NWS Medford, OR wrote its last area forecast discussion before the first event at Dec 20, 11:28 PM PST, 3 hours 20 minutes earlier.
Area forecast discussion, Dec 20, 11:28 PM PST, 3 hours 20 minutes before
Area Forecast Discussion
National Weather Service Medford OR
1128 PM PST Fri Dec 20 2024
.DISCUSSION...Updated the aviation, marine, and beach hazards
sections.
&&
.AVIATION...21/06Z TAFS...VFR conditions are expected through this
evening areawide. An incoming front will bring increasing winds and
high level clouds which will keep valley fog from forming. As winds
aloft increase late this evening through Saturday morning, low level
wind shear will be widespread, including at all terminals, North,
Bend, Roseburg, Medford, and Klamath Falls. Stronger winds will
surface along the coast, east of the Cascades and in some western
valleys (including near and south of Medford and the Shasta Valley)
beginning around 10-12z and continuing into the early afternoon. As
precipitation spreads inland late tonight and Saturday, expect
widespread MVFR conditions, local IFR conditions, and widespread
mountain obscurations to develop. Precipitation will taper off to
light showers for the afternoon. Diminishing winds are expected to
still provide enough mixing to maintaing VFR for early Saturday
evening. But, a stabilizing air mass is expected to valley low
clouds later Saturday night. -CC/DW
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.MARINE...Updated 800 PM PST Friday, December 20, 2024...Several
very strong fronts are expected through the next week with
persistent very high and very steep, chaotic, dangerous seas,
interrupted by periods of gales.
A front will move across the waters overnight. This front will bring
strong south winds that will reach gales (with gusts of 40 to 50 kt)
tonight and Saturday morning. Winds will shift southwest and
diminish below gales in the mid to late morning Saturday. However,
seas will remain very high and very steep due to a combination of
wind seas and building, long period west swell at 17 seconds.
Additional strong fronts follow Sunday into the middle of next week,
resulting in periods of gales and prolonged, very high and very
steep seas. Seas will be a mix of short period wind seas and long
period swell (with periods of around 14 to 20 seconds). This will
likely result a prolonged period of hazardous seas conditions across
the waters. Currently, seas of 15 to 24 feet are forecast Sunday
through Tuesday. Seas may briefly lower below 15 feet late Tuesday
into early Wednesday (Christmas), then build again as another strong
front arrives. The strength and timing of the fronts and resultant
sea states are not certain. But, episodes of very high and very
steep seas and dangerous bar conditions are expected. -CC
&&
.BEACH HAZARDS...Updated 800 PM PST Friday, December 20, 2024...
Numerous fronts will bring periods of increasing swells and surf
during the next week. A High Surf Advisory remains in effect this
weekend, with large breaking waves of 21 to 26 feet expected. It
will be followed immediately by a High Surf Warning from late Sunday
evening through Monday evening as the next, stronger front will
bring dangerously large breaking waves of 25 to 33 feet.
Hazardous conditions this weekend will reach a peak during Saturday
afternoon and evening. But, The highest surf is expected Monday
morning into Monday afternoon. Conditions are expected to slowly
improve on Tuesday.
High surf could cause dangerous beach conditions where beach erosion
and/or damage to exposed infrastructure will be possible. Stay tuned
to the forecast for updates. -CC/DW
&&
.PREV DISCUSSION... /Issued 412 PM PST Fri Dec 20 2024/
DISCUSSION...Satellite image shows high and mid level clouds moving
through the area, with a weak frontal boundary just offshore.
Underneath the high and mid level clouds are low clouds in portions
of the Umpqua Basin, Illinois and Rogue Valley, Applegate Valley and
Grants Pass area with patchy fog in these locations. It's possible
the low clouds could linger into early this afternoon, if not
longer. The fog will likely lift to a low overcast by the afternoon.
Radar is showing light returns over the marine waters and coastal
counties, but so far no measureable precipitation has been reported.
