NWS Medford, OR wrote its last area forecast discussion before the first event at Nov 16, 8:53 PM PST, 3 hours 7 minutes earlier.
Area forecast discussion, Nov 16, 8:53 PM PST, 3 hours 7 minutes before
Area Forecast Discussion
National Weather Service Medford OR
853 PM PST Mon Nov 16 2020
.DISCUSSION...With all the rain yesterday and the wet ground this
evening, minus any winds and breaks in the high clouds, we have
some fog developing along the Rogue Valley I-5 corridor from
Medford to Grants Pass. Many web cams are showing it is
particularly dense with visibility down to 1/4 of a mile here at
the airport. We have issued a nowcast for this, but the fog won't
likely last all night as winds are expected to increase ahead of
the incoming frontal system offshore.
Speaking of that front, it is about to get windy across a large
part of the forecast area. Low pressure will deepen rapidly (to
below 970 mb) tonight as it moves to near the NW tip of Vancouver
Island by around 10 am PST Tuesday morning. While SW Oregon is far
away from that low, it has quite an expansive wind field
associated with it. Model 700 mb winds peak around 70-80 kt late
tonight/Tuesday morning over our forecast area with gradients
peaking at 7-9 mb RDD-MFR. We've been highlighting this wind event
for a while now and don't really see any reason to change what we
have in the going forecast. Numerous wind headlines are in place
and they can be viewed at NPWMFR. The cold front extending
southward from the low will push onshore very early Tuesday
morning, then east of the Cascades Tuesday afternoon. Expect a
good shot of rain for most areas, best (1-3") in the upslope
areas of SW Oregon (Coast Ranges/Cascades/Siskiyous), but also in
the Mt. Shasta region, where 850-700mb flow is maximized for a 6-9
hour period. Since snow levels will be mostly 5500 feet and above
for this front, we aren't anticipating winter weather impacts.
Downslope flow in the Rogue/Shasta Valleys will keep precip totals
lower there with generally 0.25 of an inch or less -- with a
similar story over the east side.
Multiple short wave disturbances will move onshore behind this
initial front Tuesday night through Thursday morning, keeping the
weather wet and unsettled. Snow levels will be a little lower,
but mostly above the major passes, so winter impacts will be
reserved for the higher Cascades/Siskiyous. After that, we get a
break in the action late Thursday through Saturday as drier air
builds in under short wave ridging. This will lead to colder night
and chilly days with fog likely in the late-nights and mornings.
The next frontal system is expected to arrive late Saturday night
or Sunday. -Spilde
&&
.AVIATION...For the 17/00Z TAFS...Low level wind shear will continue
to be a concern this evening as a frontal system approaches.
Widespread turbulence is expected across the forecast area as strong
south winds overspread the region tonight into Tuesday.
VFR conditions will continue tonight as south and southeasterly flow
increases at the surface. There may be some exceptions, however, in
portions of the Illinois, Coquille, and Umpqua valleys overnight,
where some areas of shallow LIFR fog could develop.
-Miles/Sven
&&
.MARINE...Updated 830 PM PST Monday, 16 Nov 2020...
Southerly winds will increase tonight away from the near coastal
waters, then will steadily increase further this evening as the cold
front makes its approach.
Tonight winds will increase to gale force and seas will become very
steep in all areas as the cold front pushes toward the coast. A
period of storm force winds is still likely by Tuesday morning,
building seas to 15 to 25 feet. High southwest oriented swell behind
the front could create high surf for southwest facing ports and
beaches, but the bigger concern for southerly facing ports will be
with the southerly wind waves. These southerly wind waves combined
with a tide of plus 3-4 feet could bring waves into the parking lot
at Port Orford early Tuesday morning.
Thereafter, conditions are expected to slowly improve. Showery
weather in SW flow will continue through Thursday before drying
under northerly flow Friday and Saturday. ~Sven
&&
.PREV DISCUSSION... /Issued 246 PM PST Mon Nov 16 2020/
DISCUSSION...Low pressure is developing between 130W and 140W, and
this low will continue to rapidly deepen over the next 18 hours.
The center of low pressure will stay well away from the Oregon
coastline, pushing into Vancouver Island Tuesday morning, but the
wind field associated with the low will be expansive.
Wind details: Significant winds will begin to tonight. Satellite
and model guidance are showing a low pressure system forming off
the west coast and further developing into a "once a decade" sort
of wind storm. (We fully understand the irony considering that we
had a storm like this last year, but "once a decade" roughly
translates to a 10% chance of a storm forming like this. This is
similar to a 100-year storm having a 1% chance of formation any
given year.) This storm is poised to bring damaging winds to the
coast, high terrain of the Cascades and Siskiyous as well as some
of the higher terrain of the East Side, including the Warner
Mountains. The winds in this event will be more south to
southeasterly, allowing for the strong gusty winds (60 to 80 kts
aloft) to mix down into the Shasta and the Rogue Valley. This
means that portions of Highway 101, Interstate 5, Highway 31, and
some exposed mountain roads could see extremely gusty winds which
make travel difficult, if not dangerous. Power outages are
possible with some trees and powerlines falling, and roadway
blockages.
