NWS Medford, OR wrote its last area forecast discussion before the first event at Jan 11, 5:27 AM PST, 3 hours 5 minutes earlier.
Area forecast discussion, Jan 11, 5:27 AM PST, 3 hours 5 minutes before
Area Forecast Discussion
National Weather Service Medford OR
527 AM PST Thu Jan 11 2018
.SHORT TERM...Through Saturday, January 13th...
Another upper level shortwave trough is taking aim on our forecast
area this morning. Late this morning through this afternoon
westerly jet stream winds are expected to be 120 knots at 300mb
over SW Oregon per the GFS and ECMWF operational runs. Model
guidance appears to have trended a bit further south with the jet
max associated with this frontal system and associated temperature
advection over the forecast area now looks less like a warm front
and more like a weak cold front. The net effect of these
dynamical changes means snow levels today are likely to top out
around 7kft rather than any higher and wind and QPF look to be a
little higher than what it appeared they would be 24 hours ago.
All in all, today's precipitation is expected to be focused in
quasi-stable orographic waves outside of a brief period of time
when the cold front moves across the west side this afternoon.
Thus, the bulk of today's precipitation will be focused along and
near the Curry County Coastal Mountains and across the Oregon
Cascades, where 1 to 1.5 inches of water is expected. Winds will
be strongest along and near the coast mid-morning through early
afternoon, and strongest elsewhere this afternoon. High Wind
Warnings are currently in effect for portions of the coastal
counties and east side, and wind advisories are in effect for
other portions of the east side. You can view the hazard areas on
a zoomable map at https://www.wrh.noaa.gov/mfr/hazard .
Precipitation with today's frontal system will wind down tonight
through Friday morning as snow levels fall to the 5-6kft range.
Friday through Sunday will be the calm before next week's
storminess with fairly calm and mild conditions expected. We
anticipate valley fog and associated inversions, but also anticipate
that a modest east to west pressure gradient and a good potential
of frosting out some of the moisture in the valleys will lead to
enough mixing in most of the valleys such that we'll see afternoon
sun at most locations, especially east of Medford and Roseburg.
Guidance indicates that valley areas that are able to mix out
nocturnal inversions could see afternoon high temperatures surge
in to the 55 to 65 degree range. Nudged up high temperatures for
some valley areas during this time period overnight because of
this reasoning. The warmest conditions appear as if they will be
in Brookings and in the nearby Coastal Mountains.
Yesterday afternoon's Long Term portion of the discussion
summarizes the current situation for the long term very well, so
have included it, below. Some points of note for the extended
from overnight are as follows:
The leading frontal system next week, arriving Monday the 15th,
is expected to begin with high snow levels- the GFS and ECMWF models
are currently well agreed on this, with snow levels likely above
7kft. For Tuesday the 16th the ECMWF continues to indicate snow
levels crashing to 4kft or lower, while the GFS indicates them
5-7kft with much less precipitation. The ECMWF has been much more
consistent and agree with yesterday's lean ECMWF-ward due to this
consistency. Models are fairly well agreed now on a stronger and
colder frontal system coming through between the 17th and 20th,
centered on Thursday the 18th. Longer range guidance, to include
CPC's 8-14 day forecast (covering Jan 18th-24th) tilt odds toward
colder and wetter than normal conditions for our forecast area as
the pressure anomaly pattern across the Pacific begins looking
more like what we'd expect in a La Nina. BTL
.LONG TERM...Sunday, Jan 14th, through Wednesday, Jan 17th...
An upper level ridge will be in control of the weather early in
the extended period resulting in continued dry weather on Sunday.
However, we have high confidence in a pattern change next week.
All signs point to the ridge breaking down early next week with a
series of storms expected to bring an extended period of wet,
unsettled weather beginning Monday, lasting through next week and
perhaps beyond.
Models show the ridge axis pushing to the east of 120W longitude
Sunday night and this will allow a weakening frontal system offshore
to approach the coast. Light rain from this system could reach the
coastal waters, but will probably fall apart prior to reaching the
coast.