A strong front will move east and reach the Oregon coast late
tonight. There's good agreement for moderate to occasionally strong
winds setting up in the Shasta Valley Friday evening into Saturday
morning. A southeast flow will set up in the Rogue Valley and the
Redding to Medford pressure gradient is sufficient enough for
moderate to occasionally strong winds in the south end of the Rogue
Valley Friday evening into Saturday morning. Additionally, it will
be windy east of the Cascades, with the strongest winds expected
near and at the ridges, along the Warners, and along and just
downwind of Summer Rim, including highway 31 from Paisley and Summer
Lake. The models have trended higher with the pressure gradient
difference between Medford and Redding. This along with wind gusts
trending higher at Weed resulted in upgrading the Wind Advisory to a
High Wind Warning for the south end of the Shasta Valley. Please see
NPWMFR for more details.
The front will push into the area late tonight and we'll get a good
shot of precipitation along the coast, coastal mountains, western
Siskiyou County and Mount Shasta area from late tonight into
Saturday morning. Precipitation rates will drop off late Saturday
morning and afternoon as the front pushes inland, but showers will
still be plentiful. Snow levels Saturday morning will be on the high
side (between 6000-6500 feet), therefore snow will be confined to
areas around Diamond Lake, and Crater Lake. Even then were not
expecting anything significant. Snow levels will fall some in the
wake of the front Saturday afternoon, but by then precipitation
rates will be decreasing. The 12 hour storm total snow during the
day Saturday is expected to be between 3-5 inches around Crater Lake
and 2-4 inches around Diamond Lake Junction.
We'll get a relative break in the action Saturday night into Sunday
morning as weak shortwave ridging builds in. There will still be a
few showers around, but they will be far and few. Also winds will be
lighter.
The next front is on track to arrive late Sunday afternoon, bringing
another round of precipitation, gusty south to southeast winds for
the Shasta Valley, and possibly the Rogue Valley ahead of the front
during the day Sunday. Snow levels Sunday afternoon are expected to
be between 6500-7000 feet, thus the concerns for snow, even around
Crater Lake will be minor. Snow levels will lower some Sunday night,
but will still be above most pass level. Even then precipitation
rates will be on the decline as weak shortwave ridging builds in.
-Petrucelli
Monday through Christmas Day...there's high confidence in a
moderate strength upper trough and associated frontal system
reaching the CWA sometime Monday afternoon through Monday evening
with a bout of moderate to strong south winds and locally heavy
rain. With the trough digging well into California, it appears
that the best likelihood for significant rain will be across
Curry, Josephine, and Siskiyou counties Monday night and Tuesday
morning. Snow levels should remain well above the passes during
this time. Snow levels will come down between 4000-6000 feet by
Tuesday afternoon but significant accumulations are not expected
by then. Later Christmas Eve the system moves inland and things
should dry out under shortwave ridging.
There's some uncertainty in the timing of the next system so
there will be some 30-50 percent shower chances over the west
side and Cascades Christmas Day, but not likely significant
weather. Thereafter things are shaping up for a fairly wet warm
front to produce ample precipitation across the region with snow
levels near 5000 feet Christmas night through Thursday. The NBM
shows some 60% chances of at least 8" falling in the 24-hr period
ending 4am Friday, and these are mainly from Willamette Pass to
near Crater Lake and around Shasta. So remain hopeful ski bums
and board hounds, this is good news. Stay tuned. -Stavish
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 10 AM PST Saturday for ORZ026-030-031.
High Surf Advisory from 7 AM Saturday to 10 PM PST Sunday for
ORZ021-022.
High Surf Warning from 10 PM Sunday to 10 PM PST Monday for
ORZ021-022.
CA...High Wind Warning until 10 AM PST Saturday for CAZ081.
Wind Advisory until 10 AM PST Saturday for CAZ081-085.
PACIFIC COASTAL WATERS...Hazardous Seas Warning until 1 AM PST
Saturday for PZZ350-356.
Hazardous Seas Warning from 10 AM Saturday to 4 AM PST Sunday
for PZZ350-356-370-376.
Gale Warning until 10 AM PST Saturday for PZZ350-356.
Gale Warning until 10 AM PST Saturday for PZZ370-376.
&&