NWS Medford, OR wrote its last area forecast discussion before the first event at Jan 11, 4:21 AM PST, 3 hours 39 minutes earlier.
Area forecast discussion, Jan 11, 4:21 AM PST, 3 hours 39 minutes before
Area Forecast Discussion
National Weather Service Medford OR
421 AM PST Wed Jan 11 2023
.SYNOPSIS...A parent low pressure system in the Gulf of Alaska
will continue a parade of systems across the US West Coast,
including southern Oregon and northern California through the next
week. This active pattern will bring periods of strong gusty
winds, moderate snow, and rainfall to portions of the area.
Nuances in these systems as well as ridge building to the east
through the end of the work week will impact how these systems
move through our area.
&&
.SHORT TERM...Today 1/11 through Thursday night 1/12...3:00 AM
Satellite imagery is showing a band of higher clouds across
portions of southern ORegon and northern California with some
lower clouds beneath this band in northern Calfiornia, but also
offshore. Radar is indicating precipitation with the bulk of these
lower clouds offshore and just south of our area that will be
moving northward. This is part of a warm front that will move
onshore from southwest to northeast today. Most of the area may
see some light precipitation to accompany this front as it moves
through, but the south/southeast flow will mean that much of the
area will be precipitation shadowed, except for southern and
Western Siskiyou County where the terrain influences will focus
the precipitation in upslope flow. In these areas, a winter
weather advisory continues through this evening above 4000 feet.
Please see the WSWMFR for more details. Snow levels will rise in
the afternoon, and by late evening, we'll see a changeover from
snow to rain for a lot of places.
Meanwhile, a ridge building to the east will retrograde westward
slightly keeping this front stalled offshore in southerly flow
tonight into Thursday. Precipitation will continue to be forced
westward with this system, focusing mainly along the coast
overnight. Right now, we're not expecting rainfall amounts to be
significant enough to warrant flooding concerns; but we will
continue to monitor this as we've received reports of impacts in
the form of a landslide on Highway 101 already. While the best
chance for precipitation remains at the coast, ensembles do
indicate that precipitation could reach as far eastward as the
Cascades (with the West Side Valleys seeing rain shadowing due to
downsloping winds).
The main thing the combination of the aforementioned front and
ridge will do is create strong southerly flow, especially for the
Curry County coast. Have issued a High Wind Warning for this area
this evening into tomorrow morning. Meanwhile, guidance has been
a little bit wishy-washy with the Medford to Redding forecast
gradients showing around 9 hPa early on and trending downward to
now 7.5 hPa. Meanwhile, ensemble guidance is showing weaker 850
and 700 hPa winds than what one might expect with gradients that
high. These mixed signals suggest that we will indeed be windy for
the Shasta Valley and the southern end of the Rogue Valley, and a
wind advisory remains in effect (and was extended) into Thursday
for both areas. While widespread damaging winds are not expected
inland, it would not surprise me in the least to see a gust to 65
somewhere in the Shasta Valley. However, confidence was not high
enough to issue a High Wind Warning for the Shasta Valley--hence
our wind advisory. The winds will likely continue overnight, with
perhaps a slight break overnight, especially if the inversion
allows the surface to decouple from the free atmosphere above the
boundary layer. Winds products may need to be extended into Friday
as our parade of systems continue, but with confidence already
so-so, want to wait for additional high resolution guidance to
come in before making those decisions.
The pattern become a bit more progressive as the front and ridge
begin to move eastward on Thursday night. However, most of the
changes associated with this progression will occur in the Long
Term portion of the forecast. -Schaaf
.LONG TERM...Previous Long Term discussion issued 1/10/23,
slightly modified...Friday 1/13 through Tuesday 1/17...
The wet and windy pattern will continue throughout the long term
forecast period. The pattern that has set up over the Pacific
remains relatively consistent, with a large low spinning just
southwest of the Aleutians flinging system after system across the
Pacific and into the West Coast.
How each system affects southern Oregon and northern California will
depend on the track and intensity of each individual upper level
trough and associated surface low. There is a great deal of spread
across the ensemble suites, so it is very difficult, even
impossible, to nail down the details of any one system at this time.
That being said, we can expect the wet and windy pattern to
continue, with frontal systems passing every one to two days.
As the long term begins Friday, we will find our forecast area under
the influences of an atmospheric river, with a Pacific moisture
plume pushing plenty of precipitation into northern California and
the coast of southern Oregon for much of the weekend. This plume
will have a mostly southerly trajectory, and this will have
significant impact on where the bulk of precipitation will fall. The
coast, mainly Curry County, and Siskiyou County will see the bulk of
precipitation in our area, with the rest of the forecast area
downsloped and shadowed by the mountains. Snow levels should remain
above 5000 feet, so winter impacts will not be widepsread.
Additional fronts are expected through early next week, but there is
wide spread in the ensemble guidance, so the forecast will
continue to carry a general chance of precipitation through the
rest of the forecast term. Temperatures are expected to remain
around normal for this time of year. -BPN
&&
.AVIATION...11/12Z TAFs...The main concerns today into Thursday will
be gusty southerly winds, mountain wave turbulence, and low level
wind shear. Mountain wave turbulence is likely from the
Oregon/California state line southward, especially over the Mt
Shasta region and the Siskiyou mountains.
A new batch of precipitation will accompany the next front, moving
into our area from the southwest this morning. Precipitation amounts
today will be highest in Siskiyou County with a snow level around
4000 feet msl. Conditions are now mainly VFR. But, a mix of MVFR and
VFR conditions are expected to accompany the front with mountain
obscuration and precipitation becoming more widespread this
afternoon and continuing tonight into Thursday. -DW
&&
.MARINE...Updated 230 AM PST Wednesday, January 11th 2023...Deep low
pressure will remain centered farther offshore while a front stalls
just west of the outer waters. This will result in gales developing
again early this morning with strengthening winds into tonight.
This will be a long duration of gales, likely continuing Thursday
into Friday morning. At the same time as south to southeast winds
are at peak strength, a large west swell will move into the waters
Thursday, peaking out Thursday night then diminishing slowly on
Friday. The combination of wind driven seas and heavy swell will
result in very dangerous mixed seas.
Conditions will finally improve later Friday into the weekend with
south winds gradually decreasing. Though, even with winds expected
to drop below gales, advisory strength winds and steep to very steep
and hazardous seas are likely with a mix of wind waves, fresh
swell, and swell. -DW
&&
.BEACH HAZARDS...Updated 230 AM PST Wednesday, January 11th 2023...
South to southeast winds will become strong and gusty at the coast
this morning, and will likely reach peak strength this evening into
Thursday morning with gusts up to 60 mph. But, coastal winds will
then remain strong and gusty into Friday morning.
It is the combination of the building wind waves and a building long
period west swell that is expected to create the most hazardous
conditions (with breaking waves of 30 to 35 feet) Thursday morning
into Friday morning. The highest surf is likely to occur around Port
Orford and Cape Blanco. -DW
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory from 7 AM this morning to 4 PM PST Thursday for
ORZ026.
High Wind Warning from 7 PM this evening to 7 AM PST Thursday
for ORZ021-022.
High Surf Warning from 10 AM Thursday to 10 AM PST Friday for
ORZ021-022.
CA...Winter Weather Advisory until 7 PM PST this evening above 4000
feet for CAZ080-082-083.
Wind Advisory from 7 AM this morning to 4 PM PST Thursday for
CAZ081.
PACIFIC COASTAL WATERS...High Surf Warning from 10 AM Thursday to 10
AM PST Friday for PZZ350-356.
Gale Warning until 4 AM PST Friday for PZZ350-356-370-376.
&&