An upper trough becoming established over the NE Pacific will allow
a strong Pacific jet stream (160-170kt) to be directed into the
Pacific Northwest next week. The first stronger front will arrive at
the coast Monday, then push through the area Monday night into
Tuesday. After a brief break Tuesday night, then next even stronger
front will likely arrive Wednesday and move onshore Wednesday night.
There remains some uncertainty in the details, which is to be
expected at this range, so timing and strength of these systems will
play a key role in determining precipitation amounts, winds and snow
levels. Once again, we employed a blend of solutions, due to the
uncertainty in the details, but have favored the ECMWF, which
continues to demonstrate the most run-to-run consistency. We still
have time to iron out those details, so stay tuned!
The new week 2 (8-14 day) forecast from the Climate Prediction
Center indicates better odds for below normal temperatures, while
continuing better chances of above normal precipitation. Suffice it
to say, we're likely in for some weather that has been lacking much
of this winter so far, which should finally help to put a dent in
our precipitation deficits and build the mountain snowpack. -Spilde
&&
.AVIATION...11/12Z TAF CYCLE...There is a wide range of ceiling
conditions across the forecast area today as a frontal system moves
into the forecast area. LIFR currently exists along the Curry County
coast while inland areas are experiencing a mix of MVFR and VFR
conditions early this morning with partial terrain obscurations.
Ceilings are expected to be a mixture of VFR and MVFR today, though
IFR will occur at some locations around the time of frontal passage
from the Cascades westward. Low level wind shear will be a concern at
all four of the terminals today until surface winds increase. Expect
light to moderate precipitation today will be mostly orographically
forced along and west of the Cascades (briefly moderate at the
coast) and along and near the Coastal Mountains. Winds will be quite
strong along the coast, over the ridges, and east of the Cascades
late today, so expect some turbulence, as well.
KLMT could see wind gusts of 35 knots this afternoon around 21Z, but
guidance indicates gusts are most likely to fall just short of this
value, so have held off on the issuance of an Airport Weather
Warning for now and will track trends for greater accuracy. BTL
&&
.MARINE...Updated 330 AM PST Thursday 11 Jan 2018...A front will
move onshore today. The models are in good agreement showing a
onshore component at 925mb with winds between 50-60 kts peaking
around 10 am pst Thursday along with gale force surface winds.
A gale warning remains in effect for today, mostly north of Cape
Blanco. With the onshore component of the 925 mb winds, these should
tuck up close to the coast.
There will be several moderate to heavy swell events. The first will
begin today. The latest model run shows the swell peaking at 16 to
17 feet at 16 seconds tonight. A Hazardous Seas Warning remains
in effect, and these conditions will support High Surf Advisory
conditions as well.
The second round of heavy swell will occur Sunday night and it is
forecast to peak at 16 feet at 18 seconds. Yet another round will
move in Monday night, peaking at 16 feet at 16 seconds. -Sven
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...High Wind Warning until 4 PM PST this afternoon for ORZ021-022.
High Surf Advisory from 10 AM this morning to 4 AM PST Friday
for ORZ021-022.
High Wind Warning until 1 AM PST Friday for ORZ030-031.
Wind Advisory until 1 AM PST Friday for ORZ030-031.
CA...Wind Advisory until 1 AM PST Friday for CAZ085.
Pacific Coastal Waters...
- High Surf Advisory from 10 AM this morning to 4 AM PST Friday
for PZZ350-356.
- Small Craft Advisory for hazardous seas from 4 AM to 10 PM PST
Friday for PZZ350-356-370-376.
- Gale Warning until 4 PM PST this afternoon for PZZ350-356-370-376.
- Hazardous Seas Warning until 4 AM PST Friday for
PZZ350-356-376.
- Hazardous Seas Warning from 4 PM this afternoon to 4 AM PST
Friday for PZZ370.
Lutz/Sven/Spilde