
will likely be some snowfall but it should be light and affect
mainly the high terrain of Klamath and Lake Counties. Along Highway
97, road temperatures are well above freezing and air temperatures
are just above freezing, so snow should change to rain before
having significant impacts there.
Heavy rain will be another feature of this front. Satellite imagery
shows a long fetch of deep moisture, an Atmospheric River (AR),
stretching across the East Pacific waters. 1.5 inch precipitable
water values are being depicted by satellite imagery, and this
moisture will bring a prolonged period of moderate to heavy rain
from the coast inland to the Cascades. Even with months of
relatively dry conditions, the expected duration of heavy rain could
cause some landslides and flooding of small streams and creeks, so
we've issued a an Areal Flood Watch covering much of Curry County
and portions of extreme Western Josephine County. No data points
to rainfall rates reaching 0.5 inches per hour or 1.5 inches per 6
hours over the Slater wildfire, so we have not issued any Flash
Flood Watches for burn scar debris flows. We will still be
monitoring this of course as the peak of the AR event reaches that
area Sunday morning. Last but not least, in terms of impacts, dangerous
travel conditions are expected on Highway 101 this evening due to
the high winds and heavy rainfall.
The front will reach the CA/OR border Sunday morning and then shift
back northwards, maintaining moderate to heavy rainfall, though rain
rates should be less Sunday afternoon with the front pushing
northward. The Cascades will get inches of rainfall so much of the
recent snowpack will wash off as runoff. Still, we don't expect any
mainstem river flooding with this system given the current "low
flows" on the mainstem rivers.
Early Monday we'll see a relative break from significant weather,
but another strong low pressure system will be pushing towards the
area from the offshore waters.
Long Term...Monday night (11/16) through Saturday night(11/20)...
The overall forecast has not changed much from the previous shift.
The main concern on Monday night will be the strong, gusty winds
across areas of southern Oregon and northern California. Model
guidance is showing the gradients being a little weaker than the one
system occuring today. That being said, some of our guidance is
indicating 60 to 80 kt winds at 700 mb. The main difference with
this system will be the direction of the winds. The winds will be
more from south with a bit of a southeast component. This direction
will allow winds to align with our north-south valleys (instead of
scream over the top of the valleys which will be what occurs with
the ongoing storm), and allows for what feels like windier
conditions across southern Oregon and northern California. These
winds will be particularly strong at the coast, and along the higher
terrain along and east of the Cascades. But the Shasta Valley and
Rogue Valley could see some gusty winds, too. These winds will make
travel difficult to dangerous for vehicles, especially high profile
vehicles like semi trucks and large vans who are driving along the
roads. Some trees may fall as well.
The other big thing with this system will be the precipitation,
which will largely begin after the winds shift to be from the
southwest with the frontal passage on Tuesday morning. This sort of
pattern favors periods of heavy rain for the coast and in particular
the coast range, which will have already seen some significant
rainfall from earlier in the week. Additionally, the Cascades
will see some heavier rainfall as well while our valleys see
less rain due to downsloping. Have gone with the general consensus
with the ensembles and the operational models which seem to be
coming into better focus, and have made some tweaks that make sense
to the pattern. Additionally, snow levels will start out high:
Around 7000 feet or so, and will slowly drop through the week to
around 4000 feet by Thursday afternoon. Unfortunately, this sort of
rain combined with the previous storm's rain could work to wash away
the existing snow pack on the Cascades. That being said, we're going
to continue hoping that this does not occur.
The system looks to stall out somewhat on Tuesday into Wednesday,
with an additional impulse coming through Wednesday afternoon.
Overall light to moderate rain is expected in showers, and these
showers will linger through Friday, with snow levels starting to
drop, more winter-time impacts may become possible in any
particularly heavy shower for some of our mountain passes.
In the far extended forecast, it looks like a break from the active
weather will occur next weekend before the next from appears to
approach Sunday or Monday.
&&
.AVIATION...For the 13/18Z TAFS...The main change for this TAF cycle
was to add in low level wind shear (LLWS) for KOTH, KRBG, and KMFR
for this afternoon/evening and into the overnight hours. Currently a
mix of VFR and MVFR with terrain obscuration is ongoing across the
area with some light rain falling at coastal locations. Conditions
will gradually worsen this afternoon and evening as a strong warm
front pushes into the area. Ceilings and visibilities will lower
along and near the coast this afternoon, with worsening conditions
expanding to inland areas overnight, especially after 06Z. In
addition, this will bring increasing southeast through south winds,
first along and near the coast, and then across inland areas this
afternoon through tonight. Strong winds aloft associated with this
front will bring the concern for LLWS for the aforementioned areas.
/BR-y
&&
.MARINE...Updated 200 PM PST Saturday, 14 Nov 2020...A strong front
will push into the waters this afternoon, bringing very strong winds
with dangerous wind driven seas. Storm force winds are expected,
mainly beyond 5 nm and within 30 nm of shore and from Port Orford
northward, with gales expected elsewhere beginning this afternoon
and continuing overnight. Very steep and hazardous to dangerous seas
of 15 to 25 feet are expected during this time, with the highest
seas expected north of Cape Blanco. Seas will remain very high and
very steep until about sunrise Sunday morning, but winds will
diminish with time overnight tonight. While conditions will improve
some, seas will remain high and steep and hazardous to small craft
through Monday. Then, another strong front is expected late Monday
into Tuesday. Gales are almost certain with this front as well as
another round of very steep and hazardous to dangerous wind driven
seas of 15 to 25 feet. A gale watch remains in effect for this next
system, however, it should be noted that another round of storm
force winds is not out of the realm of possibilities.
After this front expected Monday into Tuesday, conditions will
slowly improve. Showery weather will continue through Thursday,
however, winds will be considerably weaker, around 15 to 25 kts, and
seas will gradually subside to below 10 feet late Thursday into
Friday. BR-y/~BTL
&&
.BEACH HAZARD...Updated 200 PM PST Sunday 8 Nov 2020...A high
surf advisory has been issued for the beaches of southern Oregon
from Port Orford northward and remains in effect through 4 am
Sunday. Large breaking waves of 20 to 25 are expected, leading to
hazardous conditions along and within the surf zone, especially
along jetties and exposed infrastructure. These large breaking
waves could inundate beaches and low lying shorelines. Surf will
diminish early Sunday, but may become hazardous again late Monday
night into Tuesday. /BR-y
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 4 AM PST Sunday for ORZ030-031.
Wind Advisory until 4 AM PST Sunday for ORZ030-031.
Winter Weather Advisory until midnight PST tonight for ORZ027.
High Wind Warning until 10 PM PST this evening for ORZ021-022.
Flood Watch from 10 PM PST this evening through Sunday evening
for ORZ022-024.
Wind Advisory until 4 AM PST Sunday for ORZ023>025.
High Surf Advisory until 4 AM PST Sunday for ORZ021.
CA...Wind Advisory until 4 AM PST Sunday for CAZ081.
High Wind Warning until 4 AM PST Sunday for CAZ085.
Wind Advisory until 4 AM PST Sunday for CAZ085.
Pacific Coastal Waters...Gale Watch from Monday morning through Tuesday morning for
PZZ350-356-370-376.
Small Craft Advisory from 4 AM Sunday to 10 AM PST Monday for
PZZ350-356-370-376.
Storm Warning until 4 AM PST Sunday for PZZ350-356-370-376.
Gale Warning until 4 AM PST Sunday for PZZ350-356-370-376.