Other valleys, like the Illinois; Coquille; and Umpqua Valleys; as
well as the Klamath Falls area will see some gusty winds as well,
but these areas will be more sheltered from the strongest winds.
Furthermore, more east-west oriented valleys will not see any strong
winds as they blow over top the valleys. Numerous High Wind
Warnings and Wind Advisories have been issued across southern Oregon
and northern California. Please see the NPWMFR for more details.
Moderate to heavy precipitation will accompany the front on Tuesday,
with some valleys such as the Rogue initially being sheltered from
the precipitation via drying, downsloping winds. All areas will see
precipitation by late Tuesday. Rainfall rates won't be as high as
the recent heavy rainmaker but will still be significant, with
rainfall amounts from Tuesday to Tuesday night at 1-2 inches at
the coast, quarter inch in the West Side valleys, around an inch
in the Cascades, and a quarter inch east of the Cascades. Rain
will change to snow early Wednesday morning around Crater Lake
(~6500ft), and snow levels will dip to around 4500 feet (higher
east of the Cascades) by Wednesday afternoon. The upper trough
that will be bringing the colder air in will maintain a 20% chance
of thunderstorms over the coast/coastal waters and bring
additional rainfall for lower elevations on Wednesday. Another
inch of rain is expected at the coast Wednesday. None of this
rainfall is expected to produce flooding and will continue to be
beneficial in putting a dent in the ongoing drought.
AVIATION...For the 16/18Z TAFS...Low level wind shear will continue
to be a concern along and near the coast through the day, developing
further inland this evening as a frontal system approaches.
Widespread turbulence is expected across the forecast area as
strong south winds overspread the region tonight into Tuesday.
Conditions are expected to become VFR this afternoon for all areas.
This period of VFR will continue tonight as south and southeasterly
flow increases at the surface. There may be some exceptions,
however, in portions of the Illinois, Coquille, and Umpqua valleys
overnight, where some areas of shallow LIFR fog could develop.
-Miles
MARINE...Updated 200 PM PST Monday, 16 Nov 2020...Southerly
winds will increase today away from the near coastal waters as a
warm front lifts northward through the area, then will steadily
increase further this afternoon and evening as the cold front
makes its approach. Seas will also steepen late this morning
through this evening, particularly in the outer waters.
Tonight winds will increase to gale force and seas will become very
steep in all areas as the cold front and its parent low pressure
center push toward the coast. Numerical model trends suggest the low
pressure will just move inside of 130W longitude tonight into
Tuesday morning while deepening substantially, which is typical of
our stronger storms, and this is no exception.
A period of storm force winds is still likely by Tuesday morning,
building seas to 15 to 25 feet. High southwest oriented swell behind
the front could create high surf for southwest facing ports and
beaches, but the bigger concern for southerly facing ports will be
with the southerly wind waves. These southerly wind waves combined
with a tide of plus 3-4 feet could bring waves into the parking lot
at Port Orford early Tuesday morning.
Thereafter, conditions are expected to slowly improve. Showery
weather in SW flow will continue through Thursday before drying
under northerly flow Friday and Saturday. ~BTL/BPN/Miles
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning from 4 AM to 7 PM PST Tuesday for ORZ030-031.
Wind Advisory from 4 AM to 7 PM PST Tuesday for ORZ030-031.
High Wind Warning until 1 PM PST Tuesday for ORZ021-022.
Wind Advisory from 1 AM to 1 PM PST Tuesday for ORZ023>025.
High Wind Warning until 7 PM PST Tuesday for ORZ027-028.
Wind Advisory from 4 AM to 7 PM PST Tuesday for ORZ029.
High Wind Warning from 1 AM to 4 PM PST Tuesday for ORZ026.
Wind Advisory from 1 AM to 4 PM PST Tuesday for ORZ026.
CA...High Wind Warning from 4 AM to 7 PM PST Tuesday for CAZ085.
Wind Advisory from 4 AM to 7 PM PST Tuesday for CAZ085.
High Wind Warning until 7 PM PST Tuesday for CAZ082.
High Wind Warning until 7 PM PST Tuesday for CAZ083.
Wind Advisory from 4 AM to 7 PM PST Tuesday for CAZ084.
High Wind Warning from 1 AM to 4 PM PST Tuesday for CAZ081.
Pacific Coastal Waters...Small Craft Advisory until 10 PM PST this evening for
PZZ350-356.
Storm Warning from 4 AM to 10 AM PST Tuesday for
PZZ350-356-370-376.
Gale Warning from 4 AM to 1 PM PST Tuesday for PZZ350-356.
Hazardous Seas Warning until 4 AM PST Tuesday for PZZ350-356.
Hazardous Seas Warning from 1 PM Tuesday to 10 PM PST Wednesday
for PZZ350-356-370-376.
Gale Warning until 1 PM PST Tuesday for PZZ370-376.
Hazardous Seas Warning until 10 PM PST this evening for
PZZ370-376.
MAS/SBN/NSK/BMS/MCB